(Radiology. 1999;213:364-368.)
© RSNA, 1999
Case 16: Facial Nerve Schwannoma with Middle Cranial Fossa Involvement1
Lawrence E. Ginsberg, MD and
Franco DeMonte, MD, FRCSC
1 From the Departments of Diagnostic Radiology (L.E.G.) and Neurosurgery (F.D.), University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030. Received August 28, 1998; revision requested September 23; revision received October 8; accepted December 22. Address reprint requests to L.E.G. (e-mail: lginsberg@di.mdacc.tmc.edu)
Index terms: Diagnosis please • Gadolinium • Nerves, facial, 2123.364 • Schwannoma, 21.364 • Temporal bone, CT, 21.1211 • Temporal bone, MR, 21.12141, 21.121415, 21.12143 • Temporal bone, neoplasms, 21.364
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HISTORY
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A 26-year-old man presented with a 6–8-month history of progressive right-sided facial weakness. This was preceded by dryness of the right eye. The patient also reported a sensation of fullness or fluid within his right ear, and he subsequently experienced decreased hearing in that ear.
At physical examination, facial sensation and visual acuity were normal. There was a House grade III right-sided facial paresis. Audiometry revealed right-sided conductive hearing loss. The lower cranial nerves were intact, and other neurologic test results were unremarkable.
Magnetic resonance (MR) imaging (Fig 1) and computed tomography (CT) (Fig 2) were performed.
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Figure 1a. (a) Axial T1-weighted (616/12 [repetition time msec/echo time msec]) MR image shows a nearly isointense extraaxial mass (arrows) in the right middle cranial fossa. A hypointense zone centrally (*) represents cystic degeneration. (b) Coronal fast spin-echo, T2-weighted (5,433/108) MR image shows that the solid tumor component (arrowheads) more inferiorly is mildly hyperintense relative to brain. The cystic component (arrow) more superiorly is hyperintense. (c) Axial T1-weighted (616/12), contrast material-enhanced, fat-suppressed MR image obtained at approximately the same level as a shows increased enhancement of the solid tumor component (arrow) and nonenhancement of the cystic tumor component (arrowhead). (d) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to c. Enhancing tumor (arrow) can be seen in an enlarged labyrinthine segment of the right facial nerve and internal auditory canal (large arrowhead). In comparison, there is faint visibility of the contralateral, normal labyrinthine facial nerve segment (small arrowhead). (e) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to d shows enhancing tumor (arrow) extending into the petrous temporal bone through a widened facial hiatus for the greater superficial petrosal nerve. There is tumor involvement of the geniculate ganglion (large black dot) and the tympanic or horizontal segment (small black dots) of the right facial nerve. Enhancing tumor (arrowhead) is also seen in the internal auditory canal.
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Figure 1b. (a) Axial T1-weighted (616/12 [repetition time msec/echo time msec]) MR image shows a nearly isointense extraaxial mass (arrows) in the right middle cranial fossa. A hypointense zone centrally (*) represents cystic degeneration. (b) Coronal fast spin-echo, T2-weighted (5,433/108) MR image shows that the solid tumor component (arrowheads) more inferiorly is mildly hyperintense relative to brain. The cystic component (arrow) more superiorly is hyperintense. (c) Axial T1-weighted (616/12), contrast material-enhanced, fat-suppressed MR image obtained at approximately the same level as a shows increased enhancement of the solid tumor component (arrow) and nonenhancement of the cystic tumor component (arrowhead). (d) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to c. Enhancing tumor (arrow) can be seen in an enlarged labyrinthine segment of the right facial nerve and internal auditory canal (large arrowhead). In comparison, there is faint visibility of the contralateral, normal labyrinthine facial nerve segment (small arrowhead). (e) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to d shows enhancing tumor (arrow) extending into the petrous temporal bone through a widened facial hiatus for the greater superficial petrosal nerve. There is tumor involvement of the geniculate ganglion (large black dot) and the tympanic or horizontal segment (small black dots) of the right facial nerve. Enhancing tumor (arrowhead) is also seen in the internal auditory canal.
