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ORIGINAL
ARTICLES
THE FORAMEN OVALE MR AND CT CORRELATION WILLIAM M. MERENICH, M.D., JOEL D. SWARTZ, PHILIP S. YUSSEN, M.D., GEORGE L. POPKY, M.D. STEPHEN D. SILBERSTEIN, M.D.
Six patients with lesions involving theforamen ovale are presented and analyzed. Anatomy, pathology and imaging of diseases occurring in the vicinity of the foramen ovale are reviewed. Computerized tomography (CT) and magnetic resonance imaging (MRI) are complimentary in the evaluation ofpathology in this region. CT is better able to evaluate bony detail while MR imaging is useful in detailing the anatomical extent and tissue characteristics. KEY WORDS:
Foramen ovale, Middle cranial fossa, Trigeminal Computed
tomography,
Magnetic
resonance
nerve, imaging
INTRODUCTION The value of High Resolution Computed Tomography (CT) in evaluating the skull base is well established. CT is especially useful in delineating bony detail and soft tissue calcification. This modality is limited in demonstrating soft tissue detail and anatomic extent of disease in many cases. Since its development magnetic resonance imaging (MRI) has established itself as an essential part of the evaluation of the skull base. The superiority of this technique in delineating soft tissue detail in both normal and pathologic states is well accepted. Six cases are presented which demon-
From the Department of Radiologic Sciences [M.M.M.; J.D.S.; P.S.Y.: G.L.P.], Medical College of Pennsylvania, Philadelphia, Pennsylvania and Germantown Neurological Associates [S.D.S.], Philadelphia, Pennsylvania. Address requests for reprints to: William M. Merenich, M.D., Department of Radiologic Sciences, Medical College of Pennsylvania, 3300 Henry Avenue, Philadelphia, Pennsylvania 19129. Received December 27, 1989; accepted June 20, 1990. 0 1991 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0899/7071/91/$3.50
strate the complimentary nature of these two techniques in evaluating abnormalities in the region of the foramen ovale. The anatomy and pathology of this region is then reviewed.
MATERIAL AND METHODS Six patients found to have abnormalities in the foramen ovale region were reviewed. These patients were examined by a combination of CT, MR and in one case angiography. Pathologic diagnoses were obtained in four cases. Surgical intervention was refused by two patients, however radiologic and clinical findings were felt adequate to make presumptive diagnoses. All CT scanning was performed on a 9800 scanner (General Electric Medical Systems, Milwaukee), with 120 kV, 170 mA, 5-10mm collimation, and 4 second scanning time. Intravenous contrast enhancement was obtained using a bolus injection of 100 cc of a diatrizoate meglumine contrast agent (Renographin M-60; Squibb, Princeton NJ). Angiography was performed via a femoral approach with selective catheterization of the common carotid artery. MR images were obtained using a .5 T magnet (Vista; Picker International) with a 25 cm FOV, 192 x 256 matrix, and 3, 5, or 8 mm thick sections. Spin Echo sequences included repetition time (TR) of 750 ms and echo time of 20 ms for Tl weighted images; and a TR of 2000-2400 ms and 90 ms TE for T2 weighted images.
CASE HISTORIES Case 1 A 63-year-old
white man presented with anorexia, fatigue, weight loss and left hip pain. Physical examination demonstrated a peripheral facial nerve palsy. MRI axial Tl weighted (Figure la) and T2 weighted
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2
A 54-year-old black woman presented with a right conductive hearing loss. Axial CT (Figure 2a) demonstrates a homogeneous, expansile mass within the region of the foramen ovale. Coronal (Figure 2b) and sagittal (Figure 2d) Tl weighted MR images reveals the mass to be isointense and contiguous with cerebral parenchyma. Coronal T2 weighted image (Figure 2c) confirms similar signal characteristics as normal brain parenchyma with demonstration of normal gray-white matter differentiation. Presumptive Diagnosis: Basilar Encephalocele.
Case
3
A 63-year-old black woman presented with proptosis of the left eye, local left eye pain and facial pain. Sensory and motor nerve evaluation were unremarkable. Enhanced Coronal CT (Figure 3a) demonstrates a expansile low density mass of the sphenoid sinus. The mass compresses the temporal lobe and extends inferiorly into the masticator space through the foramen ovale. Coronal [Figure 3b) and Sagittal [Figure images demonstrate a hyperintense 3c), Tl weighted dumbbell shaped mass extending through the foramen ovale. The mass is even more hyperintense using T2 weighted images (Figure 3d). Surgical Diagnosis: Sphenoid Mucocele.
Case
B lung carcinoma (A) Axial Tl weighFIGURE 1. Metastatic ted image. Mass obliterates cranial base and extends into the infratemporal fossa [ *). (B) Coronal T2 weighted image. Mass extends through foramen ovale (arrow). The lateral pterygoid muscle (*) is displaced laterally. Note that mass extends into middle cranial fossa as well as into the infratemporal fossa.
Coronal
(Figure
within the fossa. The through the struction of static Lung
lb)
images
demonstrate
a
mass
middle cranial fossa and infratemporal coronal images demonstrate extension Foramen Ovale. There is extensive dethe cranial base. Tissue Diagnosis: MetaCarcinoma to the cranial base
4
A 76-year-old black woman with acute onset of pain involving the left malar region. Physical exam revealed inferomedial gaze palsy on the left with absence of a cornea1 reflex, and mild decreased sensation in the distribution of ophthalmic and maxillary divisions of the trigeminal nerve. There were no trigeminal nerve motor findings. Axial non-enhanced CT (Figure 4a) shows a particularly calcified, hyperdense mass lateral to the cavernous sinus. Dense homogeneous enhancement is demonstrated on CECT Axial and Coronal images (Figure 4b). Tl weighted (Figures 4c, d, f) demonstrate an inhomogeneous intensity mass that extends into the foramen ovale region Continuity with the cavernous carotid artery is seen on both projections. Atrophy and fatty replacement of the muscles of mastication are demonstrated. Signal void in the periphery of the lesion is due to flowing blood. Anteroposterior view of a left common carotid angiogram (Figure 4e) confirms a large carotid aneurysm. Diagnosis: Cavernous Carotid Aneurysm.
