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The masticator space: From anatomy to pathology
Journal of Neuroradiology (2009) 36, 121—130
REVIEW
The masticator space: From anatomy to pathology Espace masticateur : de l’anatomie à la pathologie N. Fayea,∗, F. Lafitteb, M. Williamsb, A. Guermazic, M. Sahli-Amord, J. Chirasd, E. Diona a
Department of radiology, hôpital Louis-Mourier, 178, rue des Renouillers, 92700 Colombes, France Department of neuroradiology, fondation Rothschild, rue Manin, Paris, France c Department of Radiology Services Synarc Inc, Market street, San Francisco, CA, États-Unis d Department of neuroradiology, hôpital Pitié-Salpêtrière, boulevard de l’Hôpital, Paris, France b
Available online 5 October 2008
KEYWORDS Masticator space; CT; MRI; Imaging; Anatomy
MOTS CLÉS Espace masticateur ; Scanner ; IRM ; Imagerie ; Anatomie
∗
Summary The masticator space is a deep facial space with a complex anatomical structure. The purpose of the present study was to precisely define the masticator space to eliminate the use of obsolete and confusing terms to describe the area, and to illustrate the common mass syndromes. Primary tumors are uncommon, usually benign and of a vascular or neural origin. Adjacent lesions, mainly pharyngeal with secondary extension into the masticator space, are especially frequent. Metastases are rare, and infectious pathology is often odontogenic. The most frequent lesion of the masticator space is the odontogenic abscess. Multidetector CT and MRI enable precise study of the space, its communications with other deep spaces and the etiology of any mass syndrome. Understanding the anatomy of the masticator space and how it links up with the other deep facial spaces helps the radiologist to recognize the different lesions of this space and to avoid unnecessary surgery, or any other less than optimal management. © 2008 Elsevier Masson SAS. All rights reserved. Résumé L’espace masticateur appartient aux espaces profonds de la face et possède une structure anatomique complexe. L’objectif de ce travail est de donner une définition anatomique précise de cet espace en évitant les termes obsolètes pour décrire cette région anatomique et d’illustrer les principaux syndromes de masses que l’on peut rencontrer. Les tumeurs primitives sont rares, le plus souvent bénignes et d’origine vasculaire ou nerveuse. Les lésions les plus fréquentes sont d’origine pharyngées avec une extension secondaire par contiguïté à l’espace masticateur. Les métastases sont très rares. La pathologie infectieuse est le plus souvent d’origine odontogène. L’abcès odontogène constitue le syndrome de masse le plus fréquent de l’espace masticateur. Le scanner multidétecteur et l’IRM permettent une analyse anatomique précise de cet espace, étudient ses communications avec les espaces voisins et diagnostiquent les syndromes de masse. Comprendre l’anatomie de cet espace et les communications avec les espaces de voisinage aide le radiologue à reconnaître les différentes lésions de
Corresponding author. E-mail address: [email protected] (N. Faye).
0150-9861/$ – see front matter © 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.neurad.2008.08.005
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N. Faye et al. cet espace et permet d’éviter une chirurgie contre-indiquée ou une mauvaise prise en charge thérapeutique. © 2008 Elsevier Masson SAS. All rights reserved.
Introduction There are deep facial spaces lying between the skull base and hyoid bone [1] that have a complex anatomical structure. They are divided into several areas that need to be well understood to provide a precise etiological analysis. The masticator space is a deep facial space that is outlined by the superficial layer of the deep cervical fascia [2,3], and lies laterally and evenly [2] in front of the prestyloid space, medial to the pharyngeal space and beneath the skull base. It may be affected by developmental, neoplastic or infectious lesions. This review discusses the anatomy, and CT and MRI findings, of masses in the masticator space and illustrates the imaging features of these lesions.
are no clinical signs or, if they do occur, they are so common as to be overlooked. Patients complain of facial pain with swelling and trismus which, in themselves, often complicate evaluation of the masticator space. In the case of perineural spread, patients present with dysesthesia along the course of the trigeminal nerve (V).
Tumors originating in the masticator space Masses originating in the masticator space [2] are typically centered anterior to the parapharyngeal fat space, displacing the parapharyngeal fat posteriorly and medially, and obliterating the fat planes of the masticator space itself. Primary tumors are rare [7] and usually benign. Those most frequently seen are neural and vascular lesions Table 1.
Anatomy Neurinomas The literature on the masticator space uses a wide-ranging and variable vocabulary, often including obsolete terms that can be confusing in clinical practice. For this reason, it is necessary to review the anatomy and to clearly define the terms used to describe this space. The masticator space as an anatomical and functional entity centered on the mandibular ramus, which divides it into medial and lateral compartments [4,5]. It is separated from the adjacent face and neck spaces by a superficial layer of deep cervical fascia except superiorly, where it freely communicates with the external temporal fossa, which we consider an upper extension of the masticator space. Adjacent to the masticator space are the buccal space anteriorly, the parotid space posteriorly, the parapharyngeal space medially, the submandibular and sublingual spaces inferiorly, and the skull base superiorly. The masticator space contains the four muscles of mastication (masseter, medial and lateral pterygoids, and temporalis), the ramus and posterior portion of the body of the mandible, the pterygopalatine node, the maxillary vessels, and the mandibular (V3) and maxillary (V2) branches of the trigeminal nerve (cranial nerve V) (Figs. 1—3). The medial compartment of the masticator space (infratemporal and pterygopalatine fossa) is an important route of communication with the other deep facial spaces (Fig. 4). The infratemporal fossa is linked to the middle space via the oval foramen and to the pterygopalatine fossa via the pterygomaxillary foramen. The pterygopalatine fossa communicates with the middle space and Meckel’s cavum via the round foramen, with the orbit via the inferior orbital fissure and with the palate via the palatine foramen.
Physical examination Clinical examination of the masticator space is difficult because it is deep-lying and not easily accessible. Lesions are often discovered only at a late stage either because there
Neural tumors are the most frequent benign tumors of the masticator space. They are related to the divisional branches of the trigeminal nerve [8,9]. Usually, computed tomography (CT) and magnetic resonance imaging (MRI) can reveal the typical features of neurinoma and neurofibroma, and are sufficient to establish the diagnosis. Neurinomas are
Figure 1 Graphic representation (axial view) of structures of the left masticator space: (1) masseter muscle; (2) medial pterygoid muscle; (3) lateral pterygoid muscle; (4) temporalis muscle; (5) pterygopalatine fossa; and (6) sphenopalatine foramen. Schéma en vue axiale de l’espace masticateur gauche : (1) muscle masséter ; (2) muscle ptérygoïdien medial ; (3) muscle ptérygoïdien latéral ; (4) muscle temporal ; (5) fosse ptérygopalatine ; (6) foramen sphénopalatin.
