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Oral cavity: Anatomy and pathology
Oral Cavity: Anatomy and Pathology Fred J. Laine a n d W e n d u R.K. S m o k e r
The oral cavity and oropharynx comprise the upper portion of the aerodigestive tract. These two regions are distinguished from each other because pathologic processes differ in their presentations, prognoses, and histologic grades. The normal anatomy of the oral cavity, vestibule, and oral cavity proper is discussed and is followed by a discussion of the sublingual and submandibular spaces. The diversity of pathologic processes that occur in these regions is then presented as well as the more common pitfalls.
HE UPPER portion of the aerodigestive
T tract is composed of the oral cavity and oropharynx. The oral cavity and oropharynx are
separated from each other by a ring of structures that includes the soft palate, anterior tonsillar pillars, pterygomandibular raphe, and circumvallate papillae of the tongue. These regions are distinguished from each other because pathologic processes differ in their presentations, prognoses, and histologic grades. 1 The normal anatomy of the oral cavity, which includes the lips, gingivobuccal mucosa, superior and inferior alveolar ridges and teeth, mandible, oral tongue (anterior two thirds), and the hard palate, is discussed. A more detailed review of the jaw and dentition can be found in "Anatomy of the Jaw, Dentition, and Related Regions," which appears in this issue. After a discussion of the anatomy, a review of the pathologic processes found within the oral cavity and tongue is presented. ANATOMY
Vestibule The vestibule (Fig 1) is the space between the dental arches and teeth and the lips and cheeks. The vestibule communicates with the oral cavity proper via the interdental spaces and the space posterior to the last molar teeth in the alveolar arch. The mucosal surface of the lips and cheek is termed the "buccal mucosa," whereas the mucosal lining of the teeth, alveolar arches, and gums (gingiva) is termed the "gingival mucosa." Gingival mucosa joins the buccal mucosa at the gingivobuccal sulcus, a common site in which squamous cell carcinomas arise. Reflections of the labial mucosa, the labial frenula, appear as midline, vertically oriented folds of tissue that attach the superior and inferior lips to the gingiva. The interdental papilla, where the vestibular gingiva becomes continuous with the oral cavity gingiva, lies between the teeth in the interdental spaces. The
sharp mucogingival line separates the gingival mucosa from the alveolar mucosa and is produced by the greater vascularity of the latter. A fold of mucosa in the posteriormost boundary of the vestibule covers the pterygomandibular raphe. 2 This raphe, a tendinous junction between the buccinator and superior constrictor muscles, is a thick fascial band that originates from the hamulus of the medial pterygoid plate and inserts along the mylohyoid ridge of the mandible. The raphe connects the maxillary and mandibular alveolar ridges and is the junction between the oral cavity and oropharynx. The wall of the cheek is formed by the buccinator muscle and an overlying subcutaneous pad of fat, the buccal fat pad (Fig 1). The buccinator arises from the pterygomandibular raphe and the outer surfaces of the maxilla and mandible in the region of the molar teeth. The fibers run forward into the substance of the lips and are pierced along their course by the tensor veli palatini tendon and the parotid gland duct (Stenson's duct). Stenson's duct pierces the buccinator muscle and drains into the vestibule opposite the second maxillary molar (Fig 1). Posterior to the last mandibular molar teeth, the mandibular alveolar process forms a flat bony surface, the retromolar triangle covered by a triangular area of mucosa, the retromolar trigone. Squamous cell carcinomas commonly arise in the retromolar trigone.
Oral Cavity Proper The oral cavity proper lies internal to the mandibular and maxillary alveolar arches. It is
From the Department of Radiology, Medical College of Virginia, Richmond, VA. Address reprint requests to Fred J. Laine, MD, Assistant Professor of Radiology, PO Box 980615 MCV Station, Medical College of Virginia, Richmond, VA 23298. Copyright 9 1995 by W.B. Saunders Company 0887-2171/95/1606-000555. 00/0
Seminars in Ultrasound, CT, andMRI, Vo116, No 6 (December), 1995: pp 527-545
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Fig 1. Normal buccomasseteric region. Axial Tl-weighted MRI scan demonstrates the buccal fat situated between the zygomaticus major muscle (arrowheads), masseter muscle (asterisk), and buccinator muscle (dots). The parotid gland duct (arrow) pierces the buccal fat pad and the buccinator muscle to open into the vestibule of the mouth opposite the second maxillary molars. The facial artery (small curved arrow) is seen anteriorly to the parotid gland duct, and the superior aspect of the pterygomandibular raphe (large curved arrow} is seen at the posterior aspect of the alveolar arch.
bounded superiorly by the hard palate and inferiorly by the muscular tongue. The muscular tongue is partially separated from the floor of the mouth by the sublingual sulcus laterally and anteriorly. This is a mucosal reflection continuous with the lingual gingiva and the lingual alveolar mucosa. The mylohyoid muscle arises from the entire length of the mylohyoid ridge on the inner surface of the mandible and extends posteriorly to insert on the body of the hyoid bone. A diagramatic representation of this and related anatomy can be found in "Anatomy of the Jaw, Dentition, and Related Regions." The two mylohyoid muscles are joined by a fibrous median raphe and form a U-shaped sling, which forms the "floor of the mouth." Two additional muscle bundles help provide support to the floor of the mouth: the anterior belly of the digastric situated below the mylohyoid muscle and the geniohyoid muscles situated above the mylohyoid muscle. The digastric muscle consists of a posterior belly, which arises from the mastoid notch of the temporal bone, and an anterior belly, which arises from the digastric fossa of the anterior lower border of the mandible. Both bellies descend to the hyoid bone and terminate in an intermediate tendon. The tendon is enveloped by a fibrous loop that attaches to the body and greater cornu of the
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hyoid bone. Attaching anteriorly to the inferior mental spine (genial tubercle) of the mandible, the geniohyoid courses above the mylohyoid to insert onto the anterior surface of the body of the hyoid bone. The mylohyoid sling, as well as the anterior digastric and geniohyoid muscles, are best depicted on coronal CT and MRI (Figs 2D, 3B). The anterior two thirds of the tongue, which includes both the tip and the body of the tongue, is considered part of the oral cavity, whereas the posterior one third is considered part of the oropharynx. The tongue muscles are composed of two groups: intrinsic and extrinsic. The intrinsic muscles, having no bony attachments, are within the superior aspect of the tongue itself and are described as longitudinal, transverse, and vertical muscle groups. The tissue planes and intrinsic muscle orientation are not well appreciated on CT. 3 The extrinsic muscles, which have bony attachments, originate outside the tongue and are composed of four paired bundles: genioglossus, hyoglossus, styloglossus, and palatoglossus. The genioglossus muscle arises from the superior mental spine (genial tubercle) of the inner surface of the mandible and fans out along the inferior aspect of the tongue, passing to the tongue base and body of the hyoid. Anterior fibers curve upward into the tip of the tongue. The bellies of the two genioglossus muscles are separated by the midline lingual septum and fatty tissue and are easily identified on axial CT and Tl-weighted MRI (Figs 2A and 3A). The hyoglossus muscle originates from the body and greater cornu of the hyoid bone, lateral to the genioglossus, enters the tongue, and intermingles with fibers of the styloglossus muscle (Figs. 2A and 3A). The styloglossus muscle arises from the styloid process of the temporal bone and the stylomandibular ligament. Most of the fibers continue to the tip of the tongue, whereas some of the posterior fibers decussate with fibers of the hyoglossus muscle. The palatoglossus muscle arises from the fascia and lateral aspect of the soft palate and interdigitates with the intrinsic muscles of the tongue along the lateral margin.
Spaces of the Floor of Mouth The paired bellies of the genioglossus and geniohyoid muscles are separated by a midline
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i;
Fig 2. Normal CT anatomy, floor of the mouth. Axial CT scans through the (A) high, (B) middle, and (C) low floor of the mouth. (D) Coronal CT image of the floor of the mouth. 1, mylohyoid muscle; 2, genioglossus muscle; 3, hyoglossus muscle; 4, anterior belly of the digastric muscle; 5, geniohyoid muscle; 6, platysma muscle; 7, lateral pterygoid muscle; 8, medial pterygoid muscle; 9, masseter muscle; 10, lingual tonsil; 11, sublingual space; 12, submandibular space; 13, submandibular gland; T, base of the tongue; M, mandible; S, lingual septum; P, soft palate.
fat-containing lingual septum (Fig 2). The mylohyoid muscle separates the floor of mouth into two spaces: the sublingual space and the submandibular space. These are a descriptive convenience only as there is no fascia that surrounds the sublingual space and both spaces communicate with each other posteriorly at the free margin of the mylohyoid muscle. Sublingual space (SLS). The SLS is a potential space without a fasciaI Iining. 4 Its medial boundaries are the genioglossus muscle, superiorly, and the geniohyoid muscle, inferiorly. The mylohyoid muscle makes up its inferior border and part of the lateral border. The sublingual sulcus is found at the superior lateral aspect of
the SLS. The contents of the SLS include the sublingual gland and ducts (ducts of Rivinus), which open into the sublingual sulcus, along the surface of the plica sublingualis. Medially to the gland lie the anteriormost fibers of the hyoglossus muscle, an important surgical landmark. The lingual artery and vein lie medially to the hyoglossus muscle, whereas the submandibular gland duct and the hypoglossal and lingual nerves lie laterally to it. The deep portion of the submandibuiar gland lies in the posterior aspect of the SLS. The submandibular g[and duct (Wharton's duct) arises from this portion of the submandibular gland and courses, first, between the hyoglossus and genioglossus muscles, then
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Fig 3. Normal MRI anatomy, floor of the mouth. (A) Axial, (B) coronal, and (C) sagittal Tl-weighted MRI of the floor of the mouth. 1, mylohyoid muscle; 2, genioglossus muscle; 3, hyoglossus muscle; 4, anterior belly of the digastric muscle; 5, geniohyoid muscle; 6, platysma muscle; 9, masseter muscle; 10, lingual tonsil; 11, sublingual space; 12, submandibular space; 13, submandibular gland; T, base of the tongue; M, mandible; S, lingual septum; P, soft palate; dots, hard palate.
crosses the hyoglossus muscle, lying between it and the sublingual gland, to empty in the sublingual caruncle, just lateral to the base of the frenulum. The submandibular space (SMS). The SMS is a U-shaped area located inferolaterally to the mylohyoid muscle and superiorly to the hyoid bone. The SMS is fascially defined except in its posterior aspect where it communicates with both the sublingual and the parapharyngeal spaces. The SMS contains the superficial portion of the submandibular gland, the facial vein and artery, and the submandibular and submental lymph nodes. The anterior bellies of the two digastric muscles form the margins of the small, midline, submental space.
Innervation The mylohyoid and anterior belly of the digastric muscles are innervated by the third
(mandibular) division of cranial nerve V. The posterior belly of the digastric muscle receives innervation from cranial nerve VII. Motor innervation to the geniohyoid muscle is variably described as originating from the hypoglossal nerve or from motor fibers of C1 and C2. 5 All extrinsic tongue muscles, with the exception of the palatoglossus muscle, are innervated by the hypoglossal nerve. The palatoglossus muscle is innervated by the pharyngeal plexus. 2
Lymphatics The oral cavity drains via the regional submental, submandibular, and parotid nodes into the internal jugular (deep cervical) chain. The drainage is both ipsilateral and contralateral. PATHOLOGY
The majority of lesions are encountered in both the SLS and SMS and are discussed
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together (Table 1). Those lesions that are specific to a particular space are noted.