MERENICH ET AL.
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B
Case
CLINICAL IMAGING VOL. 15, NO. 1
D
5
A 30-year-old white woman presented with burning paresthesias involving the angle of the mouth which were relieved by applying pressure over the mental nerve. Physical examination demonstrated decreased sensation to pinprick at the angle of the mouth. A positive Tinel’s sign was elicited over the mental
FIGURE 2. Basilar encephalocele (A) Axial CT. Smoothly erosive mass involving cranial base on right side (*). V, arrow-foramen Vesalius; 0, arrow-foramen ovale; S, arrow-foramen spinosum on normal left side (B) Coronal weighted image (C) Coronal T2 weighted image. Mass enlarging foramen ovale is contiguous and isointense with cerebral parenchyma. Note the gray-white matter differentiation. (D) Sagittal Tl weighted image. Inferior margin of mass is identified (arrow).
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D
FIGURE 3. Sphenoid mucocele (A) Coronal CT. Image demonstrates low density expansile mass emanating from sphenoid sinus, compressing the temporal lobe and extending through foramen ovale inferiorly into the masticator space. (B) Coronal Tl weighted image. Hyperintense mass extending through an expanded foramen ovale (arrow). (C) Sagittal Tl weighted image. Superior and inferior borders of hyperintense dumbbell mass are identified (arrows). (D) Axial T2 weighted image. Mass (*) is more hyperintense on this sequence. Note debris in mastoid secondary to eustachian tube compression.
Axial CT demonstrates smooth enlargement of the right foramen ovale (Figure 5a). A small mass within the foramen ovale is seen with MR. This mass is hypointense to cerebral parenchyma on a Tl weighted coronal image (Figure 5b) and hyperintense on a T2 weighted image (Figure 5~). Presumptive
nerve region.
Diagnosis:
Trigeminal
Nerve
Neuroma.
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CLINICAL IMAGING VOL. 15. NO. 1
B
FIGURE 4. Cavernous carotid aneurysm. (A) Axial noncontrast CT. Hyperdense partially calcified mass (arrow). (B) Axial contrast enhanced CT. Homogeneously enhancing mass is identified (arrow). (C) Axial Tl weighted MR image. Inhomogeneous mass (*) identified. Note the peripheral signal voids and apparent continuity of the lesion with the cavernous carotid artery (arrow). (D) Coronal Tl weighted MR image. Mass extends inferiorly to the level of the foramen ovale (arrow). (E) Left common carotid angiogram, frontal projection. Large aneurysm is demonstrated. (F) Axial T1 weighted image. There is atrophy with fatty replacement of the muscles of mastication on left side. Note normal masseter (M), lateral pterygoid (L) and deep head of temporalis (T) musculature on unaffected right side.
Case
6
black woman with history of transcraA 39-year-old nial resection of a pituitary adenoma 17 years previously. The patient presented with increased serum prolactin level (1900 ng per ml). Physical examination was unremarkable. Tl weighted coronal and sa-
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on the T2 weighted coronal image. sis: Recurrent Pituitary Adenoma.
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Diagno-
ANATOMY
FIGURE 4 continued
gittal images (Figures 6a and c) demonstrate a isointense mass extending through an expanded foramen ovale. The inferior extent of the mass is better defined
Prior to the twelfth week of gestation, three principle fenestrations are present within the skull base; the foramen lacerum anterius, medius and posterius. The foramen ovale develops from the posteromedial aspect of the foramen lacerum medius, to accommodate the mandibular division of the fifth cranial nerve. In the adult, the foramen ovale lies l-l.5 cm posterolatera1 to the foramen rotundum, lateral to the foramen lacerum and 0.75-1.5 cm anterior to the foramen spinosum (1). Variations in formation of the foramen ovale are common. Partial formation or incomplete separation from the foramen lacerum medius may occur. Bony spiculations may partially or completely divide the foramen ovale. One of the more common anomalies is the formation of the sphenoid emissary foramen (foramen of Vesalius) (Figure 2a); formed by a bony spiculation that completely divides the anterior portion of the foramen (2). The foramen may be oval, round or pyriform in shape. Wood-Jones (3) and Lindblom (4) found the size of the foramen ovale in dry skulls to measure 4 x 7 mm in size, with a range of 3.6 mm-10 mm. They found the main determinator of size and shape of the foramen ovale to be the number of veins within the foramen. The pterygospinous and pterygoalar ligaments are located in close proximity to the extracranial foramen ovale. The pterygospinous ligament extends from the angular spine of the sphenoid bone to the lateral pterygoid plate (the spine of Civini). The pterygoalar ligament extends from the undersurface of the greater wing of the sphenoid bone, lateral to the foramen spinosum, to the base of the lateral pterygoid plate. Calcification of the pterygospinous ligament and pterygoalar ligament occurs infrequently (5). When calcified, these are referred to as bars and may be visualized with CT. The foramen ovale allows communication between the middle cranial fossa and infratemporal fossa (nasopharyngeal-masticator space). The main structure traversing the foramen is the mandibular division of the trigeminal nerve (V3). Within the foramen the motor and sensory nerve components are separated, with the motor branches traversing medially. These roots unite below the skull base forming the mandibular nerve. As this is the nerve of the first branchial arch, it provides innervation for the muscles of mastication (masseter, temporalis, and
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CLINICAL IMAGING VOL. 15, NO. 1
C
FIGURE 5. Fifth nerve neuroma. (A) Axial CT. Smoothly enlarged right foramen ovale (curved arrow). Compare to normal left side (arrowhead). (B) Coronal Tl weighted image. Hypointense mass extending through a slightly expanded foramen ovale (arrowhead). (C) Coronal T2 weighted image. Small high signal soft tissue mass within an enlarged right foramen ovale (arrowhead).
