- Email: [email protected]
Mandibulectomy techniques
Chapter
46
Mandibulectomy techniques Gary C. Lantz
DEFINITIONS Mandibulectomy techniques involve removal of various segments of a mandible, one entire mandible, or one mandible with a rostral portion of the other mandible, with adjacent neoplastic and soft tissues. Closure of the surgical defects is accomplished using buccal mucosal–submucosal and alveolar mucosal flaps. A rim excision, with reference to mandibulectomy, is defined as a partial segmental exci sion leaving the ventral border of the mandible intact.1 The term hemimandibulectomy is often used in the veterinary literature to denote the complete excision of one of the two mandibles. The term total mandibulectomy is more appropriate. The term hemimandibulectomy should only be used to denote the excision of half of one mandible, but the term partial mandibulectomy, with a reference to which part (rostral, central or caudal) is more appropriately used for this. Simi larly, when referring to the excision of one entire mandible and half of the other mandible, the term one-and-one-half mandibulectomy is preferred over three-quarter mandibulectomy.
INDICATIONS Mandibulectomy techniques are most commonly indicated for exci sion of malignant and benign oral neoplasms. They are also used as salvage procedures for mandibular fractures that are severely com minuted or complicated by missing bone fragments or severe perio dontitis (see Ch. 34).2,3
PREOPERATIVE CONCERNS Diagnosis The histopathologic diagnosis of an oral mass must be aggressively pursued and the patient ‘staged’ using the TNM (tumor, node, metas tasis) classification.22,23 Further details are found in Chapters 38 and 45. Especially relevant to mandibulectomy techniques is to assess how far apically tumors originating on the gingiva have infiltrated. This will largely determine whether a surgically aggressive or more con servative approach is indicated. It is also very important to determine whether and to what extent the root of the tongue is involved; com puted tomography with soft tissue contrast enhancement or nuclear magnetic resonance imaging are especially useful in this respect. Com puted tomography is also helpful in determining the extent of bone and mandibular canal involvement.
Client communication Topics to discuss with the client include intent of surgery (local cure or palliation) and prognosis, operative concerns (blood loss, anes thesia risk), postoperative appearance and oral function, and recommended follow-up. A photograph album including preopera tive and postoperative photographs of patients that have had various types of partial mandibulectomy aids this aspect of client communication.
THERAPEUTIC DECISION-MAKING BACKGROUND Partial mandibulectomy techniques for the treatment of oral neoplasms were introduced by Withrow and Holmberg.4 Clinical investigation for treatment of neoplastic5–16 and non-neoplastic oral conditions2,3 and review publications16–25 have followed, documenting clinical results. © 2012 Elsevier Ltd DOI: 10.1016/B978-0-7020-4618-6.00046-4
Types of osseous excisions The most common types of mandibulectomy are shown in Figure 46.1. The extent of any excision is determined by the oral physical examination and diagnostic imaging findings, the histopathological diagnosis, the recommended surgical margins, intent of the surgery and the tissue available for closure of the defect.
467
Section
|8|
Management of maxillofacial tumors and cysts
C
A
E
B
F
D
G
Fig. 46.1 Examples of mandibulectomy techniques (shaded areas). (A) Unilateral rostral mandibulectomy. (B) Bilateral rostral mandibulectomy. (C) Central or segmental mandibulectomy with preservation of the mandibular canal and ventral margin (‘rim excision’). (D) Central or segmental mandibulectomy (full thickness). (E) Caudal mandibulectomy. (F) Total mandibulectomy. (G) One-and-a-half mandibulectomy.
468
Mandibulectomy techniques
Chapter
| 46 |
Preoperative management The reader is referred to Chapter 45 and other chapters for anesthetic considerations, preemptive analgesia, antibiotics and oral cavity disinfection.
Patient positioning Dorsal and lateral recumbency The head is secured into position with a vacuum-charged surgical positioning system (Vac-Pac, Olympic Medical, Seattle, WA). This device allows the head to be held in any position. A mouth gag is positioned away from the surgery site to keep the mouth open. The endotracheal tube is secured to the muzzle and the tongue retracted from the surgery site and packed off with gauze sponges. For bilateral rostral mandibulectomy, the patient is placed in dorsal recumbency, with the neck flexed to allow access to both oral and cutaneous sur faces of the rostral mandibles. For unilateral rostral or central man dibulectomy, the patient is placed in lateral or dorsal recumbency with the head rotated to facilitate visualization of the surgical field. The head is held parallel with the table top or the rostral end of the muzzle and lower jaw slightly elevated to improve site access. The neck is extended when the patient is in lateral recumbency. For caudal and total mandibulectomy, the patient is placed in lateral recumbency with the neck extended and the rostral end of the muzzle and lower jaw elevated so the surgeon can look into the open mouth. After positioning, a layer of water-repellant gauze (Exodontia Sponges, Henry Schein, Melville, NY) packing is placed in the pharynx around the endotracheal tube then covered with a layer of absorbent gauze.
Sternal recumbency Sternal recumbency, with the head elevated and the maxilla sus pended, is an alternative method of positioning for mandibulectomy procedures. The maxilla is suspended by perforating the maxillary canine teeth through a long strip of adhesive tape. The ends of the tape are then extended and wrapped high around IV poles placed on either side of the patient’s head. The mandible should be level with or slightly lower than the surface of the surgery table. Sternal recumbency offers excellent visualization of the mandible and oral cavity. In this position, all mandibulectomy procedures can be performed using an intraoral approach. The main hazard of sternal recumbency is fluid aspiration. The use of a cuffed endotracheal tube and pharyngeal pack is necessary to prevent aspiration. Having continuous suction available is very helpful.
SURGICAL ANATOMY26–28 The inferior alveolar artery originates from the maxillary artery. It enters the mandibular foramen, and traverses the mandibular canal with numerous arterioles branching to the bone and teeth. There are no direct vascular anastomoses across the fibrocartilaginous mandibu lar symphysis; however, small extraosseous arterioles span the sym physis in the submucosal tissue. Blood supply to the cortical bone at the symphysis is from endosteal and periosteal surfaces. This extraos seous supply may be important to the viability of a rostral mandibular segment after interruption of the inferior alveolar artery secondary to a caudal or central mandibulectomy. The inferior alveolar artery ter minates in the caudal, middle and rostral mental arteries.
Fig. 46.2 Lingual aspect of mandibular ramus. The mandibular foramen is located in the middle of and immediately ventral to an imaginary line between the palpable landmarks of the angular process and the distal aspect of the mandibular third molar tooth.
The mandibular canal mainly contains the inferior alveolar artery, vein and nerve, and some loose connective tissue and fat. The nerve is dorsolateral, the artery is in the central area and vein ventromedial. Bone convexities from the apical alveolar bone of the mandibular teeth border the lingual or dorsal lingual aspect of the canal. The mandibular canal terminates at the mental foramina. The mandibular foramen is located on the medial aspect of the mandible. It is immediately below and centered on a line from the tip of the angular process to the distal aspect of the third molar tooth in the dog (Fig. 46.2) and the first molar tooth in the cat. Palpation of these landmarks during caudal mandibulectomy aids in dissection of the inferior alveolar artery and nerve as they enter the foramen. The middle mental foramen in the dog is at the level of the rostral root of the second premolar tooth, immediately distal to the apex of the canine tooth and approximately midway between the alveolar margin and ventral bone margin (Fig. 46.3A). In the cat, this foramen is located at the level of the apex of the canine tooth. The caudal mental foramen is at the level of the third premolar tooth and approximately midway between the alveolar margin and ventral margin in the dog and cat. The rostral mental foramen is generally at the level of the second incisor tooth and a short distance ventral to the alveolar margin. Multiple small foramina may be present. The apex of the large curved root of the mandibular canine tooth in the dog extends as far as the apex of the distal root of the second premolar tooth. Therefore, bone resection to remove the canine tooth alveolus would also result in removal of the first and second premolar teeth. In the cat, the apex of the canine tooth is immediately rostral to the mesial root of the third premolar tooth. Complete removal of the bone segment encasing the canine tooth root may also require removal of the third premolar tooth and surrounding bone. The inferior labial artery originates from the facial artery and sup plies the soft tissue of the lower lip. The sublingual artery also origi nates from the facial artery and courses along the medial aspect of the mandible. The ventral buccal branch of the facial nerve provides motor innervation to the muscles of the lip. The mandibular branch of the trigeminal nerve provides motor innervation to the muscles of mastication and sensory innervation to the lower lips, rostral twothirds of the tongue, mandibular teeth (as the inferior alveolar nerve) and buccal cavity. The muscles of mastication insert on the ramus of the mandible and some lingual and hyoid muscles insert on the body of the mandible (Fig. 46.3B). The mandibular and sublingual salivary ducts are visible through the thin oral mucosa and course lateral to the tongue frenulum to end in the sublingual caruncle located just rostrolateral to the rostral margin of the frenulum.
469
Section
|8|
Management of maxillofacial tumors and cysts Temporal muscle
Parotid duct
Masseter muscle
Digastric muscle
Dorsal buccal branch of facial nerve
Facial artery
Ventral buccal branch of facial nerve
Superior labial artery
Inferior labial artery
Caudal, middle, rostral mental nerves and arteries
A
Temporal muscle
Mandibular foramen
Lateral pterygoid muscle Medial pterygoid muscle
Genioglossal muscle B
Geniohyoid muscle
Mylohyoid muscle Sublingual artery
Digastric muscle
Fig. 46.3 (A, B) Surgical anatomy of arteries, nerves and muscles pertaining to mandibulectomy techniques.
470
Mandibulectomy techniques
General surgical principles21–23 Surgical plan The surgical plan for a mandibulectomy procedure includes the fol lowing important points: (1) plan for adequate surgical margins; (2) plan for complete mucosal closure; (3) perform atraumatic surgery and preserve local blood supply; (4) employ minimal use of electro surgery; (5) harvest large mucosal flaps to avoid suture line tension; (6) use double-layer closure if possible; and (7) support suture lines with grossly healthy bone if possible.
Surgical margins Surgical margins are indicated by the biological behavior of the neo plasm as determined by the preoperative histopathological diagnosis, and diagnostic imaging and oral physical examination findings (see Ch. 43). The preoperative histopathological diagnosis is essential for definitive surgical planning. In general, a minimum of 10-mm margin should be obtained for all benign and malignant neoplasms except fibrosarcoma where a minimum margin of 20 mm is recommended due to the higher local recurrence rate.21–23 These recommendations have not been correlated with clinical outcome. Wider margins are obtained for malignant neoplasms if a tension-free oral mucosal reconstruction can be obtained. The surgical margins are measured and marked around the circumference of the mass using a sterile surgi cal marker before starting the surgery. It is important to remember that the periodontal ligament spaces and mandibular canal may facilitate neoplastic cell infiltration. Therefore, if the canine tooth is included in the measured surgical margins, the ostectomy is usually performed between the second and third premolar teeth (in the dog) to ensure complete removal of the canine tooth alveolus. Invasion of the man dibular canal by a malignancy requires total mandibulectomy. Postoperative radiographs of the excised specimen or surgery site are made to document adequate gross surgical margins. The entire specimen is sent for histopathological examination to confirm the diagnosis and to assess the bone and soft tissue margins for neoplastic cells. Finding neoplastic cells on the excision margin implies incom plete removal of local microscopic disease and the need to consider adjunct radiation or chemotherapy.