Congenital Vascular lesions. Two major types of vascular lesions have been described: hemangiomas and vascular malformations. 6 Hemangiomas are neoplastic, present early in infancy, rapidly enlarge, and involute by adolescence. 6 Previously termed "strawberry hemangiomas," these lesions are most often superficial (cutaneous). Occasionally, they may extend deeply and infiltrate underlying muscles (subcuTable 1. Sublingual Space and Submandibular Space Pathology Congenital Vascular lesions Hemangioma Vascular malformations Capillary malformation Venous malformation (cavernous hemangiomas) Arterial malformation Lymphatic malformation (lymphangioma) Dermoid cysts Lingual artery aneurysm Digastric muscle anomalies (SMS) Thyroglossal duct cysts (Second branchial cleft cysts) Inflammatory/infection Cellulitis Abscess Ludwig's angina Ranula Simple ranula (SLS) Plunging or "diving" ranula (SMS Tumors Benign Pleomorphic adenoma (benign mixed tumor) Lipoma Rhabdomyoma Neurogenic tumors Granular cell tumors Aggressive fibromatosis Malignant Squamous cell carcinoma--primary~metastatic Salivary gland and minor salivary gland malignancies Adenoid cystic carcinoma Mucoepidermoid carcinoma Adenocarcinoma Lymphoma
Hodgkin's Non-Hodgkin's Pseudotumor Hypoglossal nerve denervation muscle atrophy Mandibular nerve denervation muscle atrophy
Fig 4. Venous malformation. Contrast-enhanced CT image demonstrates an extensive venous malformation involving the left buccomasseteric region and oral cavity. The presence of multiple calcifications (phleboliths) is almost diagnostic of venous malformation.
taneous). 7 On MRI, hemangiomas are isointense to muscle on T1W] and hyperintense on T2WI and enhance after contrast administration. 8 As hemangiomas involute, fatty deposition, which appears hyperintense on T1W], occurs. Vascular malformations are not tumors but rather are congenital vascular anomalies that are present at birth. They manifest slow steady growth and no involution and are classified, based on their predominant anomalous vessel, into arterial, capillary, venous, and lymphatic malformations. Capillarymalformations are lowflow lesions and are observed most frequently as a component of a syndrome such as SturgeWeber. Venousmalformations, previously termed "cavernous hemangiomas," are the most common vascular malformations to affect the oral cavity. They are similar to subcutaneous hemangiomas in imaging characteristics and may attain enormous size. They are low-flow lesions and infiltrate along fascial planes. CT scans demonstrate a mass of muscle intensity with variable enhancement. The presence of phleboliths is diagnostic (Fig 4). On MRI, venous malformations are isointense to hyperintense on T1WI and hyperintense on T2WI (Fig 5). 9 Arterial malformations are high-flow lesions that result from abnormal vessel morphogenesis. On MRI, flow voids are observed, which correspond to the enlarged arterial components.
Lymphatic malformations (lymphangiomas) are believed to arise from primitive embryonic
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Fig 5. Venous malformation. (A) Sagittal, (B) coronal contrast-enhanced Tl-weighted, and (C) sagittal T2-weighted MRI demonstrate a large venous malformation involving the oral tongue, which bulges superiorly into the oral cavity and extends posteriorly into the oropharynx. The true extent of this lesion is best appreciated on the T2-weighted image.
lymph sac sequestrations. These lesions are believed to enlarge because of inadequate drainage, from lack of communication with the central lymphatic channels, or from excessive secretions of lining cells. 1~ Lymphangiomas are classified into three groups, based on the size of the abnormal lymphatic spaces: (1) lymphangioma simplex, composed of small, capillarysized, thin-walled lymphatic channels; (2) cavernous lymphangiomas, composed of dilated lymphatic channels with a fibrous adventitia; and (3) cystic lymphangiomas, or cystic hygromas, which are cysts ranging in size from a few millimeters to several centimeters in diameter. 1~ Most of the lymphatic malformations found in the oral cavity are cystic hygromas. Fifty to 60% are present at birth, and 80% to 90% are diagnosed by the age of 2. ll Cystic hygromas appear as large, heterogeneous, multiloculated,
fluid-filled masses on imaging studies. They frequently wrap around and adhere to adjacent structures. 4 In infants, they most frequently occur in the posterior cervical space and superior mediastinum. Although they are rare in adults, when they do occur, they are more commonly found in the submandibular space. Cystic hygromas are hypointense to isointense to muscle on TlWI and hyperintense on T2WI (Fig 6). 12 Most have a signal intensity greater than that of cerebrospinal fluid on both TlWI and T2WI, suggesting proteinaceous fluid. Dermoid cysts. Three varieties of dermoid cysts are found in the oral cavity. Epidermoids, arrising from ectodermal elements, are cysts with simple squamous epithelium lining a fibrous wall (Fig 7). Dermoid cysts, from both ectoderm and mesoderm, are similar but contain skin appendages (hair follicles, sebaceous
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Fig 6. Cystic hygroma. Axial (A) Tl-weighted, (B) T2-weighted, and (C) coronal, contrast-enhanced Tl-weighted MRI show a cystic mass (asterisk) in the right submandibular space. The lesion is hypointense to muscle on the T1-weighted image and hyperintense on the T2-weighted image and does not enhance. The lesion and its relation to the mylohyoid (dots) and digastric (arrow) muscles are best seen on the coronal image (C).
glands). Teratoid cysts contain all three germ cell layers, ectoderm, mesoderm, and endoderm, and are therefore composed of a diverse range of tissues. 13 These lesions appear as unilocular masses on imaging studies and may have minimal peripheral rim enhancement. Epidermoids display fluid characteristics (Fig 7), whereas the imaging appearance of dermoids reflects their fat content (Fig 8). 14 Epidermoids seem to involve the SLS more often, whereas dermoids are more commonly found within the SMS.4 Lingual artery aneurysm. Although they usually result from trauma, lingual artery aneurysms of congenital origin have been reported. 15 Their appearance is variable and depends on the degree of thrombosis.
Digastric muscle anomalies.
Bilateral and unilateral accessory anterior digastric muscles and hypoplasia/aplasia of these muscles have been described but are uncommon. 16,17They are important to recognize so as not to confuse them with actual pathology.16Accessory digastric muscles can be confused with masses in the floor of the mouth or enlarged lymph nodes. Hypoplasia may be mistaken for denervation atrophy. 16 Identification of a normal-sized mylohyoid muscle, also receiving innervation from the mylohyoid branch of the inferior alveolar nerve, is strong evidence against denervation atrophy. Thyroglossal duct cysts. Embryologically, the thyroid gland develops at the foramen cecum of the tongue and descends into the neck. The migration of the thyroid gland and thyroglossal
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Fig 7. Epidermoid cyst. Axial CT shows a unilocular, hypodense cystic lesion in the floor of the mouth. The cyst is
homogeneous density, but otherwise indistinguishable from other cystic lesions in the floor of the mouth.
duct may be arrested anywhere along its path. Because the duct is lined with secretory epithelium, failure of the duct to involute may give rise to a cyst. Thirty-five percent of thyroglossal duct cysts are hyoid or suprahyoid in location. Is In the suprahyoid neck, these lesions are typically midline, between the bellies of the anterior digastric muscles, below the mylohyoid sling, and present as masses in the floor of the mouth. 19 On CT, they are well-circumscribed,
Fig 8. Dermoid cyst. Coronalcontrast-enhanced CT demonstrates a large unilocular cyst in the floor of the mouth deep to the mylohyoid muscles (dots), The presence of a single, lowdensity fat globule (curved arrow) within this cyst assures the diagnosis of a dermoid cyst. (Courtesy of Deborah Reede, MD.)
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low-density lesions and have thin-rim enhancement (Fig 9) and are occasionally septated giving a multilocular appearance. On MRI, the signal characteristics of these lesions are dependent on the protein content but are usually isointense on T1WI and hyperintense on T2WI.10 Less than 1% of thyroglossal cysts are associated with carcinomas, papillary carcinoma being the most common. 1~176 Second branchial cleft cysts (BCC). Although BCCs are not intrinsic to the sublingual or submandibular spaces, the most common cysts displace the submandibular gland and may, clinically, be confused with submandibular gland pathology (Fig 10). The majority of branchial cleft anomalies arise from the second branchial arch. 21Most of these cysts are unilocular, thin-walled, oval to round masses with cystic characteristics on CT and MRI. They are typically located in the posterior aspect of the submandibular space, at the angle of the mandible, and displace the gland anteriorly, the sternocleidomastoid muscle posteriorly, and the carotid space structures medially.= Their characteristic location between the submandibular gland and the sternocleidomastoid muscle make the diagnosis easy; however, a large necrotic lymph node from metastasis can have a similar appearance. Extension of the cyst between the internal and external carotid arteries, its embryologic course, is virtually pathogenomoic of second branchial cleft cysts. 23 On CT and MR, they
Fig 9. Thyroglossal duct cyst. Axial contrast-enhanced CT demonstrates a midline cyst between the anterior bellies of the digastric muscle (dots). The mass is homogeneous and exhibits a thin rim of capsular enhancement. (Courtesy of Deborah Reede, MD,}
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Fig 10. Infected second branchial cleft cyst. Axial contrastenhanced Tl-weighted MRI shows a large cystic mass (C) that displaces the sternocleidomastoid muscle (S) posteriorly, the submandibular gland (asterisk) anteriorly, and the carotid space vessels (dots) medially. The thick, enhancing wall is characteristic of an infected cyst. Although not a true floor of the mouth lesion, the location mimics other submandibular space lesions.
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myositis is also present, there is enlargement of the involved muscle. Abscesses. Abscesses are single or multiloculated collections that usually conform to the fascial spaces. On CT, they are typically lowdensity collections that demonstrate peripheral rim enhancement (Figs 12 and 13). Signs of surrounding cellulitis may also be present. On MRI, the collections are usually hypointense to isointense on TlWI and hyperintense on T2WI. Ludwig's angina. Ludwig's angina is a severe form of cellulitis, usually caused by streptococcal or staphylococcal bacteria. Before the development of antibiotics the infection would often spread inferiorly along fascial planes into the mediastinum, thus producing chest pain. The diagnosis of Ludwig's angina requires that four criteria be met: (1) The process always involves both the SLS and SMS and is frequently bilateral; (2) there is gangrene or serosanguinous phlegmon but little or no frank pus; (3) it involves connective tissue, fascia, and muscle but spares glandular structures; and (4) it spreads by contiguity, not by lymphatics. 25 Ludwig's angina is typically encountered in association with a 2- to 4-day history of prior man-
are fluid density/intensity with a thin wall. A thickened, enhancing wall suggests infection (Fig 10).
Infection/Inflammation Infections of the oral cavity and floor of the mouth generally arise from ductal stenosis or calculi or from dental infections or manipulation of the mandibular teeth. The mandibular teeth and mylohyoid sling have a relationship that determines which space is primarily involved by dental infections. The apices of the second and third molars lie below the mylohyoid ridge such that apical infections tend to involve the SMS, primarily, whereas infections of the first or premolar root apices, located above the mylohyoid ridge, involve the S L S . 24 Cellulitis. Cellulitis is a diffuse infection that involves cutaneous and subcutaneous tissues. On imaging studies, thickening of the skin, edematous fat, and enhancement of the fascial planes are all easily identified (Fig 11). If
Fig 11. Cellulitis. Axial contrast-enhanced CT scan demonstrates diffuse infection involving the floor of the mouth and buccomasserteric regions. The subcutaneous fat (arrows) is edematous, and the right mylohyoid muscle (curved arrow) is enlarged suggesting myositis. Reactive adenopathy is also seen in the deep cervical chain (asterisk).
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distinguish from epidermoid or retention cysts. On MRI, these lesions are homogeneously hypointense on T1WI and hyperintense on T2WI (Fig 16).28 Diving ranulas can have a "tail" extending into the SLS, the bulk of the lesion residing within the SMS (Fig 17).4
Benign Tumors In general, benign tumors are rare in this region.
