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Selected midfacial access procedures to the skull base
Journal of Clinical Neuroscience (2003) 10(3), 340–345 ª 2003 Published by Elsevier Science Ltd. doi:10.1016/S0967-5868(03)00009-2
Operative technical review
Selected midfacial access procedures to the skull base K.R. Spencer
BHB MBCHB MDSC FRACDS (OMS),
A.L. Nastri
MBBS MDSC FRACDS (OMS),
D. Wiesenfeld
MDSC FDSRCPS FRACDS (OMS)
Oral and Maxillofacial Surgery Unit, The Royal Melbourne Hospital, Melbourne, Australia
Summary The indications and operative technique of various procedures commonly used to provide or increase access to the central skull base, anterior and middle cranial fossae, nasopharynx, infratemporal fossa and retromaxillary space are discussed with illustrative cases. ª 2003 Published by Elsevier Science Ltd. Keywords: transfacial access, osteotomy, skull base, infratemporal fossa, anterior cranial fossa, middle cranial fossa, retromaxillary space
INTRODUCTION Lesions involving the central and lateral skull base, infratemporal fossa and retromaxillary region are difficult to access. Tumours once considered inoperable by virtue of their site are accessible using various techniques that have been developed over many years to allow access to these sites with minimal morbidity. In cooperation with the neurosurgeon, the oral and maxillofacial surgeon is able to select and provide appropriate access in these cases. The purpose of this article is to review some of the more commonly used approaches and discuss their indications, operative details and limitations. Anatomy of the skull base A systematic approach to tumours of the base of the skull has previously been described1 in which the base of skull is divided into right and left lateral and central compartments by the internal carotid arteries. The lateral compartments are further subdivided into anterior, middle and posterior segments. The central compartment contains the anterior cranial fossa (cribriform plate, planum sphenoidale, orbital roofs and greater wing of sphenoid), clivus, body of sphenoid and upper cervical spine. The anterior segment of the lateral compartment extends from the anterior middle cranial fossa back to the anterior edge of the petrous temporal bone and contains part of the greater wing of the sphenoid and the inferior surface of the petrous temporal bone (the infratemporal and retromaxillary areas) (Fig. 1). The middle and posterior segments of the lateral compartment are not accessible via transfacial approaches and will not be discussed in this article. Access to the central compartment is achieved via anterior approaches whilst the anterior segment of the lateral compartment is accessed from lateral or combined anterolateral approaches.
nasopharyngeal polyp. Kocher described a midline lip and palatal split to provide improved access to the pituitary fossa.2 In 1987, Archer et al.3 used the approach to access distal vertebral and midbasilar aneurysms and in 1991, James and Crockard4 added a midline sagittal split of both maxilla and soft palate to improve access to the cranio-vertebral junction. Horizontal osteotomy and down-fracture of the maxilla offers wide exposure to the postnasal space, central skull base, and upper clivus and is the procedure of choice for the removal of benign lesions such as clival chordomas and nasopharyngeal tumours. When combined with a mid-palatal split, the improved access to the cranio-vertebral junction facilitates access to tumours that extend above and below the foramen magnum, and enables surgical decompression in cases of severe basilar invagination. The development of bone miniplate systems has enabled surgeons to rigidly replace the osteotomised segments, and pre-location of the miniplates before the osteotomy is completed enables rapid fixation with restoration of the occlusion at the completion of the procedure.
ANTERIOR APPROACHES Le Fort I approach Osteotomy of the maxilla at the Le Fort I level is not a new concept and was first described by von Langenbeck over 140 years ago. Cheever subsequently used this procedure to remove a Received 14 August 2002 Accepted 19 September 2002 Correspondence to: Mr. K.R. Spencer BHB MBChB MDSc FRACDS (OMS), Oral and Maxillofacial Surgery Unit, The Royal Melbourne Hospital, 5th Floor, 766 Elizabeth Street, Melbourne 3000, Australia. Tel.: +9347-3788; Fax: +9347-3058.
340
Fig. 1
Compartments of the skull base.
Selected midfacial access procedures to the skull base
Fig. 2
341
Anterior view of Le Fort I level osteotomy lines and mini-plate fixation.