P3
P2
P1
| 46 |
Surgical incision
SURGICAL TECHNIQUE
P4
Chapter
Canine
The incision is made along the measured and marked surgical margins. The initial incision is a light scoring of the mucosa to produce a minimally bleeding incision line. Once the margins of the proposed excision are verified the incision is taken to bone. Once incised, the alveolar mucosal margins may retract and result in some distortion of the proposed margins. The described incision method maintains accu rate surgical margins. In the regions of foramina, the dissection is continued to identify, ligate and transect the vessels and transect the nerves. Hemorrhage is controlled by ligation, pressure and minimal focal use of electrocoagulation. Depending on surgical margins, muscles attaching to the mandible are subperiosteally elevated or transected. Concurrent lip wedge excision may be needed to obtain adequate surgical margins. This is true for large neoplasms along the body of the mandible and when a bilateral rostral mandibulectomy is per formed. Wedge excision is also performed during the latter procedure to remove excess skin. Lip excision compromises blood supply to the remaining rostral lip segment; however, viability is maintained by submucosal arterial branches.
Management of adjacent teeth Maintaining teeth is secondary to achieving adequate surgical margins and tension-free closure. Ostectomy performed at a narrow interden tal space may result in injury requiring extraction of a tooth adjacent to the ostectomy site if inadvertent severe periodontal or endodontal injury (root canal exposure) occurred during ostectomy. Ostectomy at the level of a wider interdental space may not result in similar tooth injury. Therefore, to minimize tooth loss, the ostectomy margins are planned to transect a tooth at the margin level (Fig. 46.4). This may require margin extension, which is acceptable. Margins should never be compromised to save teeth. Once the en-bloc tissue mass is excised, the remnant of the transected tooth is extracted. The adjacent teeth and periodontal structures are not injured, leaving a margin of attached and free gingiva adjacent to the ostectomy.
Ostectomy and osteoplasty Ostectomy often removes a full-thickness (dorsoventral) segment of the mandible. However, in the case of smaller neoplasms, adequate surgical margins may be achieved by partial-thickness excision or rim
Mass
P4
P3
P2
P1
Canine
Mass
A
Ostectomy line
B
Ostectomy line
Fig. 46.4 Ostectomy lines for (A) rostral mandibulectomy, and (B) caudal mandibulectomy in relation to adjacent teeth. Transecting a tooth at the time of excision will not injure adjacent teeth; the remaining tooth fragment is removed after the en-bloc excision is completed. The specific level of ostectomy is dependent upon measured surgical margins.
471
Section
|8|
Management of maxillofacial tumors and cysts
excision allowing the mandibular canal and thick ventral cortical bone or a portion of the mandibular symphysis to remain intact (see Fig. 46.1).1 Postoperative mandibular instability is avoided. The soft tissues are subperiosteally elevated away from the ostec tomy site. The ostectomy is performed as determined by the premeas ured surgical margins. The excision is planned so that all root structures of teeth within the surgical margins are part of the en-bloc excision. Any remaining tooth root tips from transected teeth at the excision periphery are extracted after the en-bloc tissue segment is removed. Ostectomy may be performed with a thin osteotome and mallet. The instruments are used with gentle technique to slowly advance the depth of bone cut. Aggressive use may result in fractures of remaining bone. Increased resistance will be found when tooth roots are encoun tered and may require extraction of the tooth or deviation of the ostectomy course to include the entire tooth. The mandibular sym physis is split using an osteotome and mallet. Power equipment that cuts bone with saw blades or burs offers the most efficient ostectomy method. The most control is gained when using a surgical handpiece with continuous irrigation and bone cutting burs. Carbide steel bone cutting burs may leave a roughened bone edge. Medium grit diamond tapered cylinder burs produce a smooth bone cut. Once the en-bloc tissue segment is removed, osteo plasty is performed. Cut bone margins are smoothed with a round, medium or fine grit diamond bur or carbide bur. The goal is to remove all sharp bone ridges and bone spikes that may result in ischemic pressure injury and potential perforation of the mucosal flaps. Osteotomy of the ventral third of the mandible is performed last. Ideally, the inferior alveolar artery is isolated, ligated and transected. In the event of inadvertent transection of the artery during osteotomy, the artery is retrieved and ligated. If the artery cannot be retrieved, a hemostatic agent is firmly packed into the mandibular canal.
Flap design General principles Recommended oral mucosal flap length to base width ratio is 2 : 1 in humans29 and is unknown in the dog and cat. In general, the flap is made slightly larger than necessary to ensure adequate tissue for tension-free closure and should, ideally, not have vertical releasing incisions, as flap blood supply may be compromised.29 If vertical releasing incisions are needed, they are divergent from the flap apex to base to maintain a broad-based flap for blood supply conservation.29 The flaps are gently handled. Excessive pulling, crushing or dessica tion may injure flap blood supply.29 Tissue forceps are not closed tightly, to avoid crushing the tissue and potential marginal ischemic necrosis. Thin tissue flaps may be atraumatically manipulated by placement of two stay sutures. Defect closure is most commonly achieved using local mucosal tissues. Advanced closure techniques are discussed in Chapter 48.
Vestibular mucosal–submucosal flap The flap is harvested by dissecting from the mandibulectomy site toward the lip margin. The plane of dissection is immediately below the submucosa. Branches of the inferior labial artery, vein, ventral buccal branch of the facial nerve and adjacent skeletal muscle are visualized during flap elevation and remain in their original position. Flap elevation is continued until there is enough tissue for a tensionfree closure. The flap blood supply is from the inferior labial artery. The amount of remaining buccal mucosa is determined by the size of the excision. A lesser amount of remaining buccal mucosa results in a larger lingual deviation of the lip and a mandibular concavity.
472
Surgical defect closure Reconstruction of an oral mucosal lining is essential and is deter mined by preoperative planning. Healing without complication depends largely on accurate tension-free apposition of incised soft tissue margins. Inverted epithelium from poor approximation and suture line tension will delay wound healing. A two-layer closure, when possible, is preferred.
Closure at the rostral mandible Separation of the mandible for unilateral rostral or total mandibulec tomy is commonly performed at the mandibular symphysis. The ves tibular mucosal–submucosal flap is sutured to the mucoperiosteal fibrous tissue at the symphysis. The needle is passed from the intact mucoperiosteum toward the symphysis. A wide bite is taken and the needle ‘walked off’ the bone at the level of the symphysis. Excellent suture retention is provided and accurate placement will not tear the tissue. The suture is then passed through the vestibular flap (Fig. 46.5A). If an ostectomy of the rostral mandible is performed, the muco periosteal tissue margin is trimmed back 1–3 mm to expose a bone rim that will support the suture line. The new soft tissue margin is subperiosteally elevated to facilitate suture placement. A one-layer closure is performed and the suture line is supported by bone (Fig. 46.5B, C).
Closure at the mandibular body Full-thickness ostectomies of the body of the mandible are made per pendicular to the long axis of the bone. For closure, the ostectomy is modified to provide tension-free tissue apposition over the cut bone margin (Fig. 46.6).2 As needed, an alveolar margin incision, combined with a sulcular incision partially around the adjacent intact tooth, is made. The attached gingiva along with the proximal alveolar mucosa on the buccal and lingual side is subperiosteally elevated. The corner of the ostectomy at the level of the alveolar margin is tapered 30–60 degrees with a saw blade or bur. Osteoplasty is then performed. The adjacent intact tooth is not injured. The attached gingiva is contoured and then sutured over the tapered area with simple interrupted sutures using generous tissue bites. The buccal and alveolar mucosal– submucosal flaps are apposed using simple interrupted sutures. Although this technique provides tension-free tissue apposition, the suture line in the attached gingiva may have stress applied during pre hension and mouth closure. This is especially true for bilateral rostral mandibulectomies. The thick keratinized attached gingiva provides excellent suture retention. However, during early healing all tension is placed on the sutures; therefore, larger-gauge sutures may be used for suturing the attached gingiva over the tapered alveolar bone margin.
Unilateral rostral mandibulectomy This procedure usually includes removal of the incisor teeth, canine tooth and first and second premolar teeth in the dog, and incisor teeth, canine tooth and possibly the third premolar tooth in the cat. It may be difficult to obtain an adequate surgical margin on the medial aspect. In this case, instead of splitting the mandibular sym physis, an ostectomy of the rostral aspect of the opposite mandible may be needed. In the dog, the ostectomy generally includes the first and second premolar teeth, as the root of the canine tooth extends up to the level of the distal root of the second premolar tooth. If only incisor teeth are removed, a portion of the mandibular symphysis remains intact. Removal of the incisor part is only rarely indicated due to the proximity of the canine tooth and the need for adequate surgi cal margins. The labial vestibular mucosal–submucosal flap is sutured to the mucoperiosteum of the remaining rostral mandible (see Fig. 46.5) and alveolar mucosa if the excision extends caudal to the
Mandibulectomy techniques Tongue frenulum
Suture
Cut soft tissue cross-section
Sublingual caruncles
Soft tissue margin
Exposed bone shelf Symphysis Lip margin Labial mucosal flap margin
A
Tapered bone margin
New lip margin
Chapter
| 46 |
the canine teeth alveoli. The incision is made as a lip wedge excision to include surgical margins and estimated excess skin. For tumors centered at the incisive part and extending facially, a single wide sym metrical wedge of skin is excised on the facial aspect as part of the en-bloc excision (Fig. 46.7). For tumors that occur more caudally or laterally, two skin wedges are removed at the level of the lateral lower labial frenula or a single large asymmetrical skin wedge is removed. Wedge resection is conservatively performed to ensure that an ade quate amount of skin is present for tension-free closure. Bilateral fullthickness wedge removal of lip margins does sacrifice the inferior labial blood flow to the remaining rostral lip and skin segment. Large bilateral wedge resections may compromise the remaining random blood supply to this rostral segment. A small portion of the caudal mandibular symphysis may remain intact. Mandibular and sublin gual salivary ducts and caruncles are avoided. If the ducts must be transected, as in mandibulectomies at the level of the third or fourth premolar teeth, they are ligated. The mucoperiosteum at the rostral mandible is tightly attached, and sharp dissection may be more effi cient than blunt tissue elevation. The rostral mental blood vessels at the level of the apex of the second incisor teeth are coagulated. When transecting the lateral lower labial frenula, the middle mental blood vessels are encountered and are ligated to prevent unnecessary blood loss. The osteotomy is preferably performed with an osteotomy bur on a surgical handpiece with continuous irrigation in a careful manner in order to avoid transecting the inferior alveolar blood vessels without prior ligation. After excision, osteoplasty of the ventral margin is performed using a bur to provide a more normal ‘chin’ contour. If the excision removed the entire symphysis, the ostectomies of each mandibular body are tapered at the alveolar margin (see Figs 46.1 and 46.6) and the attached gingiva closed. A suture is placed in the lip margin to main tain alignment for cosmetic closure. The oral mucosa is apposed using simple interrupted sutures with knots placed in the oral cavity. The remaining closure is routine. For large active dogs with heavy, thick, pendulous lips, the intraoral suture lines can be bilaterally bolstered to reduce tension during the early phase of healing. A polypropylene suture is passed distal to the third premolar tooth on each side. A 22-gauge hypodermic needle is placed through the gingiva immediately distal to the tooth and dorsal to the alveolar margin. The suture is passed through the needle. The arms of the suture are passed through the full-thickness rostral soft tissue and tied over a button or suture bolster. The suture is held in position by the gingiva but is anchored by the tooth. A similar suture is placed on the opposite side. These sutures are removed in 7 to 10 days.
Central or segmental mandibulectomy B Fig. 46.5 Closure of a unilateral rostral mandibulectomy. (A) The vestibular mucosal–submucosal flap is sutured to the large amount of mandibular mucoperiosteal fibrous tissue using wide suture bites. (B) Closure results in an asymmetrical rostral mandible.
symphysis. Lip wedge excision to remove excess tissue before closure is not needed.