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Figure 1c. (a) Axial T1-weighted (616/12 [repetition time msec/echo time msec]) MR image shows a nearly isointense extraaxial mass (arrows) in the right middle cranial fossa. A hypointense zone centrally (*) represents cystic degeneration. (b) Coronal fast spin-echo, T2-weighted (5,433/108) MR image shows that the solid tumor component (arrowheads) more inferiorly is mildly hyperintense relative to brain. The cystic component (arrow) more superiorly is hyperintense. (c) Axial T1-weighted (616/12), contrast material-enhanced, fat-suppressed MR image obtained at approximately the same level as a shows increased enhancement of the solid tumor component (arrow) and nonenhancement of the cystic tumor component (arrowhead). (d) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to c. Enhancing tumor (arrow) can be seen in an enlarged labyrinthine segment of the right facial nerve and internal auditory canal (large arrowhead). In comparison, there is faint visibility of the contralateral, normal labyrinthine facial nerve segment (small arrowhead). (e) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to d shows enhancing tumor (arrow) extending into the petrous temporal bone through a widened facial hiatus for the greater superficial petrosal nerve. There is tumor involvement of the geniculate ganglion (large black dot) and the tympanic or horizontal segment (small black dots) of the right facial nerve. Enhancing tumor (arrowhead) is also seen in the internal auditory canal.
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Figure 1d. (a) Axial T1-weighted (616/12 [repetition time msec/echo time msec]) MR image shows a nearly isointense extraaxial mass (arrows) in the right middle cranial fossa. A hypointense zone centrally (*) represents cystic degeneration. (b) Coronal fast spin-echo, T2-weighted (5,433/108) MR image shows that the solid tumor component (arrowheads) more inferiorly is mildly hyperintense relative to brain. The cystic component (arrow) more superiorly is hyperintense. (c) Axial T1-weighted (616/12), contrast material-enhanced, fat-suppressed MR image obtained at approximately the same level as a shows increased enhancement of the solid tumor component (arrow) and nonenhancement of the cystic tumor component (arrowhead). (d) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to c. Enhancing tumor (arrow) can be seen in an enlarged labyrinthine segment of the right facial nerve and internal auditory canal (large arrowhead). In comparison, there is faint visibility of the contralateral, normal labyrinthine facial nerve segment (small arrowhead). (e) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to d shows enhancing tumor (arrow) extending into the petrous temporal bone through a widened facial hiatus for the greater superficial petrosal nerve. There is tumor involvement of the geniculate ganglion (large black dot) and the tympanic or horizontal segment (small black dots) of the right facial nerve. Enhancing tumor (arrowhead) is also seen in the internal auditory canal.
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Figure 1e. (a) Axial T1-weighted (616/12 [repetition time msec/echo time msec]) MR image shows a nearly isointense extraaxial mass (arrows) in the right middle cranial fossa. A hypointense zone centrally (*) represents cystic degeneration. (b) Coronal fast spin-echo, T2-weighted (5,433/108) MR image shows that the solid tumor component (arrowheads) more inferiorly is mildly hyperintense relative to brain. The cystic component (arrow) more superiorly is hyperintense. (c) Axial T1-weighted (616/12), contrast material-enhanced, fat-suppressed MR image obtained at approximately the same level as a shows increased enhancement of the solid tumor component (arrow) and nonenhancement of the cystic tumor component (arrowhead). (d) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to c. Enhancing tumor (arrow) can be seen in an enlarged labyrinthine segment of the right facial nerve and internal auditory canal (large arrowhead). In comparison, there is faint visibility of the contralateral, normal labyrinthine facial nerve segment (small arrowhead). (e) Axial T1-weighted (616/12), contrast-enhanced, fat-suppressed MR image obtained caudad to d shows enhancing tumor (arrow) extending into the petrous temporal bone through a widened facial hiatus for the greater superficial petrosal nerve. There is tumor involvement of the geniculate ganglion (large black dot) and the tympanic or horizontal segment (small black dots) of the right facial nerve. Enhancing tumor (arrowhead) is also seen in the internal auditory canal.