Operative technique Following either tracheostomy or more commonly, orotracheal intubation, a local anaesthetic containing adrenalin is infiltrated along the maxillary mucogingival reflection. A horizontal incision is performed at this level and a mucoperiosteal flap is raised over the anterior surface of the maxilla. Subperiosteal dissection is developed medially to expose the piriform apertures, laterally around the zygomatic buttress areas and superiorly to the level of the infraorbital nerves. The nasal mucosa is then elevated from the floor and lateral walls of the nose, and nasal septum. Using a reciprocating saw or fissure bur, a horizontal osteotomy is performed above the apices of the teeth. Before any further bone cuts are made, four 2 mm titanium miniplates are adapted to the bony surface to enable the occlusion to be restored at the end of the procedure (Fig. 2). The lateral nasal wall and septum are divided with guarded osteotomes, and the pterygoid plates are separated by means of a curved osteotome. The maxilla can now be downfractured, exposing the nasal floor. An Archer or modifiedDingman gag, which is inserted to retract the maxilla inferiorly, provides approximately 8 cm of horizontal anterior exposure and 5 cm posteriorly5 (Fig. 3). For access to the lower clivus, and cranio-vertebral junction, a midline palatal split through the hard and soft palate can be performed (Fig. 4). The divided maxilla can be separated by a selfretaining retractor and maintains its blood supply from the greater palatine and ascending pharyngeal arteries, as well as smaller unnamed pharyngeal vessels traversing the fauceal pillars. At the end of the procedure, the maxilla is returned to its initial position, stabilised with the previously adapted miniplates and the wound is closed in layers with a continuous absorbable suture. This approach has the advantage of being a commonly performed, well-understood, predictable and safe procedure that provides wide anatomical exposure with minimal morbidity, and a hidden intraoral incision. Alternative transfacial approaches offer limited exposure; have the potential to divide sensory or motor nerves, or destroy the anterior facial skeleton. Reported complications include CSF fistula and meningitis (intradural lesions), postoperative nasal haemorrhage,6 and ischaemic necrosis of the maxilla.7 Oronasal fistulae can occur in those cases where the palate is split, but offsetting the mucosal incision with respect to the palatal ª 2003 Published by Elsevier Science Ltd.
Fig. 3
Diagram demonstrating arc of maxillary rotation.
osteotomy reduces this risk. Occasional velo-pharyngeal incompetence can occur, especially when extensive vertebral bone removal leaves a depression in the posterior pharyngeal wall. This risk can be diminished if a dermal fat graft is placed before closure. Maxillo-nasal-cheek flap approach This technique was popularised by Curioni et al.8 and is useful in providing access to tumours extending to involve the central skull base from the soft palate, retromaxillary and postnasal spaces.8;9 The maxillo-nasal-cheek flap has been used to remove a wide variety of tumours including adenocarcinomas, malignant schwannomas, and adenoid cystic carcinomas, and provides excellent access for oncologic surgery in this region.10 Variations of this procedure follow the same basic concept of mobilising facial structures on a viable pedicle, and when increased exposure is required, the nose can be included in the flap (maxillo-nasal cheek flap), or the face can be opened like a book (maxillo-nasal cheek flap and contralateral maxillo-cheek flap). Journal of Clinical Neuroscience (2003) 10(3), 340–345
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Fig. 4
Spencer et al.
Intra-operative photo following mid-palatal osteotomy (NF, nasal floor; RP, right palate; LP, left palate; NP, nasopharynx).
Operative technique Following tracheostomy or orotracheal intubation, a standard Weber–Ferguson skin incision is made, for a maxillo-cheek flap. For a maxillo-nasal-cheek flap, the paranasal incision is made on the contra-lateral side, extended across the nasal bridge and then into the ipsilateral lower eyelid. As the blood supply to the skeletal segments is derived from the cheek flap, minimal periosteal elevation is performed. A horizontal osteotomy is made along the anterior surface of the maxilla inferior to the orbital rim, and extended laterally through the body of the zygoma to the pterygomaxillary fissure. The medial extent of this osteotomy depends on the type of flap. With a maxillo-cheek flap the medial extent of the osteotomy runs vertically and lateral to the piriform aperture, then inferiorly between the ipsilateral central and lateral incisors. With a maxillo-nasal-cheek flap the horizontal osteotomy is extended across the nasal bridge anterior to the lacrimal fossa to join a vertical osteotomy on the contra-lateral side (Fig. 5). To allow for mobilisation, a palatal Osteotomy is performed backwards between the central and lateral incisors, and the pterygoid plates are separated with a curved osteotome through a small vestibular incision. The infraorbital nerve is divided, and after miniplate pre-localisation, the osteotomised segment is mobilised (Fig. 6). At the conclusion of the procedure the segment is replaced and fixed with the pre-contoured plates, and the wounds closed. This versatile procedure is mainly used to access malignant lesions in the postnasal and retromaxillary spaces as it provides wider access than the Le Fort I approach and can be modified to include sub-total maxillary resection. This approach allows access to the buccal fat pad, which can be used for palatal reconstruction in selected cases.10 This procedure has increased morbidity compared with a Le Fort I maxillotomy, with facial scarring and infra-orbital anaesthesia.