Bilateral rostral mandibulectomy The surgical margins are determined and the amount of skin left for tension-free closure is estimated. The osteotomy is made at the distal aspect of the second premolar teeth to ensure complete removal of
A segment of the mandibular body is excised leaving behind two ostectomy cuts. Each ostectomy is tapered at the alveolar margin (Figs. 46.1 and 46.6). The attached gingiva and mucosal tissues are sutured. The salivary ducts are avoided when possible. If the ducts are transected, they are ligated. With a more conservative variation of this technique, known as a rim excision, a horizontal osteotomy is made at the level of the dorsal border of the mandibular canal.1 This leaves the neurovascular struc tures in the mandibular canal and the ventral margin intact (see Fig. 46.1E). Closure is the same as described above.
Caudal mandibulectomy Depending on neoplasm size and location, a full-thickness cheek incision may be made from the commissure and extended caudally
473
Section
|8|
Management of maxillofacial tumors and cysts
Mucogingival junction
Mucogingival flaps Partial alveolus
Bone margin tapered Ostectomy site
A
B
Mandibular canal
Mucogingival junction
Rounded corners of bones
C
D
Fig. 46.6 Tapering the alveolar bone margin to reduce suture line tension. The adjacent tooth was transected during ostectomy; the root remnant has been extracted leaving a partial alveolus. (A) Alveolar margin and sulcular incisions are made and the attached gingiva and proximal alveolar mucosa are subperiosteally elevated. (B) The alveolar margin bone is tapered approximately 30–60 degrees. (C) Osteoplasty is performed by rounding the bony edges. (D) The attached gingiva and alveolar mucosa is closed over the surgical defect.
as needed. Mucosal incisions are made along the measured surgical margins. However, it is often unnecessary to incise the cheek to achieve surgical margins and have good site exposure, especially when dorso lateral or sternal positioning is used. Using the intraoral approach, a mucosal incision is made over the rostral edge of the ramus then extended in a buccal and lingual direction around the mandibular body along surgical margins. After dissection of the caudal part of the mandibular body and ostectomy, dissection along the ramus is per formed. The insertions of the muscles of mastication are subperio steally elevated or the muscle body transected, depending on surgical margins. If needed, the masseter is excised as part of the en-bloc exci sion. The digastric and pterygoid muscles are elevated or transected, as determined by surgical margins. The mandibular foramen is located and the inferior alveolar artery is ligated and transected close to the
474
foramen to avoid injury to the maxillary artery. The inferior alveolar nerve is also transected as close as possible to the foramen, in order to avoid damage to the lingual nerve. The temporalis muscle inser tions on the medial and lateral aspects of the ramus and coronoid process are elevated or transected, as determined by the surgical margins. The temporomandibular joint is located by palpation during manipulation of the caudal mandibular en-bloc segment. The capsule is incised on the medial aspect. As the mandible is manipulated to aid visualization, adjacent soft tissues are gently ‘wiped’ off the capsule and the capsule incision extended laterally. The rostral and caudal aspects of the capsule are incised in this manner and the lateral liga ment is incised last. It is essential that dissection and joint capsule incision occur immediately adjacent to the condylar process to avoid injury to adjacent vessels and nerves. The tortuous course and close
Mandibulectomy techniques
Chapter
| 46 |
Lip margin
Skin incision
Suture line
B
A Tongue frenulum Lip margin
Lip margin
Sublingual caruncle
Wedge excision of skin
Intraoral suture line
D
C Fig. 46.7 Bilateral rostral mandibulectomy. The patient is in dorsal recumbency. (A) The wedge incision (either symmetrical, left, or asymmetrical, right) incorporates the surgical margins and estimated excess skin and lip for closure. (B, C) Closure results in a linear skin suture line and a transverse oral mucosal suture line. (D) Alternative skin and lip closure with bilateral removal of full-thickness labial tissue.
proximity of the maxillary artery on the ventromedial aspect of the joint, and its local branches, make them vulnerable to inadvertent transection. Once the joint is disarticulated, any remaining soft tissue attachments are cut. A local anesthetic ‘splash’ block may be applied to the surgery site. Placement of local hemostatic agents (see Ch. 7) may be needed to help control bleeding from transected muscles. Oral mucosal tissues are opposed using simple interrupted sutures. Closure is routine.
Unilateral (total) mandibulectomy Penetration of the mandibular canal implies potential spread of neo plasm along the length of the mandible, indicating the need for total mandibulectomy. This procedure can be performed with the patient in lateral recumbency using an incision of the cheek. This may facili tate the caudal dissection, especially in some large patients and in patients with more caudally located masses necessitating excision of the masseter muscle, and transection rather than subperiosteal eleva tion of other muscles. The procedure can be performed intraorally with the patient in sternal recumbency. The intraoral incision is started as described for caudal mandibulectomy and continued along the predetermined surgical margins. The mandibular symphysis is split using a thin osteotome and mallet and the body and ramus dissected free of all tissue attachments, as described above for the various partial mandibulectomy techniques. If necessary for surgical margins, the tongue frenulum can be removed without altering tongue function. Soft tissue excision may extend toward the opposite mandible.
However, this excision margin is limited by the need for primary mucosal closure. Extensive removal of sublingual muscle may result in impairment of tongue function. The mandible is excised intact. The commissure is moved rostrally to minimize drooling and help prevent tongue protrusion. Commissurorrhaphy is performed by exci sion of the lip margin followed by a three-layer closure. The new commissure is approximately at the level of the mandibular second premolar tooth. A full-thickness horizontal mattress suture may be placed to span between the upper and lower lip immediately rostral to the new commissure. This suture is tied over buttons or suture bolsters. Its purpose is to restrain mouth opening to keep tension off the commissure suture line and promote normal healing.
Stabilization of mandibular segments To date, reconstruction following mandibulectomy is infrequently performed.30 An ulnar autograft combined with rigid internal fixation was used to bridge a central mandibulectomy site for benign neo plasm excision, with good results.31 This technique has the potential to eliminate mandibular instability and malocclusion and improve cosmetic results for central mandibulectomies. Stabilization of the remaining lower jaw after bilateral rostral mandibulectomy has been attempted using orthopedic pins,32 screws,4,7 and screws and bone graft.33 The screws and pins are placed before the excision is performed. Mandibular instability is avoided and prehension is similar to that of patients not having any stabilization technique performed.
475
Section
|8|
Management of maxillofacial tumors and cysts
A microvascular bone autograft using coccygeal vertebrae has been reported for fracture reconstruction of a central mandibular defect in a dog.34 Microvascular transfer of bone autografts is the preferred method of mandibular reconstruction in humans and may be of benefit to selected small animal patients.35
POSTOPERATIVE CARE AND ASSESSMENT Most aspects of postoperative care, including pain management and nutritional support, are similar to those described for maxillectomy (see Ch. 45).
Postoperative patient appearance21–23 Swelling of the surgical site is usually resolved by 3 to 7 days postop eratively. Cosmetic appearances are generally good and depend on the extent of excision. Smaller excisions result in unnoticeable or minimal cosmetic abnormalities. Regrowth of hair will conceal many surgically created facial asymmetries. Unilateral rostral mandibulectomy without canine tooth removal results in no obvious abnormality. When the canine tooth is removed, the tongue hangs out from that side when panting. Bilateral rostral mandibulectomy results in relative mandibu lar brachygnathism and the most noticeable uncosmetic appearance (Fig. 46.8). The tongue protrudes from the mouth during panting. Drooling may occur. Central mandibulectomy results in a mild facial concavity. Caudal and complete mandibulectomy result in facial con cavity and tongue protrusion from the side of surgery during panting (Fig. 46.9). Malocclusion occurs as the remaining mandible shifts toward the operated side.
A
Homecare and follow-up Most patients are sent home in 2 to 3 days postoperatively. A soft food diet and removal of chew toys is recommended for 2 to 3 weeks. The client is shown how to administer any oral medications so as not to disrupt the suture line. Medications are concealed in soft food snacks. If oral manipulation is needed, the manipulation is performed away from the surgical site. The surgical site is examined in 2 weeks and any skin sutures removed. The surgical site is reexamined at 1 month postoperatively and any residual oral sutures removed at this time. Most oral sutures are extruded in approximately 2 to 3 weeks. A com plete physical examination, including the surgical site, is performed at 3-month intervals for 1 year. In case of malignant neoplasms, threeview thoracic radiographs are obtained at these examinations.
COMPLICATIONS19–23 Intraoperative complications Hemorrhage is the major intraoperative complication. It is managed as it is encountered by ligation, pressure or focal use of electrocoagula tion. The risk for excessive bleeding is the highest during ostectomy and during dissection of the caudal mandible. Blood loss during ostectomy is minimized by cutting the bone of the ventral mandible last and isolating and ligating the inferior alveolar artery. In the event of inadvertent transection of the artery, rapid completion of the ostec tomy is done and the vessel retrieved and ligated. If the artery retracts into the canal and cannot be retrieved, the mandibular canal is packed with a suitable hemostatic agent (see Ch. 7). Careful dissection for disarticulation of the temporomandibular joint is required to avoid vascular injury and profuse hemorrhage.
476
B Fig. 46.8 (A) Lateral and (B) ventrodorsal view of a patient after bilateral rostral mandibulectomy.
Mandibulectomy techniques
Chapter
| 46 |
Functional complications Malocclusion
A
The contralateral mandible is initially unstable and drifts toward the midline. Elastic training using orthodontic buttons and power chain between the buccal aspect of the maxillary fourth premolar tooth and the lingual aspect of the mandibular canine tooth is a simple method for prevention of mandibular drift but requires good client compli ance.36 Abnormal contact with the remaining mandibular canine tooth may result in palatal or upper lip ulceration. Crown reduction and partial coronal pulpectomy, or extraction of the mandibular canine tooth, is needed to resolve the palatal ulceration.37 The remain ing mandible may occasionally drift away from the midline. When this happens the mandibular and maxillary teeth meet end on. Click ing is briefly audible until the mandible drifts medially. The unstable mandibular movement is reduced 4–6 weeks after surgery; however, occlusion may remain abnormal. Long-term follow-up of clinical cases does not suggest abnormal temporomandibular joint clinical effects. After experimental unilateral rostral mandibulectomy, tempo romandibular degenerative joint disease occurred and did not impair the dogs at 3 and 6 months postoperatively.38
Prehension Most patients prehend and drink normally after partial mandibulec tomy. Patients with more extensive excisions practice eating and adapt after a short period of time. Some dogs spill a large amount of food around the food-bowl during this period. Food with a consistency similar to ground meat or soaked kibble seems the easiest to prehend. Hand-feeding may be permanently necessary with some patients after a one-and-one-half mandibulectomy. These patients usually adapt to drinking by a combination of lapping and sucking water.
Drooling Drooling occurs with bilateral rostral mandibulectomies and total mandibulectomies. Drooling often decreases over time. If the new lip margin is immediately rostral to the sublingual caruncles when closing a bilateral rostral mandibulectomy, the mandibular and sub lingual salivary ducts may be ligated to reduce drooling potential. Moving the commissure rostrally during closure of a total man dibulectomy usually prevents drooling.
Tongue protrusion Lateral tongue protrusion occurs when a mandibular canine tooth is absent, as in a unilateral rostral mandibulectomy or total mandibulec tomy. Ventral tongue protrusion occurs following a bilateral rostral mandibulectomy. The protrusion is most evident when panting. Dessication of the tongue rarely occurs. B
Ranula
Fig. 46.9 (A) Lateral and (B) ventrodorsal view of a patient after a total mandibulectomy of the right mandible. Lateral tongue protrusion during panting and mandibular drift to the right side are visible.
A ranula may result from surgical trauma to the salivary duct or papilla or postoperative swelling that temporarily impairs flow of saliva from the sublingual caruncle. This condition may occur at 1 to 2 days postoperatively and usually resolves by 5 to 7 days. Treatment is not needed.
Dehiscence
Dental calculus
Dehiscence of the commissurorrhaphy may occur and is repaired by delayed primary closure. A small dehiscence over the ostectomy site exposing bone will usually heal by second intention. A larger dehis cence requires debridement and resuturing.