B
medial and lateral pterygoid), anterior belly of the digastric, mylohyoid, tensor tympani and the tensor veli palatini; and sensory innervation to the temporomandibular joint, cheek, mouth, lower lip, chin, lower teeth, and anterior two-thirds of the tongue. Venous dural sinuses situated anteromedial to the mandibular nerve provide communication between the cavernous sinus and the pterygoid plexus (6). The accessory meningeal artery, a branch of the second portion of the internal maxillary artery and the lesser superficial petrosal nerve may traverse the foramen. The anatomical definition of the subcranial fascial spaces must be clearly understood in order to under-
stand disease transmission via the foramen (7-8). The most important structure in this regard is the superficial layer of deep cervical fascia. This layer splits covering the lateral surface of the masseter muscle and the medial surface of the medial pterygoid, and thus demarcates the masticator space. The fascia lining the medial surface of the medial pterygoid extends superiorly to the cranial base and attaches medial to the foramen ovale. Therefore, as might be expected by its function, the mandibular nerve enters the masticator space upon exiting the foramen. As the more medial parapharyngeal space is separated from the masticator space by this fascial plane, pathologic processes involving the parapharyngeal space rarely involve the foramen ovale. Deep lobe parotid neoplasia, schwannomas and paragangliomas have on occasion been reported to cause bone destruction in the region of the foramen ovale presumably due to invasion of or congenital breaches in the fascial planes. PATHOLOGY
REVIEW
Lesions of the foramen ovale may arise from the cavernous sinus, trigeminal nerve and its branches,
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C FIGURE 6. Recurrent pituitary adenoma. (A) Coronal Tl weighted image. Lower border of mass extending through the foramen ovale is identified (white arrowhead). Borders of the enlarged foramen are identified (arrows). (B) Coronal T2 weighted image. The mass is identified (*). The inferior margin is noted (arrow). (C) Sagittal Tl weighted image. The mass is subtle, but distinctly abnormal (“). Inferior margin is noted (arrow).
Meckel’s cave, masticator space, rarely from other infracranial sites and from the adjacent cranial base. Both neoplasms and inflammatory processes can disrupt the normal bony architecture.
Skull Base
Disease
Metastatic disease is the most common skull base spread may occur neoplasia (Figure 1). Metastatic either from a hematogeneous route or by perineural extension. Hematogeneous metastasis may be lytic or blastic in nature. The most common primaries are
breast, lung, renal and prostate carcinomas. The MR appearance is highly variable. Perineural spread is discussed below. Primary bone tumors of the skull base are rare. The skull base is of cartilaginous origin (chondrocranium), and therefore not surprisingly cartilaginous tumors predominate. Chondrosarcomas and chondromas are the most frequently described (9). Usually these tumors are located in the parasellar region, the cerebellopontine angle or the convexities. Plain film findings include matrix calcification and bone lysis. CT may demonstrate a soft tissue mass with variable contrast enhancement (10). Multiple noncartilaginous bone tumors have also been described. Chordomas are rare tumors arising from primitive notochordal remnants. These lesions are intracranial in 35% of cases, mostly involving the clivus, sella and parasellar regions (11). CT examination often demonstrates bone destruction and a soft tissue mass. On MRI these lesions are isointense or hypointense on Tl and hyperintense on TZ weighted imaging. Most are lobulated and heterogeneous with areas of both hyper and hypointensity. MR and CT are both capa-
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CLINICAL IMAGING VOL. 15, NO. 1
ble of detecting and characterizing this tumor, however MR is better able to define the anatomical extent of disease (12). Epidermoids, osteogenic sarcoma, osteomas, plasmocytomas, eosinophilic granuloma and giant cell tumors also may involve the skull base (13, 14, 15). Encephaloceles, congenital anomalies in neural tube formation, may be classified by location into convexity encephaloceles and those involving the skull base (16). Of the convexity encephaloceles, the inferior occipital type is most common. Basilar encephaloceles are even more unusual and may be divided into fronto-ethmoid (most common) sphenoorbital, spheno-maxillary or nasopharyngeal categories. As these defects contain brain parenchyma, CT and MRI characteristics parallel that of normal brain parenchyma. Our second case is a very unusual example (Figure 2). Paget’s disease, fibrous dysplasia and osteopetrosis may diffusely involve the skull base (17, 18). Pagetoid skull base involvement is usually lytic and diffuse. Fibrous dysplasia involving the skull base is densely sclerotic and asymmetric. Osteopetrosis is a rare but a well known cause of cranial base sclerosis (19). Meckel
Cave and
Trigeminal
Nerve
Disease
Meningioma is the most common primary intracranial neoplasm. Meningiomas in the middle cranial fossa may arise in or around Meckel’s cave or from dura elsewhere in the middle cranial fossa. Extrameningeal lesions may (very rarely) arise via aberrant arachnoid rests. CT reveals a hyperdense/isodense mass that may contain focal or diffuse calcifications (20). Homogeneous intravenous contrast enhancement is usually seen. The presence and severity of edema are highly variable. With MR a mass isointense with surrounding brain on Tl weighted images and isointense-hypointense on T2 weighted images is seen (21). Marked Gadolinium enhancement is usually present. Epidermoid tumors account for 0.2 to 1.8% of endocranial neoplasms (22). Most commonly these tumors occur at the CP angle or middle cranial fossa (23). On CT a low density mass with a attenuation coefficient value close to CSF is found and often no contrast enhancement occurs. The tumor most commonly exhibits a low intensity signal on Tl and a high signal intensity on T2 weighted images. Neurofibroma, melanotic schwannoma and arachnoid cyst have also been reported in Meckel’s cave (24). Mucoceles predominately involve the frontal or ethmoid sinuses. Less frequently the sphenoid and