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Table 1 Imaging features of tumors originating in the masticator space. Aspects en imagerie des tumeurs primitives de l’espace masticateur. Tumor
Characteristics
CT features
MRI features
Neurinoma
Well-defined Foramen widening
Hypoattenuating Homogeneous enhancement
Isointense T1 Hyperintense T2 Homogeneous enhancement
Hemolymphangioma
Childhood Cystic with septa
Hyperattenuating Septal enhancement
Hypointense T1 Highly hyperintense T2 Septal enhancement
Hemangioma
Adult Low flow
Hypoattenuating ‘Apple-tree’ enhancement
Hypointense T1 Highly hyperintense T2 ‘Apple-tree’ enhancement
Capillary hemangioma
Childhood Mandibular hypoplasia
Strong enhancement
Highly hyperintense T2 Strong enhancement
Lipoma
Well-defined
Hypoattenuating No enhancement
Hyperintense T1 No enhancement
Aneurysmal cyst
Multilocular with fluid levels
Lytic Heterogeneous Calcifications
Heterogeneous Septal enhancement
Lymphoma
Infiltrative lesion
Isoattenuating Variable enhancement
Isointense T1 Hyperintense T2 Variable enhancement
Osteosarcoma
Primitive or secondary lesion (radiotherapy, Paget)
Lytic lesion
Soft-tissue involvement
Calcifications
Heterogeneous enhancement
Lytic lesion Calcifications Variable enhancement
Variable enhancement
Heterogeneous Bone lysis
Soft-tissue involvement Heterogeneous enhancement
Chondrosarcoma
Rhabdomyosarcoma
Extensive lesion
fusiform, well-circumscribed, capsulated lesions without nerve-fiber involvement. They demonstrate an intermediate signal on T1-weighted images and hyperintensity on T2weighted images, with enhancement after contrast-medium injection. They can be heterogeneous in the case of cystic or hemorrhagic transformations and may undergo malignant transformation, which is suggested by pain and rapid growth. Their spread follows the course of the nerves with smooth enlargement of their foramina. Neurofibromas are more complex lesions that involve the nerve fibers. It can exhibit a target-like pattern of increased peripheral signal intensity and decreased central signal intensity on T2-weighted images because of its fibrous central core.
malformations, whereas MRI can detect areas of signal void [11] from associated high-flow vessels within arteriovenous malformations and proliferating capillary hemangiomas. Capillary hemangiomas arise in early infancy, and involution occurs by adolescence. Hemolymphangioma is a pediatric condition that tends to recur and, thus, has a less-thanfavorable outcome. Imaging shows multicystic lesions with septa, and some of these loculi are hyperattenuating on CT as a consequence of hemorrhage. Hemangiomas affect adults and, when contrast-enhanced, present with a characteristic ‘apple tree’ appearance.
Lipoma Vascular lesions Vascular lesions include tumors and vascular abnormalities (Figs. 5—7). They can be histologically arterial, venous or lymphatic, or all three combined [10]. These lesions are usually hyperintense on T2-weighted images and tend to involve more than one deep facial space. CT may reveal the classic phleboliths within capillary hemangiomas or venous
Lipomas [12] are homogeneous, fatty, hypoattenuating lesions seen on CT scans with a characteristic homogeneous high signal intensity on T1-weighted images that decreases on fat-suppressed images. There is no enhancement with contrast. Therefore, non-enhanced T1-weighted imaging should be performed when evaluating a masticator space syndrome for spontaneous hyperintense lesions such as lipoma.
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Figure 2 Anatomical view of structures of the left masticator space: (1) masseter muscle; (2) medial pterygoid muscle; (3) lateral pterygoid muscle; (7) mandible; (8) internal jugular vein; (9) parotid gland; (10) internal carotid artery; (11) pharyngeal space; and (12) maxillary nerve. Coupe anatomique de l’espace masticateur gauche : (1) muscle masséter ; (2) muscle ptérygoïdien médial ; (3) muscle ptérygoïdien latéral ; (7) mandibule ; (8) veine jugulaire interne ; (9) glande parotide ; (10) carotide interne ; (11) espace pharyngé ; (12) nerf maxillaire.
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Figure 4 Graphic representation of the masticator space and its communications with other deep facial spaces: the infratemporal fossa (ITF) (red arrows) connects with the middle space via the oval foramen (A), and the pterygopalatine fossa (PPF) via the pterygomaxillary foramen (B); PPF ([5,6] green star, green arrows) connects with the middle space, and Meckel’s cavum with the round foramen (1), infraorbital area via the suborbital canal (2), orbit via the inferior orbital fissure (3), palate via the palatine foramen (4), and petrous apex via the pterygoid foramen (5). Schéma illustrant les principales voies de communication de l’espace masticateur : communication de la fosse infratemporale (ITF) (flèche rouge) avec l’espace moyen par le foramen ovale (A) et la fosse ptérygopalatine (PPF) par le foramen ptérygomaxillaire (B). Communication de la PPF [5,6] (étoile verte et flèche verte) avec l’espace moyen et le cavum de Meckel par le foramen rond (1) et la région infraorbitaire par le canal sous-orbitaire (2), l’orbite par la fissure orbitaire inférieure (3), le palais par le foramen palatin (4), et l’apex pétreux par le foramen ptérygoïdien (5).
Sarcoma Sarcomas are the most frequent malignant tumor of the masticator space [10] and appear as large heterogeneous lesions with (osteosarcoma, chondrosarcoma) or without (rhabdomyosarcoma) calcifications. Enhancement with contrast media is variable and heterogeneous. These lesions are associated with bone lysis and cortical disruption (Fig. 8).
Lymphoma Figure 3 Graphic representation (coronal view) of structures of the left masticator space: (1) masseter muscle; (2) medial pterygoid muscle; (3) lateral pterygoid muscle; (4) temporalis muscle; and oval foramen (blue arrow), the passageway for the third branch of the trigeminal nerve (V3). Schéma en vue coronale de l’espace masticateur gauche : (1) muscle masséter ; (2) muscle ptérygoïdien médial ; (3) muscle ptérygoïdien latéral ; (4) muscle temporal ; foramen ovale (flèche bleue) voie du V3.
Primary lymphomas are rare [13], but can be seen in the masticator space, especially in immunodeficient patients. They have no specific imaging features, but appear as isoattenuating, homogeneous, infiltrative masses with variable degrees of enhancement with contrast administration. They are isointense on T1-weighted images and moderately hyperintense on T2-weighted images. Enhancement also varies with MRI.
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Figure 5 Angioma involving the subcutaneous tissues is seen on axial MRI T1-weighted (A), T2- and fat-saturation-weighted (B), and T1-weighted after injection and fat saturation (C) images as a serpiginous lesion in the right masticator space, with hyperintense signals on T2 and enhancement after gadolinium contrast administration. MR angiography reveals the vascular origin of this lesion (D). Angiome. IRM en coupes axiales pondérées T1 (A), T2 avec saturation de graisse (B) et T1 après injection et saturation de graisse (C) montrant une lésion serpigineuse de l’espace masticateur droit en hypersignal T2 se rehaussant après injection. Cette lésion envahit les tissus sous-cutanés. L’angio-IRM confirme son origine vasculaire (D).