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Figure 2a. (a) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) shows benign bone remodeling secondary to tumor. There is widening of the facial hiatus (arrows) through which tumor extends, as seen on MR images (Fig 1e). Note the scalloping or remodeling (arrowhead) of the apex of the right petrous temporal bone. (b) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) and caudad to a shows enlargement of the bony canal (arrow) for the labyrinthine segment of the right facial nerve. There is also opacification of the epitympanum (arrowhead) with ossicular encasement. (c) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) and caudad to b shows soft-tissue opacification and ossicular encasement (arrowheads) representing tumor within the mesotympanum.
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Figure 2b. (a) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) shows benign bone remodeling secondary to tumor. There is widening of the facial hiatus (arrows) through which tumor extends, as seen on MR images (Fig 1e). Note the scalloping or remodeling (arrowhead) of the apex of the right petrous temporal bone. (b) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) and caudad to a shows enlargement of the bony canal (arrow) for the labyrinthine segment of the right facial nerve. There is also opacification of the epitympanum (arrowhead) with ossicular encasement. (c) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) and caudad to b shows soft-tissue opacification and ossicular encasement (arrowheads) representing tumor within the mesotympanum.
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Figure 2c. (a) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) shows benign bone remodeling secondary to tumor. There is widening of the facial hiatus (arrows) through which tumor extends, as seen on MR images (Fig 1e). Note the scalloping or remodeling (arrowhead) of the apex of the right petrous temporal bone. (b) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) and caudad to a shows enlargement of the bony canal (arrow) for the labyrinthine segment of the right facial nerve. There is also opacification of the epitympanum (arrowhead) with ossicular encasement. (c) Axial CT image obtained with bone window settings (width, 2,924 HU; level, 690 HU) and caudad to b shows soft-tissue opacification and ossicular encasement (arrowheads) representing tumor within the mesotympanum.
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IMAGING FINDINGS
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At MR imaging with a 1.5-T imager, there was an extraaxial right middle cranial fossa mass that was nearly isointense to brain on T1-weighted images, with a more hypointense cystic component centrally (Fig 1a). The lesion was mildly hyperintense relative to brain on T2-weighted images (the cyst is hyperintense) (Fig 1b), and it enhanced brightly following intravenous administration of 0.1 mmol of gadopentetate dimeglumine per kilogram of body weight (Fig 1c–1e). In Figure 1e, the lesion can be seen to extend from the geniculate ganglion of the right facial nerve through a widened facial hiatus for the greater superficial petrosal nerve. Involvement of the tympanic segment of the right facial nerve can be seen in Figure 1e. The labyrinthine segment of the facial nerve is involved with tumor (Fig 1d), and there is tumor enhancement in the internal auditory canal (Fig 1d, 1e).
CT images demonstrated the enhancing cystic, solid mass with soft-tissue window settings (width, 194 HU; level, 70 HU; not shown). Images obtained with a bone window setting (Fig 2a–2c) show the benign, expansile changes within the petrous temporal bone.
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DISCUSSION
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Facial nerve schwannomas are uncommon tumors arising from the Schwann cell sheath (1–6). These tumors may arise anywhere along the course of the facial nerve, from the cerebellopontine angle to the neuromuscular junction, but there is a predilection for involvement of the geniculate ganglion (3,5,6). From the geniculate ganglion, a facial nerve schwannoma may extend to involve the tympanic and/or labyrinthine portions of the facial nerve (1,4–6). Uncommonly, facial nerve schwannomas extend to involve the middle cranial fossa by means of direct upward spread through the roof of the temporal bone or anterior spread through the facial hiatus for the greater superficial petrosal nerve (2,3,5–9).
The clinical presentation of facial nerve schwannoma is variable and depends on the site of tumor involvement, but some component of facial paresis is expected (1–10). This facial paresis is of variable severity but is often gradually progressive or fluctuating in nature (3,4,9,10). The presence of persistent or progressive facial paresis argues against simple Bell palsy. Conductive hearing loss due to tympanic segment involvement and ossicular compression is the second most common presenting symptom and may be seen in up to 76% of cases (1). Other less common presenting symptoms include tinnitus, hemifacial spasm, and otalgia (1–6,8,9). Involvement of the greater superficial petrosal nerve can result in loss of lacrimation (10,11). This was not tested in our patient, but the initial symptom of ocular dryness was consistent with denervation of the lacrimal gland.