maxillary sinuses are affected. The CT appearance is variable and may be either isodense or hyperdense on NCCT, possibly with contrast ring enhancement if infected. The mass is expansile although bony integrity is usually preserved. The affected sinus is generally completely opacified. MR findings vary depending on the hydration state of the sinus contents. Inspissated material appears hypointense on Tl and T2 weighted images whereas hydrated material appears hyperintense on these spin echo sequences (25). Our example of dumbbell extension of a sphenoid mucocele into the masticator space via the foramen ovale is unique (Figure 3). Giant aneurysms have received considerable attention both with respect to the CT and MR findings (26-28). Although it is not surprising that a cavernous carotid aneurysms might behave in a manner similar to our case #S, we found no other such cases in our review (Figure 4). Trigeminal Schwannomas are rare, accounting for less than 0.4% of all brain tumors. Classification into three types by anatomical location was proposed by Lesoin et al (29). Type I neuromas involve the roots in the posterior fossa, Type II neuromas involve the ganglion region and Type III neuromas involve the trigeminal branches (Figure 5). Usually peripheral involvement of the trigeminal branches involves the ophthalmic division. CT examination demonstrates a hypodense or isodense soft tissue mass with homogeneous contrast enhancement. Well defined bony margins heralds the benign, slow growing nature of these tumors (30). MR readily demonstrates the extent of the trigeminal division involvement by this tumor which has a high signal intensity on T2 and a decreased signal intensity on Tl weighted images. In a case report, Rigamunti et al (31) described a Schwannoma extending into and expanding the foramen ovale. This mass was centered in the middle cranial fossa and caused atrophy of the masticator muscles. Lipomas are the most common neoplasm of mesenchymal origin and involve the head and neck region in 13% of cases (22). Infiltration of nerve fascicles is common, making surgical removal very difficult. CT usually demonstrates a homogeneous low attenuation mass ( - 65 to - 125 hu) with no clearly definable capsule (32). MR intensity characteristics parallel that of subcutaneous fat; high intensity characteristics parallel that of subcutaneous fat; high intensity on Tl and intermediate-high intensity on T2 weighted images. Better characterization of low density CT masses common to this region (arachnoid cyst, epidermoid tumors, cholesteatomas, metastasis or abscess formation) is possible with MR imaging. More
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importantly, MR is able to define the anatomical extent of these tumors, which aids in surgical resection
2. Boyd GI. Emissary foramina of the cranium in anthropods. Anat 1930;65:108-121. Mosby Co., 1971:297-314.
(33).
3. Wood-Jones F. Non metrical morphological characteristics of the skull as criteria for racial diagnosis. J Anat, 1931;65:179-195.
Masticator
Space Disease
Anatomic fascial planes allow masticator space lesions easy access to the foramen ovale. Hardin et al (34) reviewed 36 patients with lesions of the masticator space. Sixteen patients had inflammatory masses, most often odontogenic in origin. Only four patients in this series had primary neoplasms. Metastatic disease from the major and minor salivary gland tumors and squamous cell carcinoma accounted for most of the tumors within the masticator space. Som et al (35) presented MR images of metastatic adenoid cystic carcinoma extending through the foramen ovale. MR signal characteristics of this tumor were similar to other salivary gland tumors; intermediate signal intensity on Tl and proton density and high signal intensity on T2 weighted images. Teresi et al (36) presented 46 patients who had malignant tumors of the nasopharynx, parapharyngeal space and infratemporal fossa. Direct invasion of the skull base occurred in seven patients with nasopharyngeal carcinoma. Route of spread was through the foramen ovale, foramen lacerum and stylomastoid foramen. Perineural spread of disease occurs by direct extension along the endoneurium and perineurium (37). Squamous cell carcinoma, lymphomas, adenocarcinoma, basal cell carcinoma, adenoid cystic carcinoma (minor and major salivary gland origin) and mucoepidermoid carcinomas have been reported to exhibit perineural spread (38). Of the tumors, squamous cell carcinoma is the most frequently reported to extend al&g the trigeminal and facial nerves (39). Atri et al (40) reported a case of actinomycosis granuloma of the trigeminal ganglia with perineural extension via the mandibular branch of the trigeminal nerve. CT demonstrated widening of the foramen ovale and an intracranial soft tissue mass. CT findings in perineural spread of disease is limited to identifying enlargement of the basal foramina or if present, a soft tissue mass within the cavernous sinus, Meckel’s cave or middle cranial fossa. MR appearance of perineural spread has been recently reviewed by Lain et al. Consistent with our experience their findings included: thickening of the nerve, expansion of the foramen ovale, mass within the foramen and masticator muscle atrophy. Lateral bulging of the cavernous sinus dural membranes was also described (41). REFERENCES 1. Sondheimer
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34. Hardin C, Harnsberger H, &born A, Doxey G, Davis R, and Nyberg D. Infection and tumor of the masticator space: CT evaluation. Radiology 1985:157:413-417, 35. Som P, Braun I, Shapiro M, Reede D, Curtin H and Zimmerman R. Tumors of the parapharyngeal space and upper neck: MR imaging characteristics. Radiology 1987:164:823-829. 36. Teresi L, Lufkin R, Vinuela F, Dietrich R, Wilson G, Bentson I, and Hanadee W. MR imagine. of the nasooharvnx and floor of the middle cranial fossa_R&ology 1987;164:817-821. 37. Larson DL, Roden AE, Roberts DK, O’Steen WK, Rapperport AS and Lewis SR. Perineurolymphatics: myth or fact. Am J Surg 1966;112:488-492.