Extended transbasal approach Over the past two decades many craniofacial techniques have been described which improve exposure to the anterior cranial fossa and central skull base. Based on the outlines described by Tessier et al.11 of the fronto-orbital bandeau as used in craniofacial Journal of Clinical Neuroscience (2003) 10(3), 340–345
Fig. 5
Diagram of left maxillo-cheek flap.
surgery for congenital anomalies, and the Ôlow fronto-orbital technique for sphenoethmoid tumoursÕ or transbasal approach described by Derome etal.12 , various skull base teams introduced more direct approaches.13;14 Raveh15 described the extended subcranial or transbasal approach for use in craniofacial trauma and later adapted it to tumour resection.16 Spetzler further modified the approach to involve an osteotomy of the cribriform plate with a view to olfactory preservation in appropriate cases, and to facilitate reconstruction of the anterior fossa.17 The extended transbasal approach involves the en-bloc mobilisation of the supra-orbital rim, orbital roofs and nasoethmoidal complex. This approach provides access to the sphenoethmoidal region, clivus and foramen magnum. Operative technique A bicoronal flap is raised and developed further anteriorly so that the subperiosteal dissection exposes the nasal bones, nasal process ª 2003 Published by Elsevier Science Ltd.
Selected midfacial access procedures to the skull base
Fig. 6
343
Intra-operative photo of reflected right maxillo-nasal-cheek flap.
of the maxilla and continues into the orbits to the level of the anterior ethmoidal artery. The medial canthal ligaments and upper lateral nasal cartilages are detached, and the nasolacrimal duct is exposed and preserved. After bifrontal craniotomy and dural exploration and/or dissection have been performed, the fronto-nasal complex is outlined and osteomised (Fig. 7). The anterior osteotomies run upwards from the piriform aperture, across the nasal process of the maxilla to the medial orbital floor. Crossing the medial orbital floor onto the medial orbital wall, they end at the level of the anterior ethmoidal artery. The medial orbital walls and roof are osteotomised, and if this technique is used to approach a tumour that does not involve the cribriform plate, the design of the orbital roof osteotomy is modified to include a circumferential cribriform plate osteotomy to preserve the plate and olfactory nerves.18 Following removal of the frontonasal unit, an osteotomy is performed posterior to the cribriform plate through the planum sphenoidale. The cribriform plate, released from all bony connections, can then be elevated attached to the frontal lobe dura (Fig. 8). At the conclusion of the procedure fixation of the osteotomised bones is accomplished with a combination of plates and/ or wires, and the upper lateral nasal cartilages and medial canthal
Fig. 8
Anatomical dissection showing access on removal of fronto-nasal unit.
ligaments are reattached. The cribriform region is usually repaired with a pericranial flap. Advantages of this procedure include a wide vertical exposure of the anterior cranial fossa and central skull base with minimal brain retraction, avoidance of facial incisions and preservation of olfaction in some cases. Complications of this procedure include CSF leakage, transient pituitary dysfunction, cranial nerve deficits, and nasolacrimal duct injury.18 LATERAL APPROACH Transzygomatic approach
Fig. 7 Anatomical dissection showing osteotomy lines of extended transbasal approach.
ª 2003 Published by Elsevier Science Ltd.
Described by Obwegeser19 as an approach to the temporomandibular joint, orbit and retromaxillary-infracranial region, this approach has many applications. It can be used to access tumours arising within the infratemporal fossa such as schwannomas, and can provide access to the posterior extension of orbital, maxillary and palatal tumours, as well as those tumours with perineural spread along the trigeminal nerve. This approach can also access tumours of the anterolateral skull base, and intracranial tumours with inferior extension such as meningiomas as when combined Journal of Clinical Neuroscience (2003) 10(3), 340–345
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Spencer et al.
with a pteryonal approach it provides excellent access to the middle cranial fossa, allowing tumours above and below the skull base to be simultaneously accessed. This versatile approach can also be combined with an anterior approach if required.20 Operative technique The planned surgical incision is marked and local anaesthetic infiltrated. A full bicoronal scalp flap is raised from the most caudal point of the tragus to the contralateral temporo-parietal suture, approximately 2 cm posterior and parallel to the hairline. No hair is shaven, and the incorporation of a wavy coronal incision helps to better camouflage the scar, especially when the hair is wet.21 The incision is deepened to the subgaleal plane, superficial to the pericranium over the top of the scalp and temporalis fascia laterally. The flap is developed forwards in this plane to 3–4 cm superior to the orbital rims where the pericranium is incised across the forehead from one superior temporal line to the other. The scalp flap is turned back from the root of the zygomatic arch to the ipsilateral supraorbital rim. Near the ear, the flap is dissected inferiorly to the root of the zygomatic arch. Starting at the root of the zygomatic arch, an incision running 45 upwards and forwards is made through the superficial layer of temporalis fascia, joining the cross-forehead incision previously made through the pericranium. The periosteum of the zygoma is incised, and the layers turned forwards as one flap. The upper branches of the facial nerve lie superficial to the dissection on the undersurface of the temporo-parietal fascia and are thus preserved.22 Depending on the requirements of the case, the body of the zygoma or the arch alone is osteotimised and outfractured after miniplate prelocalisation. Now the separated body or arch can be swung downward, pedicled to the masseter muscle. The upper half of the mandibular ramus, with the insertion of the temporalis muscle, is now presented in the operative field (Fig. 9). The temporalis muscle is carefully detached from its origin to avoid damaging its blood supply from the anterior and posterior deep temporal arteries which enter the muscle below the zygomatic arch and deep to the coronoid process. The temporalis is