Pleomorphic adenoma (benign mixed tumor).
Fig 12. Abscoss. Axial contrast-enhanced CT scan shows a large gas-containing abscess collection. The margins exhibit peripheral rim enhancement and adjacent nodes are involved (asterisks), The right platysma muscle (arrows) is thickened, and the overlying fat is edematous indicating associated myositis and cellulitis, respectively.
dibular dental extraction. Infections of the mandibular molars account for up to 90% of reported cases. 26 On imaging studies, Ludwig's angina appears as a diffuse cellulitis (Fig 14). The role of imaging is to determine airway patency, document the presence of any gasproducing organisms, detect any underlying dental infection, detect osteomyelitis, and identify any drainable abscess. Ranulas. When confined to the SLS, these lesions are termed "simple" ranulas and appear as unilocular cystic masses. They result from obstruction of a minor salivary gland or sublingual gland duct and are true epithelial-lined cysts. With rupture of the wall of a simple ranula, fluid may dissect posteriorly from the SLS into the SMS around the free posterior edge of the mylohyoid muscle because of the lack of fascial boundary. This lesion is termed a "plunging" or "diving" ranula. 27 Diving ranulas are not true epithelial-lined retention cysts, but "pseudocysts" lined by dense connective or granulation tissue. On CT, ranulas are sharplymarginated, unenhancing lesions of low density that conform to the fascial boundaries of the SLS and/or SMS (Fig 15). They are difficult to
Pleomorphic adenomas, arising from major or minor salivary gland tissue, are the most common benign tumors that occur in the SLS and SMS. The imaging characteristics of pleomorphic adenomas in these regions are similar to other pleomorphic adenomas. On CT, they are usually round, well-marginated, noninfiltrative masses that may have a heterogeneous internal composition owing to areas of mucoid material interspersed among cellular nests. Enhancement is usually absent or minimal. On MRI,
Fig 13. Abscess. Axial contrast-enhanced CT scan discloses a low-density fluid collection (asterisk) within the right submandibular space. A smaller collection is seen in the left submandibular space (small arrow). This patient had a history of a
previous infections of multiple mandibular molar teeth. The right submandibular gland (large arrow) is pushed posteriorly and the lingual septum (arrowhead) is displaced laterally.
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Fig 14. Ludwig's angina. Axial contrast-enhanced CT scans at (A) higher and (B) lower levels of the floor of the mouth reveal diffuse cellulitis in this patient with a history of poor dentition and recent dental manipulation. The sublingual and submandibular spaces are involved bilaterally, but the glands are normal in appearance. Areas of phlegmon (arrows) are present, but frank abscess collections are not seen. Adenopathy is minimal. Bilateral drainage catheters were placed (curved arrows), but no pus could be drained. S, submandibular gland.
Fig 15. Simple ranula. Axial contrast-enhanced CT scan demonstrates a unilocular cystic mass in the right sublingual space. The mylohyoid (arrow) and genioglossus (curved arrow) muscles are surrounding the cyst. An enhancing rim is not seen, which is typical for a simple ranula.
they are usually isointense to muscle on T1WI and hyperintense on T2WI. Lipoma. Lipomas, common throughout the body, are uncommon in the head and neck. a~ Only 13% of lipomas occur in the head and neck in general, and they represent only 1% of benign neoplasms occurring in the tongue. 29 These lesions are composed of mature fat cells, separated by fibrous-tissue septae and surrounded by a thin capsule? ~ On CT and MRI, they typically exhibit the same imaging characteristics as subcutaneous fat (Fig 18). Although the CT appearance is specific, the MRI appearance may be confused with an old hematoma. 1~ Rhabdomyorna. These are rare, benign tumors of skeletal muscle but have a predilection for the head and neck, especially the tongue, larynx, and pharynx. 31 On imaging studies, they are well circumscribed and have a density/ intensity similar to muscle and only enhance slightly after contrast administration. 32 Neurogenic neoplasms. Schwannomas, neuromas, and neurofibromas may all occur in the oral cavity, especially within the tongue. 33 On CT, these lesions are focal, well-defined, homogeneous masses. On MRI, they are typically
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Fig 16. Simple ranula. Axial (A) contrast-enhanced Tl-weighted and (B) T2-weighted MR images show a cystic mass (asterisk) in the left sublingual space. The cyst is hypointense to muscle on T1 weighting and hyperintense on T2 weighting. Mylohyoid muscle (black arrowheads) and genioglossus muscle (white arrowheads) are seen.
isointense to muscle on TIWI and hyperintense on T2WI. Granular cell t u m o r These tumors contain neurogenous elements in addition to skeletal muscle, histiocytes, and fibrous elements. The tumor has two forms: a congenital, infantile
Fig 17. Diving ranula. Axial T2-weighted MRI discloses a homogeneous hyperintense cystic lesion centered in the submandibular space (asterisk). A "tail" (arrow) extends anteriorly into the sublingual space.
form (epulis) and an adult form (granular cell myoblastoma).32 Fifty percent of these lesions involve the tongue and floor of the mouth. Although they are benign and do not metasta-
Fig 18. Lipoma. Axial contrast-enhanced CT scan shows a fat-density mass (asterisk) anterior to the right mandible and deep to the platysma muscle (arrows). There is no surrounding enhancement, and the mass is isodense to the subcutaneous fat.
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size, they frequently infiltrate surrounding tissue, making complete surgical excision difficult? The CT appearance is nonspecific and resembles squamous cell carcinoma because of its infiltrative characteristics. On MRI, these lesions tend to exhibit hypointensity on both T1WI and T 2 W I , 32 Aggressive fibromatosis. These tumors, of fibrous origin, rapidly enlarge and infiltrate surrounding fascia and muscle. The term "desmoid" has been applied to a subgroup of these lesions. They most commonly occur in children less than 5 years of age. Although these lesions have a benign histology and do not metastasize, they are so locally aggressive that they are considered by some to be low-grade fibrosarcomas. 32 There is a 50% to 70% recurrence rate
Fig 19. Aggressive fibromatosis, Axial (A) Tl-weighted, (B) T2-weighted, and (C) coronal contrast-enhanced Tl-weighted MRI demonstrate a large mass in the left submandibular space. The mass is minimally hyperintense to muscle on the Tl-weighted image and hyperintense on the T2-weighted image. There is marked homogeneous enhancement of this mass. Note compression of the left genioglossus muscle (arrow, A); left hyoglossus muscle (arrows, C); and displacement of the lingual septum (arrowhead, A) to the right. The aggressive nature of this lesion is evidenced by its wrapping around the mandible (C), infiltration into the masseter muscle (curved arrow, C), and its invasion of the lingual cortex of the mandible (open arrows, A, C), (Courtesy of Jan Casselman, MD.)
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after incomplete surgical excision. 34 On imaging studies, aggressive fibromatosis is difficult to distinguish from a malignant lesion because of its infiltration of fatty planes. On MRI, fibromatosis has relatively well-defined margins and is hypointense to isointense to muscle on T l W l and hyperintense on T2WI (Fig 19). 3`5
Malignant Tumors Squamous cell carcinoma (SCCA).
The most common malignant tumor that occurs in the oral cavity and floor of mouth is SCCA, which accounts for more than 90% of malignant oral cavity lesions. ~4 When encountered in the SLS or SMS, it usually indicates spread from the tongue base or adjacent oral tongue.
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Fig 20. Squamous cell carcinoma. (A) Axial and (B) coronal contrast-enhanced CT scans show a large enhancing mass involving the oral tongue, oropharynx, right tonsillar pillar, and base of the tongue. Extension into the right carotid and parapharngeal spaces is also seen (arrowheads). Normal left carotid and jugular (white arrow) are seen. Although the primary site of origin is difficult to ascertain on this study, the clear demonstration of extension across the midline [arrows) precludes a hemiglossectomy as a treatment option.
The anterior aspect of the floor of the mouth is the most common site of SCCA in the oral cavity. Evaluation must include pathways of extension. Medially, tumor may spread across the midline (Fig 20). This is important to document because it precludes hemiglossectomy as a treatment option. Laterally and anteriorly, the tumor may infiltrate the mylohyoid muscle and mandibular periosteum (Fig 21). Posteriorly, the tumor may enter the submandibular space and, inferiorly, it may extend along the mylohyoid muscle to reach the hyoid bone. SCCA extension is recognized on CT images by obliteration of fat planes surrounding muscle (Fig 22). Secondary changes, such as ductal obstruction, leading to inflammatory enlargement of the submandibular gland, and denervation atrophy from invasion of hypoglossal and lingual nerves must also be noted. Tumors that involve the anterior two thirds of the tongue are free to spread in any direction along bundles of intrinsic and extrinsic muscles. Submucosal spread to the floor of the mouth, tongue base, mandible, and tonsils also occurs. The rich lymphatics of the tongue are responsible for the high incidence of bilateral nodal disease. Indeed, 30% to 40% of patients with stage T1 or T2 carcinoma have clinically palpable nodes. 32 On CT imaging, SCCA appears
similar to surrounding tongue musculature and is recognized by infiltration and distortion of the normal fat planes. On MRI, carcinomas are hyperintense to muscle on T2WI. Carcinomas arising from the gingiva of the upper or lower alveolar ridges have the added danger of possible mandibular invasion (Fig 23). This may occur by perineural extension, along the inferior alveolar nerve, or by intramedullary extension, between bony trabeculae. Carcinoma of the buccal mucosa may extend into the buccinator muscle, subcutaneous tissues of the cheek, and/or posteriorly into the retromolar trigone. Tumors that arise in the retromolar trigone may extend cephalad, deep to the maxillary tuberosity, invade the fat pad posterolaterally to the maxillary antrum, and continue to spread superiorly to the infratemporal fossa and along neurovascular bundles into the cavernous sinus, frequently through the foramen ovale (Fig 24). Spread to these areas may be clinically silent, and detailed assessment by CT or MRI is essential for accurate staging. Posterolateral spread may invade the ascending ramus of the mandible, masseter muscle, and the cheek. Medial spread can involve the medial pterygoid muscle, and inferomedial spread may reach the
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Fig 21. Squamous cell carcinoma. Axial contrast-enhanced CT scans in (A) soft tissue and (B) bone windows depicts a large destructive tumor in the anterior aspect of the floor of the mouth, extending into the vestibule, The tumor invades and destroys the lingual and buccal surfaces of the mandible. (C) Axial and (D) sagittal Tl-weighted and (E) axial T2-weighted MRI help define the extension of the tumor by demonstrating preservation of fat planes, indicating absence of tumor spread (curved arrows). MRI also greatly defines mandibular involvement. Although the CT (B) scan demonstrates bone destruction, it fails to adequately depict marrow extension. T1-weighted MRI (C) helps depict marrow extension by demonstrating loss of the bright signal from marrow fat (arrow).
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cal to those that occur in the major salivary glands. These include malignant mixed cell tumors, adenoid cystic carcinoma (ACCA), mucoepidermoid carcinoma, and adenocarcinoma. ACCA tends to invade and infiltrate along neurovascular bundles early. This feature accounts for its high incidence of local recurrence as tumor cells have often extended beyond the resection. 1 Mucoepidermoid carcinomas arise from duct cells and are likely to recur locally and metastasize to regional nodes. Adenocarcinomas are rare in the oral cavity, but they have the worst prognosis of any of the minor salivary gland neoplasms. 32 On CT and MRI, minor salivary tumors cannot be distinguished from SCCA (Fig 25). MRI has an advantage over CT in better demonstrating perineural spread of tumor, especially if contrast and fat suppression techniques are u s e d . 36
Lymphoma.