Figure 6 Vascular malformation on axial CT shows (A) a tubular lesion of the left masticator space lying between the masticatory muscles but without their involvement, and (B) strong enhancement after contrast injection. The lesion was hyperintense on T2weighted images (C). Malformation vasculaire. TDM en coupe axiale (A) montre une lésion tubulée de l’espace masticateur gauche située entre les muscles de la mastication sans les envahir avec un important rehaussement après injection (B). Cette lésion est hyperintense en T2 (C).
Figure 7 Aneurysmal bone cyst on axial (A) and coronal (B) CT scans appears as an extensive and heterogeneous lesion of the right masticator space, with considerable involvement of the right middle cerebral fossa and lysis of the mandible. Kyste anévrismal. TDM en coupe axiale (A) et coronale (B) montre une lésion extensive hétérogène de l’espace masticateur droit envahissant largement la fosse cérébrale moyenne avec lyse de la mandibule.
Figure 8 Rhabdomyosarcoma on axial (A) and coronal (B) CT scans after contrast injection appears as a huge multicystic mass in the left masticator space, with lysis of the left maxillary posterior wall and left mandible. Rhabdomyosarcome. TDM en coupe axiale (A) et coronale (B) après injection montre une volumineuse masse multikystique de l’espace masticateur gauche avec lyse de la paroi maxillaire postérieure et de la mandibule gauches.
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Figure 9 Temporal meningioma on axial MRI T2-weighted (A), and axial (B) and coronal (C) T1-weighted images after contrast injection appears as a right temporal extra-axial lesion involving the inferior orbital fissure (IOF), cavernous sinus and masticator space via the oval foramen (OF). Méningiome temporal. IRM en coupe axiale T2 (A) et axiale (B) et coronale (C) T1 après injection montre une masse extra-axiale temporale droite s’étendant à la fissure (IOF) orbitaire inférieure, le sinus caverneux et l’espace masticateur par le foramen ovale (OF).
Figure 10 Cavum carcinoma (axial view) on T1-weighted MRI images appears as (A) an expansive right rhinopharyngeal lesion (isointense signals) involving the parapharyngeal and prevertebral spaces. The lesion is also isointense on T2-weighted imaging (B) with enhancement after gadolinium administration (C). Carcinome du cavum. IRM en coupe axiale T1 (A) montre une lésion extensive rhinopharyngée en isosignal avec extension aux espaces parapharyngé et prévertébral. Cette lésion est iso-intense en T2 (B) et se rehausse après gadolinium (C).
Figure 11 Maxillary carcinoma on axial MRI T1-weighted imaging appears as (A) an obstruction in the left maxillary sinus with isointense signals involving the masticator space. The lesion is hyperintense on T2-weighted images (inflammation and retention) and shows heterogeneous enhancement (C) with abnormal enhancement of the left masticatory muscles. There is no enhancement of the retained component, but inflammation and tumor are enhanced after contrast injection. Carcinome maxillaire. IRM en coupe axiale T1 montrant un comblement du sinus maxillaire gauche en isosignal avec extension à l’espace masticateur. Cette lésion est hyperintense en T2 (inflammation et rétention) et se rehausse de manière hétérogène (C). Il s’associe un rehaussement anormal des muscles masticateurs gauches.
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Table 2 Imaging features of tumors originating from other sites with masticator space involvement. Aspects en imagerie des lésions à distance envahissant l’espace masticateur. Tumor
Characteristics
CT features
MRI features
Cavum carcinoma
Ethnic origin
Serous otitis
Oropharyngeal carcinoma
Alcohol
Enhancement less than normal mucosa Enhancement less than normal mucosa
Median lesion
Tobacco Maxillary sinus carcinoma
Posterior wall lysis
Isointense T1 Hyperintense T2 Enhancement less than normal mucosa
Adenoid cystic carcinoma
Oval foramen enlargement
Thickening and enhancement of neural sheath
Nasopharyngeal fibroma
Male adolescent Centered around sphenopalatine foramen
Heterogeneous Early and intense enhancement
Heterogeneous Early and intense enhancement
Ameloblastoma
Odontogenic lesion Localized malignancy Mandibular angle
‘Soap-bubble’ appearance
Heterogeneous
Chordoma
Median
Hypo- or isoattenuating Calcifications Moderate enhancement
Heterogeneous Hypointense T1 Septa with hypointense T2
Figure 12 Nasopharyngeal fibroma on axial (A) and coronal (B) T1-weighted MRI after contrast and fat-saturation sequences is seen extending into the left masticator space and nasal fossa. The lesion is strongly enhanced after contrast injection, and is associated with bone lysis on CT, especially at the pterygopalatine fossa boundaries (C). The key feature of this lesion is that it originates from the sphenopalatine foramen. Fibrome nasopharyngé. IRM en coupe axiale (A) et coronale (B) T1 après injection et saturation de graisse met en évidence un fibrome nasopharyngé gauche qui envahit l’espace masticateur et la fosse nasale gauches. Cette lésion se rehausse intensément après injection et s’accompagne d’une lyse osseuse en TDM notamment de la fosse ptérygopalatine (C). L’origine au niveau du foramen sphénopalatin constitue le point clé pour le diagnostic de cette lésion.
Tumors originating from other sites with masticator space involvement
Direct extension
Tumor extension into the masticator space can be direct through adjacent progression or indirect via perineural spread Table 2.
Lesions can directly involve a component of the masticator space (such as a skin tumor or parotid tumor involving the masseter muscle), cross a bone (maxillary lesion with posterior wall destruction) or fascia (oropharyngeal lesion over
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the pharyngobasilar fascia) boundary, or spread via vascular or neural foramina (temporal meningioma and oval foramen; Fig. 9). Otorhinolaryngeal carcinoma Pharyngeal lesions (Fig. 10) are the most common tumors with secondary extension into the masticator space. The center of the mass lies near the median line and usually displaces the parapharyngeal fat laterally. Maxillary lesions (Fig. 11) can also involve the masticator space. CT scans give a precise analysis of the bone structures, while MRI can help to differentiate between tumor and inflammatory parts of the mass. It is important in clinical practice not to overestimate the size of the tumor. Maxillary lesions are isointense on T1-weighted and hyperintense on T2-weighted images, and enhance less than the normal pharyngeal mucosa with contrast media. Necrotic and retentive components are hypointense on T1-weighted images and hyperintense on T2-weighted images, with no enhancement after contrast injection. Areas of inflammation demonstrate a highly hyperintense signal on T2-weighted imaging and significant enhancement with contrast. Nasopharyngeal fibroma Nasopharyngeal fibromas [14] are centered on the sphenopalatine foramen and widen the pterygopalatine fossa (Fig. 12). This pathology affects young men with recurrent epistaxis, a sign that suggests the diagnosis. The parts of the fibroma within bone must be surgically removed to avoid recurrence. The tumor is heterogeneous with necrotic components, and enhances early and significantly with contrast. Numerical angiography remains an important examination before treatment to study the feeding arterial vessels originating from the external carotid or ascending pharyngeal artery. Presurgical embolization can change the prognosis of these lesions. MRI reveals a heterogeneous lesion, with vascular components as hypointense signals and tissue components as isointense signals. MR angiography after contrast administration displays the feeding arterial vessels. Ameloblastoma This odontogenic lesion presents as a localized malignancy that usually originates in the angle of the mandible. It is a mixed expansive tumor with cystic and cellular parts, and a characteristic ‘soap-bubble’ appearance.