swung inferiorly, or alternatively the coronoid process is cut off from the ramus of the mandible and the temporalis and attached coronoid swung superiorly. The site of the pathology dictates the direction of displacement of the muscle. If the lesion is primarily intracranial with extension into the infratemporal fossa, the temporalis muscle is usually displaced inferiorly. Sub-cranial lesions extending to the skull base require superior temporalis muscle reflection. Access to the middle cranial fossa is achieved with a fronto-temporal craniotomy. If access to the retromaxillary and infratemporal regions is required, the pterygoid muscles are divided and the maxillary artery ligated and divided. The lateral aspect of the lateral pterygoid plate should now be visible and if followed superiorly to its junction with the base of the skull, will guide the surgeon to foramen ovale. At the completion of the procedure, the zygomatic body or arch is replaced and secured with pre-contoured miniplates. If the temporalis muscle has been devitalised it will need to be excised. If it is viable it can be replaced, the coronoid process is removed to minimise post-operative limitation of mouth opening. This approach provides direct lateral access, preserving the facial nerve and temporo-mandibular joint, whilst avoiding a visible facial scar. The disadvantages of this approach are an increasingly restricted medial exposure as the depth of the dissection increases, and the inability to follow the internal carotid artery through the skull base. Should exposure of the internal carotid artery be necessary, the post-auricular approach described by Fisch and Pillsbury23 may be used. DISCUSSION The most important step in access surgery is the selection of the most appropriate technique or combinations thereof. This depends on the anatomical location as well as the nature of the pathology in question, with each approach designed to provide short, straight-line access, maximal exposure, and minimal morbidity. The Le Fort 1 downfracture is generally reserved for access to benign pathology in the nasopharynx and central skull base and is the most cosmetic and least morbid of all the approaches described. It however lacks the versatility of the maxillo-nasal-cheek flap and gives poor access when dealing with malignant lesions. In these cases, the maxillo-nasal-cheek flap, which can include maxillary resection, is the approach of choice. Access to lesions within the anterior cranial fossa, as well as those extending into the superior, medial and posterior aspects of the orbit is achieved via the extended transbasal approach. For lesions in the middle cranial fossa, infratemporal fossa, retromaxillary space, and lateral orbit the lateral transzygomatic approach is the procedure of choice and can be combined with other mid-facial approaches for extensive oncological resections. ACKNOWLEDGEMENTS The authors gratefully acknowledge contributions by Mr B.T. Evans and members of the Departments of Neurosurgery and Head and Neck Oncology at The Royal Melbourne and Southampton University Hospitals. REFERENCES
Fig. 9 Diagram of zygoma reflected inferiorly and pedicled on origin of masseter muscle.
Journal of Clinical Neuroscience (2003) 10(3), 340–345
1. Jackson IT, Hide TAH. A systematic approach to tumours of the base of the skull. J Maxillofac Surg 1982; 10: 92–98. 2. Drommer RB. The history of the Le Fort I osteotomy. J Max Fac Surg 1986; 14: 119–122. 3. Archer DJ, Young S, Uttley D. Basilar aneurysms: a new transclival approach via maxillotomy. J Neurosurg 1987; 67: 54–58.
ª 2003 Published by Elsevier Science Ltd.
Selected midfacial access procedures to the skull base
4. James D, Crockard HA. Surgical access to the base of skull and upper cervical spine by extended maxillotomy. Neurosurg 1991; 29: 411–416. 5. Sasaki CT, Lowlicht RA, Astrachan DI, Friedman CD, Goodwin WJ, Morales M. Le Fort 1 osteotomy approach to the skull base. Laryngoscope 1990; 100: 1073–1076. 6. Lanigan DT, Hey JH, West RA. Major vascular complications of orthognathic surgery: haemorrhage associated with Le Fort 1 osteotomies. J Oral Maxillofac Surg 1990; 48: 561–573. 7. Lanigan DT, Hey JH, West RA. Aseptic necrosis following maxillary osteotomy. J Oral Maxillofac Surg 1990; 48: 142–156. 8. Curioni C, Clauser L. Facial splitting: indications and techniques for the transfacial approach to the anterior skull base. Skull Base Surgery – Update 1 1995: 285–290. 9. Altemir HF. Transfacial access to the retromaxillary area. J Maxillofac Surg 1986; 14: 165–170. 10. Brown AMS, Lavery KM, Millar BG. The transfacial approach to the postnasal space and retromaxillary structures. Br J Oral Maxillofac Surg 1991; 29: 230– 236. 11. Tessier P, Guiot G, Rougerie J, Delbet JP, Pastoriza J. Cranio-naso-orbito-facial osteotomies: hypertelorism. Ann Chir Plast 1967; 12(2): 103–118. 12. Derome P, Ackerman M, Anquez L et al. Les tumeurs spheno-ethmoidales. Possibilites dÕexerese et de reparation dhirurgicales. Neurochurugie 1972; 18(Suppl. 1): 1–64. 13. Jane JA, Park TS, Pobereskin LG, Winn R, Butler AB. The supraorbital approach: technical note. Neurosurgery 1982; 11: 537–542.