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CLINICAL IMAGING 1991;15:20-30
ORIGINAL
ARTICLES
THE FORAMEN OVALE MR AND CT CORRELATION WILLIAM M. MERENICH, M.D., JOEL D. SWARTZ, PHILIP S. YUSSEN, M.D., GEORGE L. POPKY, M.D. STEPHEN D. SILBERSTEIN, M.D.
Six patients with lesions involving theforamen ovale are presented and analyzed. Anatomy, pathology and imaging of diseases occurring in the vicinity of the foramen ovale are reviewed. Computerized tomography (CT) and magnetic resonance imaging (MRI) are complimentary in the evaluation ofpathology in this region. CT is better able to evaluate bony detail while MR imaging is useful in detailing the anatomical extent and tissue characteristics. KEY WORDS:
Foramen ovale, Middle cranial fossa, Trigeminal Computed
tomography,
Magnetic
resonance
nerve, imaging
INTRODUCTION The value of High Resolution Computed Tomography (CT) in evaluating the skull base is well established. CT is especially useful in delineating bony detail and soft tissue calcification. This modality is limited in demonstrating soft tissue detail and anatomic extent of disease in many cases. Since its development magnetic resonance imaging (MRI) has established itself as an essential part of the evaluation of the skull base. The superiority of this technique in delineating soft tissue detail in both normal and pathologic states is well accepted. Six cases are presented which demon-
From the Department of Radiologic Sciences [M.M.M.; J.D.S.; P.S.Y.: G.L.P.], Medical College of Pennsylvania, Philadelphia, Pennsylvania and Germantown Neurological Associates [S.D.S.], Philadelphia, Pennsylvania. Address requests for reprints to: William M. Merenich, M.D., Department of Radiologic Sciences, Medical College of Pennsylvania, 3300 Henry Avenue, Philadelphia, Pennsylvania 19129. Received December 27, 1989; accepted June 20, 1990. 0 1991 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0899/7071/91/$3.50
strate the complimentary nature of these two techniques in evaluating abnormalities in the region of the foramen ovale. The anatomy and pathology of this region is then reviewed.
MATERIAL AND METHODS Six patients found to have abnormalities in the foramen ovale region were reviewed. These patients were examined by a combination of CT, MR and in one case angiography. Pathologic diagnoses were obtained in four cases. Surgical intervention was refused by two patients, however radiologic and clinical findings were felt adequate to make presumptive diagnoses. All CT scanning was performed on a 9800 scanner (General Electric Medical Systems, Milwaukee), with 120 kV, 170 mA, 5-10mm collimation, and 4 second scanning time. Intravenous contrast enhancement was obtained using a bolus injection of 100 cc of a diatrizoate meglumine contrast agent (Renographin M-60; Squibb, Princeton NJ). Angiography was performed via a femoral approach with selective catheterization of the common carotid artery. MR images were obtained using a .5 T magnet (Vista; Picker International) with a 25 cm FOV, 192 x 256 matrix, and 3, 5, or 8 mm thick sections. Spin Echo sequences included repetition time (TR) of 750 ms and echo time of 20 ms for Tl weighted images; and a TR of 2000-2400 ms and 90 ms TE for T2 weighted images.
CASE HISTORIES Case 1 A 63-year-old
white man presented with anorexia, fatigue, weight loss and left hip pain. Physical examination demonstrated a peripheral facial nerve palsy. MRI axial Tl weighted (Figure la) and T2 weighted
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2
A 54-year-old black woman presented with a right conductive hearing loss. Axial CT (Figure 2a) demonstrates a homogeneous, expansile mass within the region of the foramen ovale. Coronal (Figure 2b) and sagittal (Figure 2d) Tl weighted MR images reveals the mass to be isointense and contiguous with cerebral parenchyma. Coronal T2 weighted image (Figure 2c) confirms similar signal characteristics as normal brain parenchyma with demonstration of normal gray-white matter differentiation. Presumptive Diagnosis: Basilar Encephalocele.
Case
3
A 63-year-old black woman presented with proptosis of the left eye, local left eye pain and facial pain. Sensory and motor nerve evaluation were unremarkable. Enhanced Coronal CT (Figure 3a) demonstrates a expansile low density mass of the sphenoid sinus. The mass compresses the temporal lobe and extends inferiorly into the masticator space through the foramen ovale. Coronal [Figure 3b) and Sagittal [Figure images demonstrate a hyperintense 3c), Tl weighted dumbbell shaped mass extending through the foramen ovale. The mass is even more hyperintense using T2 weighted images (Figure 3d). Surgical Diagnosis: Sphenoid Mucocele.
Case
B lung carcinoma (A) Axial Tl weighFIGURE 1. Metastatic ted image. Mass obliterates cranial base and extends into the infratemporal fossa [ *). (B) Coronal T2 weighted image. Mass extends through foramen ovale (arrow). The lateral pterygoid muscle (*) is displaced laterally. Note that mass extends into middle cranial fossa as well as into the infratemporal fossa.