Perineural extension The masticator space can be involved via extension through the neural sheaths of branches of cranial nerve V [15] in cases of squamous cell carcinoma (Fig. 13) or adenoid cystic carcinoma [16,17]. Adenoid cystic carcinoma Extension is perineural, and follows the course of the neural sheath (of V) with widening of its foramina into the masticator space. CT scans show bone changes in particular as widening of the oval foramen. MRI is particularly effective in these cases, and shows thickening with pathological enhancement of the neural structure [17,18], filling
Figure 13 Squamous cell carcinoma of the gums is seen on axial (A, B) T1-weighted MRIs with contrast as a perineural extension into the right masticator space via V3. It involves the right cavernous sinus (CS), right temporal lobe and cerebral arterial trunk. Carcinome épidermoïde gingival. IRM en coupe axiale (A, B) T1 après injection montre une lésion gingivale avec extension périneurale à l’espace masticateur droit via le V3. Elle envahit le sinus caverneux droit (CS), le lobe temporal droit et le tronc cérébral.
of the cavernous sinus and Meckel’s cavum, and widening of the oval foramen. The differential diagnosis of an adenoid cystic carcinoma with perineural extension is squamous cell carcinoma.
Metastasis CT and MRI of masticator space metastases [19] may show a lesion with ring enhancement. The most frequent primary lesions originate from the lung (Fig. 14), kidney or breast.
Infectious lesions of the masticator space Odontogenic abscess (Fig. 15) is the most common lesion of the masticator space. Infection of the space arises from a dental cause in 80% of cases, and other causes are facial infection, post-trauma from foreign bodies and iatrogenic (maxillary sinus puncture) [4]. Trismus is the initial symptom and may prevent adequate clinic examination, which explains why imaging is so important in this pathology. Infectious lesions often involve several deep spaces with no respect for anatomical boundaries. CT is particularly useful for guiding treatment in emergency cases: if it reveals only inflammatory changes (cellulitis) (Fig. 16), then antibiotic therapy should be started. Fluid collections must be treated surgically by intra- or extraoral drainage. CT can also reveal signs of osteomyelitis (lytic changes with mandible cortical disruption, thickening and abnormal enhancement of the muscles of mastication), which require subperiosteal drainage. Sometimes, CT is not able to diagnose osteomyelitis (Fig. 17), in which case, MRI may show loss of the normal signal void of cortical bone with obliteration of the normal signal from medullary fat on T1-weighted images, and hyperintense signals from within the medullary part of the mandible on T2-weighted images. The masticator muscles are hyperintense on T2 with significant enhancement after contrast administration. Osteoradionecrosis can
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Figure 14 Pulmonary metastases are seen on axial MRI T2- (A) and T1-weighted images with contrast (B, C) as an infiltrative pterygoid lesion (P) on the right, with hyperintense signals on T2 and contrast enhancement, involving the right masticator space and sphenopalatine foramen. Métastase pulmonaire. IRM en coupe axiale T2 (A) et T1 après injection (B, C) montre une lésion infiltrant la ptérygoïde (P) droite en hypersignal T2 et se rehaussant après injection. Elle s’étend à l’espace masticateur droit et au foramen sphénopalatin.
Figure 15 Abscess on axial CT with contrast is seen as a heterogeneous lesion with a hypoattenuating center in the right masticator space. Abcès. TDM en coupe axiale après injection montre un syndrome de masse hétérogène de l’espace masticateur droit à centre hypodense.
Figure 17 Osteitis on axial CT (A) and MRI T1-weighted (B) images is seen as a mass centered on the right mandible with lysis and loss of the bone marrow T1 hyperintense signals. The right masticatory muscles are also involved. Ostéite. TDM en coupe axiale (A) et IRM pondérée T1 (B) montrent une masse centrée sur la mandibule droite avec lyse et disparition de l’hypersignal médullaire en T1. Les muscles masticateurs homolatéraux sont aussi atteints.
mimic osteomyelitis on radiology [10]. CT in these patients reveals cortical disruption while MRI will show abnormal T1 hypointense signals and T2 hyperintense signals, with strong enhancement of the mandible bone marrow. The masticator muscles also show abnormal T2 hyperintense signals and strong enhancement that is often difficult to distinguish from a recurrent tumor.
Conclusion Figure 16 Cervicofacial cellulitis on axial CT after contrast injection (A, B) is seen as an odontogenic cellulitis involving the right masticator space with no fluid collections. Cellulite cervico faciale. TDM en coupe axiale après injection (A, B) met en évidence une cellulite d’origine dentaire qui s’étend à l’espace masticateur droit sans collection organisée.
The masticator space represents a complex anatomical and functional entity that has many connections with its adjacent deep facial spaces. Multidetector CT and MRI provide precise imaging information, and may be necessary for making the diagnosis. In addition, imaging data can help to differentiate infection from tumor lesions, and (rare) primary tumors from secondary tumors.