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14. Sekhar LN, Nanda A, Sen CN, Snyderman CN, Janecka IP. The extended frontal approach to tumours of the anterior, middle and posterior skull base. J Neurosurgery 1992; 76: 198–206. 15. Raveh J. 1-Stage procedure in the reconstruction of frontobasal middle face fractures: modifications and treatment modalities. Chirurg 1983; 54(10): 677–686. 16. Raveh J, Laedrach K, Speiser M, Chen J, Vuillemin T, Seiler R, Ebeling U, Leibinger K. The subcranial approach for fronto-orbital and anteroposterior skull-base tumors. Arch Otolaryngol Head Neck Surg 1993; 119(4): 385–393. 17. Spetzler RF, Herman JM, Beals S, Joganic E, Milligan J. Preservation in anterior craniofacial approaches. J Neurosurgery 1993; 79: 48–52. 18. Beals SP, Joganic EF, Hamilton MG, Spetzler RF. Posterior skull base transfacial approaches. Clin Plast Surg 1995; 22: 491–511. 19. Obwegeser HL. Temporal approach to the TMJ, the orbit, and the retromaxillary-infracranial region. Head Neck Surg 1985; 7: 185–199. 20. Shahinian HK, Suh RH, Jarrahy R. Combined infratemporal fossa and transfacial approach to excising massive tumors. Ear Nose & Throat 1999; 78: 350–356. 21. Fearon JA, Munro IR, Bruce DA. Transfacial approaches to the cranial base. Clin Plast Surg 1995; 22: 483–490. 22. Al-Kayat A, Bramley P. A modified pre-auricular approach to the temporomandibular joint and malar arch. Br J Oral Surg 1979–80; 17: 91–103. 23. Fisch U, Pillsbury HC. Infratemporal fossa approach to lesions in the temporal bone and base of the skull. Arch Otolaryngol 1979; 105: 99–107.
Journal of Clinical Neuroscience (2003) 10(3), 340–345
Operative technical review
Selected midfacial access procedures to the skull base K.R. Spencer
BHB MBCHB MDSC FRACDS (OMS),
A.L. Nastri
MBBS MDSC FRACDS (OMS),
D. Wiesenfeld
MDSC FDSRCPS FRACDS (OMS)
Oral and Maxillofacial Surgery Unit, The Royal Melbourne Hospital, Melbourne, Australia
Summary The indications and operative technique of various procedures commonly used to provide or increase access to the central skull base, anterior and middle cranial fossae, nasopharynx, infratemporal fossa and retromaxillary space are discussed with illustrative cases. ª 2003 Published by Elsevier Science Ltd. Keywords: transfacial access, osteotomy, skull base, infratemporal fossa, anterior cranial fossa, middle cranial fossa, retromaxillary space
INTRODUCTION Lesions involving the central and lateral skull base, infratemporal fossa and retromaxillary region are difficult to access. Tumours once considered inoperable by virtue of their site are accessible using various techniques that have been developed over many years to allow access to these sites with minimal morbidity. In cooperation with the neurosurgeon, the oral and maxillofacial surgeon is able to select and provide appropriate access in these cases. The purpose of this article is to review some of the more commonly used approaches and discuss their indications, operative details and limitations. Anatomy of the skull base A systematic approach to tumours of the base of the skull has previously been described1 in which the base of skull is divided into right and left lateral and central compartments by the internal carotid arteries. The lateral compartments are further subdivided into anterior, middle and posterior segments. The central compartment contains the anterior cranial fossa (cribriform plate, planum sphenoidale, orbital roofs and greater wing of sphenoid), clivus, body of sphenoid and upper cervical spine. The anterior segment of the lateral compartment extends from the anterior middle cranial fossa back to the anterior edge of the petrous temporal bone and contains part of the greater wing of the sphenoid and the inferior surface of the petrous temporal bone (the infratemporal and retromaxillary areas) (Fig. 1). The middle and posterior segments of the lateral compartment are not accessible via transfacial approaches and will not be discussed in this article. Access to the central compartment is achieved via anterior approaches whilst the anterior segment of the lateral compartment is accessed from lateral or combined anterolateral approaches.
nasopharyngeal polyp. Kocher described a midline lip and palatal split to provide improved access to the pituitary fossa.2 In 1987, Archer et al.3 used the approach to access distal vertebral and midbasilar aneurysms and in 1991, James and Crockard4 added a midline sagittal split of both maxilla and soft palate to improve access to the cranio-vertebral junction. Horizontal osteotomy and down-fracture of the maxilla offers wide exposure to the postnasal space, central skull base, and upper clivus and is the procedure of choice for the removal of benign lesions such as clival chordomas and nasopharyngeal tumours. When combined with a mid-palatal split, the improved access to the cranio-vertebral junction facilitates access to tumours that extend above and below the foramen magnum, and enables surgical decompression in cases of severe basilar invagination. The development of bone miniplate systems has enabled surgeons to rigidly replace the osteotomised segments, and pre-location of the miniplates before the osteotomy is completed enables rapid fixation with restoration of the occlusion at the completion of the procedure.