The ipsilateral maxillary fourth premolar tooth and molar teeth may accumulate dental calculus more rapidly, as compared to the contral ateral side, in patients with central, caudal and total mandibulecto mies. There is an apparent compromise of normal oral cleansing,
477
Section
|8|
Management of maxillofacial tumors and cysts
possibly due to a closer postoperative adaptation of the cheek to the maxillary teeth surfaces. Oral health checks are essential for the life of the patient.
sucking water. A very extensive mandibulectomy may interfere with the patient’s ability to maintain hydration.
Subtotal mandibulectomy Local tumor recurrence Local tumor recurrence is common with certain tumor types. Suspi cious areas noted during recheck examinations must be biopsied to differentiate neoplasm recurrence from suture reaction and scar tissue.
PROGNOSIS The overall prognosis for mandibulectomy techniques regarding oral function, operative and postoperative complications, postoperative appearance and client satisfaction is good to excellent.15,21–23 This seems directly related to surgeon experience with appropriate patient selection, technical performance of the surgery and preoperative client communications to set realistic expectations. Less positive results may occur in patients with more aggressive disease and more radical surgery. One study reported an overall 85% client satisfaction with maxillectomy and mandibulectomy procedures. The satisfaction level correlated with the postoperative survival time of the patient.15 Local recurrence rates, survival times and biologic behavior of benign and malignant oral tumors reported in various clinical studies have been reviewed.23,24,39 Fibrosarcoma has the highest local recur rence rate (46%) followed by melanoma (25%), osteosarcoma (25%), squamous cell carcinoma (15%) and benign neoplasms (0–4%).23,39 Early recognition, accurate diagnosis and aggressive, planned excision are essential for optimal results.
OTHER CONSIDERATIONS Extent of mandibulectomy Ideally, the functions of prehension and mastication for normal ali mentation and hydration are maintained. When a one-and-one-half mandibulectomy is performed (see Fig. 46.1), many patients require manual assistance with eating and must be hand-fed food shaped into balls. Drinking is accomplished by a combination of lapping and
This procedure leaves most of the ramus intact with a normal coro noid process and temporomandibular joint. This avoids the more difficult dissection to remove the caudal aspect of the mandible, thereby reducing surgical trauma. However, the surgeon must be sure that the soft tissue and bone surgical margins are not compromised. The mandibular foramen is located approximately halfway between the coronoid crest and medial aspect of the condylar process. There fore, transection of the mandibular body distal to the third molar will result in a portion of intact mandibular canal being left behind. This is of particular concern when surgery is performed for a tumor that potentially invaded the mandibular canal. Osteoplasty is important before mucosal closure. The normal movement of the intact caudal mandible may result in perforation of the oral mucosa or suture line disruption by sharp bone areas left at the ostectomy site.
Teeth rostral to ostectomy Central and caudal mandibulectomy transect the inferior alveolar artery and nerve that are the major neurovascular supply to the remaining rostral mandibular teeth.28 Primate studies of teeth encased in an ostectomized segment of bone that maintains most of its original soft tissue attachments and is stabilized in position with orthopedic wire somewhat mimics the clinical picture of central and caudal mandibulectomy in dogs and in cats in which intact teeth are in a rostrally located bone segment.40–42 In these studies, it appeared that the periodontal vessels continued to provide blood supply to the dental pulp by anastomosis with apical vessels and through lateral canals.40–42 This periodontal blood supply originated from the intact soft tissue vessels. The pulp vessel density was initially reduced but was found to increase over time. Ischemic injury was suggested by loss of odontoblasts, inflammation, fibrosis and foci of pulp necro sis. The pulp vessel density increased over time and odontoblasts with secondary dentin production and reduced inflammation and necrosis were found. Pulp nerve fiber degeneration occurred. There fore, dental pulp of teeth in isolated segments of bone with intact soft tissues maintain vascularity although ischemia may initially occur. Endodontic intervention is not recommended unless clinically indicated.
REFERENCES 1. Brown JS, Kalavrezos N, D’Souza J, et al. Factors that influence the method of mandibular resection in the management of oral squamous cell carcinoma. Br J Oral Maxillofac Surg 2002;40:275–84. 2. Lantz GC, Salisbury SK. Partial mandibulectomy for treatment of mandibular fractures in dogs: eight cases (1981–1984). J Am Vet Med Assoc 1987; 191:243–5. 3. Manfra Marretta S. Maxillofacial surgery. Vet Clin North Am Small Anim Pract 1998;28:1285–96. 4. Withrow SJ, Holmberg DL. Mandibulectomy in the treatment of oral
478
cancer. J Am Anim Hosp Assoc 1983; 19:273–86. 5. Bradley RL, MacEwen EG, Loar AS. Mandibular resection for removal of oral tumors in 30 dogs and 6 cats. J Am Vet Med Assoc 1984;184: 460–3. 6. White RAS, Gorman SB, Watkins SB, et al. The surgical management of bone-involved oral tumors in the dog. J Small Anim Pract 1985;26:693–708. 7. Penwick RC, Nunamaker DM. Rostral mandibulectomy: a treatment for oral neoplasia in the dog and cat. J Am Anim Hosp Assoc 1987;23:19–25.
8. Salisbury SK, Lantz GC. Long-term results of partial mandibulectomy for treatment of oral tumors in 30 dogs. J Am Anim Hosp Assoc 1987;24: 285–94. 9. White RAS, Gorman NT. Wide local excision of acanthomatous epulides in the dog. Vet Surg 1989;18:12–14. 10. Kosovsky JK, Matthiesen DT, Manfra Marretta S, et al. Results of partial mandibulectomy for the treatment of oral tumors in 142 dogs. Vet Surg 1991; 20:397–401. 11. Schwarz PD, Withrow SJ, Curtis CR, et al. Mandibular resection as a treatment for
Mandibulectomy techniques oral cancer in 81 dogs. J Am Anim Hosp Assoc 1991;27:601–10. 12. White RAS. Mandibulectomy and maxillectomy in the dog: long term survival in 100 cases. J Small Anim Pract 1991;32:69–74. 13. Hutson CA, Willauer CC, Walder EJ, et al. Treatment of mandibular squamous cell carcinoma in cats by use of mandibulectomy and radiotherapy: seven cases (1987–1989). J Am Anim Hosp Assoc 1992;201:777–81. 14. Straw RC, Powers BE, Klausner J, et al. Canine mandibular osteosarcoma: 51 cases (1980–1992). J Am Anim Hosp Assoc 1996;32:257–62. 15. Fox LE, Geoghegan SL, Davis LH, et al. Owner satisfaction with partial mandibulectomy or maxillectomy for treatment of oral tumors in 27 dogs. J Am Anim Hosp Assoc 1997;33:25–31. 16. Northrup NC, Selting KA, Rassnick KM, et al. Outcomes of cats with oral tumors treated with mandibulectomy:42 cases. J Am Anim Hosp Assoc 2006;42:350–60. 17. Harvey CE. Oral surgery, radical resection of maxillary and mandibular lesions. Vet Clin North Am Small Anim Pract 1986;16:983–93. 18. Birchard S, Carothers M. Aggressive surgery in the management of oral neoplasia. Vet Clin North Am Small Anim Pract 1990;20:1117–40. 19. Matthiesen DT, Manfra Marretta S. Results and complications associated with partial mandibulectomy and maxillectomy techniques. Probl Vet Med 1990;2:248–75. 20. Salisbury SK. Problems and complications associated with maxillectomy, mandibulectomy, and oronasal fistula repair. Probl Vet Med 1991:3:153–69. 21. Salisbury SK. Maxillectomy and mandibulectomy. In: Slatter DH, editor. Textbook of small animal surgery. 3rd ed. Philadelphia, PA: WB Saunders; 2003. p. 561–72.
22. Hedlund CS. Surgery of the digestive system, surgery of the oral cavity and oropharynx. In: Fossum TW, editor. Small animal surgery. 3rd ed. St. Louis, MO: Mosby; 2007. p. 339–47. 23. Dernell WS, Schwarz PD, Withrow SJ. Mandibulectomy. In: Bojrab MJ, editor. Current techniques in small animal surgery. 4th ed. Philadelphia, PA: Williams and Wilkins; 1998. p. 132–42. 24. Salisbury SK. Aggressive cancer surgery and aftercare. In: Morrison WB, editor. Cancer in dogs and cats, medical and surgical treatment. Philadelphia, PA: Williams and Wilkins; 1998. p. 265–321. 25. Verstraete FJM. Mandibulectomy and maxillectomy. Vet Clin North Am Small Anim Pract 2005;35:1009–39. 26. Evans HE. Miller’s anatomy of the dog. 3rd ed. Philadelphia, PA: WB Saunders; 1993. 27. Smith MM. Lingual approach for surgical extraction of the mandibular canine tooth in dogs and cats. J Am Anim Hosp Assoc 1996;32:359–64. 28. Roush JK, Howard PE, Wilson JW. Normal blood supply to the canine mandible and mandibular teeth. Am J Vet Res 1989;50: 904–7. 29. Hupp JR. Principles of surgery. In: Peterson LJ, Ellis III E, Hupp JR, et al. editors. Contemporary oral and maxillofacial surgery. 4th ed. St. Louis, MO: Mosby; 2003. p. 42–8. 30. Boudrieau RJ, Mitchell SL, Seeherman H. Mandibular reconstruction of a partial hemimandibulectomy in a dog with severe malocclusion. Vet Surg 2004;33: 119–30. 31. Bracker KE, Trout NJ. Use of a free cortical ulnar autograft following en bloc resection of a mandibular tumor. J Am Anim Hosp Assoc 2000;36:76–8. 32. Vernon FF, Helphrey M. Rostral mandibulectomy – three case reports in dogs. Vet Surg 1983:12:26–9.
Chapter
| 46 |
33. Bradney IW, Hobson HP, Stromberg PC. Rostral mandibulectomy combined with intermandibular bone graft in treatment of oral neoplasia. J Am Anim Hosp Assoc 1987;23:611–15. 34. Yeh LS, Hou SM. Repair of a mandibular defect with a free vascularized coccygeal vertebra transfer in a dog. Vet Surg 1994; 23:281–5. 35. Disa JJ, Cordeiro PG. Mandible reconstruction with microvascular surgery. Semin Surg Oncol 2000;19:226–34. 36. Bar-Am Y, Verstraete FJM. Elastic training for the prevention of mandibular drift following mandibulectomy in dogs: 18 cases (2005-2008). Vet Surg 2010;39: 574–80. 37. Niemiec BA, Mulligan TW. Vital pulp therapy. J Vet Dent 2001;18:154–6. 38. Umphlet RC, Johnson AL, Eurell JC, et al. The effect of partial rostral hemimandibulectomy on mandibular mobility and temporomandibular joint morphology in the dog. Vet Surg 1988;17: 186–93. 39. Liptak JM, Withrow SJ. Cancer of the gastrointestinal tract, oral tumors. In: Withrow SJ, Vail DM, editors. Small animal clinical oncology. 4th ed. Philadelphia, PA: WB Saunders; 2007. p. 455–75. 40. Lownie JF, Cleaton-Jones PE, Fatti LP, et al. Vascularity of the dental pulp after segmental osteotomy in the chacma baboon (Papio ursinus). Brit J Oral Maxillofac Surg 1998;36:285–9. 41. Lownie JF, Cleaton-Jones PE, Coleman H, et al. Long-term histologic changes in the dental pulp after posterior segmental osteotomies. Oral Surg Oral Med Oral Path 1999;87:299–304. 42. Lownie JF, Cleaton-Jones PE, Fatti LP, et al. Nerve degeneration within the dental pulp after segmental osteotomies in the baboon (Papio ursinus). J Dent Assoc S Afr 1996;51:754–8.