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N. Faye et al. [10] Connor SE, Davitt SM. Masticator space masses and pseudomasses. Clin Radiol 2004;59(3):237—45. [11] Barnes PD, Burrows PE, Hoffer FA, Mulliken JB. Hemangiomas and vascular malformations of the head and neck: MR characterization. Am J Neuroradiol 1994;15(1):193—5. [12] Suh JS, Abenoza P, Galloway HR, Everson LI, Griffiths HJ. Peripheral (extracranial) nerve tumors: correlation of MR imaging and histologic findings. Radiology 1992;183(2):341—6. [13] Chong J, Som PM, Silvers AR, Dalton JF. Extranodal non Hodgkin lymphoma involving the muscles of mastication. Am J Neuroradiol 1998;19(10):1849—51. [14] Jacobsson M, Petruson B, Svendsen P, Berthelsen B. Juvenile nasopharyngeal angiofibromas. A report of eighteen cases. Acta Otolaryngol 1988;105(1-2):132—9. [15] Marsot-Dupuch K, De Givry SC, Ouayoun M. Wegener granulomatosis involving the pterygopalatine fossa: an unusual case of trigeminal neuropathy. Am J Neuroradiol 2002;23(2): 312—5. [16] Majoie CB, Hulsmans FJ, Verbeeten B. Perineural tumor extension along the trigeminal nerve: magnetic resonance imaging findings. Eur J Radiol 1997;24(3):191—205. [17] Parker GD, Harnsberger HR. Clinical radiologic issues in perineural tumor spread of malignant diseases of the extracranial head and neck. Radiographics 1991;11(3):383—99. [18] Curtin HD, Williams R, Johnson J. CT of perineural tumor extension: pterygopalatine fossa. Am J Roentgenol 1985;144(1):163—9. [19] Danikas D, Theodorou SJ, Arvanitis ML, Zinterhofer LM, Rienzo AA. Malar metastasis from rectal carcinoma: a case report. Am Surg 1999;65(12):1150—2.
REVIEW
The masticator space: From anatomy to pathology Espace masticateur : de l’anatomie à la pathologie N. Fayea,∗, F. Lafitteb, M. Williamsb, A. Guermazic, M. Sahli-Amord, J. Chirasd, E. Diona a
Department of radiology, hôpital Louis-Mourier, 178, rue des Renouillers, 92700 Colombes, France Department of neuroradiology, fondation Rothschild, rue Manin, Paris, France c Department of Radiology Services Synarc Inc, Market street, San Francisco, CA, États-Unis d Department of neuroradiology, hôpital Pitié-Salpêtrière, boulevard de l’Hôpital, Paris, France b
Available online 5 October 2008
KEYWORDS Masticator space; CT; MRI; Imaging; Anatomy
MOTS CLÉS Espace masticateur ; Scanner ; IRM ; Imagerie ; Anatomie
∗
Summary The masticator space is a deep facial space with a complex anatomical structure. The purpose of the present study was to precisely define the masticator space to eliminate the use of obsolete and confusing terms to describe the area, and to illustrate the common mass syndromes. Primary tumors are uncommon, usually benign and of a vascular or neural origin. Adjacent lesions, mainly pharyngeal with secondary extension into the masticator space, are especially frequent. Metastases are rare, and infectious pathology is often odontogenic. The most frequent lesion of the masticator space is the odontogenic abscess. Multidetector CT and MRI enable precise study of the space, its communications with other deep spaces and the etiology of any mass syndrome. Understanding the anatomy of the masticator space and how it links up with the other deep facial spaces helps the radiologist to recognize the different lesions of this space and to avoid unnecessary surgery, or any other less than optimal management. © 2008 Elsevier Masson SAS. All rights reserved. Résumé L’espace masticateur appartient aux espaces profonds de la face et possède une structure anatomique complexe. L’objectif de ce travail est de donner une définition anatomique précise de cet espace en évitant les termes obsolètes pour décrire cette région anatomique et d’illustrer les principaux syndromes de masses que l’on peut rencontrer. Les tumeurs primitives sont rares, le plus souvent bénignes et d’origine vasculaire ou nerveuse. Les lésions les plus fréquentes sont d’origine pharyngées avec une extension secondaire par contiguïté à l’espace masticateur. Les métastases sont très rares. La pathologie infectieuse est le plus souvent d’origine odontogène. L’abcès odontogène constitue le syndrome de masse le plus fréquent de l’espace masticateur. Le scanner multidétecteur et l’IRM permettent une analyse anatomique précise de cet espace, étudient ses communications avec les espaces voisins et diagnostiquent les syndromes de masse. Comprendre l’anatomie de cet espace et les communications avec les espaces de voisinage aide le radiologue à reconnaître les différentes lésions de
Corresponding author. E-mail address: [email protected] (N. Faye).
0150-9861/$ – see front matter © 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.neurad.2008.08.005
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N. Faye et al. cet espace et permet d’éviter une chirurgie contre-indiquée ou une mauvaise prise en charge thérapeutique. © 2008 Elsevier Masson SAS. All rights reserved.
Introduction There are deep facial spaces lying between the skull base and hyoid bone [1] that have a complex anatomical structure. They are divided into several areas that need to be well understood to provide a precise etiological analysis. The masticator space is a deep facial space that is outlined by the superficial layer of the deep cervical fascia [2,3], and lies laterally and evenly [2] in front of the prestyloid space, medial to the pharyngeal space and beneath the skull base. It may be affected by developmental, neoplastic or infectious lesions. This review discusses the anatomy, and CT and MRI findings, of masses in the masticator space and illustrates the imaging features of these lesions.
are no clinical signs or, if they do occur, they are so common as to be overlooked. Patients complain of facial pain with swelling and trismus which, in themselves, often complicate evaluation of the masticator space. In the case of perineural spread, patients present with dysesthesia along the course of the trigeminal nerve (V).
Tumors originating in the masticator space Masses originating in the masticator space [2] are typically centered anterior to the parapharyngeal fat space, displacing the parapharyngeal fat posteriorly and medially, and obliterating the fat planes of the masticator space itself. Primary tumors are rare [7] and usually benign. Those most frequently seen are neural and vascular lesions Table 1.
Anatomy Neurinomas The literature on the masticator space uses a wide-ranging and variable vocabulary, often including obsolete terms that can be confusing in clinical practice. For this reason, it is necessary to review the anatomy and to clearly define the terms used to describe this space. The masticator space as an anatomical and functional entity centered on the mandibular ramus, which divides it into medial and lateral compartments [4,5]. It is separated from the adjacent face and neck spaces by a superficial layer of deep cervical fascia except superiorly, where it freely communicates with the external temporal fossa, which we consider an upper extension of the masticator space. Adjacent to the masticator space are the buccal space anteriorly, the parotid space posteriorly, the parapharyngeal space medially, the submandibular and sublingual spaces inferiorly, and the skull base superiorly. The masticator space contains the four muscles of mastication (masseter, medial and lateral pterygoids, and temporalis), the ramus and posterior portion of the body of the mandible, the pterygopalatine node, the maxillary vessels, and the mandibular (V3) and maxillary (V2) branches of the trigeminal nerve (cranial nerve V) (Figs. 1—3). The medial compartment of the masticator space (infratemporal and pterygopalatine fossa) is an important route of communication with the other deep facial spaces (Fig. 4). The infratemporal fossa is linked to the middle space via the oval foramen and to the pterygopalatine fossa via the pterygomaxillary foramen. The pterygopalatine fossa communicates with the middle space and Meckel’s cavum via the round foramen, with the orbit via the inferior orbital fissure and with the palate via the palatine foramen.