ANTERIOR APPROACHES Le Fort I approach Osteotomy of the maxilla at the Le Fort I level is not a new concept and was first described by von Langenbeck over 140 years ago. Cheever subsequently used this procedure to remove a Received 14 August 2002 Accepted 19 September 2002 Correspondence to: Mr. K.R. Spencer BHB MBChB MDSc FRACDS (OMS), Oral and Maxillofacial Surgery Unit, The Royal Melbourne Hospital, 5th Floor, 766 Elizabeth Street, Melbourne 3000, Australia. Tel.: +9347-3788; Fax: +9347-3058.
340
Fig. 1
Compartments of the skull base.
Selected midfacial access procedures to the skull base
Fig. 2
341
Anterior view of Le Fort I level osteotomy lines and mini-plate fixation.
Operative technique Following either tracheostomy or more commonly, orotracheal intubation, a local anaesthetic containing adrenalin is infiltrated along the maxillary mucogingival reflection. A horizontal incision is performed at this level and a mucoperiosteal flap is raised over the anterior surface of the maxilla. Subperiosteal dissection is developed medially to expose the piriform apertures, laterally around the zygomatic buttress areas and superiorly to the level of the infraorbital nerves. The nasal mucosa is then elevated from the floor and lateral walls of the nose, and nasal septum. Using a reciprocating saw or fissure bur, a horizontal osteotomy is performed above the apices of the teeth. Before any further bone cuts are made, four 2 mm titanium miniplates are adapted to the bony surface to enable the occlusion to be restored at the end of the procedure (Fig. 2). The lateral nasal wall and septum are divided with guarded osteotomes, and the pterygoid plates are separated by means of a curved osteotome. The maxilla can now be downfractured, exposing the nasal floor. An Archer or modifiedDingman gag, which is inserted to retract the maxilla inferiorly, provides approximately 8 cm of horizontal anterior exposure and 5 cm posteriorly5 (Fig. 3). For access to the lower clivus, and cranio-vertebral junction, a midline palatal split through the hard and soft palate can be performed (Fig. 4). The divided maxilla can be separated by a selfretaining retractor and maintains its blood supply from the greater palatine and ascending pharyngeal arteries, as well as smaller unnamed pharyngeal vessels traversing the fauceal pillars. At the end of the procedure, the maxilla is returned to its initial position, stabilised with the previously adapted miniplates and the wound is closed in layers with a continuous absorbable suture. This approach has the advantage of being a commonly performed, well-understood, predictable and safe procedure that provides wide anatomical exposure with minimal morbidity, and a hidden intraoral incision. Alternative transfacial approaches offer limited exposure; have the potential to divide sensory or motor nerves, or destroy the anterior facial skeleton. Reported complications include CSF fistula and meningitis (intradural lesions), postoperative nasal haemorrhage,6 and ischaemic necrosis of the maxilla.7 Oronasal fistulae can occur in those cases where the palate is split, but offsetting the mucosal incision with respect to the palatal ª 2003 Published by Elsevier Science Ltd.
Fig. 3
Diagram demonstrating arc of maxillary rotation.
osteotomy reduces this risk. Occasional velo-pharyngeal incompetence can occur, especially when extensive vertebral bone removal leaves a depression in the posterior pharyngeal wall. This risk can be diminished if a dermal fat graft is placed before closure. Maxillo-nasal-cheek flap approach This technique was popularised by Curioni et al.8 and is useful in providing access to tumours extending to involve the central skull base from the soft palate, retromaxillary and postnasal spaces.8;9 The maxillo-nasal-cheek flap has been used to remove a wide variety of tumours including adenocarcinomas, malignant schwannomas, and adenoid cystic carcinomas, and provides excellent access for oncologic surgery in this region.10 Variations of this procedure follow the same basic concept of mobilising facial structures on a viable pedicle, and when increased exposure is required, the nose can be included in the flap (maxillo-nasal cheek flap), or the face can be opened like a book (maxillo-nasal cheek flap and contralateral maxillo-cheek flap). Journal of Clinical Neuroscience (2003) 10(3), 340–345
342
Fig. 4
Spencer et al.
Intra-operative photo following mid-palatal osteotomy (NF, nasal floor; RP, right palate; LP, left palate; NP, nasopharynx).