Fig 22. Squamous cell carcinoma. Axial contrast-enhanced CT scan shows a subtle enhancing mass (arrow) that replaces the fat along the left anterior aspect of the floor of mouth, adjacent to the mandible. Compare with the normal right side.
mylohyoid muscle and posterior aspect of the floor of the mouth. Minor salivary gland malignancies. Carcinomas other than SCCA are rare in the oral cavity. The majority are carcinomas that arise from the numerous minor salivary glands and are identi-
Fig 23. Squamous cell carcinoma. Axial contrast-enhanced Tl-weighted MRI demonstrates a mass (asterisk) centered along the right gingivobuccal sulcus. The mass mildly enhances and destroys the anterior aspect of the right mandible, including the buccal and lingual cortices.
Hodgkin's and non-Hodgkin's lymphoma occur in the head and neck but can rarely occur isolated to the oral cavity. Lymph node enlargement is the most common finding for both types, although non-Hodgkin's lymphoma more frequently involves extranodal and/or extralymphatic sites. 37,38 On imaging, involved nodes are variable in size, homogeneous, and may demonstrate rim enhancement (Fig 26). Central necrosis is rare unless treatment has been given, and this may help distinguish lymphoma from metastatic adenopathy, which frequently has central necrosis. Malignant adenopathy. Submandibular and jugulodigastric adenopathy of less than 2 cm in diameter is present in 30% of patients with carcinoma of the floor of the mouth. However, 30% of these nodes are enlarged by benign reactive changes. 1,32 Submental nodes are usually not involved. Bilateral nodal metastases occur in approximately 50% of patients who have not received treatment to the nodal drainage sites. SCCA of the lips and gingivobuccal sulcus involves the submental, submandibular, and jugulodigastric nodes in 10% to 20% of patients by the time of initial presentation. 32 SCCA of the tongue has a high incidence of nodal disease because of the rich lymphatics. Thirty percent to 40% of patients with T1- or T2-stage carcinomas have clinically palpable nodes. 32
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Fig 24.
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Squamous cell carcinoma of the retromolar trigone,
{A) Axial contrast-enhanced Tl-weighted MRI demonstrates an enhancing infiltrative mass centered at the left retromolar trigone, The mass extends into the oral tongue and left tonsillar fossa, Tumor can also be seen extending into the mandibular foramen (arrow). (B) Coronal contrast-enhanced Tl-weighted MRI again demonstrates an infiltrative mass in the left retromolar trigone with extension of the mass through the floor of the left maxillary sinus (arrow). Note that there is fatty infiltration of the left hemi-tongue and left masseter muscle (dots) secondary to denervation atrophy. (C) Coronal contrastenhanced MRI further posterior shows perineural tumor extension along the left mandibular nerve, through a widened foramen ovale (curved arrow), into the cavernous sinus (arrow),
Fig 25. Adenoid cystic carcinoma, (A and B) Axial CT scans shows a soft tissue mass (asterisks) with mild peripheral and central enhancement in the left floor of the mouth. The mass is deep to the mylohyoid muscle (arrow, B) and obliterates the fat-filled sublingual space. This mass cannot be distinguished from squamous cell carcinoma.
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The mandibular nerve (V3) provides motor innervation to not only the muscles of mastication, tensor tympani, and tensor palatini muscles, but also to the anterior belly of the digastric muscle and the mylohyoid muscle via the mylohyoid nerve. Injury to the mandibular nerve results in fatty atrophy of all the muscle bundles, whereas isolated injury to the mylohyoid nerve (see "Anatomy of the Jaw, Dentition, and Related Regions") results in fatty infiltration and atrophy of only the anterior belly of the digastric and mylohyoid muscles (Fig 27). As with hypoglossal injury, a search for neural pathology along the entire course of the nerve, back to the brainstem, is required when V3 atrophy is identified.
Fig 26. Non-Hodgkin's lymphoma. Axial contrast-enhanced CT scan demonstrates a large submandibular space nodal mass (arrowheads). There is mild peripheral rim enhancement on CT with homogeneous enhancement on MRI. Central necrosis is not identified. A carotid space node (asterisk) is also identified that compresses the internal jugular vein (arrow),
Miscellaneous Lesions Denervation muscle atrophy (pseudotumor). Cranial nerves provide motor supply to various muscles and muscle groups in the head and neck. When the innervation is interrupted by neural involvement with tumor or infection, there is a loss of motor function ipsilateral to the lesion. This results in muscle wasting, fatty infiltration, and hemiatrophy of involved muscles (Fig 24)? 9 On imaging studies, the fatty atrophy is easily appreciated. However, the asymmetry can be mistaken for tumor because the normal side appears enlarged when compared with the atrophic side. The hypoglossal nerve provides motor innervation to the intrinsic and extrinsic muscles of the tongue. Lesions that affect the nerve can produce muscle atrophy and fatty replacement in 2 to 3 weeks. 4~ When present, a search for pathology must be made along the entire course of the hypoglossal nerve including the brainstem.
Fig 27. Mandibular nerve denervation atrophy. (A) Axial and (B) coronal contrast-enhanced CT scans shows atrophy involving the right digastric and mylohyoid muscles secondary to mandibular nerve tumor involvement. This is easily identified when compared with the normal left-sided muscles (D, left digastric muscle; M, left mylohyoid muscle).
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REFERENCES
1. Batsakis J'G: Tumors of the Head and Neck (ed 2). Baltimore, Williams & Wilkins, 1979 2. Hiatt JL, Gartner LP: Textbook of Head and Neck Anatomy (ed 2). Baltimore, MD, Williams & Wilkins, 1987, pp 31-56 3. Kassel EE: Radiographic evaluation of the floor of the mouth and tongue base, in DelBalso AM (ed): Maxillofacial Imaging. Philadelphia, Saunders, 1990, pp 375-407 4. Harnsberger HR: Handbooks in Radiology. Head and Neck Imaging. Chicago, Year Book, 1990, pp 112-138 5. Smoker WRK: The hypoglossal nerve. Neuroimag Clin North Am 3:193-206, 1993 6. Mulliken JB, Glowacki J: Hemangiomas and vascular malformations in infants and children: A classification based on endothelial characteristics. Plast Reconstr Surg 69:412-420, 1982 7. Baker LL, Dillon WP, Hieshima GB, et al: Hemangiomas and vascular malformations of the head and neck: MR characterization. AJNR Am J Neuroradiol 14:307-314, 1993 8. Meyer JS, Holier FA, Barnes PD, et al: Biological classification of soft-tissue vascular anomalies: MR correlation. AJR 157:559-564, 1991 9. Gelbert F, Riche MC, Reizine D, et al: MR imaging of head and neck vascular malformations. JMRI 1:579-584, 1991 10. Reede DL, Holliday RA, Sore PM, et al: Nonnodal pathologic conditions of the neck, in Som PM, Bergeron RT (ed): Head and Neck Imaging (ed 2). St Louis, Mosby-Year Book, 1991, pp 531-557 11. Som PM: Salivary glands, in Som PM, Bergeron RT (ed): Head and Neck Imaging (ed 2). St Louis, Mosby-Year Book, 1991, p 341 12. Siegel MJ, Glazer HS, St. Amour TE, et al: Lymphangiomas in children: MR imaging. Radiology 170:467-470, 1989 13. Hunter TB, Paplanus SH, Chernin MM, el al: Dermold cyst of the floor of the mouth: CT appearance. AJR 141:1239-1240, 1983 14. Smoker WRK: MR imaging of the tongue and oral cavity. Syllabus for the Categorical Course on Body Magnetic Resonance Imaging. Amer College of Radiology, 1993, pp 125-136 15. Adib A, Gluckman JL, Mendelson D: Bilateral idiopathic aneurysms of the lingual arteries. Otolaryngol Head Neck Surg 108:87-90, 1993 16. Larsson SG, Lufkin RB: Anomalies of the digastric muscles: CT and MR demonstration. J Comput Assist Tomogr 11:422-425, 1987 17. Traini M: Bilateral accessory digastric muscles. Anat Clin 5:199-201, 1983 18. Reede DL, Bergeron RT, Som PM: CT of thyroglossal duct cysts. Radiology 157:121-125, 1985 19. Dolata J: Thyroglossal duct cyst in the mouth floor: An unusual location. Otolaryngol Head Neck Surg 110:580583, 1994 20. Yildiz K, Koksal H, Ozoran Y, et aI: Papillary carcinoma in a thyroglossal duct remnant with normal thyroid gland. J Laryngol Otol 107:1174-1176, 1993
21. Benson MT, Daten K, Mancuso AA, et al: Congenital anomalies of the branchial apparatus: Embryology and pathologic anatomy. RadioGrapbics 12:943-960, 1992 22. Harnsberger HR, Mancuso AA, Muraki AS, et al: Branchial cleft anomalies and their mimics: Computed tomographic evaluation. Radiology 152:739-748, 1984 23. Salazar JE, Duke RA, Ellis JV: Second branchial cleft cyst: Unusual location and a new CT diagnostic sign. AJR t45:965-966, 1985 24. Tschiassny K: Ludwig's angina: An anatomic study of the lower molar teeth in its pathogenesis. Arch Otolaryngol 38:485-496, 1943 25. Grodinsky MD: Ludwig's angina: An anatomical and clinical study with review of the literature. Surgery 5:678696, 1939 26. Nguyen VD, Potter JL, Hersh-Schick MR: Ludwig angina: An uncommon and potentially lethal neck infection. AJNR Am J Neuroradiol 13:2t5-219, 1992 27. Charnoff SK, Carter BL: Plunging ranula: CT diagnosis. Radiology 158:467-468, 1986 28. Silverstein MI, Castillo M, Hudgins PA, et al: MR imaging of intralingual ranula in a child. J Comput Assist Tomogr 14:672-674, 1990 29. Jablokow VR, Bavafa S: Lipomas of the tongue: report of two cases. J Surg Oncol 21:114-116, 1982 30. Fujimura N, Enomoto S: Lipoma of the tongue with cartilaginous changes: A case report and review of the literature. J Oral Maxillofac Surg 50:1015-t017, 1992 31. Boysen M, Scott H, Hovig T, et ak Rhabdomyoma of the tongue. J Laryngol Otol 102:1185-1188, 1988 32. Dillon WP: The pharynx and oral cavity, in Som PM, Bergeron RT (ed): Head and Neck Imaging (ed 2). St Louis, Mosby-Year Book, 1991, pp 450-462 33. Flickinger FW, Loranzo RL, Yuh WTC, et al: Neurolemoma of the tongue: MR findings. J Comput Assist Tomogr 13:886-888, 1989 34. Shah AC, Katz RL: Infantile aggressive fibromatosis of the base of the tongue. Otolaryngol Head Neck Surg 98:346-349, 1988 35. Chen PC, Ball WS, Towbin RB: Aggressive fibromatosis of the tongue: MR demonstration. J Comput Assist Tomogr 13:343-345, 1989 36. Tien RD: Fat-suppression MR imaging in neuroradiology: Techniques and clinical application. AJR 158:369379, 1992 37. Harnsberger HR, Bragg DG, Osborn AG, et al: Non-Hodgkin's lymphoma of the head and neck: CT evaluation of nodal and extranodal sites. AJNR Am J Neuroradiol 8:673-679, 1987 38. Lee YY, Van Tassel P, Nauert C, et al: Lymphomas of the head and neck: CT findings at initial presentation. AJNR Am J Neuroradiol 8:665-671, 1987 39. Harnsberger HR, Dillon WP: Major motor atrophic patterns in the face and neck: CT evaluation. Radiology 155:665-670, 1985 40. Larsson SG: Hemiatrophy of the tongue and floor of the mouth demonstrated by computed tomography. J Comput Assist Tomogr 9:914-918, 1985
The oral cavity and oropharynx comprise the upper portion of the aerodigestive tract. These two regions are distinguished from each other because pathologic processes differ in their presentations, prognoses, and histologic grades. The normal anatomy of the oral cavity, vestibule, and oral cavity proper is discussed and is followed by a discussion of the sublingual and submandibular spaces. The diversity of pathologic processes that occur in these regions is then presented as well as the more common pitfalls.