Physical examination Clinical examination of the masticator space is difficult because it is deep-lying and not easily accessible. Lesions are often discovered only at a late stage either because there
Neural tumors are the most frequent benign tumors of the masticator space. They are related to the divisional branches of the trigeminal nerve [8,9]. Usually, computed tomography (CT) and magnetic resonance imaging (MRI) can reveal the typical features of neurinoma and neurofibroma, and are sufficient to establish the diagnosis. Neurinomas are
Figure 1 Graphic representation (axial view) of structures of the left masticator space: (1) masseter muscle; (2) medial pterygoid muscle; (3) lateral pterygoid muscle; (4) temporalis muscle; (5) pterygopalatine fossa; and (6) sphenopalatine foramen. Schéma en vue axiale de l’espace masticateur gauche : (1) muscle masséter ; (2) muscle ptérygoïdien medial ; (3) muscle ptérygoïdien latéral ; (4) muscle temporal ; (5) fosse ptérygopalatine ; (6) foramen sphénopalatin.
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Table 1 Imaging features of tumors originating in the masticator space. Aspects en imagerie des tumeurs primitives de l’espace masticateur. Tumor
Characteristics
CT features
MRI features
Neurinoma
Well-defined Foramen widening
Hypoattenuating Homogeneous enhancement
Isointense T1 Hyperintense T2 Homogeneous enhancement
Hemolymphangioma
Childhood Cystic with septa
Hyperattenuating Septal enhancement
Hypointense T1 Highly hyperintense T2 Septal enhancement
Hemangioma
Adult Low flow
Hypoattenuating ‘Apple-tree’ enhancement
Hypointense T1 Highly hyperintense T2 ‘Apple-tree’ enhancement
Capillary hemangioma
Childhood Mandibular hypoplasia
Strong enhancement
Highly hyperintense T2 Strong enhancement
Lipoma
Well-defined
Hypoattenuating No enhancement
Hyperintense T1 No enhancement
Aneurysmal cyst
Multilocular with fluid levels
Lytic Heterogeneous Calcifications
Heterogeneous Septal enhancement
Lymphoma
Infiltrative lesion
Isoattenuating Variable enhancement
Isointense T1 Hyperintense T2 Variable enhancement
Osteosarcoma
Primitive or secondary lesion (radiotherapy, Paget)
Lytic lesion
Soft-tissue involvement
Calcifications
Heterogeneous enhancement
Lytic lesion Calcifications Variable enhancement
Variable enhancement
Heterogeneous Bone lysis
Soft-tissue involvement Heterogeneous enhancement
Chondrosarcoma
Rhabdomyosarcoma
Extensive lesion
fusiform, well-circumscribed, capsulated lesions without nerve-fiber involvement. They demonstrate an intermediate signal on T1-weighted images and hyperintensity on T2weighted images, with enhancement after contrast-medium injection. They can be heterogeneous in the case of cystic or hemorrhagic transformations and may undergo malignant transformation, which is suggested by pain and rapid growth. Their spread follows the course of the nerves with smooth enlargement of their foramina. Neurofibromas are more complex lesions that involve the nerve fibers. It can exhibit a target-like pattern of increased peripheral signal intensity and decreased central signal intensity on T2-weighted images because of its fibrous central core.
malformations, whereas MRI can detect areas of signal void [11] from associated high-flow vessels within arteriovenous malformations and proliferating capillary hemangiomas. Capillary hemangiomas arise in early infancy, and involution occurs by adolescence. Hemolymphangioma is a pediatric condition that tends to recur and, thus, has a less-thanfavorable outcome. Imaging shows multicystic lesions with septa, and some of these loculi are hyperattenuating on CT as a consequence of hemorrhage. Hemangiomas affect adults and, when contrast-enhanced, present with a characteristic ‘apple tree’ appearance.
Lipoma Vascular lesions Vascular lesions include tumors and vascular abnormalities (Figs. 5—7). They can be histologically arterial, venous or lymphatic, or all three combined [10]. These lesions are usually hyperintense on T2-weighted images and tend to involve more than one deep facial space. CT may reveal the classic phleboliths within capillary hemangiomas or venous
Lipomas [12] are homogeneous, fatty, hypoattenuating lesions seen on CT scans with a characteristic homogeneous high signal intensity on T1-weighted images that decreases on fat-suppressed images. There is no enhancement with contrast. Therefore, non-enhanced T1-weighted imaging should be performed when evaluating a masticator space syndrome for spontaneous hyperintense lesions such as lipoma.
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Figure 2 Anatomical view of structures of the left masticator space: (1) masseter muscle; (2) medial pterygoid muscle; (3) lateral pterygoid muscle; (7) mandible; (8) internal jugular vein; (9) parotid gland; (10) internal carotid artery; (11) pharyngeal space; and (12) maxillary nerve. Coupe anatomique de l’espace masticateur gauche : (1) muscle masséter ; (2) muscle ptérygoïdien médial ; (3) muscle ptérygoïdien latéral ; (7) mandibule ; (8) veine jugulaire interne ; (9) glande parotide ; (10) carotide interne ; (11) espace pharyngé ; (12) nerf maxillaire.
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Figure 4 Graphic representation of the masticator space and its communications with other deep facial spaces: the infratemporal fossa (ITF) (red arrows) connects with the middle space via the oval foramen (A), and the pterygopalatine fossa (PPF) via the pterygomaxillary foramen (B); PPF ([5,6] green star, green arrows) connects with the middle space, and Meckel’s cavum with the round foramen (1), infraorbital area via the suborbital canal (2), orbit via the inferior orbital fissure (3), palate via the palatine foramen (4), and petrous apex via the pterygoid foramen (5). Schéma illustrant les principales voies de communication de l’espace masticateur : communication de la fosse infratemporale (ITF) (flèche rouge) avec l’espace moyen par le foramen ovale (A) et la fosse ptérygopalatine (PPF) par le foramen ptérygomaxillaire (B). Communication de la PPF [5,6] (étoile verte et flèche verte) avec l’espace moyen et le cavum de Meckel par le foramen rond (1) et la région infraorbitaire par le canal sous-orbitaire (2), l’orbite par la fissure orbitaire inférieure (3), le palais par le foramen palatin (4), et l’apex pétreux par le foramen ptérygoïdien (5).
Sarcoma Sarcomas are the most frequent malignant tumor of the masticator space [10] and appear as large heterogeneous lesions with (osteosarcoma, chondrosarcoma) or without (rhabdomyosarcoma) calcifications. Enhancement with contrast media is variable and heterogeneous. These lesions are associated with bone lysis and cortical disruption (Fig. 8).
Lymphoma Figure 3 Graphic representation (coronal view) of structures of the left masticator space: (1) masseter muscle; (2) medial pterygoid muscle; (3) lateral pterygoid muscle; (4) temporalis muscle; and oval foramen (blue arrow), the passageway for the third branch of the trigeminal nerve (V3). Schéma en vue coronale de l’espace masticateur gauche : (1) muscle masséter ; (2) muscle ptérygoïdien médial ; (3) muscle ptérygoïdien latéral ; (4) muscle temporal ; foramen ovale (flèche bleue) voie du V3.