Operative technique Following tracheostomy or orotracheal intubation, a standard Weber–Ferguson skin incision is made, for a maxillo-cheek flap. For a maxillo-nasal-cheek flap, the paranasal incision is made on the contra-lateral side, extended across the nasal bridge and then into the ipsilateral lower eyelid. As the blood supply to the skeletal segments is derived from the cheek flap, minimal periosteal elevation is performed. A horizontal osteotomy is made along the anterior surface of the maxilla inferior to the orbital rim, and extended laterally through the body of the zygoma to the pterygomaxillary fissure. The medial extent of this osteotomy depends on the type of flap. With a maxillo-cheek flap the medial extent of the osteotomy runs vertically and lateral to the piriform aperture, then inferiorly between the ipsilateral central and lateral incisors. With a maxillo-nasal-cheek flap the horizontal osteotomy is extended across the nasal bridge anterior to the lacrimal fossa to join a vertical osteotomy on the contra-lateral side (Fig. 5). To allow for mobilisation, a palatal Osteotomy is performed backwards between the central and lateral incisors, and the pterygoid plates are separated with a curved osteotome through a small vestibular incision. The infraorbital nerve is divided, and after miniplate pre-localisation, the osteotomised segment is mobilised (Fig. 6). At the conclusion of the procedure the segment is replaced and fixed with the pre-contoured plates, and the wounds closed. This versatile procedure is mainly used to access malignant lesions in the postnasal and retromaxillary spaces as it provides wider access than the Le Fort I approach and can be modified to include sub-total maxillary resection. This approach allows access to the buccal fat pad, which can be used for palatal reconstruction in selected cases.10 This procedure has increased morbidity compared with a Le Fort I maxillotomy, with facial scarring and infra-orbital anaesthesia.
Extended transbasal approach Over the past two decades many craniofacial techniques have been described which improve exposure to the anterior cranial fossa and central skull base. Based on the outlines described by Tessier et al.11 of the fronto-orbital bandeau as used in craniofacial Journal of Clinical Neuroscience (2003) 10(3), 340–345
Fig. 5
Diagram of left maxillo-cheek flap.
surgery for congenital anomalies, and the Ôlow fronto-orbital technique for sphenoethmoid tumoursÕ or transbasal approach described by Derome etal.12 , various skull base teams introduced more direct approaches.13;14 Raveh15 described the extended subcranial or transbasal approach for use in craniofacial trauma and later adapted it to tumour resection.16 Spetzler further modified the approach to involve an osteotomy of the cribriform plate with a view to olfactory preservation in appropriate cases, and to facilitate reconstruction of the anterior fossa.17 The extended transbasal approach involves the en-bloc mobilisation of the supra-orbital rim, orbital roofs and nasoethmoidal complex. This approach provides access to the sphenoethmoidal region, clivus and foramen magnum. Operative technique A bicoronal flap is raised and developed further anteriorly so that the subperiosteal dissection exposes the nasal bones, nasal process ª 2003 Published by Elsevier Science Ltd.
Selected midfacial access procedures to the skull base
Fig. 6
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Intra-operative photo of reflected right maxillo-nasal-cheek flap.
of the maxilla and continues into the orbits to the level of the anterior ethmoidal artery. The medial canthal ligaments and upper lateral nasal cartilages are detached, and the nasolacrimal duct is exposed and preserved. After bifrontal craniotomy and dural exploration and/or dissection have been performed, the fronto-nasal complex is outlined and osteomised (Fig. 7). The anterior osteotomies run upwards from the piriform aperture, across the nasal process of the maxilla to the medial orbital floor. Crossing the medial orbital floor onto the medial orbital wall, they end at the level of the anterior ethmoidal artery. The medial orbital walls and roof are osteotomised, and if this technique is used to approach a tumour that does not involve the cribriform plate, the design of the orbital roof osteotomy is modified to include a circumferential cribriform plate osteotomy to preserve the plate and olfactory nerves.18 Following removal of the frontonasal unit, an osteotomy is performed posterior to the cribriform plate through the planum sphenoidale. The cribriform plate, released from all bony connections, can then be elevated attached to the frontal lobe dura (Fig. 8). At the conclusion of the procedure fixation of the osteotomised bones is accomplished with a combination of plates and/ or wires, and the upper lateral nasal cartilages and medial canthal
Fig. 8
Anatomical dissection showing access on removal of fronto-nasal unit.
ligaments are reattached. The cribriform region is usually repaired with a pericranial flap. Advantages of this procedure include a wide vertical exposure of the anterior cranial fossa and central skull base with minimal brain retraction, avoidance of facial incisions and preservation of olfaction in some cases. Complications of this procedure include CSF leakage, transient pituitary dysfunction, cranial nerve deficits, and nasolacrimal duct injury.18 LATERAL APPROACH Transzygomatic approach
Fig. 7 Anatomical dissection showing osteotomy lines of extended transbasal approach.