HE UPPER portion of the aerodigestive
T tract is composed of the oral cavity and oropharynx. The oral cavity and oropharynx are
separated from each other by a ring of structures that includes the soft palate, anterior tonsillar pillars, pterygomandibular raphe, and circumvallate papillae of the tongue. These regions are distinguished from each other because pathologic processes differ in their presentations, prognoses, and histologic grades. 1 The normal anatomy of the oral cavity, which includes the lips, gingivobuccal mucosa, superior and inferior alveolar ridges and teeth, mandible, oral tongue (anterior two thirds), and the hard palate, is discussed. A more detailed review of the jaw and dentition can be found in "Anatomy of the Jaw, Dentition, and Related Regions," which appears in this issue. After a discussion of the anatomy, a review of the pathologic processes found within the oral cavity and tongue is presented. ANATOMY
Vestibule The vestibule (Fig 1) is the space between the dental arches and teeth and the lips and cheeks. The vestibule communicates with the oral cavity proper via the interdental spaces and the space posterior to the last molar teeth in the alveolar arch. The mucosal surface of the lips and cheek is termed the "buccal mucosa," whereas the mucosal lining of the teeth, alveolar arches, and gums (gingiva) is termed the "gingival mucosa." Gingival mucosa joins the buccal mucosa at the gingivobuccal sulcus, a common site in which squamous cell carcinomas arise. Reflections of the labial mucosa, the labial frenula, appear as midline, vertically oriented folds of tissue that attach the superior and inferior lips to the gingiva. The interdental papilla, where the vestibular gingiva becomes continuous with the oral cavity gingiva, lies between the teeth in the interdental spaces. The
sharp mucogingival line separates the gingival mucosa from the alveolar mucosa and is produced by the greater vascularity of the latter. A fold of mucosa in the posteriormost boundary of the vestibule covers the pterygomandibular raphe. 2 This raphe, a tendinous junction between the buccinator and superior constrictor muscles, is a thick fascial band that originates from the hamulus of the medial pterygoid plate and inserts along the mylohyoid ridge of the mandible. The raphe connects the maxillary and mandibular alveolar ridges and is the junction between the oral cavity and oropharynx. The wall of the cheek is formed by the buccinator muscle and an overlying subcutaneous pad of fat, the buccal fat pad (Fig 1). The buccinator arises from the pterygomandibular raphe and the outer surfaces of the maxilla and mandible in the region of the molar teeth. The fibers run forward into the substance of the lips and are pierced along their course by the tensor veli palatini tendon and the parotid gland duct (Stenson's duct). Stenson's duct pierces the buccinator muscle and drains into the vestibule opposite the second maxillary molar (Fig 1). Posterior to the last mandibular molar teeth, the mandibular alveolar process forms a flat bony surface, the retromolar triangle covered by a triangular area of mucosa, the retromolar trigone. Squamous cell carcinomas commonly arise in the retromolar trigone.
Oral Cavity Proper The oral cavity proper lies internal to the mandibular and maxillary alveolar arches. It is
From the Department of Radiology, Medical College of Virginia, Richmond, VA. Address reprint requests to Fred J. Laine, MD, Assistant Professor of Radiology, PO Box 980615 MCV Station, Medical College of Virginia, Richmond, VA 23298. Copyright 9 1995 by W.B. Saunders Company 0887-2171/95/1606-000555. 00/0
Seminars in Ultrasound, CT, andMRI, Vo116, No 6 (December), 1995: pp 527-545
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Fig 1. Normal buccomasseteric region. Axial Tl-weighted MRI scan demonstrates the buccal fat situated between the zygomaticus major muscle (arrowheads), masseter muscle (asterisk), and buccinator muscle (dots). The parotid gland duct (arrow) pierces the buccal fat pad and the buccinator muscle to open into the vestibule of the mouth opposite the second maxillary molars. The facial artery (small curved arrow) is seen anteriorly to the parotid gland duct, and the superior aspect of the pterygomandibular raphe (large curved arrow} is seen at the posterior aspect of the alveolar arch.
bounded superiorly by the hard palate and inferiorly by the muscular tongue. The muscular tongue is partially separated from the floor of the mouth by the sublingual sulcus laterally and anteriorly. This is a mucosal reflection continuous with the lingual gingiva and the lingual alveolar mucosa. The mylohyoid muscle arises from the entire length of the mylohyoid ridge on the inner surface of the mandible and extends posteriorly to insert on the body of the hyoid bone. A diagramatic representation of this and related anatomy can be found in "Anatomy of the Jaw, Dentition, and Related Regions." The two mylohyoid muscles are joined by a fibrous median raphe and form a U-shaped sling, which forms the "floor of the mouth." Two additional muscle bundles help provide support to the floor of the mouth: the anterior belly of the digastric situated below the mylohyoid muscle and the geniohyoid muscles situated above the mylohyoid muscle. The digastric muscle consists of a posterior belly, which arises from the mastoid notch of the temporal bone, and an anterior belly, which arises from the digastric fossa of the anterior lower border of the mandible. Both bellies descend to the hyoid bone and terminate in an intermediate tendon. The tendon is enveloped by a fibrous loop that attaches to the body and greater cornu of the
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hyoid bone. Attaching anteriorly to the inferior mental spine (genial tubercle) of the mandible, the geniohyoid courses above the mylohyoid to insert onto the anterior surface of the body of the hyoid bone. The mylohyoid sling, as well as the anterior digastric and geniohyoid muscles, are best depicted on coronal CT and MRI (Figs 2D, 3B). The anterior two thirds of the tongue, which includes both the tip and the body of the tongue, is considered part of the oral cavity, whereas the posterior one third is considered part of the oropharynx. The tongue muscles are composed of two groups: intrinsic and extrinsic. The intrinsic muscles, having no bony attachments, are within the superior aspect of the tongue itself and are described as longitudinal, transverse, and vertical muscle groups. The tissue planes and intrinsic muscle orientation are not well appreciated on CT. 3 The extrinsic muscles, which have bony attachments, originate outside the tongue and are composed of four paired bundles: genioglossus, hyoglossus, styloglossus, and palatoglossus. The genioglossus muscle arises from the superior mental spine (genial tubercle) of the inner surface of the mandible and fans out along the inferior aspect of the tongue, passing to the tongue base and body of the hyoid. Anterior fibers curve upward into the tip of the tongue. The bellies of the two genioglossus muscles are separated by the midline lingual septum and fatty tissue and are easily identified on axial CT and Tl-weighted MRI (Figs 2A and 3A). The hyoglossus muscle originates from the body and greater cornu of the hyoid bone, lateral to the genioglossus, enters the tongue, and intermingles with fibers of the styloglossus muscle (Figs. 2A and 3A). The styloglossus muscle arises from the styloid process of the temporal bone and the stylomandibular ligament. Most of the fibers continue to the tip of the tongue, whereas some of the posterior fibers decussate with fibers of the hyoglossus muscle. The palatoglossus muscle arises from the fascia and lateral aspect of the soft palate and interdigitates with the intrinsic muscles of the tongue along the lateral margin.
Spaces of the Floor of Mouth The paired bellies of the genioglossus and geniohyoid muscles are separated by a midline
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i;
Fig 2. Normal CT anatomy, floor of the mouth. Axial CT scans through the (A) high, (B) middle, and (C) low floor of the mouth. (D) Coronal CT image of the floor of the mouth. 1, mylohyoid muscle; 2, genioglossus muscle; 3, hyoglossus muscle; 4, anterior belly of the digastric muscle; 5, geniohyoid muscle; 6, platysma muscle; 7, lateral pterygoid muscle; 8, medial pterygoid muscle; 9, masseter muscle; 10, lingual tonsil; 11, sublingual space; 12, submandibular space; 13, submandibular gland; T, base of the tongue; M, mandible; S, lingual septum; P, soft palate.
fat-containing lingual septum (Fig 2). The mylohyoid muscle separates the floor of mouth into two spaces: the sublingual space and the submandibular space. These are a descriptive convenience only as there is no fascia that surrounds the sublingual space and both spaces communicate with each other posteriorly at the free margin of the mylohyoid muscle. Sublingual space (SLS). The SLS is a potential space without a fasciaI Iining. 4 Its medial boundaries are the genioglossus muscle, superiorly, and the geniohyoid muscle, inferiorly. The mylohyoid muscle makes up its inferior border and part of the lateral border. The sublingual sulcus is found at the superior lateral aspect of
the SLS. The contents of the SLS include the sublingual gland and ducts (ducts of Rivinus), which open into the sublingual sulcus, along the surface of the plica sublingualis. Medially to the gland lie the anteriormost fibers of the hyoglossus muscle, an important surgical landmark. The lingual artery and vein lie medially to the hyoglossus muscle, whereas the submandibular gland duct and the hypoglossal and lingual nerves lie laterally to it. The deep portion of the submandibuiar gland lies in the posterior aspect of the SLS. The submandibular g[and duct (Wharton's duct) arises from this portion of the submandibular gland and courses, first, between the hyoglossus and genioglossus muscles, then
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Fig 3. Normal MRI anatomy, floor of the mouth. (A) Axial, (B) coronal, and (C) sagittal Tl-weighted MRI of the floor of the mouth. 1, mylohyoid muscle; 2, genioglossus muscle; 3, hyoglossus muscle; 4, anterior belly of the digastric muscle; 5, geniohyoid muscle; 6, platysma muscle; 9, masseter muscle; 10, lingual tonsil; 11, sublingual space; 12, submandibular space; 13, submandibular gland; T, base of the tongue; M, mandible; S, lingual septum; P, soft palate; dots, hard palate.
crosses the hyoglossus muscle, lying between it and the sublingual gland, to empty in the sublingual caruncle, just lateral to the base of the frenulum. The submandibular space (SMS). The SMS is a U-shaped area located inferolaterally to the mylohyoid muscle and superiorly to the hyoid bone. The SMS is fascially defined except in its posterior aspect where it communicates with both the sublingual and the parapharyngeal spaces. The SMS contains the superficial portion of the submandibular gland, the facial vein and artery, and the submandibular and submental lymph nodes. The anterior bellies of the two digastric muscles form the margins of the small, midline, submental space.
Innervation The mylohyoid and anterior belly of the digastric muscles are innervated by the third
(mandibular) division of cranial nerve V. The posterior belly of the digastric muscle receives innervation from cranial nerve VII. Motor innervation to the geniohyoid muscle is variably described as originating from the hypoglossal nerve or from motor fibers of C1 and C2. 5 All extrinsic tongue muscles, with the exception of the palatoglossus muscle, are innervated by the hypoglossal nerve. The palatoglossus muscle is innervated by the pharyngeal plexus. 2
Lymphatics The oral cavity drains via the regional submental, submandibular, and parotid nodes into the internal jugular (deep cervical) chain. The drainage is both ipsilateral and contralateral. PATHOLOGY
The majority of lesions are encountered in both the SLS and SMS and are discussed
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together (Table 1). Those lesions that are specific to a particular space are noted.