479
46
Mandibulectomy techniques Gary C. Lantz
DEFINITIONS Mandibulectomy techniques involve removal of various segments of a mandible, one entire mandible, or one mandible with a rostral portion of the other mandible, with adjacent neoplastic and soft tissues. Closure of the surgical defects is accomplished using buccal mucosal–submucosal and alveolar mucosal flaps. A rim excision, with reference to mandibulectomy, is defined as a partial segmental exci sion leaving the ventral border of the mandible intact.1 The term hemimandibulectomy is often used in the veterinary literature to denote the complete excision of one of the two mandibles. The term total mandibulectomy is more appropriate. The term hemimandibulectomy should only be used to denote the excision of half of one mandible, but the term partial mandibulectomy, with a reference to which part (rostral, central or caudal) is more appropriately used for this. Simi larly, when referring to the excision of one entire mandible and half of the other mandible, the term one-and-one-half mandibulectomy is preferred over three-quarter mandibulectomy.
INDICATIONS Mandibulectomy techniques are most commonly indicated for exci sion of malignant and benign oral neoplasms. They are also used as salvage procedures for mandibular fractures that are severely com minuted or complicated by missing bone fragments or severe perio dontitis (see Ch. 34).2,3
PREOPERATIVE CONCERNS Diagnosis The histopathologic diagnosis of an oral mass must be aggressively pursued and the patient ‘staged’ using the TNM (tumor, node, metas tasis) classification.22,23 Further details are found in Chapters 38 and 45. Especially relevant to mandibulectomy techniques is to assess how far apically tumors originating on the gingiva have infiltrated. This will largely determine whether a surgically aggressive or more con servative approach is indicated. It is also very important to determine whether and to what extent the root of the tongue is involved; com puted tomography with soft tissue contrast enhancement or nuclear magnetic resonance imaging are especially useful in this respect. Com puted tomography is also helpful in determining the extent of bone and mandibular canal involvement.
Client communication Topics to discuss with the client include intent of surgery (local cure or palliation) and prognosis, operative concerns (blood loss, anes thesia risk), postoperative appearance and oral function, and recommended follow-up. A photograph album including preopera tive and postoperative photographs of patients that have had various types of partial mandibulectomy aids this aspect of client communication.
THERAPEUTIC DECISION-MAKING BACKGROUND Partial mandibulectomy techniques for the treatment of oral neoplasms were introduced by Withrow and Holmberg.4 Clinical investigation for treatment of neoplastic5–16 and non-neoplastic oral conditions2,3 and review publications16–25 have followed, documenting clinical results. © 2012 Elsevier Ltd DOI: 10.1016/B978-0-7020-4618-6.00046-4
Types of osseous excisions The most common types of mandibulectomy are shown in Figure 46.1. The extent of any excision is determined by the oral physical examination and diagnostic imaging findings, the histopathological diagnosis, the recommended surgical margins, intent of the surgery and the tissue available for closure of the defect.
467
Section
|8|
Management of maxillofacial tumors and cysts
C
A
E
B
F
D
G
Fig. 46.1 Examples of mandibulectomy techniques (shaded areas). (A) Unilateral rostral mandibulectomy. (B) Bilateral rostral mandibulectomy. (C) Central or segmental mandibulectomy with preservation of the mandibular canal and ventral margin (‘rim excision’). (D) Central or segmental mandibulectomy (full thickness). (E) Caudal mandibulectomy. (F) Total mandibulectomy. (G) One-and-a-half mandibulectomy.
468
Mandibulectomy techniques
Chapter
| 46 |
Preoperative management The reader is referred to Chapter 45 and other chapters for anesthetic considerations, preemptive analgesia, antibiotics and oral cavity disinfection.
Patient positioning Dorsal and lateral recumbency The head is secured into position with a vacuum-charged surgical positioning system (Vac-Pac, Olympic Medical, Seattle, WA). This device allows the head to be held in any position. A mouth gag is positioned away from the surgery site to keep the mouth open. The endotracheal tube is secured to the muzzle and the tongue retracted from the surgery site and packed off with gauze sponges. For bilateral rostral mandibulectomy, the patient is placed in dorsal recumbency, with the neck flexed to allow access to both oral and cutaneous sur faces of the rostral mandibles. For unilateral rostral or central man dibulectomy, the patient is placed in lateral or dorsal recumbency with the head rotated to facilitate visualization of the surgical field. The head is held parallel with the table top or the rostral end of the muzzle and lower jaw slightly elevated to improve site access. The neck is extended when the patient is in lateral recumbency. For caudal and total mandibulectomy, the patient is placed in lateral recumbency with the neck extended and the rostral end of the muzzle and lower jaw elevated so the surgeon can look into the open mouth. After positioning, a layer of water-repellant gauze (Exodontia Sponges, Henry Schein, Melville, NY) packing is placed in the pharynx around the endotracheal tube then covered with a layer of absorbent gauze.
Sternal recumbency Sternal recumbency, with the head elevated and the maxilla sus pended, is an alternative method of positioning for mandibulectomy procedures. The maxilla is suspended by perforating the maxillary canine teeth through a long strip of adhesive tape. The ends of the tape are then extended and wrapped high around IV poles placed on either side of the patient’s head. The mandible should be level with or slightly lower than the surface of the surgery table. Sternal recumbency offers excellent visualization of the mandible and oral cavity. In this position, all mandibulectomy procedures can be performed using an intraoral approach. The main hazard of sternal recumbency is fluid aspiration. The use of a cuffed endotracheal tube and pharyngeal pack is necessary to prevent aspiration. Having continuous suction available is very helpful.
SURGICAL ANATOMY26–28 The inferior alveolar artery originates from the maxillary artery. It enters the mandibular foramen, and traverses the mandibular canal with numerous arterioles branching to the bone and teeth. There are no direct vascular anastomoses across the fibrocartilaginous mandibu lar symphysis; however, small extraosseous arterioles span the sym physis in the submucosal tissue. Blood supply to the cortical bone at the symphysis is from endosteal and periosteal surfaces. This extraos seous supply may be important to the viability of a rostral mandibular segment after interruption of the inferior alveolar artery secondary to a caudal or central mandibulectomy. The inferior alveolar artery ter minates in the caudal, middle and rostral mental arteries.
Fig. 46.2 Lingual aspect of mandibular ramus. The mandibular foramen is located in the middle of and immediately ventral to an imaginary line between the palpable landmarks of the angular process and the distal aspect of the mandibular third molar tooth.
The mandibular canal mainly contains the inferior alveolar artery, vein and nerve, and some loose connective tissue and fat. The nerve is dorsolateral, the artery is in the central area and vein ventromedial. Bone convexities from the apical alveolar bone of the mandibular teeth border the lingual or dorsal lingual aspect of the canal. The mandibular canal terminates at the mental foramina. The mandibular foramen is located on the medial aspect of the mandible. It is immediately below and centered on a line from the tip of the angular process to the distal aspect of the third molar tooth in the dog (Fig. 46.2) and the first molar tooth in the cat. Palpation of these landmarks during caudal mandibulectomy aids in dissection of the inferior alveolar artery and nerve as they enter the foramen. The middle mental foramen in the dog is at the level of the rostral root of the second premolar tooth, immediately distal to the apex of the canine tooth and approximately midway between the alveolar margin and ventral bone margin (Fig. 46.3A). In the cat, this foramen is located at the level of the apex of the canine tooth. The caudal mental foramen is at the level of the third premolar tooth and approximately midway between the alveolar margin and ventral margin in the dog and cat. The rostral mental foramen is generally at the level of the second incisor tooth and a short distance ventral to the alveolar margin. Multiple small foramina may be present. The apex of the large curved root of the mandibular canine tooth in the dog extends as far as the apex of the distal root of the second premolar tooth. Therefore, bone resection to remove the canine tooth alveolus would also result in removal of the first and second premolar teeth. In the cat, the apex of the canine tooth is immediately rostral to the mesial root of the third premolar tooth. Complete removal of the bone segment encasing the canine tooth root may also require removal of the third premolar tooth and surrounding bone. The inferior labial artery originates from the facial artery and sup plies the soft tissue of the lower lip. The sublingual artery also origi nates from the facial artery and courses along the medial aspect of the mandible. The ventral buccal branch of the facial nerve provides motor innervation to the muscles of the lip. The mandibular branch of the trigeminal nerve provides motor innervation to the muscles of mastication and sensory innervation to the lower lips, rostral twothirds of the tongue, mandibular teeth (as the inferior alveolar nerve) and buccal cavity. The muscles of mastication insert on the ramus of the mandible and some lingual and hyoid muscles insert on the body of the mandible (Fig. 46.3B). The mandibular and sublingual salivary ducts are visible through the thin oral mucosa and course lateral to the tongue frenulum to end in the sublingual caruncle located just rostrolateral to the rostral margin of the frenulum.
469
Section
|8|
Management of maxillofacial tumors and cysts Temporal muscle
Parotid duct
Masseter muscle
Digastric muscle
Dorsal buccal branch of facial nerve
Facial artery
Ventral buccal branch of facial nerve
Superior labial artery
Inferior labial artery
Caudal, middle, rostral mental nerves and arteries
A
Temporal muscle
Mandibular foramen
Lateral pterygoid muscle Medial pterygoid muscle
Genioglossal muscle B
Geniohyoid muscle
Mylohyoid muscle Sublingual artery
Digastric muscle
Fig. 46.3 (A, B) Surgical anatomy of arteries, nerves and muscles pertaining to mandibulectomy techniques.
470
Mandibulectomy techniques
General surgical principles21–23 Surgical plan The surgical plan for a mandibulectomy procedure includes the fol lowing important points: (1) plan for adequate surgical margins; (2) plan for complete mucosal closure; (3) perform atraumatic surgery and preserve local blood supply; (4) employ minimal use of electro surgery; (5) harvest large mucosal flaps to avoid suture line tension; (6) use double-layer closure if possible; and (7) support suture lines with grossly healthy bone if possible.
Surgical margins Surgical margins are indicated by the biological behavior of the neo plasm as determined by the preoperative histopathological diagnosis, and diagnostic imaging and oral physical examination findings (see Ch. 43). The preoperative histopathological diagnosis is essential for definitive surgical planning. In general, a minimum of 10-mm margin should be obtained for all benign and malignant neoplasms except fibrosarcoma where a minimum margin of 20 mm is recommended due to the higher local recurrence rate.21–23 These recommendations have not been correlated with clinical outcome. Wider margins are obtained for malignant neoplasms if a tension-free oral mucosal reconstruction can be obtained. The surgical margins are measured and marked around the circumference of the mass using a sterile surgi cal marker before starting the surgery. It is important to remember that the periodontal ligament spaces and mandibular canal may facilitate neoplastic cell infiltration. Therefore, if the canine tooth is included in the measured surgical margins, the ostectomy is usually performed between the second and third premolar teeth (in the dog) to ensure complete removal of the canine tooth alveolus. Invasion of the man dibular canal by a malignancy requires total mandibulectomy. Postoperative radiographs of the excised specimen or surgery site are made to document adequate gross surgical margins. The entire specimen is sent for histopathological examination to confirm the diagnosis and to assess the bone and soft tissue margins for neoplastic cells. Finding neoplastic cells on the excision margin implies incom plete removal of local microscopic disease and the need to consider adjunct radiation or chemotherapy.