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Described by Obwegeser19 as an approach to the temporomandibular joint, orbit and retromaxillary-infracranial region, this approach has many applications. It can be used to access tumours arising within the infratemporal fossa such as schwannomas, and can provide access to the posterior extension of orbital, maxillary and palatal tumours, as well as those tumours with perineural spread along the trigeminal nerve. This approach can also access tumours of the anterolateral skull base, and intracranial tumours with inferior extension such as meningiomas as when combined Journal of Clinical Neuroscience (2003) 10(3), 340–345
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with a pteryonal approach it provides excellent access to the middle cranial fossa, allowing tumours above and below the skull base to be simultaneously accessed. This versatile approach can also be combined with an anterior approach if required.20 Operative technique The planned surgical incision is marked and local anaesthetic infiltrated. A full bicoronal scalp flap is raised from the most caudal point of the tragus to the contralateral temporo-parietal suture, approximately 2 cm posterior and parallel to the hairline. No hair is shaven, and the incorporation of a wavy coronal incision helps to better camouflage the scar, especially when the hair is wet.21 The incision is deepened to the subgaleal plane, superficial to the pericranium over the top of the scalp and temporalis fascia laterally. The flap is developed forwards in this plane to 3–4 cm superior to the orbital rims where the pericranium is incised across the forehead from one superior temporal line to the other. The scalp flap is turned back from the root of the zygomatic arch to the ipsilateral supraorbital rim. Near the ear, the flap is dissected inferiorly to the root of the zygomatic arch. Starting at the root of the zygomatic arch, an incision running 45 upwards and forwards is made through the superficial layer of temporalis fascia, joining the cross-forehead incision previously made through the pericranium. The periosteum of the zygoma is incised, and the layers turned forwards as one flap. The upper branches of the facial nerve lie superficial to the dissection on the undersurface of the temporo-parietal fascia and are thus preserved.22 Depending on the requirements of the case, the body of the zygoma or the arch alone is osteotimised and outfractured after miniplate prelocalisation. Now the separated body or arch can be swung downward, pedicled to the masseter muscle. The upper half of the mandibular ramus, with the insertion of the temporalis muscle, is now presented in the operative field (Fig. 9). The temporalis muscle is carefully detached from its origin to avoid damaging its blood supply from the anterior and posterior deep temporal arteries which enter the muscle below the zygomatic arch and deep to the coronoid process. The temporalis is
swung inferiorly, or alternatively the coronoid process is cut off from the ramus of the mandible and the temporalis and attached coronoid swung superiorly. The site of the pathology dictates the direction of displacement of the muscle. If the lesion is primarily intracranial with extension into the infratemporal fossa, the temporalis muscle is usually displaced inferiorly. Sub-cranial lesions extending to the skull base require superior temporalis muscle reflection. Access to the middle cranial fossa is achieved with a fronto-temporal craniotomy. If access to the retromaxillary and infratemporal regions is required, the pterygoid muscles are divided and the maxillary artery ligated and divided. The lateral aspect of the lateral pterygoid plate should now be visible and if followed superiorly to its junction with the base of the skull, will guide the surgeon to foramen ovale. At the completion of the procedure, the zygomatic body or arch is replaced and secured with pre-contoured miniplates. If the temporalis muscle has been devitalised it will need to be excised. If it is viable it can be replaced, the coronoid process is removed to minimise post-operative limitation of mouth opening. This approach provides direct lateral access, preserving the facial nerve and temporo-mandibular joint, whilst avoiding a visible facial scar. The disadvantages of this approach are an increasingly restricted medial exposure as the depth of the dissection increases, and the inability to follow the internal carotid artery through the skull base. Should exposure of the internal carotid artery be necessary, the post-auricular approach described by Fisch and Pillsbury23 may be used. DISCUSSION The most important step in access surgery is the selection of the most appropriate technique or combinations thereof. This depends on the anatomical location as well as the nature of the pathology in question, with each approach designed to provide short, straight-line access, maximal exposure, and minimal morbidity. The Le Fort 1 downfracture is generally reserved for access to benign pathology in the nasopharynx and central skull base and is the most cosmetic and least morbid of all the approaches described. It however lacks the versatility of the maxillo-nasal-cheek flap and gives poor access when dealing with malignant lesions. In these cases, the maxillo-nasal-cheek flap, which can include maxillary resection, is the approach of choice. Access to lesions within the anterior cranial fossa, as well as those extending into the superior, medial and posterior aspects of the orbit is achieved via the extended transbasal approach. For lesions in the middle cranial fossa, infratemporal fossa, retromaxillary space, and lateral orbit the lateral transzygomatic approach is the procedure of choice and can be combined with other mid-facial approaches for extensive oncological resections. ACKNOWLEDGEMENTS The authors gratefully acknowledge contributions by Mr B.T. Evans and members of the Departments of Neurosurgery and Head and Neck Oncology at The Royal Melbourne and Southampton University Hospitals. REFERENCES
Fig. 9 Diagram of zygoma reflected inferiorly and pedicled on origin of masseter muscle.
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