Congenital Vascular lesions. Two major types of vascular lesions have been described: hemangiomas and vascular malformations. 6 Hemangiomas are neoplastic, present early in infancy, rapidly enlarge, and involute by adolescence. 6 Previously termed "strawberry hemangiomas," these lesions are most often superficial (cutaneous). Occasionally, they may extend deeply and infiltrate underlying muscles (subcuTable 1. Sublingual Space and Submandibular Space Pathology Congenital Vascular lesions Hemangioma Vascular malformations Capillary malformation Venous malformation (cavernous hemangiomas) Arterial malformation Lymphatic malformation (lymphangioma) Dermoid cysts Lingual artery aneurysm Digastric muscle anomalies (SMS) Thyroglossal duct cysts (Second branchial cleft cysts) Inflammatory/infection Cellulitis Abscess Ludwig's angina Ranula Simple ranula (SLS) Plunging or "diving" ranula (SMS Tumors Benign Pleomorphic adenoma (benign mixed tumor) Lipoma Rhabdomyoma Neurogenic tumors Granular cell tumors Aggressive fibromatosis Malignant Squamous cell carcinoma--primary~metastatic Salivary gland and minor salivary gland malignancies Adenoid cystic carcinoma Mucoepidermoid carcinoma Adenocarcinoma Lymphoma
Hodgkin's Non-Hodgkin's Pseudotumor Hypoglossal nerve denervation muscle atrophy Mandibular nerve denervation muscle atrophy
Fig 4. Venous malformation. Contrast-enhanced CT image demonstrates an extensive venous malformation involving the left buccomasseteric region and oral cavity. The presence of multiple calcifications (phleboliths) is almost diagnostic of venous malformation.
taneous). 7 On MRI, hemangiomas are isointense to muscle on T1W] and hyperintense on T2WI and enhance after contrast administration. 8 As hemangiomas involute, fatty deposition, which appears hyperintense on T1W], occurs. Vascular malformations are not tumors but rather are congenital vascular anomalies that are present at birth. They manifest slow steady growth and no involution and are classified, based on their predominant anomalous vessel, into arterial, capillary, venous, and lymphatic malformations. Capillarymalformations are lowflow lesions and are observed most frequently as a component of a syndrome such as SturgeWeber. Venousmalformations, previously termed "cavernous hemangiomas," are the most common vascular malformations to affect the oral cavity. They are similar to subcutaneous hemangiomas in imaging characteristics and may attain enormous size. They are low-flow lesions and infiltrate along fascial planes. CT scans demonstrate a mass of muscle intensity with variable enhancement. The presence of phleboliths is diagnostic (Fig 4). On MRI, venous malformations are isointense to hyperintense on T1WI and hyperintense on T2WI (Fig 5). 9 Arterial malformations are high-flow lesions that result from abnormal vessel morphogenesis. On MRI, flow voids are observed, which correspond to the enlarged arterial components.
Lymphatic malformations (lymphangiomas) are believed to arise from primitive embryonic
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Fig 5. Venous malformation. (A) Sagittal, (B) coronal contrast-enhanced Tl-weighted, and (C) sagittal T2-weighted MRI demonstrate a large venous malformation involving the oral tongue, which bulges superiorly into the oral cavity and extends posteriorly into the oropharynx. The true extent of this lesion is best appreciated on the T2-weighted image.
lymph sac sequestrations. These lesions are believed to enlarge because of inadequate drainage, from lack of communication with the central lymphatic channels, or from excessive secretions of lining cells. 1~ Lymphangiomas are classified into three groups, based on the size of the abnormal lymphatic spaces: (1) lymphangioma simplex, composed of small, capillarysized, thin-walled lymphatic channels; (2) cavernous lymphangiomas, composed of dilated lymphatic channels with a fibrous adventitia; and (3) cystic lymphangiomas, or cystic hygromas, which are cysts ranging in size from a few millimeters to several centimeters in diameter. 1~ Most of the lymphatic malformations found in the oral cavity are cystic hygromas. Fifty to 60% are present at birth, and 80% to 90% are diagnosed by the age of 2. ll Cystic hygromas appear as large, heterogeneous, multiloculated,
fluid-filled masses on imaging studies. They frequently wrap around and adhere to adjacent structures. 4 In infants, they most frequently occur in the posterior cervical space and superior mediastinum. Although they are rare in adults, when they do occur, they are more commonly found in the submandibular space. Cystic hygromas are hypointense to isointense to muscle on TlWI and hyperintense on T2WI (Fig 6). 12 Most have a signal intensity greater than that of cerebrospinal fluid on both TlWI and T2WI, suggesting proteinaceous fluid. Dermoid cysts. Three varieties of dermoid cysts are found in the oral cavity. Epidermoids, arrising from ectodermal elements, are cysts with simple squamous epithelium lining a fibrous wall (Fig 7). Dermoid cysts, from both ectoderm and mesoderm, are similar but contain skin appendages (hair follicles, sebaceous
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Fig 6. Cystic hygroma. Axial (A) Tl-weighted, (B) T2-weighted, and (C) coronal, contrast-enhanced Tl-weighted MRI show a cystic mass (asterisk) in the right submandibular space. The lesion is hypointense to muscle on the T1-weighted image and hyperintense on the T2-weighted image and does not enhance. The lesion and its relation to the mylohyoid (dots) and digastric (arrow) muscles are best seen on the coronal image (C).
glands). Teratoid cysts contain all three germ cell layers, ectoderm, mesoderm, and endoderm, and are therefore composed of a diverse range of tissues. 13 These lesions appear as unilocular masses on imaging studies and may have minimal peripheral rim enhancement. Epidermoids display fluid characteristics (Fig 7), whereas the imaging appearance of dermoids reflects their fat content (Fig 8). 14 Epidermoids seem to involve the SLS more often, whereas dermoids are more commonly found within the SMS.4 Lingual artery aneurysm. Although they usually result from trauma, lingual artery aneurysms of congenital origin have been reported. 15 Their appearance is variable and depends on the degree of thrombosis.
Digastric muscle anomalies.
Bilateral and unilateral accessory anterior digastric muscles and hypoplasia/aplasia of these muscles have been described but are uncommon. 16,17They are important to recognize so as not to confuse them with actual pathology.16Accessory digastric muscles can be confused with masses in the floor of the mouth or enlarged lymph nodes. Hypoplasia may be mistaken for denervation atrophy. 16 Identification of a normal-sized mylohyoid muscle, also receiving innervation from the mylohyoid branch of the inferior alveolar nerve, is strong evidence against denervation atrophy. Thyroglossal duct cysts. Embryologically, the thyroid gland develops at the foramen cecum of the tongue and descends into the neck. The migration of the thyroid gland and thyroglossal
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Fig 7. Epidermoid cyst. Axial CT shows a unilocular, hypodense cystic lesion in the floor of the mouth. The cyst is
homogeneous density, but otherwise indistinguishable from other cystic lesions in the floor of the mouth.
duct may be arrested anywhere along its path. Because the duct is lined with secretory epithelium, failure of the duct to involute may give rise to a cyst. Thirty-five percent of thyroglossal duct cysts are hyoid or suprahyoid in location. Is In the suprahyoid neck, these lesions are typically midline, between the bellies of the anterior digastric muscles, below the mylohyoid sling, and present as masses in the floor of the mouth. 19 On CT, they are well-circumscribed,
Fig 8. Dermoid cyst. Coronalcontrast-enhanced CT demonstrates a large unilocular cyst in the floor of the mouth deep to the mylohyoid muscles (dots), The presence of a single, lowdensity fat globule (curved arrow) within this cyst assures the diagnosis of a dermoid cyst. (Courtesy of Deborah Reede, MD.)
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low-density lesions and have thin-rim enhancement (Fig 9) and are occasionally septated giving a multilocular appearance. On MRI, the signal characteristics of these lesions are dependent on the protein content but are usually isointense on T1WI and hyperintense on T2WI.10 Less than 1% of thyroglossal cysts are associated with carcinomas, papillary carcinoma being the most common. 1~176 Second branchial cleft cysts (BCC). Although BCCs are not intrinsic to the sublingual or submandibular spaces, the most common cysts displace the submandibular gland and may, clinically, be confused with submandibular gland pathology (Fig 10). The majority of branchial cleft anomalies arise from the second branchial arch. 21Most of these cysts are unilocular, thin-walled, oval to round masses with cystic characteristics on CT and MRI. They are typically located in the posterior aspect of the submandibular space, at the angle of the mandible, and displace the gland anteriorly, the sternocleidomastoid muscle posteriorly, and the carotid space structures medially.= Their characteristic location between the submandibular gland and the sternocleidomastoid muscle make the diagnosis easy; however, a large necrotic lymph node from metastasis can have a similar appearance. Extension of the cyst between the internal and external carotid arteries, its embryologic course, is virtually pathogenomoic of second branchial cleft cysts. 23 On CT and MR, they
Fig 9. Thyroglossal duct cyst. Axial contrast-enhanced CT demonstrates a midline cyst between the anterior bellies of the digastric muscle (dots). The mass is homogeneous and exhibits a thin rim of capsular enhancement. (Courtesy of Deborah Reede, MD,}
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Fig 10. Infected second branchial cleft cyst. Axial contrastenhanced Tl-weighted MRI shows a large cystic mass (C) that displaces the sternocleidomastoid muscle (S) posteriorly, the submandibular gland (asterisk) anteriorly, and the carotid space vessels (dots) medially. The thick, enhancing wall is characteristic of an infected cyst. Although not a true floor of the mouth lesion, the location mimics other submandibular space lesions.
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myositis is also present, there is enlargement of the involved muscle. Abscesses. Abscesses are single or multiloculated collections that usually conform to the fascial spaces. On CT, they are typically lowdensity collections that demonstrate peripheral rim enhancement (Figs 12 and 13). Signs of surrounding cellulitis may also be present. On MRI, the collections are usually hypointense to isointense on TlWI and hyperintense on T2WI. Ludwig's angina. Ludwig's angina is a severe form of cellulitis, usually caused by streptococcal or staphylococcal bacteria. Before the development of antibiotics the infection would often spread inferiorly along fascial planes into the mediastinum, thus producing chest pain. The diagnosis of Ludwig's angina requires that four criteria be met: (1) The process always involves both the SLS and SMS and is frequently bilateral; (2) there is gangrene or serosanguinous phlegmon but little or no frank pus; (3) it involves connective tissue, fascia, and muscle but spares glandular structures; and (4) it spreads by contiguity, not by lymphatics. 25 Ludwig's angina is typically encountered in association with a 2- to 4-day history of prior man-
are fluid density/intensity with a thin wall. A thickened, enhancing wall suggests infection (Fig 10).
Infection/Inflammation Infections of the oral cavity and floor of the mouth generally arise from ductal stenosis or calculi or from dental infections or manipulation of the mandibular teeth. The mandibular teeth and mylohyoid sling have a relationship that determines which space is primarily involved by dental infections. The apices of the second and third molars lie below the mylohyoid ridge such that apical infections tend to involve the SMS, primarily, whereas infections of the first or premolar root apices, located above the mylohyoid ridge, involve the S L S . 24 Cellulitis. Cellulitis is a diffuse infection that involves cutaneous and subcutaneous tissues. On imaging studies, thickening of the skin, edematous fat, and enhancement of the fascial planes are all easily identified (Fig 11). If
Fig 11. Cellulitis. Axial contrast-enhanced CT scan demonstrates diffuse infection involving the floor of the mouth and buccomasserteric regions. The subcutaneous fat (arrows) is edematous, and the right mylohyoid muscle (curved arrow) is enlarged suggesting myositis. Reactive adenopathy is also seen in the deep cervical chain (asterisk).
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distinguish from epidermoid or retention cysts. On MRI, these lesions are homogeneously hypointense on T1WI and hyperintense on T2WI (Fig 16).28 Diving ranulas can have a "tail" extending into the SLS, the bulk of the lesion residing within the SMS (Fig 17).4
Benign Tumors In general, benign tumors are rare in this region.