P3
P2
P1
| 46 |
Surgical incision
SURGICAL TECHNIQUE
P4
Chapter
Canine
The incision is made along the measured and marked surgical margins. The initial incision is a light scoring of the mucosa to produce a minimally bleeding incision line. Once the margins of the proposed excision are verified the incision is taken to bone. Once incised, the alveolar mucosal margins may retract and result in some distortion of the proposed margins. The described incision method maintains accu rate surgical margins. In the regions of foramina, the dissection is continued to identify, ligate and transect the vessels and transect the nerves. Hemorrhage is controlled by ligation, pressure and minimal focal use of electrocoagulation. Depending on surgical margins, muscles attaching to the mandible are subperiosteally elevated or transected. Concurrent lip wedge excision may be needed to obtain adequate surgical margins. This is true for large neoplasms along the body of the mandible and when a bilateral rostral mandibulectomy is per formed. Wedge excision is also performed during the latter procedure to remove excess skin. Lip excision compromises blood supply to the remaining rostral lip segment; however, viability is maintained by submucosal arterial branches.
Management of adjacent teeth Maintaining teeth is secondary to achieving adequate surgical margins and tension-free closure. Ostectomy performed at a narrow interden tal space may result in injury requiring extraction of a tooth adjacent to the ostectomy site if inadvertent severe periodontal or endodontal injury (root canal exposure) occurred during ostectomy. Ostectomy at the level of a wider interdental space may not result in similar tooth injury. Therefore, to minimize tooth loss, the ostectomy margins are planned to transect a tooth at the margin level (Fig. 46.4). This may require margin extension, which is acceptable. Margins should never be compromised to save teeth. Once the en-bloc tissue mass is excised, the remnant of the transected tooth is extracted. The adjacent teeth and periodontal structures are not injured, leaving a margin of attached and free gingiva adjacent to the ostectomy.
Ostectomy and osteoplasty Ostectomy often removes a full-thickness (dorsoventral) segment of the mandible. However, in the case of smaller neoplasms, adequate surgical margins may be achieved by partial-thickness excision or rim
Mass
P4
P3
P2
P1
Canine
Mass
A
Ostectomy line
B
Ostectomy line
Fig. 46.4 Ostectomy lines for (A) rostral mandibulectomy, and (B) caudal mandibulectomy in relation to adjacent teeth. Transecting a tooth at the time of excision will not injure adjacent teeth; the remaining tooth fragment is removed after the en-bloc excision is completed. The specific level of ostectomy is dependent upon measured surgical margins.
471
Section
|8|
Management of maxillofacial tumors and cysts
excision allowing the mandibular canal and thick ventral cortical bone or a portion of the mandibular symphysis to remain intact (see Fig. 46.1).1 Postoperative mandibular instability is avoided. The soft tissues are subperiosteally elevated away from the ostec tomy site. The ostectomy is performed as determined by the premeas ured surgical margins. The excision is planned so that all root structures of teeth within the surgical margins are part of the en-bloc excision. Any remaining tooth root tips from transected teeth at the excision periphery are extracted after the en-bloc tissue segment is removed. Ostectomy may be performed with a thin osteotome and mallet. The instruments are used with gentle technique to slowly advance the depth of bone cut. Aggressive use may result in fractures of remaining bone. Increased resistance will be found when tooth roots are encoun tered and may require extraction of the tooth or deviation of the ostectomy course to include the entire tooth. The mandibular sym physis is split using an osteotome and mallet. Power equipment that cuts bone with saw blades or burs offers the most efficient ostectomy method. The most control is gained when using a surgical handpiece with continuous irrigation and bone cutting burs. Carbide steel bone cutting burs may leave a roughened bone edge. Medium grit diamond tapered cylinder burs produce a smooth bone cut. Once the en-bloc tissue segment is removed, osteo plasty is performed. Cut bone margins are smoothed with a round, medium or fine grit diamond bur or carbide bur. The goal is to remove all sharp bone ridges and bone spikes that may result in ischemic pressure injury and potential perforation of the mucosal flaps. Osteotomy of the ventral third of the mandible is performed last. Ideally, the inferior alveolar artery is isolated, ligated and transected. In the event of inadvertent transection of the artery during osteotomy, the artery is retrieved and ligated. If the artery cannot be retrieved, a hemostatic agent is firmly packed into the mandibular canal.
Flap design General principles Recommended oral mucosal flap length to base width ratio is 2 : 1 in humans29 and is unknown in the dog and cat. In general, the flap is made slightly larger than necessary to ensure adequate tissue for tension-free closure and should, ideally, not have vertical releasing incisions, as flap blood supply may be compromised.29 If vertical releasing incisions are needed, they are divergent from the flap apex to base to maintain a broad-based flap for blood supply conservation.29 The flaps are gently handled. Excessive pulling, crushing or dessica tion may injure flap blood supply.29 Tissue forceps are not closed tightly, to avoid crushing the tissue and potential marginal ischemic necrosis. Thin tissue flaps may be atraumatically manipulated by placement of two stay sutures. Defect closure is most commonly achieved using local mucosal tissues. Advanced closure techniques are discussed in Chapter 48.
Vestibular mucosal–submucosal flap The flap is harvested by dissecting from the mandibulectomy site toward the lip margin. The plane of dissection is immediately below the submucosa. Branches of the inferior labial artery, vein, ventral buccal branch of the facial nerve and adjacent skeletal muscle are visualized during flap elevation and remain in their original position. Flap elevation is continued until there is enough tissue for a tensionfree closure. The flap blood supply is from the inferior labial artery. The amount of remaining buccal mucosa is determined by the size of the excision. A lesser amount of remaining buccal mucosa results in a larger lingual deviation of the lip and a mandibular concavity.
472
Surgical defect closure Reconstruction of an oral mucosal lining is essential and is deter mined by preoperative planning. Healing without complication depends largely on accurate tension-free apposition of incised soft tissue margins. Inverted epithelium from poor approximation and suture line tension will delay wound healing. A two-layer closure, when possible, is preferred.
Closure at the rostral mandible Separation of the mandible for unilateral rostral or total mandibulec tomy is commonly performed at the mandibular symphysis. The ves tibular mucosal–submucosal flap is sutured to the mucoperiosteal fibrous tissue at the symphysis. The needle is passed from the intact mucoperiosteum toward the symphysis. A wide bite is taken and the needle ‘walked off’ the bone at the level of the symphysis. Excellent suture retention is provided and accurate placement will not tear the tissue. The suture is then passed through the vestibular flap (Fig. 46.5A). If an ostectomy of the rostral mandible is performed, the muco periosteal tissue margin is trimmed back 1–3 mm to expose a bone rim that will support the suture line. The new soft tissue margin is subperiosteally elevated to facilitate suture placement. A one-layer closure is performed and the suture line is supported by bone (Fig. 46.5B, C).
Closure at the mandibular body Full-thickness ostectomies of the body of the mandible are made per pendicular to the long axis of the bone. For closure, the ostectomy is modified to provide tension-free tissue apposition over the cut bone margin (Fig. 46.6).2 As needed, an alveolar margin incision, combined with a sulcular incision partially around the adjacent intact tooth, is made. The attached gingiva along with the proximal alveolar mucosa on the buccal and lingual side is subperiosteally elevated. The corner of the ostectomy at the level of the alveolar margin is tapered 30–60 degrees with a saw blade or bur. Osteoplasty is then performed. The adjacent intact tooth is not injured. The attached gingiva is contoured and then sutured over the tapered area with simple interrupted sutures using generous tissue bites. The buccal and alveolar mucosal– submucosal flaps are apposed using simple interrupted sutures. Although this technique provides tension-free tissue apposition, the suture line in the attached gingiva may have stress applied during pre hension and mouth closure. This is especially true for bilateral rostral mandibulectomies. The thick keratinized attached gingiva provides excellent suture retention. However, during early healing all tension is placed on the sutures; therefore, larger-gauge sutures may be used for suturing the attached gingiva over the tapered alveolar bone margin.
Unilateral rostral mandibulectomy This procedure usually includes removal of the incisor teeth, canine tooth and first and second premolar teeth in the dog, and incisor teeth, canine tooth and possibly the third premolar tooth in the cat. It may be difficult to obtain an adequate surgical margin on the medial aspect. In this case, instead of splitting the mandibular sym physis, an ostectomy of the rostral aspect of the opposite mandible may be needed. In the dog, the ostectomy generally includes the first and second premolar teeth, as the root of the canine tooth extends up to the level of the distal root of the second premolar tooth. If only incisor teeth are removed, a portion of the mandibular symphysis remains intact. Removal of the incisor part is only rarely indicated due to the proximity of the canine tooth and the need for adequate surgi cal margins. The labial vestibular mucosal–submucosal flap is sutured to the mucoperiosteum of the remaining rostral mandible (see Fig. 46.5) and alveolar mucosa if the excision extends caudal to the
Mandibulectomy techniques Tongue frenulum
Suture
Cut soft tissue cross-section
Sublingual caruncles
Soft tissue margin
Exposed bone shelf Symphysis Lip margin Labial mucosal flap margin
A
Tapered bone margin
New lip margin
Chapter
| 46 |
the canine teeth alveoli. The incision is made as a lip wedge excision to include surgical margins and estimated excess skin. For tumors centered at the incisive part and extending facially, a single wide sym metrical wedge of skin is excised on the facial aspect as part of the en-bloc excision (Fig. 46.7). For tumors that occur more caudally or laterally, two skin wedges are removed at the level of the lateral lower labial frenula or a single large asymmetrical skin wedge is removed. Wedge resection is conservatively performed to ensure that an ade quate amount of skin is present for tension-free closure. Bilateral fullthickness wedge removal of lip margins does sacrifice the inferior labial blood flow to the remaining rostral lip and skin segment. Large bilateral wedge resections may compromise the remaining random blood supply to this rostral segment. A small portion of the caudal mandibular symphysis may remain intact. Mandibular and sublin gual salivary ducts and caruncles are avoided. If the ducts must be transected, as in mandibulectomies at the level of the third or fourth premolar teeth, they are ligated. The mucoperiosteum at the rostral mandible is tightly attached, and sharp dissection may be more effi cient than blunt tissue elevation. The rostral mental blood vessels at the level of the apex of the second incisor teeth are coagulated. When transecting the lateral lower labial frenula, the middle mental blood vessels are encountered and are ligated to prevent unnecessary blood loss. The osteotomy is preferably performed with an osteotomy bur on a surgical handpiece with continuous irrigation in a careful manner in order to avoid transecting the inferior alveolar blood vessels without prior ligation. After excision, osteoplasty of the ventral margin is performed using a bur to provide a more normal ‘chin’ contour. If the excision removed the entire symphysis, the ostectomies of each mandibular body are tapered at the alveolar margin (see Figs 46.1 and 46.6) and the attached gingiva closed. A suture is placed in the lip margin to main tain alignment for cosmetic closure. The oral mucosa is apposed using simple interrupted sutures with knots placed in the oral cavity. The remaining closure is routine. For large active dogs with heavy, thick, pendulous lips, the intraoral suture lines can be bilaterally bolstered to reduce tension during the early phase of healing. A polypropylene suture is passed distal to the third premolar tooth on each side. A 22-gauge hypodermic needle is placed through the gingiva immediately distal to the tooth and dorsal to the alveolar margin. The suture is passed through the needle. The arms of the suture are passed through the full-thickness rostral soft tissue and tied over a button or suture bolster. The suture is held in position by the gingiva but is anchored by the tooth. A similar suture is placed on the opposite side. These sutures are removed in 7 to 10 days.
Central or segmental mandibulectomy B Fig. 46.5 Closure of a unilateral rostral mandibulectomy. (A) The vestibular mucosal–submucosal flap is sutured to the large amount of mandibular mucoperiosteal fibrous tissue using wide suture bites. (B) Closure results in an asymmetrical rostral mandible.
symphysis. Lip wedge excision to remove excess tissue before closure is not needed.