Coronal
(Figure
within the fossa. The through the struction of static Lung
lb)
images
demonstrate
a
mass
middle cranial fossa and infratemporal coronal images demonstrate extension Foramen Ovale. There is extensive dethe cranial base. Tissue Diagnosis: MetaCarcinoma to the cranial base
4
A 76-year-old black woman with acute onset of pain involving the left malar region. Physical exam revealed inferomedial gaze palsy on the left with absence of a cornea1 reflex, and mild decreased sensation in the distribution of ophthalmic and maxillary divisions of the trigeminal nerve. There were no trigeminal nerve motor findings. Axial non-enhanced CT (Figure 4a) shows a particularly calcified, hyperdense mass lateral to the cavernous sinus. Dense homogeneous enhancement is demonstrated on CECT Axial and Coronal images (Figure 4b). Tl weighted (Figures 4c, d, f) demonstrate an inhomogeneous intensity mass that extends into the foramen ovale region Continuity with the cavernous carotid artery is seen on both projections. Atrophy and fatty replacement of the muscles of mastication are demonstrated. Signal void in the periphery of the lesion is due to flowing blood. Anteroposterior view of a left common carotid angiogram (Figure 4e) confirms a large carotid aneurysm. Diagnosis: Cavernous Carotid Aneurysm.
MERENICH ET AL.
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B
Case
CLINICAL IMAGING VOL. 15, NO. 1
D
5
A 30-year-old white woman presented with burning paresthesias involving the angle of the mouth which were relieved by applying pressure over the mental nerve. Physical examination demonstrated decreased sensation to pinprick at the angle of the mouth. A positive Tinel’s sign was elicited over the mental
FIGURE 2. Basilar encephalocele (A) Axial CT. Smoothly erosive mass involving cranial base on right side (*). V, arrow-foramen Vesalius; 0, arrow-foramen ovale; S, arrow-foramen spinosum on normal left side (B) Coronal weighted image (C) Coronal T2 weighted image. Mass enlarging foramen ovale is contiguous and isointense with cerebral parenchyma. Note the gray-white matter differentiation. (D) Sagittal Tl weighted image. Inferior margin of mass is identified (arrow).
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D
FIGURE 3. Sphenoid mucocele (A) Coronal CT. Image demonstrates low density expansile mass emanating from sphenoid sinus, compressing the temporal lobe and extending through foramen ovale inferiorly into the masticator space. (B) Coronal Tl weighted image. Hyperintense mass extending through an expanded foramen ovale (arrow). (C) Sagittal Tl weighted image. Superior and inferior borders of hyperintense dumbbell mass are identified (arrows). (D) Axial T2 weighted image. Mass (*) is more hyperintense on this sequence. Note debris in mastoid secondary to eustachian tube compression.
Axial CT demonstrates smooth enlargement of the right foramen ovale (Figure 5a). A small mass within the foramen ovale is seen with MR. This mass is hypointense to cerebral parenchyma on a Tl weighted coronal image (Figure 5b) and hyperintense on a T2 weighted image (Figure 5~). Presumptive
nerve region.
Diagnosis:
Trigeminal
Nerve
Neuroma.
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B
FIGURE 4. Cavernous carotid aneurysm. (A) Axial noncontrast CT. Hyperdense partially calcified mass (arrow). (B) Axial contrast enhanced CT. Homogeneously enhancing mass is identified (arrow). (C) Axial Tl weighted MR image. Inhomogeneous mass (*) identified. Note the peripheral signal voids and apparent continuity of the lesion with the cavernous carotid artery (arrow). (D) Coronal Tl weighted MR image. Mass extends inferiorly to the level of the foramen ovale (arrow). (E) Left common carotid angiogram, frontal projection. Large aneurysm is demonstrated. (F) Axial T1 weighted image. There is atrophy with fatty replacement of the muscles of mastication on left side. Note normal masseter (M), lateral pterygoid (L) and deep head of temporalis (T) musculature on unaffected right side.
Case
6
black woman with history of transcraA 39-year-old nial resection of a pituitary adenoma 17 years previously. The patient presented with increased serum prolactin level (1900 ng per ml). Physical examination was unremarkable. Tl weighted coronal and sa-
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on the T2 weighted coronal image. sis: Recurrent Pituitary Adenoma.
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Diagno-
ANATOMY
FIGURE 4 continued
gittal images (Figures 6a and c) demonstrate a isointense mass extending through an expanded foramen ovale. The inferior extent of the mass is better defined
Prior to the twelfth week of gestation, three principle fenestrations are present within the skull base; the foramen lacerum anterius, medius and posterius. The foramen ovale develops from the posteromedial aspect of the foramen lacerum medius, to accommodate the mandibular division of the fifth cranial nerve. In the adult, the foramen ovale lies l-l.5 cm posterolatera1 to the foramen rotundum, lateral to the foramen lacerum and 0.75-1.5 cm anterior to the foramen spinosum (1). Variations in formation of the foramen ovale are common. Partial formation or incomplete separation from the foramen lacerum medius may occur. Bony spiculations may partially or completely divide the foramen ovale. One of the more common anomalies is the formation of the sphenoid emissary foramen (foramen of Vesalius) (Figure 2a); formed by a bony spiculation that completely divides the anterior portion of the foramen (2). The foramen may be oval, round or pyriform in shape. Wood-Jones (3) and Lindblom (4) found the size of the foramen ovale in dry skulls to measure 4 x 7 mm in size, with a range of 3.6 mm-10 mm. They found the main determinator of size and shape of the foramen ovale to be the number of veins within the foramen. The pterygospinous and pterygoalar ligaments are located in close proximity to the extracranial foramen ovale. The pterygospinous ligament extends from the angular spine of the sphenoid bone to the lateral pterygoid plate (the spine of Civini). The pterygoalar ligament extends from the undersurface of the greater wing of the sphenoid bone, lateral to the foramen spinosum, to the base of the lateral pterygoid plate. Calcification of the pterygospinous ligament and pterygoalar ligament occurs infrequently (5). When calcified, these are referred to as bars and may be visualized with CT. The foramen ovale allows communication between the middle cranial fossa and infratemporal fossa (nasopharyngeal-masticator space). The main structure traversing the foramen is the mandibular division of the trigeminal nerve (V3). Within the foramen the motor and sensory nerve components are separated, with the motor branches traversing medially. These roots unite below the skull base forming the mandibular nerve. As this is the nerve of the first branchial arch, it provides innervation for the muscles of mastication (masseter, temporalis, and
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C
FIGURE 5. Fifth nerve neuroma. (A) Axial CT. Smoothly enlarged right foramen ovale (curved arrow). Compare to normal left side (arrowhead). (B) Coronal Tl weighted image. Hypointense mass extending through a slightly expanded foramen ovale (arrowhead). (C) Coronal T2 weighted image. Small high signal soft tissue mass within an enlarged right foramen ovale (arrowhead).