Primary lymphomas are rare [13], but can be seen in the masticator space, especially in immunodeficient patients. They have no specific imaging features, but appear as isoattenuating, homogeneous, infiltrative masses with variable degrees of enhancement with contrast administration. They are isointense on T1-weighted images and moderately hyperintense on T2-weighted images. Enhancement also varies with MRI.
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Figure 5 Angioma involving the subcutaneous tissues is seen on axial MRI T1-weighted (A), T2- and fat-saturation-weighted (B), and T1-weighted after injection and fat saturation (C) images as a serpiginous lesion in the right masticator space, with hyperintense signals on T2 and enhancement after gadolinium contrast administration. MR angiography reveals the vascular origin of this lesion (D). Angiome. IRM en coupes axiales pondérées T1 (A), T2 avec saturation de graisse (B) et T1 après injection et saturation de graisse (C) montrant une lésion serpigineuse de l’espace masticateur droit en hypersignal T2 se rehaussant après injection. Cette lésion envahit les tissus sous-cutanés. L’angio-IRM confirme son origine vasculaire (D).
Figure 6 Vascular malformation on axial CT shows (A) a tubular lesion of the left masticator space lying between the masticatory muscles but without their involvement, and (B) strong enhancement after contrast injection. The lesion was hyperintense on T2weighted images (C). Malformation vasculaire. TDM en coupe axiale (A) montre une lésion tubulée de l’espace masticateur gauche située entre les muscles de la mastication sans les envahir avec un important rehaussement après injection (B). Cette lésion est hyperintense en T2 (C).
Figure 7 Aneurysmal bone cyst on axial (A) and coronal (B) CT scans appears as an extensive and heterogeneous lesion of the right masticator space, with considerable involvement of the right middle cerebral fossa and lysis of the mandible. Kyste anévrismal. TDM en coupe axiale (A) et coronale (B) montre une lésion extensive hétérogène de l’espace masticateur droit envahissant largement la fosse cérébrale moyenne avec lyse de la mandibule.
Figure 8 Rhabdomyosarcoma on axial (A) and coronal (B) CT scans after contrast injection appears as a huge multicystic mass in the left masticator space, with lysis of the left maxillary posterior wall and left mandible. Rhabdomyosarcome. TDM en coupe axiale (A) et coronale (B) après injection montre une volumineuse masse multikystique de l’espace masticateur gauche avec lyse de la paroi maxillaire postérieure et de la mandibule gauches.
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Figure 9 Temporal meningioma on axial MRI T2-weighted (A), and axial (B) and coronal (C) T1-weighted images after contrast injection appears as a right temporal extra-axial lesion involving the inferior orbital fissure (IOF), cavernous sinus and masticator space via the oval foramen (OF). Méningiome temporal. IRM en coupe axiale T2 (A) et axiale (B) et coronale (C) T1 après injection montre une masse extra-axiale temporale droite s’étendant à la fissure (IOF) orbitaire inférieure, le sinus caverneux et l’espace masticateur par le foramen ovale (OF).
Figure 10 Cavum carcinoma (axial view) on T1-weighted MRI images appears as (A) an expansive right rhinopharyngeal lesion (isointense signals) involving the parapharyngeal and prevertebral spaces. The lesion is also isointense on T2-weighted imaging (B) with enhancement after gadolinium administration (C). Carcinome du cavum. IRM en coupe axiale T1 (A) montre une lésion extensive rhinopharyngée en isosignal avec extension aux espaces parapharyngé et prévertébral. Cette lésion est iso-intense en T2 (B) et se rehausse après gadolinium (C).
Figure 11 Maxillary carcinoma on axial MRI T1-weighted imaging appears as (A) an obstruction in the left maxillary sinus with isointense signals involving the masticator space. The lesion is hyperintense on T2-weighted images (inflammation and retention) and shows heterogeneous enhancement (C) with abnormal enhancement of the left masticatory muscles. There is no enhancement of the retained component, but inflammation and tumor are enhanced after contrast injection. Carcinome maxillaire. IRM en coupe axiale T1 montrant un comblement du sinus maxillaire gauche en isosignal avec extension à l’espace masticateur. Cette lésion est hyperintense en T2 (inflammation et rétention) et se rehausse de manière hétérogène (C). Il s’associe un rehaussement anormal des muscles masticateurs gauches.
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Table 2 Imaging features of tumors originating from other sites with masticator space involvement. Aspects en imagerie des lésions à distance envahissant l’espace masticateur. Tumor
Characteristics
CT features
MRI features
Cavum carcinoma
Ethnic origin
Serous otitis
Oropharyngeal carcinoma
Alcohol
Enhancement less than normal mucosa Enhancement less than normal mucosa
Median lesion
Tobacco Maxillary sinus carcinoma
Posterior wall lysis
Isointense T1 Hyperintense T2 Enhancement less than normal mucosa
Adenoid cystic carcinoma
Oval foramen enlargement
Thickening and enhancement of neural sheath
Nasopharyngeal fibroma
Male adolescent Centered around sphenopalatine foramen
Heterogeneous Early and intense enhancement
Heterogeneous Early and intense enhancement
Ameloblastoma
Odontogenic lesion Localized malignancy Mandibular angle
‘Soap-bubble’ appearance
Heterogeneous
Chordoma
Median
Hypo- or isoattenuating Calcifications Moderate enhancement
Heterogeneous Hypointense T1 Septa with hypointense T2
Figure 12 Nasopharyngeal fibroma on axial (A) and coronal (B) T1-weighted MRI after contrast and fat-saturation sequences is seen extending into the left masticator space and nasal fossa. The lesion is strongly enhanced after contrast injection, and is associated with bone lysis on CT, especially at the pterygopalatine fossa boundaries (C). The key feature of this lesion is that it originates from the sphenopalatine foramen. Fibrome nasopharyngé. IRM en coupe axiale (A) et coronale (B) T1 après injection et saturation de graisse met en évidence un fibrome nasopharyngé gauche qui envahit l’espace masticateur et la fosse nasale gauches. Cette lésion se rehausse intensément après injection et s’accompagne d’une lyse osseuse en TDM notamment de la fosse ptérygopalatine (C). L’origine au niveau du foramen sphénopalatin constitue le point clé pour le diagnostic de cette lésion.
Tumors originating from other sites with masticator space involvement
Direct extension
Tumor extension into the masticator space can be direct through adjacent progression or indirect via perineural spread Table 2.