Bilateral rostral mandibulectomy The surgical margins are determined and the amount of skin left for tension-free closure is estimated. The osteotomy is made at the distal aspect of the second premolar teeth to ensure complete removal of
A segment of the mandibular body is excised leaving behind two ostectomy cuts. Each ostectomy is tapered at the alveolar margin (Figs. 46.1 and 46.6). The attached gingiva and mucosal tissues are sutured. The salivary ducts are avoided when possible. If the ducts are transected, they are ligated. With a more conservative variation of this technique, known as a rim excision, a horizontal osteotomy is made at the level of the dorsal border of the mandibular canal.1 This leaves the neurovascular struc tures in the mandibular canal and the ventral margin intact (see Fig. 46.1E). Closure is the same as described above.
Caudal mandibulectomy Depending on neoplasm size and location, a full-thickness cheek incision may be made from the commissure and extended caudally
473
Section
|8|
Management of maxillofacial tumors and cysts
Mucogingival junction
Mucogingival flaps Partial alveolus
Bone margin tapered Ostectomy site
A
B
Mandibular canal
Mucogingival junction
Rounded corners of bones
C
D
Fig. 46.6 Tapering the alveolar bone margin to reduce suture line tension. The adjacent tooth was transected during ostectomy; the root remnant has been extracted leaving a partial alveolus. (A) Alveolar margin and sulcular incisions are made and the attached gingiva and proximal alveolar mucosa are subperiosteally elevated. (B) The alveolar margin bone is tapered approximately 30–60 degrees. (C) Osteoplasty is performed by rounding the bony edges. (D) The attached gingiva and alveolar mucosa is closed over the surgical defect.
as needed. Mucosal incisions are made along the measured surgical margins. However, it is often unnecessary to incise the cheek to achieve surgical margins and have good site exposure, especially when dorso lateral or sternal positioning is used. Using the intraoral approach, a mucosal incision is made over the rostral edge of the ramus then extended in a buccal and lingual direction around the mandibular body along surgical margins. After dissection of the caudal part of the mandibular body and ostectomy, dissection along the ramus is per formed. The insertions of the muscles of mastication are subperio steally elevated or the muscle body transected, depending on surgical margins. If needed, the masseter is excised as part of the en-bloc exci sion. The digastric and pterygoid muscles are elevated or transected, as determined by surgical margins. The mandibular foramen is located and the inferior alveolar artery is ligated and transected close to the
474
foramen to avoid injury to the maxillary artery. The inferior alveolar nerve is also transected as close as possible to the foramen, in order to avoid damage to the lingual nerve. The temporalis muscle inser tions on the medial and lateral aspects of the ramus and coronoid process are elevated or transected, as determined by the surgical margins. The temporomandibular joint is located by palpation during manipulation of the caudal mandibular en-bloc segment. The capsule is incised on the medial aspect. As the mandible is manipulated to aid visualization, adjacent soft tissues are gently ‘wiped’ off the capsule and the capsule incision extended laterally. The rostral and caudal aspects of the capsule are incised in this manner and the lateral liga ment is incised last. It is essential that dissection and joint capsule incision occur immediately adjacent to the condylar process to avoid injury to adjacent vessels and nerves. The tortuous course and close
Mandibulectomy techniques
Chapter
| 46 |
Lip margin
Skin incision
Suture line
B
A Tongue frenulum Lip margin
Lip margin
Sublingual caruncle
Wedge excision of skin
Intraoral suture line
D
C Fig. 46.7 Bilateral rostral mandibulectomy. The patient is in dorsal recumbency. (A) The wedge incision (either symmetrical, left, or asymmetrical, right) incorporates the surgical margins and estimated excess skin and lip for closure. (B, C) Closure results in a linear skin suture line and a transverse oral mucosal suture line. (D) Alternative skin and lip closure with bilateral removal of full-thickness labial tissue.
proximity of the maxillary artery on the ventromedial aspect of the joint, and its local branches, make them vulnerable to inadvertent transection. Once the joint is disarticulated, any remaining soft tissue attachments are cut. A local anesthetic ‘splash’ block may be applied to the surgery site. Placement of local hemostatic agents (see Ch. 7) may be needed to help control bleeding from transected muscles. Oral mucosal tissues are opposed using simple interrupted sutures. Closure is routine.
Unilateral (total) mandibulectomy Penetration of the mandibular canal implies potential spread of neo plasm along the length of the mandible, indicating the need for total mandibulectomy. This procedure can be performed with the patient in lateral recumbency using an incision of the cheek. This may facili tate the caudal dissection, especially in some large patients and in patients with more caudally located masses necessitating excision of the masseter muscle, and transection rather than subperiosteal eleva tion of other muscles. The procedure can be performed intraorally with the patient in sternal recumbency. The intraoral incision is started as described for caudal mandibulectomy and continued along the predetermined surgical margins. The mandibular symphysis is split using a thin osteotome and mallet and the body and ramus dissected free of all tissue attachments, as described above for the various partial mandibulectomy techniques. If necessary for surgical margins, the tongue frenulum can be removed without altering tongue function. Soft tissue excision may extend toward the opposite mandible.
However, this excision margin is limited by the need for primary mucosal closure. Extensive removal of sublingual muscle may result in impairment of tongue function. The mandible is excised intact. The commissure is moved rostrally to minimize drooling and help prevent tongue protrusion. Commissurorrhaphy is performed by exci sion of the lip margin followed by a three-layer closure. The new commissure is approximately at the level of the mandibular second premolar tooth. A full-thickness horizontal mattress suture may be placed to span between the upper and lower lip immediately rostral to the new commissure. This suture is tied over buttons or suture bolsters. Its purpose is to restrain mouth opening to keep tension off the commissure suture line and promote normal healing.
Stabilization of mandibular segments To date, reconstruction following mandibulectomy is infrequently performed.30 An ulnar autograft combined with rigid internal fixation was used to bridge a central mandibulectomy site for benign neo plasm excision, with good results.31 This technique has the potential to eliminate mandibular instability and malocclusion and improve cosmetic results for central mandibulectomies. Stabilization of the remaining lower jaw after bilateral rostral mandibulectomy has been attempted using orthopedic pins,32 screws,4,7 and screws and bone graft.33 The screws and pins are placed before the excision is performed. Mandibular instability is avoided and prehension is similar to that of patients not having any stabilization technique performed.
475
Section
|8|
Management of maxillofacial tumors and cysts
A microvascular bone autograft using coccygeal vertebrae has been reported for fracture reconstruction of a central mandibular defect in a dog.34 Microvascular transfer of bone autografts is the preferred method of mandibular reconstruction in humans and may be of benefit to selected small animal patients.35
POSTOPERATIVE CARE AND ASSESSMENT Most aspects of postoperative care, including pain management and nutritional support, are similar to those described for maxillectomy (see Ch. 45).
Postoperative patient appearance21–23 Swelling of the surgical site is usually resolved by 3 to 7 days postop eratively. Cosmetic appearances are generally good and depend on the extent of excision. Smaller excisions result in unnoticeable or minimal cosmetic abnormalities. Regrowth of hair will conceal many surgically created facial asymmetries. Unilateral rostral mandibulectomy without canine tooth removal results in no obvious abnormality. When the canine tooth is removed, the tongue hangs out from that side when panting. Bilateral rostral mandibulectomy results in relative mandibu lar brachygnathism and the most noticeable uncosmetic appearance (Fig. 46.8). The tongue protrudes from the mouth during panting. Drooling may occur. Central mandibulectomy results in a mild facial concavity. Caudal and complete mandibulectomy result in facial con cavity and tongue protrusion from the side of surgery during panting (Fig. 46.9). Malocclusion occurs as the remaining mandible shifts toward the operated side.
A
Homecare and follow-up Most patients are sent home in 2 to 3 days postoperatively. A soft food diet and removal of chew toys is recommended for 2 to 3 weeks. The client is shown how to administer any oral medications so as not to disrupt the suture line. Medications are concealed in soft food snacks. If oral manipulation is needed, the manipulation is performed away from the surgical site. The surgical site is examined in 2 weeks and any skin sutures removed. The surgical site is reexamined at 1 month postoperatively and any residual oral sutures removed at this time. Most oral sutures are extruded in approximately 2 to 3 weeks. A com plete physical examination, including the surgical site, is performed at 3-month intervals for 1 year. In case of malignant neoplasms, threeview thoracic radiographs are obtained at these examinations.
COMPLICATIONS19–23 Intraoperative complications Hemorrhage is the major intraoperative complication. It is managed as it is encountered by ligation, pressure or focal use of electrocoagula tion. The risk for excessive bleeding is the highest during ostectomy and during dissection of the caudal mandible. Blood loss during ostectomy is minimized by cutting the bone of the ventral mandible last and isolating and ligating the inferior alveolar artery. In the event of inadvertent transection of the artery, rapid completion of the ostec tomy is done and the vessel retrieved and ligated. If the artery retracts into the canal and cannot be retrieved, the mandibular canal is packed with a suitable hemostatic agent (see Ch. 7). Careful dissection for disarticulation of the temporomandibular joint is required to avoid vascular injury and profuse hemorrhage.
476
B Fig. 46.8 (A) Lateral and (B) ventrodorsal view of a patient after bilateral rostral mandibulectomy.
Mandibulectomy techniques
Chapter
| 46 |
Functional complications Malocclusion
A
The contralateral mandible is initially unstable and drifts toward the midline. Elastic training using orthodontic buttons and power chain between the buccal aspect of the maxillary fourth premolar tooth and the lingual aspect of the mandibular canine tooth is a simple method for prevention of mandibular drift but requires good client compli ance.36 Abnormal contact with the remaining mandibular canine tooth may result in palatal or upper lip ulceration. Crown reduction and partial coronal pulpectomy, or extraction of the mandibular canine tooth, is needed to resolve the palatal ulceration.37 The remain ing mandible may occasionally drift away from the midline. When this happens the mandibular and maxillary teeth meet end on. Click ing is briefly audible until the mandible drifts medially. The unstable mandibular movement is reduced 4–6 weeks after surgery; however, occlusion may remain abnormal. Long-term follow-up of clinical cases does not suggest abnormal temporomandibular joint clinical effects. After experimental unilateral rostral mandibulectomy, tempo romandibular degenerative joint disease occurred and did not impair the dogs at 3 and 6 months postoperatively.38
Prehension Most patients prehend and drink normally after partial mandibulec tomy. Patients with more extensive excisions practice eating and adapt after a short period of time. Some dogs spill a large amount of food around the food-bowl during this period. Food with a consistency similar to ground meat or soaked kibble seems the easiest to prehend. Hand-feeding may be permanently necessary with some patients after a one-and-one-half mandibulectomy. These patients usually adapt to drinking by a combination of lapping and sucking water.
Drooling Drooling occurs with bilateral rostral mandibulectomies and total mandibulectomies. Drooling often decreases over time. If the new lip margin is immediately rostral to the sublingual caruncles when closing a bilateral rostral mandibulectomy, the mandibular and sub lingual salivary ducts may be ligated to reduce drooling potential. Moving the commissure rostrally during closure of a total man dibulectomy usually prevents drooling.
Tongue protrusion Lateral tongue protrusion occurs when a mandibular canine tooth is absent, as in a unilateral rostral mandibulectomy or total mandibulec tomy. Ventral tongue protrusion occurs following a bilateral rostral mandibulectomy. The protrusion is most evident when panting. Dessication of the tongue rarely occurs. B
Ranula
Fig. 46.9 (A) Lateral and (B) ventrodorsal view of a patient after a total mandibulectomy of the right mandible. Lateral tongue protrusion during panting and mandibular drift to the right side are visible.
A ranula may result from surgical trauma to the salivary duct or papilla or postoperative swelling that temporarily impairs flow of saliva from the sublingual caruncle. This condition may occur at 1 to 2 days postoperatively and usually resolves by 5 to 7 days. Treatment is not needed.
Dehiscence
Dental calculus
Dehiscence of the commissurorrhaphy may occur and is repaired by delayed primary closure. A small dehiscence over the ostectomy site exposing bone will usually heal by second intention. A larger dehis cence requires debridement and resuturing.