B
medial and lateral pterygoid), anterior belly of the digastric, mylohyoid, tensor tympani and the tensor veli palatini; and sensory innervation to the temporomandibular joint, cheek, mouth, lower lip, chin, lower teeth, and anterior two-thirds of the tongue. Venous dural sinuses situated anteromedial to the mandibular nerve provide communication between the cavernous sinus and the pterygoid plexus (6). The accessory meningeal artery, a branch of the second portion of the internal maxillary artery and the lesser superficial petrosal nerve may traverse the foramen. The anatomical definition of the subcranial fascial spaces must be clearly understood in order to under-
stand disease transmission via the foramen (7-8). The most important structure in this regard is the superficial layer of deep cervical fascia. This layer splits covering the lateral surface of the masseter muscle and the medial surface of the medial pterygoid, and thus demarcates the masticator space. The fascia lining the medial surface of the medial pterygoid extends superiorly to the cranial base and attaches medial to the foramen ovale. Therefore, as might be expected by its function, the mandibular nerve enters the masticator space upon exiting the foramen. As the more medial parapharyngeal space is separated from the masticator space by this fascial plane, pathologic processes involving the parapharyngeal space rarely involve the foramen ovale. Deep lobe parotid neoplasia, schwannomas and paragangliomas have on occasion been reported to cause bone destruction in the region of the foramen ovale presumably due to invasion of or congenital breaches in the fascial planes. PATHOLOGY
REVIEW
Lesions of the foramen ovale may arise from the cavernous sinus, trigeminal nerve and its branches,
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C FIGURE 6. Recurrent pituitary adenoma. (A) Coronal Tl weighted image. Lower border of mass extending through the foramen ovale is identified (white arrowhead). Borders of the enlarged foramen are identified (arrows). (B) Coronal T2 weighted image. The mass is identified (*). The inferior margin is noted (arrow). (C) Sagittal Tl weighted image. The mass is subtle, but distinctly abnormal (“). Inferior margin is noted (arrow).
Meckel’s cave, masticator space, rarely from other infracranial sites and from the adjacent cranial base. Both neoplasms and inflammatory processes can disrupt the normal bony architecture.
Skull Base
Disease
Metastatic disease is the most common skull base spread may occur neoplasia (Figure 1). Metastatic either from a hematogeneous route or by perineural extension. Hematogeneous metastasis may be lytic or blastic in nature. The most common primaries are
breast, lung, renal and prostate carcinomas. The MR appearance is highly variable. Perineural spread is discussed below. Primary bone tumors of the skull base are rare. The skull base is of cartilaginous origin (chondrocranium), and therefore not surprisingly cartilaginous tumors predominate. Chondrosarcomas and chondromas are the most frequently described (9). Usually these tumors are located in the parasellar region, the cerebellopontine angle or the convexities. Plain film findings include matrix calcification and bone lysis. CT may demonstrate a soft tissue mass with variable contrast enhancement (10). Multiple noncartilaginous bone tumors have also been described. Chordomas are rare tumors arising from primitive notochordal remnants. These lesions are intracranial in 35% of cases, mostly involving the clivus, sella and parasellar regions (11). CT examination often demonstrates bone destruction and a soft tissue mass. On MRI these lesions are isointense or hypointense on Tl and hyperintense on TZ weighted imaging. Most are lobulated and heterogeneous with areas of both hyper and hypointensity. MR and CT are both capa-
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ble of detecting and characterizing this tumor, however MR is better able to define the anatomical extent of disease (12). Epidermoids, osteogenic sarcoma, osteomas, plasmocytomas, eosinophilic granuloma and giant cell tumors also may involve the skull base (13, 14, 15). Encephaloceles, congenital anomalies in neural tube formation, may be classified by location into convexity encephaloceles and those involving the skull base (16). Of the convexity encephaloceles, the inferior occipital type is most common. Basilar encephaloceles are even more unusual and may be divided into fronto-ethmoid (most common) sphenoorbital, spheno-maxillary or nasopharyngeal categories. As these defects contain brain parenchyma, CT and MRI characteristics parallel that of normal brain parenchyma. Our second case is a very unusual example (Figure 2). Paget’s disease, fibrous dysplasia and osteopetrosis may diffusely involve the skull base (17, 18). Pagetoid skull base involvement is usually lytic and diffuse. Fibrous dysplasia involving the skull base is densely sclerotic and asymmetric. Osteopetrosis is a rare but a well known cause of cranial base sclerosis (19). Meckel
Cave and
Trigeminal
Nerve
Disease
Meningioma is the most common primary intracranial neoplasm. Meningiomas in the middle cranial fossa may arise in or around Meckel’s cave or from dura elsewhere in the middle cranial fossa. Extrameningeal lesions may (very rarely) arise via aberrant arachnoid rests. CT reveals a hyperdense/isodense mass that may contain focal or diffuse calcifications (20). Homogeneous intravenous contrast enhancement is usually seen. The presence and severity of edema are highly variable. With MR a mass isointense with surrounding brain on Tl weighted images and isointense-hypointense on T2 weighted images is seen (21). Marked Gadolinium enhancement is usually present. Epidermoid tumors account for 0.2 to 1.8% of endocranial neoplasms (22). Most commonly these tumors occur at the CP angle or middle cranial fossa (23). On CT a low density mass with a attenuation coefficient value close to CSF is found and often no contrast enhancement occurs. The tumor most commonly exhibits a low intensity signal on Tl and a high signal intensity on T2 weighted images. Neurofibroma, melanotic schwannoma and arachnoid cyst have also been reported in Meckel’s cave (24). Mucoceles predominately involve the frontal or ethmoid sinuses. Less frequently the sphenoid and