Lesions can directly involve a component of the masticator space (such as a skin tumor or parotid tumor involving the masseter muscle), cross a bone (maxillary lesion with posterior wall destruction) or fascia (oropharyngeal lesion over
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the pharyngobasilar fascia) boundary, or spread via vascular or neural foramina (temporal meningioma and oval foramen; Fig. 9). Otorhinolaryngeal carcinoma Pharyngeal lesions (Fig. 10) are the most common tumors with secondary extension into the masticator space. The center of the mass lies near the median line and usually displaces the parapharyngeal fat laterally. Maxillary lesions (Fig. 11) can also involve the masticator space. CT scans give a precise analysis of the bone structures, while MRI can help to differentiate between tumor and inflammatory parts of the mass. It is important in clinical practice not to overestimate the size of the tumor. Maxillary lesions are isointense on T1-weighted and hyperintense on T2-weighted images, and enhance less than the normal pharyngeal mucosa with contrast media. Necrotic and retentive components are hypointense on T1-weighted images and hyperintense on T2-weighted images, with no enhancement after contrast injection. Areas of inflammation demonstrate a highly hyperintense signal on T2-weighted imaging and significant enhancement with contrast. Nasopharyngeal fibroma Nasopharyngeal fibromas [14] are centered on the sphenopalatine foramen and widen the pterygopalatine fossa (Fig. 12). This pathology affects young men with recurrent epistaxis, a sign that suggests the diagnosis. The parts of the fibroma within bone must be surgically removed to avoid recurrence. The tumor is heterogeneous with necrotic components, and enhances early and significantly with contrast. Numerical angiography remains an important examination before treatment to study the feeding arterial vessels originating from the external carotid or ascending pharyngeal artery. Presurgical embolization can change the prognosis of these lesions. MRI reveals a heterogeneous lesion, with vascular components as hypointense signals and tissue components as isointense signals. MR angiography after contrast administration displays the feeding arterial vessels. Ameloblastoma This odontogenic lesion presents as a localized malignancy that usually originates in the angle of the mandible. It is a mixed expansive tumor with cystic and cellular parts, and a characteristic ‘soap-bubble’ appearance.
Perineural extension The masticator space can be involved via extension through the neural sheaths of branches of cranial nerve V [15] in cases of squamous cell carcinoma (Fig. 13) or adenoid cystic carcinoma [16,17]. Adenoid cystic carcinoma Extension is perineural, and follows the course of the neural sheath (of V) with widening of its foramina into the masticator space. CT scans show bone changes in particular as widening of the oval foramen. MRI is particularly effective in these cases, and shows thickening with pathological enhancement of the neural structure [17,18], filling
Figure 13 Squamous cell carcinoma of the gums is seen on axial (A, B) T1-weighted MRIs with contrast as a perineural extension into the right masticator space via V3. It involves the right cavernous sinus (CS), right temporal lobe and cerebral arterial trunk. Carcinome épidermoïde gingival. IRM en coupe axiale (A, B) T1 après injection montre une lésion gingivale avec extension périneurale à l’espace masticateur droit via le V3. Elle envahit le sinus caverneux droit (CS), le lobe temporal droit et le tronc cérébral.
of the cavernous sinus and Meckel’s cavum, and widening of the oval foramen. The differential diagnosis of an adenoid cystic carcinoma with perineural extension is squamous cell carcinoma.
Metastasis CT and MRI of masticator space metastases [19] may show a lesion with ring enhancement. The most frequent primary lesions originate from the lung (Fig. 14), kidney or breast.
Infectious lesions of the masticator space Odontogenic abscess (Fig. 15) is the most common lesion of the masticator space. Infection of the space arises from a dental cause in 80% of cases, and other causes are facial infection, post-trauma from foreign bodies and iatrogenic (maxillary sinus puncture) [4]. Trismus is the initial symptom and may prevent adequate clinic examination, which explains why imaging is so important in this pathology. Infectious lesions often involve several deep spaces with no respect for anatomical boundaries. CT is particularly useful for guiding treatment in emergency cases: if it reveals only inflammatory changes (cellulitis) (Fig. 16), then antibiotic therapy should be started. Fluid collections must be treated surgically by intra- or extraoral drainage. CT can also reveal signs of osteomyelitis (lytic changes with mandible cortical disruption, thickening and abnormal enhancement of the muscles of mastication), which require subperiosteal drainage. Sometimes, CT is not able to diagnose osteomyelitis (Fig. 17), in which case, MRI may show loss of the normal signal void of cortical bone with obliteration of the normal signal from medullary fat on T1-weighted images, and hyperintense signals from within the medullary part of the mandible on T2-weighted images. The masticator muscles are hyperintense on T2 with significant enhancement after contrast administration. Osteoradionecrosis can
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Figure 14 Pulmonary metastases are seen on axial MRI T2- (A) and T1-weighted images with contrast (B, C) as an infiltrative pterygoid lesion (P) on the right, with hyperintense signals on T2 and contrast enhancement, involving the right masticator space and sphenopalatine foramen. Métastase pulmonaire. IRM en coupe axiale T2 (A) et T1 après injection (B, C) montre une lésion infiltrant la ptérygoïde (P) droite en hypersignal T2 et se rehaussant après injection. Elle s’étend à l’espace masticateur droit et au foramen sphénopalatin.
Figure 15 Abscess on axial CT with contrast is seen as a heterogeneous lesion with a hypoattenuating center in the right masticator space. Abcès. TDM en coupe axiale après injection montre un syndrome de masse hétérogène de l’espace masticateur droit à centre hypodense.
Figure 17 Osteitis on axial CT (A) and MRI T1-weighted (B) images is seen as a mass centered on the right mandible with lysis and loss of the bone marrow T1 hyperintense signals. The right masticatory muscles are also involved. Ostéite. TDM en coupe axiale (A) et IRM pondérée T1 (B) montrent une masse centrée sur la mandibule droite avec lyse et disparition de l’hypersignal médullaire en T1. Les muscles masticateurs homolatéraux sont aussi atteints.
mimic osteomyelitis on radiology [10]. CT in these patients reveals cortical disruption while MRI will show abnormal T1 hypointense signals and T2 hyperintense signals, with strong enhancement of the mandible bone marrow. The masticator muscles also show abnormal T2 hyperintense signals and strong enhancement that is often difficult to distinguish from a recurrent tumor.
Conclusion Figure 16 Cervicofacial cellulitis on axial CT after contrast injection (A, B) is seen as an odontogenic cellulitis involving the right masticator space with no fluid collections. Cellulite cervico faciale. TDM en coupe axiale après injection (A, B) met en évidence une cellulite d’origine dentaire qui s’étend à l’espace masticateur droit sans collection organisée.
The masticator space represents a complex anatomical and functional entity that has many connections with its adjacent deep facial spaces. Multidetector CT and MRI provide precise imaging information, and may be necessary for making the diagnosis. In addition, imaging data can help to differentiate infection from tumor lesions, and (rare) primary tumors from secondary tumors.
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