The ipsilateral maxillary fourth premolar tooth and molar teeth may accumulate dental calculus more rapidly, as compared to the contral ateral side, in patients with central, caudal and total mandibulecto mies. There is an apparent compromise of normal oral cleansing,
477
Section
|8|
Management of maxillofacial tumors and cysts
possibly due to a closer postoperative adaptation of the cheek to the maxillary teeth surfaces. Oral health checks are essential for the life of the patient.
sucking water. A very extensive mandibulectomy may interfere with the patient’s ability to maintain hydration.
Subtotal mandibulectomy Local tumor recurrence Local tumor recurrence is common with certain tumor types. Suspi cious areas noted during recheck examinations must be biopsied to differentiate neoplasm recurrence from suture reaction and scar tissue.
PROGNOSIS The overall prognosis for mandibulectomy techniques regarding oral function, operative and postoperative complications, postoperative appearance and client satisfaction is good to excellent.15,21–23 This seems directly related to surgeon experience with appropriate patient selection, technical performance of the surgery and preoperative client communications to set realistic expectations. Less positive results may occur in patients with more aggressive disease and more radical surgery. One study reported an overall 85% client satisfaction with maxillectomy and mandibulectomy procedures. The satisfaction level correlated with the postoperative survival time of the patient.15 Local recurrence rates, survival times and biologic behavior of benign and malignant oral tumors reported in various clinical studies have been reviewed.23,24,39 Fibrosarcoma has the highest local recur rence rate (46%) followed by melanoma (25%), osteosarcoma (25%), squamous cell carcinoma (15%) and benign neoplasms (0–4%).23,39 Early recognition, accurate diagnosis and aggressive, planned excision are essential for optimal results.
OTHER CONSIDERATIONS Extent of mandibulectomy Ideally, the functions of prehension and mastication for normal ali mentation and hydration are maintained. When a one-and-one-half mandibulectomy is performed (see Fig. 46.1), many patients require manual assistance with eating and must be hand-fed food shaped into balls. Drinking is accomplished by a combination of lapping and
This procedure leaves most of the ramus intact with a normal coro noid process and temporomandibular joint. This avoids the more difficult dissection to remove the caudal aspect of the mandible, thereby reducing surgical trauma. However, the surgeon must be sure that the soft tissue and bone surgical margins are not compromised. The mandibular foramen is located approximately halfway between the coronoid crest and medial aspect of the condylar process. There fore, transection of the mandibular body distal to the third molar will result in a portion of intact mandibular canal being left behind. This is of particular concern when surgery is performed for a tumor that potentially invaded the mandibular canal. Osteoplasty is important before mucosal closure. The normal movement of the intact caudal mandible may result in perforation of the oral mucosa or suture line disruption by sharp bone areas left at the ostectomy site.
Teeth rostral to ostectomy Central and caudal mandibulectomy transect the inferior alveolar artery and nerve that are the major neurovascular supply to the remaining rostral mandibular teeth.28 Primate studies of teeth encased in an ostectomized segment of bone that maintains most of its original soft tissue attachments and is stabilized in position with orthopedic wire somewhat mimics the clinical picture of central and caudal mandibulectomy in dogs and in cats in which intact teeth are in a rostrally located bone segment.40–42 In these studies, it appeared that the periodontal vessels continued to provide blood supply to the dental pulp by anastomosis with apical vessels and through lateral canals.40–42 This periodontal blood supply originated from the intact soft tissue vessels. The pulp vessel density was initially reduced but was found to increase over time. Ischemic injury was suggested by loss of odontoblasts, inflammation, fibrosis and foci of pulp necro sis. The pulp vessel density increased over time and odontoblasts with secondary dentin production and reduced inflammation and necrosis were found. Pulp nerve fiber degeneration occurred. There fore, dental pulp of teeth in isolated segments of bone with intact soft tissues maintain vascularity although ischemia may initially occur. Endodontic intervention is not recommended unless clinically indicated.
REFERENCES 1. Brown JS, Kalavrezos N, D’Souza J, et al. Factors that influence the method of mandibular resection in the management of oral squamous cell carcinoma. Br J Oral Maxillofac Surg 2002;40:275–84. 2. Lantz GC, Salisbury SK. Partial mandibulectomy for treatment of mandibular fractures in dogs: eight cases (1981–1984). J Am Vet Med Assoc 1987; 191:243–5. 3. Manfra Marretta S. Maxillofacial surgery. Vet Clin North Am Small Anim Pract 1998;28:1285–96. 4. Withrow SJ, Holmberg DL. Mandibulectomy in the treatment of oral
478
cancer. J Am Anim Hosp Assoc 1983; 19:273–86. 5. Bradley RL, MacEwen EG, Loar AS. Mandibular resection for removal of oral tumors in 30 dogs and 6 cats. J Am Vet Med Assoc 1984;184: 460–3. 6. White RAS, Gorman SB, Watkins SB, et al. The surgical management of bone-involved oral tumors in the dog. J Small Anim Pract 1985;26:693–708. 7. Penwick RC, Nunamaker DM. Rostral mandibulectomy: a treatment for oral neoplasia in the dog and cat. J Am Anim Hosp Assoc 1987;23:19–25.
8. Salisbury SK, Lantz GC. Long-term results of partial mandibulectomy for treatment of oral tumors in 30 dogs. J Am Anim Hosp Assoc 1987;24: 285–94. 9. White RAS, Gorman NT. Wide local excision of acanthomatous epulides in the dog. Vet Surg 1989;18:12–14. 10. Kosovsky JK, Matthiesen DT, Manfra Marretta S, et al. Results of partial mandibulectomy for the treatment of oral tumors in 142 dogs. Vet Surg 1991; 20:397–401. 11. Schwarz PD, Withrow SJ, Curtis CR, et al. Mandibular resection as a treatment for
Mandibulectomy techniques oral cancer in 81 dogs. J Am Anim Hosp Assoc 1991;27:601–10. 12. White RAS. Mandibulectomy and maxillectomy in the dog: long term survival in 100 cases. J Small Anim Pract 1991;32:69–74. 13. Hutson CA, Willauer CC, Walder EJ, et al. Treatment of mandibular squamous cell carcinoma in cats by use of mandibulectomy and radiotherapy: seven cases (1987–1989). J Am Anim Hosp Assoc 1992;201:777–81. 14. Straw RC, Powers BE, Klausner J, et al. Canine mandibular osteosarcoma: 51 cases (1980–1992). J Am Anim Hosp Assoc 1996;32:257–62. 15. Fox LE, Geoghegan SL, Davis LH, et al. Owner satisfaction with partial mandibulectomy or maxillectomy for treatment of oral tumors in 27 dogs. J Am Anim Hosp Assoc 1997;33:25–31. 16. Northrup NC, Selting KA, Rassnick KM, et al. Outcomes of cats with oral tumors treated with mandibulectomy:42 cases. J Am Anim Hosp Assoc 2006;42:350–60. 17. Harvey CE. Oral surgery, radical resection of maxillary and mandibular lesions. Vet Clin North Am Small Anim Pract 1986;16:983–93. 18. Birchard S, Carothers M. Aggressive surgery in the management of oral neoplasia. Vet Clin North Am Small Anim Pract 1990;20:1117–40. 19. Matthiesen DT, Manfra Marretta S. Results and complications associated with partial mandibulectomy and maxillectomy techniques. Probl Vet Med 1990;2:248–75. 20. Salisbury SK. Problems and complications associated with maxillectomy, mandibulectomy, and oronasal fistula repair. Probl Vet Med 1991:3:153–69. 21. Salisbury SK. Maxillectomy and mandibulectomy. In: Slatter DH, editor. Textbook of small animal surgery. 3rd ed. Philadelphia, PA: WB Saunders; 2003. p. 561–72.
22. Hedlund CS. Surgery of the digestive system, surgery of the oral cavity and oropharynx. In: Fossum TW, editor. Small animal surgery. 3rd ed. St. Louis, MO: Mosby; 2007. p. 339–47. 23. Dernell WS, Schwarz PD, Withrow SJ. Mandibulectomy. In: Bojrab MJ, editor. Current techniques in small animal surgery. 4th ed. Philadelphia, PA: Williams and Wilkins; 1998. p. 132–42. 24. Salisbury SK. Aggressive cancer surgery and aftercare. In: Morrison WB, editor. Cancer in dogs and cats, medical and surgical treatment. Philadelphia, PA: Williams and Wilkins; 1998. p. 265–321. 25. Verstraete FJM. Mandibulectomy and maxillectomy. Vet Clin North Am Small Anim Pract 2005;35:1009–39. 26. Evans HE. Miller’s anatomy of the dog. 3rd ed. Philadelphia, PA: WB Saunders; 1993. 27. Smith MM. Lingual approach for surgical extraction of the mandibular canine tooth in dogs and cats. J Am Anim Hosp Assoc 1996;32:359–64. 28. Roush JK, Howard PE, Wilson JW. Normal blood supply to the canine mandible and mandibular teeth. Am J Vet Res 1989;50: 904–7. 29. Hupp JR. Principles of surgery. In: Peterson LJ, Ellis III E, Hupp JR, et al. editors. Contemporary oral and maxillofacial surgery. 4th ed. St. Louis, MO: Mosby; 2003. p. 42–8. 30. Boudrieau RJ, Mitchell SL, Seeherman H. Mandibular reconstruction of a partial hemimandibulectomy in a dog with severe malocclusion. Vet Surg 2004;33: 119–30. 31. Bracker KE, Trout NJ. Use of a free cortical ulnar autograft following en bloc resection of a mandibular tumor. J Am Anim Hosp Assoc 2000;36:76–8. 32. Vernon FF, Helphrey M. Rostral mandibulectomy – three case reports in dogs. Vet Surg 1983:12:26–9.
Chapter
| 46 |
33. Bradney IW, Hobson HP, Stromberg PC. Rostral mandibulectomy combined with intermandibular bone graft in treatment of oral neoplasia. J Am Anim Hosp Assoc 1987;23:611–15. 34. Yeh LS, Hou SM. Repair of a mandibular defect with a free vascularized coccygeal vertebra transfer in a dog. Vet Surg 1994; 23:281–5. 35. Disa JJ, Cordeiro PG. Mandible reconstruction with microvascular surgery. Semin Surg Oncol 2000;19:226–34. 36. Bar-Am Y, Verstraete FJM. Elastic training for the prevention of mandibular drift following mandibulectomy in dogs: 18 cases (2005-2008). Vet Surg 2010;39: 574–80. 37. Niemiec BA, Mulligan TW. Vital pulp therapy. J Vet Dent 2001;18:154–6. 38. Umphlet RC, Johnson AL, Eurell JC, et al. The effect of partial rostral hemimandibulectomy on mandibular mobility and temporomandibular joint morphology in the dog. Vet Surg 1988;17: 186–93. 39. Liptak JM, Withrow SJ. Cancer of the gastrointestinal tract, oral tumors. In: Withrow SJ, Vail DM, editors. Small animal clinical oncology. 4th ed. Philadelphia, PA: WB Saunders; 2007. p. 455–75. 40. Lownie JF, Cleaton-Jones PE, Fatti LP, et al. Vascularity of the dental pulp after segmental osteotomy in the chacma baboon (Papio ursinus). Brit J Oral Maxillofac Surg 1998;36:285–9. 41. Lownie JF, Cleaton-Jones PE, Coleman H, et al. Long-term histologic changes in the dental pulp after posterior segmental osteotomies. Oral Surg Oral Med Oral Path 1999;87:299–304. 42. Lownie JF, Cleaton-Jones PE, Fatti LP, et al. Nerve degeneration within the dental pulp after segmental osteotomies in the baboon (Papio ursinus). J Dent Assoc S Afr 1996;51:754–8.
479