maxillary sinuses are affected. The CT appearance is variable and may be either isodense or hyperdense on NCCT, possibly with contrast ring enhancement if infected. The mass is expansile although bony integrity is usually preserved. The affected sinus is generally completely opacified. MR findings vary depending on the hydration state of the sinus contents. Inspissated material appears hypointense on Tl and T2 weighted images whereas hydrated material appears hyperintense on these spin echo sequences (25). Our example of dumbbell extension of a sphenoid mucocele into the masticator space via the foramen ovale is unique (Figure 3). Giant aneurysms have received considerable attention both with respect to the CT and MR findings (26-28). Although it is not surprising that a cavernous carotid aneurysms might behave in a manner similar to our case #S, we found no other such cases in our review (Figure 4). Trigeminal Schwannomas are rare, accounting for less than 0.4% of all brain tumors. Classification into three types by anatomical location was proposed by Lesoin et al (29). Type I neuromas involve the roots in the posterior fossa, Type II neuromas involve the ganglion region and Type III neuromas involve the trigeminal branches (Figure 5). Usually peripheral involvement of the trigeminal branches involves the ophthalmic division. CT examination demonstrates a hypodense or isodense soft tissue mass with homogeneous contrast enhancement. Well defined bony margins heralds the benign, slow growing nature of these tumors (30). MR readily demonstrates the extent of the trigeminal division involvement by this tumor which has a high signal intensity on T2 and a decreased signal intensity on Tl weighted images. In a case report, Rigamunti et al (31) described a Schwannoma extending into and expanding the foramen ovale. This mass was centered in the middle cranial fossa and caused atrophy of the masticator muscles. Lipomas are the most common neoplasm of mesenchymal origin and involve the head and neck region in 13% of cases (22). Infiltration of nerve fascicles is common, making surgical removal very difficult. CT usually demonstrates a homogeneous low attenuation mass ( - 65 to - 125 hu) with no clearly definable capsule (32). MR intensity characteristics parallel that of subcutaneous fat; high intensity characteristics parallel that of subcutaneous fat; high intensity on Tl and intermediate-high intensity on T2 weighted images. Better characterization of low density CT masses common to this region (arachnoid cyst, epidermoid tumors, cholesteatomas, metastasis or abscess formation) is possible with MR imaging. More
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importantly, MR is able to define the anatomical extent of these tumors, which aids in surgical resection
2. Boyd GI. Emissary foramina of the cranium in anthropods. Anat 1930;65:108-121. Mosby Co., 1971:297-314.
(33).
3. Wood-Jones F. Non metrical morphological characteristics of the skull as criteria for racial diagnosis. J Anat, 1931;65:179-195.
Masticator
Space Disease
Anatomic fascial planes allow masticator space lesions easy access to the foramen ovale. Hardin et al (34) reviewed 36 patients with lesions of the masticator space. Sixteen patients had inflammatory masses, most often odontogenic in origin. Only four patients in this series had primary neoplasms. Metastatic disease from the major and minor salivary gland tumors and squamous cell carcinoma accounted for most of the tumors within the masticator space. Som et al (35) presented MR images of metastatic adenoid cystic carcinoma extending through the foramen ovale. MR signal characteristics of this tumor were similar to other salivary gland tumors; intermediate signal intensity on Tl and proton density and high signal intensity on T2 weighted images. Teresi et al (36) presented 46 patients who had malignant tumors of the nasopharynx, parapharyngeal space and infratemporal fossa. Direct invasion of the skull base occurred in seven patients with nasopharyngeal carcinoma. Route of spread was through the foramen ovale, foramen lacerum and stylomastoid foramen. Perineural spread of disease occurs by direct extension along the endoneurium and perineurium (37). Squamous cell carcinoma, lymphomas, adenocarcinoma, basal cell carcinoma, adenoid cystic carcinoma (minor and major salivary gland origin) and mucoepidermoid carcinomas have been reported to exhibit perineural spread (38). Of the tumors, squamous cell carcinoma is the most frequently reported to extend al&g the trigeminal and facial nerves (39). Atri et al (40) reported a case of actinomycosis granuloma of the trigeminal ganglia with perineural extension via the mandibular branch of the trigeminal nerve. CT demonstrated widening of the foramen ovale and an intracranial soft tissue mass. CT findings in perineural spread of disease is limited to identifying enlargement of the basal foramina or if present, a soft tissue mass within the cavernous sinus, Meckel’s cave or middle cranial fossa. MR appearance of perineural spread has been recently reviewed by Lain et al. Consistent with our experience their findings included: thickening of the nerve, expansion of the foramen ovale, mass within the foramen and masticator muscle atrophy. Lateral bulging of the cavernous sinus dural membranes was also described (41). REFERENCES 1. Sondheimer
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