Pleomorphic adenoma (benign mixed tumor).
Fig 12. Abscoss. Axial contrast-enhanced CT scan shows a large gas-containing abscess collection. The margins exhibit peripheral rim enhancement and adjacent nodes are involved (asterisks), The right platysma muscle (arrows) is thickened, and the overlying fat is edematous indicating associated myositis and cellulitis, respectively.
dibular dental extraction. Infections of the mandibular molars account for up to 90% of reported cases. 26 On imaging studies, Ludwig's angina appears as a diffuse cellulitis (Fig 14). The role of imaging is to determine airway patency, document the presence of any gasproducing organisms, detect any underlying dental infection, detect osteomyelitis, and identify any drainable abscess. Ranulas. When confined to the SLS, these lesions are termed "simple" ranulas and appear as unilocular cystic masses. They result from obstruction of a minor salivary gland or sublingual gland duct and are true epithelial-lined cysts. With rupture of the wall of a simple ranula, fluid may dissect posteriorly from the SLS into the SMS around the free posterior edge of the mylohyoid muscle because of the lack of fascial boundary. This lesion is termed a "plunging" or "diving" ranula. 27 Diving ranulas are not true epithelial-lined retention cysts, but "pseudocysts" lined by dense connective or granulation tissue. On CT, ranulas are sharplymarginated, unenhancing lesions of low density that conform to the fascial boundaries of the SLS and/or SMS (Fig 15). They are difficult to
Pleomorphic adenomas, arising from major or minor salivary gland tissue, are the most common benign tumors that occur in the SLS and SMS. The imaging characteristics of pleomorphic adenomas in these regions are similar to other pleomorphic adenomas. On CT, they are usually round, well-marginated, noninfiltrative masses that may have a heterogeneous internal composition owing to areas of mucoid material interspersed among cellular nests. Enhancement is usually absent or minimal. On MRI,
Fig 13. Abscess. Axial contrast-enhanced CT scan discloses a low-density fluid collection (asterisk) within the right submandibular space. A smaller collection is seen in the left submandibular space (small arrow). This patient had a history of a
previous infections of multiple mandibular molar teeth. The right submandibular gland (large arrow) is pushed posteriorly and the lingual septum (arrowhead) is displaced laterally.
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Fig 14. Ludwig's angina. Axial contrast-enhanced CT scans at (A) higher and (B) lower levels of the floor of the mouth reveal diffuse cellulitis in this patient with a history of poor dentition and recent dental manipulation. The sublingual and submandibular spaces are involved bilaterally, but the glands are normal in appearance. Areas of phlegmon (arrows) are present, but frank abscess collections are not seen. Adenopathy is minimal. Bilateral drainage catheters were placed (curved arrows), but no pus could be drained. S, submandibular gland.
Fig 15. Simple ranula. Axial contrast-enhanced CT scan demonstrates a unilocular cystic mass in the right sublingual space. The mylohyoid (arrow) and genioglossus (curved arrow) muscles are surrounding the cyst. An enhancing rim is not seen, which is typical for a simple ranula.
they are usually isointense to muscle on T1WI and hyperintense on T2WI. Lipoma. Lipomas, common throughout the body, are uncommon in the head and neck. a~ Only 13% of lipomas occur in the head and neck in general, and they represent only 1% of benign neoplasms occurring in the tongue. 29 These lesions are composed of mature fat cells, separated by fibrous-tissue septae and surrounded by a thin capsule? ~ On CT and MRI, they typically exhibit the same imaging characteristics as subcutaneous fat (Fig 18). Although the CT appearance is specific, the MRI appearance may be confused with an old hematoma. 1~ Rhabdomyorna. These are rare, benign tumors of skeletal muscle but have a predilection for the head and neck, especially the tongue, larynx, and pharynx. 31 On imaging studies, they are well circumscribed and have a density/ intensity similar to muscle and only enhance slightly after contrast administration. 32 Neurogenic neoplasms. Schwannomas, neuromas, and neurofibromas may all occur in the oral cavity, especially within the tongue. 33 On CT, these lesions are focal, well-defined, homogeneous masses. On MRI, they are typically
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Fig 16. Simple ranula. Axial (A) contrast-enhanced Tl-weighted and (B) T2-weighted MR images show a cystic mass (asterisk) in the left sublingual space. The cyst is hypointense to muscle on T1 weighting and hyperintense on T2 weighting. Mylohyoid muscle (black arrowheads) and genioglossus muscle (white arrowheads) are seen.
isointense to muscle on TIWI and hyperintense on T2WI. Granular cell t u m o r These tumors contain neurogenous elements in addition to skeletal muscle, histiocytes, and fibrous elements. The tumor has two forms: a congenital, infantile
Fig 17. Diving ranula. Axial T2-weighted MRI discloses a homogeneous hyperintense cystic lesion centered in the submandibular space (asterisk). A "tail" (arrow) extends anteriorly into the sublingual space.
form (epulis) and an adult form (granular cell myoblastoma).32 Fifty percent of these lesions involve the tongue and floor of the mouth. Although they are benign and do not metasta-
Fig 18. Lipoma. Axial contrast-enhanced CT scan shows a fat-density mass (asterisk) anterior to the right mandible and deep to the platysma muscle (arrows). There is no surrounding enhancement, and the mass is isodense to the subcutaneous fat.
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size, they frequently infiltrate surrounding tissue, making complete surgical excision difficult? The CT appearance is nonspecific and resembles squamous cell carcinoma because of its infiltrative characteristics. On MRI, these lesions tend to exhibit hypointensity on both T1WI and T 2 W I , 32 Aggressive fibromatosis. These tumors, of fibrous origin, rapidly enlarge and infiltrate surrounding fascia and muscle. The term "desmoid" has been applied to a subgroup of these lesions. They most commonly occur in children less than 5 years of age. Although these lesions have a benign histology and do not metastasize, they are so locally aggressive that they are considered by some to be low-grade fibrosarcomas. 32 There is a 50% to 70% recurrence rate
Fig 19. Aggressive fibromatosis, Axial (A) Tl-weighted, (B) T2-weighted, and (C) coronal contrast-enhanced Tl-weighted MRI demonstrate a large mass in the left submandibular space. The mass is minimally hyperintense to muscle on the Tl-weighted image and hyperintense on the T2-weighted image. There is marked homogeneous enhancement of this mass. Note compression of the left genioglossus muscle (arrow, A); left hyoglossus muscle (arrows, C); and displacement of the lingual septum (arrowhead, A) to the right. The aggressive nature of this lesion is evidenced by its wrapping around the mandible (C), infiltration into the masseter muscle (curved arrow, C), and its invasion of the lingual cortex of the mandible (open arrows, A, C), (Courtesy of Jan Casselman, MD.)
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after incomplete surgical excision. 34 On imaging studies, aggressive fibromatosis is difficult to distinguish from a malignant lesion because of its infiltration of fatty planes. On MRI, fibromatosis has relatively well-defined margins and is hypointense to isointense to muscle on T l W l and hyperintense on T2WI (Fig 19). 3`5
Malignant Tumors Squamous cell carcinoma (SCCA).
The most common malignant tumor that occurs in the oral cavity and floor of mouth is SCCA, which accounts for more than 90% of malignant oral cavity lesions. ~4 When encountered in the SLS or SMS, it usually indicates spread from the tongue base or adjacent oral tongue.
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Fig 20. Squamous cell carcinoma. (A) Axial and (B) coronal contrast-enhanced CT scans show a large enhancing mass involving the oral tongue, oropharynx, right tonsillar pillar, and base of the tongue. Extension into the right carotid and parapharngeal spaces is also seen (arrowheads). Normal left carotid and jugular (white arrow) are seen. Although the primary site of origin is difficult to ascertain on this study, the clear demonstration of extension across the midline [arrows) precludes a hemiglossectomy as a treatment option.
The anterior aspect of the floor of the mouth is the most common site of SCCA in the oral cavity. Evaluation must include pathways of extension. Medially, tumor may spread across the midline (Fig 20). This is important to document because it precludes hemiglossectomy as a treatment option. Laterally and anteriorly, the tumor may infiltrate the mylohyoid muscle and mandibular periosteum (Fig 21). Posteriorly, the tumor may enter the submandibular space and, inferiorly, it may extend along the mylohyoid muscle to reach the hyoid bone. SCCA extension is recognized on CT images by obliteration of fat planes surrounding muscle (Fig 22). Secondary changes, such as ductal obstruction, leading to inflammatory enlargement of the submandibular gland, and denervation atrophy from invasion of hypoglossal and lingual nerves must also be noted. Tumors that involve the anterior two thirds of the tongue are free to spread in any direction along bundles of intrinsic and extrinsic muscles. Submucosal spread to the floor of the mouth, tongue base, mandible, and tonsils also occurs. The rich lymphatics of the tongue are responsible for the high incidence of bilateral nodal disease. Indeed, 30% to 40% of patients with stage T1 or T2 carcinoma have clinically palpable nodes. 32 On CT imaging, SCCA appears
similar to surrounding tongue musculature and is recognized by infiltration and distortion of the normal fat planes. On MRI, carcinomas are hyperintense to muscle on T2WI. Carcinomas arising from the gingiva of the upper or lower alveolar ridges have the added danger of possible mandibular invasion (Fig 23). This may occur by perineural extension, along the inferior alveolar nerve, or by intramedullary extension, between bony trabeculae. Carcinoma of the buccal mucosa may extend into the buccinator muscle, subcutaneous tissues of the cheek, and/or posteriorly into the retromolar trigone. Tumors that arise in the retromolar trigone may extend cephalad, deep to the maxillary tuberosity, invade the fat pad posterolaterally to the maxillary antrum, and continue to spread superiorly to the infratemporal fossa and along neurovascular bundles into the cavernous sinus, frequently through the foramen ovale (Fig 24). Spread to these areas may be clinically silent, and detailed assessment by CT or MRI is essential for accurate staging. Posterolateral spread may invade the ascending ramus of the mandible, masseter muscle, and the cheek. Medial spread can involve the medial pterygoid muscle, and inferomedial spread may reach the
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Fig 21. Squamous cell carcinoma. Axial contrast-enhanced CT scans in (A) soft tissue and (B) bone windows depicts a large destructive tumor in the anterior aspect of the floor of the mouth, extending into the vestibule, The tumor invades and destroys the lingual and buccal surfaces of the mandible. (C) Axial and (D) sagittal Tl-weighted and (E) axial T2-weighted MRI help define the extension of the tumor by demonstrating preservation of fat planes, indicating absence of tumor spread (curved arrows). MRI also greatly defines mandibular involvement. Although the CT (B) scan demonstrates bone destruction, it fails to adequately depict marrow extension. T1-weighted MRI (C) helps depict marrow extension by demonstrating loss of the bright signal from marrow fat (arrow).
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cal to those that occur in the major salivary glands. These include malignant mixed cell tumors, adenoid cystic carcinoma (ACCA), mucoepidermoid carcinoma, and adenocarcinoma. ACCA tends to invade and infiltrate along neurovascular bundles early. This feature accounts for its high incidence of local recurrence as tumor cells have often extended beyond the resection. 1 Mucoepidermoid carcinomas arise from duct cells and are likely to recur locally and metastasize to regional nodes. Adenocarcinomas are rare in the oral cavity, but they have the worst prognosis of any of the minor salivary gland neoplasms. 32 On CT and MRI, minor salivary tumors cannot be distinguished from SCCA (Fig 25). MRI has an advantage over CT in better demonstrating perineural spread of tumor, especially if contrast and fat suppression techniques are u s e d . 36
Lymphoma.
Fig 22. Squamous cell carcinoma. Axial contrast-enhanced CT scan shows a subtle enhancing mass (arrow) that replaces the fat along the left anterior aspect of the floor of mouth, adjacent to the mandible. Compare with the normal right side.
mylohyoid muscle and posterior aspect of the floor of the mouth. Minor salivary gland malignancies. Carcinomas other than SCCA are rare in the oral cavity. The majority are carcinomas that arise from the numerous minor salivary glands and are identi-
Fig 23. Squamous cell carcinoma. Axial contrast-enhanced Tl-weighted MRI demonstrates a mass (asterisk) centered along the right gingivobuccal sulcus. The mass mildly enhances and destroys the anterior aspect of the right mandible, including the buccal and lingual cortices.
Hodgkin's and non-Hodgkin's lymphoma occur in the head and neck but can rarely occur isolated to the oral cavity. Lymph node enlargement is the most common finding for both types, although non-Hodgkin's lymphoma more frequently involves extranodal and/or extralymphatic sites. 37,38 On imaging, involved nodes are variable in size, homogeneous, and may demonstrate rim enhancement (Fig 26). Central necrosis is rare unless treatment has been given, and this may help distinguish lymphoma from metastatic adenopathy, which frequently has central necrosis. Malignant adenopathy. Submandibular and jugulodigastric adenopathy of less than 2 cm in diameter is present in 30% of patients with carcinoma of the floor of the mouth. However, 30% of these nodes are enlarged by benign reactive changes. 1,32 Submental nodes are usually not involved. Bilateral nodal metastases occur in approximately 50% of patients who have not received treatment to the nodal drainage sites. SCCA of the lips and gingivobuccal sulcus involves the submental, submandibular, and jugulodigastric nodes in 10% to 20% of patients by the time of initial presentation. 32 SCCA of the tongue has a high incidence of nodal disease because of the rich lymphatics. Thirty percent to 40% of patients with T1- or T2-stage carcinomas have clinically palpable nodes. 32
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Fig 24.
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Squamous cell carcinoma of the retromolar trigone,
{A) Axial contrast-enhanced Tl-weighted MRI demonstrates an enhancing infiltrative mass centered at the left retromolar trigone, The mass extends into the oral tongue and left tonsillar fossa, Tumor can also be seen extending into the mandibular foramen (arrow). (B) Coronal contrast-enhanced Tl-weighted MRI again demonstrates an infiltrative mass in the left retromolar trigone with extension of the mass through the floor of the left maxillary sinus (arrow). Note that there is fatty infiltration of the left hemi-tongue and left masseter muscle (dots) secondary to denervation atrophy. (C) Coronal contrastenhanced MRI further posterior shows perineural tumor extension along the left mandibular nerve, through a widened foramen ovale (curved arrow), into the cavernous sinus (arrow),
Fig 25. Adenoid cystic carcinoma, (A and B) Axial CT scans shows a soft tissue mass (asterisks) with mild peripheral and central enhancement in the left floor of the mouth. The mass is deep to the mylohyoid muscle (arrow, B) and obliterates the fat-filled sublingual space. This mass cannot be distinguished from squamous cell carcinoma.
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The mandibular nerve (V3) provides motor innervation to not only the muscles of mastication, tensor tympani, and tensor palatini muscles, but also to the anterior belly of the digastric muscle and the mylohyoid muscle via the mylohyoid nerve. Injury to the mandibular nerve results in fatty atrophy of all the muscle bundles, whereas isolated injury to the mylohyoid nerve (see "Anatomy of the Jaw, Dentition, and Related Regions") results in fatty infiltration and atrophy of only the anterior belly of the digastric and mylohyoid muscles (Fig 27). As with hypoglossal injury, a search for neural pathology along the entire course of the nerve, back to the brainstem, is required when V3 atrophy is identified.
Fig 26. Non-Hodgkin's lymphoma. Axial contrast-enhanced CT scan demonstrates a large submandibular space nodal mass (arrowheads). There is mild peripheral rim enhancement on CT with homogeneous enhancement on MRI. Central necrosis is not identified. A carotid space node (asterisk) is also identified that compresses the internal jugular vein (arrow),
Miscellaneous Lesions Denervation muscle atrophy (pseudotumor). Cranial nerves provide motor supply to various muscles and muscle groups in the head and neck. When the innervation is interrupted by neural involvement with tumor or infection, there is a loss of motor function ipsilateral to the lesion. This results in muscle wasting, fatty infiltration, and hemiatrophy of involved muscles (Fig 24)? 9 On imaging studies, the fatty atrophy is easily appreciated. However, the asymmetry can be mistaken for tumor because the normal side appears enlarged when compared with the atrophic side. The hypoglossal nerve provides motor innervation to the intrinsic and extrinsic muscles of the tongue. Lesions that affect the nerve can produce muscle atrophy and fatty replacement in 2 to 3 weeks. 4~ When present, a search for pathology must be made along the entire course of the hypoglossal nerve including the brainstem.
Fig 27. Mandibular nerve denervation atrophy. (A) Axial and (B) coronal contrast-enhanced CT scans shows atrophy involving the right digastric and mylohyoid muscles secondary to mandibular nerve tumor involvement. This is easily identified when compared with the normal left-sided muscles (D, left digastric muscle; M, left mylohyoid muscle).
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REFERENCES
1. Batsakis J'G: Tumors of the Head and Neck (ed 2). Baltimore, Williams & Wilkins, 1979 2. Hiatt JL, Gartner LP: Textbook of Head and Neck Anatomy (ed 2). Baltimore, MD, Williams & Wilkins, 1987, pp 31-56 3. Kassel EE: Radiographic evaluation of the floor of the mouth and tongue base, in DelBalso AM (ed): Maxillofacial Imaging. Philadelphia, Saunders, 1990, pp 375-407 4. Harnsberger HR: Handbooks in Radiology. Head and Neck Imaging. Chicago, Year Book, 1990, pp 112-138 5. Smoker WRK: The hypoglossal nerve. Neuroimag Clin North Am 3:193-206, 1993 6. Mulliken JB, Glowacki J: Hemangiomas and vascular malformations in infants and children: A classification based on endothelial characteristics. Plast Reconstr Surg 69:412-420, 1982 7. Baker LL, Dillon WP, Hieshima GB, et al: Hemangiomas and vascular malformations of the head and neck: MR characterization. AJNR Am J Neuroradiol 14:307-314, 1993 8. Meyer JS, Holier FA, Barnes PD, et al: Biological classification of soft-tissue vascular anomalies: MR correlation. AJR 157:559-564, 1991 9. Gelbert F, Riche MC, Reizine D, et al: MR imaging of head and neck vascular malformations. JMRI 1:579-584, 1991 10. Reede DL, Holliday RA, Sore PM, et al: Nonnodal pathologic conditions of the neck, in Som PM, Bergeron RT (ed): Head and Neck Imaging (ed 2). St Louis, Mosby-Year Book, 1991, pp 531-557 11. Som PM: Salivary glands, in Som PM, Bergeron RT (ed): Head and Neck Imaging (ed 2). St Louis, Mosby-Year Book, 1991, p 341 12. Siegel MJ, Glazer HS, St. Amour TE, et al: Lymphangiomas in children: MR imaging. Radiology 170:467-470, 1989 13. Hunter TB, Paplanus SH, Chernin MM, el al: Dermold cyst of the floor of the mouth: CT appearance. AJR 141:1239-1240, 1983 14. Smoker WRK: MR imaging of the tongue and oral cavity. Syllabus for the Categorical Course on Body Magnetic Resonance Imaging. Amer College of Radiology, 1993, pp 125-136 15. Adib A, Gluckman JL, Mendelson D: Bilateral idiopathic aneurysms of the lingual arteries. Otolaryngol Head Neck Surg 108:87-90, 1993 16. Larsson SG, Lufkin RB: Anomalies of the digastric muscles: CT and MR demonstration. J Comput Assist Tomogr 11:422-425, 1987 17. Traini M: Bilateral accessory digastric muscles. Anat Clin 5:199-201, 1983 18. Reede DL, Bergeron RT, Som PM: CT of thyroglossal duct cysts. Radiology 157:121-125, 1985 19. Dolata J: Thyroglossal duct cyst in the mouth floor: An unusual location. Otolaryngol Head Neck Surg 110:580583, 1994 20. Yildiz K, Koksal H, Ozoran Y, et aI: Papillary carcinoma in a thyroglossal duct remnant with normal thyroid gland. J Laryngol Otol 107:1174-1176, 1993
21. Benson MT, Daten K, Mancuso AA, et al: Congenital anomalies of the branchial apparatus: Embryology and pathologic anatomy. RadioGrapbics 12:943-960, 1992 22. Harnsberger HR, Mancuso AA, Muraki AS, et al: Branchial cleft anomalies and their mimics: Computed tomographic evaluation. Radiology 152:739-748, 1984 23. Salazar JE, Duke RA, Ellis JV: Second branchial cleft cyst: Unusual location and a new CT diagnostic sign. AJR t45:965-966, 1985 24. Tschiassny K: Ludwig's angina: An anatomic study of the lower molar teeth in its pathogenesis. Arch Otolaryngol 38:485-496, 1943 25. Grodinsky MD: Ludwig's angina: An anatomical and clinical study with review of the literature. Surgery 5:678696, 1939 26. Nguyen VD, Potter JL, Hersh-Schick MR: Ludwig angina: An uncommon and potentially lethal neck infection. AJNR Am J Neuroradiol 13:2t5-219, 1992 27. Charnoff SK, Carter BL: Plunging ranula: CT diagnosis. Radiology 158:467-468, 1986 28. Silverstein MI, Castillo M, Hudgins PA, et al: MR imaging of intralingual ranula in a child. J Comput Assist Tomogr 14:672-674, 1990 29. Jablokow VR, Bavafa S: Lipomas of the tongue: report of two cases. J Surg Oncol 21:114-116, 1982 30. Fujimura N, Enomoto S: Lipoma of the tongue with cartilaginous changes: A case report and review of the literature. J Oral Maxillofac Surg 50:1015-t017, 1992 31. Boysen M, Scott H, Hovig T, et ak Rhabdomyoma of the tongue. J Laryngol Otol 102:1185-1188, 1988 32. Dillon WP: The pharynx and oral cavity, in Som PM, Bergeron RT (ed): Head and Neck Imaging (ed 2). St Louis, Mosby-Year Book, 1991, pp 450-462 33. Flickinger FW, Loranzo RL, Yuh WTC, et al: Neurolemoma of the tongue: MR findings. J Comput Assist Tomogr 13:886-888, 1989 34. Shah AC, Katz RL: Infantile aggressive fibromatosis of the base of the tongue. Otolaryngol Head Neck Surg 98:346-349, 1988 35. Chen PC, Ball WS, Towbin RB: Aggressive fibromatosis of the tongue: MR demonstration. J Comput Assist Tomogr 13:343-345, 1989 36. Tien RD: Fat-suppression MR imaging in neuroradiology: Techniques and clinical application. AJR 158:369379, 1992 37. Harnsberger HR, Bragg DG, Osborn AG, et al: Non-Hodgkin's lymphoma of the head and neck: CT evaluation of nodal and extranodal sites. AJNR Am J Neuroradiol 8:673-679, 1987 38. Lee YY, Van Tassel P, Nauert C, et al: Lymphomas of the head and neck: CT findings at initial presentation. AJNR Am J Neuroradiol 8:665-671, 1987 39. Harnsberger HR, Dillon WP: Major motor atrophic patterns in the face and neck: CT evaluation. Radiology 155:665-670, 1985 40. Larsson SG: Hemiatrophy of the tongue and floor of the mouth demonstrated by computed tomography. J Comput Assist Tomogr 9:914-918, 1985