For facial nerve schwannomas involving only the internal auditory canal, the cerebellopontine angle, or both, the chief symptom may be sensorineural hearing loss, with both radiologic and clinical findings more suggestive of acoustic schwannoma than facial nerve schwannoma (6,7,11). In such cases, facial paresis is rare (11,12). In this patient, the involvement of the geniculate ganglion and tympanic portions of the facial nerve help explain the symptoms of facial dysfunction. Bulky tumor involvement of the tympanic cavity accounted for the conductive hearing loss.
Regardless of tumor location, the basic imaging characteristics of schwannoma apply: CT shows an enhancing soft-tissue mass, and MR imaging shows a mass that is mildly hypo- or isointense relative to brain on T1-weighted images, is heterogeneously hyperintense on T2-weighted images, and enhances following administration of gadopentetate dimeglumine. Heterogeneity or cystic change, common in other schwannomas and present in this patient, may also be seen in large facial schwannomas (7). With use of a bone algorithm, CT demonstrates a benign type of expansile, lytic change or remodeling of bone (7). Aggressive bone destruction is not seen.
The presence of a middle cranial fossa tumor, as in this patient, should prompt consideration of various intracranial lesions. Intraaxial tumors such as primary glial neoplasms and hematogenous brain metastases would not likely extend into the temporal bone along the course of the greater superficial petrosal branch of the facial nerve as in this patient, nor would they manifest as facial paresis. Extraaxial lesions such as meningioma, dural metastasis, epidermoid cyst, or arachnoid cyst can all be excluded as well. A meningioma may be associated with frank bone destruction if aggressive, or may cause hyperostosis, but would not typically extend into the petrous temporal bone with benign bone remodeling. In addition, tumor extension along the course of the facial nerve would not be expected in a middle cranial fossa meningioma. A dural metastasis would probably destroy bone, rather than extend into the temporal bone with a benign type of bone expansion, as in this patient. Perineural extension of a head and neck malignancy may follow the course of the greater superficial petrosal nerve and gain access to the temporal bone through the facial hiatus (13). In such patients, there is usually clinical or radiologic evidence of either a primary lesion or tumor in the pterygopalatine fossa, vidian canal, or Meckel cave (13). None was present in this patient. An epidermoid tumor should not enhance as this lesion does, and the signal characteristics of this lesion are not consistent with those of an epidermoid tumor. Arachnoid cysts can erode or remodel bone but should not enhance.
Given the intratemporal tumor component in this patient, various primary and secondary lesions of petrous temporal bone origin would also merit diagnostic consideration. A metastasis would more likely destroy bone than give the benign type of remodeling seen in this patient. Langerhans cell histiocytosis commonly affects the temporal bone; not only is it rare for this disease to produce a facial palsy, but also more aggressive or destructive bone changes would be expected in Langerhans cell histiocytosis (7,14). Vascular tumors of the temporal bone such as hemangioma and ossifying hemangioma can be excluded on the basis of the absence of the moth-eaten irregular bone margins typically seen in hemangioma and the lack of internal calcifications characteristic of ossifying hemangioma (12,15,16). Also, vascular lesions typically do not extend into the middle cranial fossa. A cholesteatoma of primary temporal bone origin (intraosseous epidermoid) or cholesterol granuloma, though either can manifest as a facial paresis, would not be expected to enhance (7).
The images in this patient demonstrate an enhancing mass involving the geniculate ganglion and the labyrinthine, tympanic, and intracanalicular portions of the right facial nerve and extension through the facial hiatus for the greater superficial petrosal nerve to involve the middle cranial fossa. The bone changes are not aggressive in nature. Considering this patient's clinical presentation and the imaging findings of a lesion clearly involving the facial nerve, the most likely diagnosis is facial nerve schwannoma. A combined transmastoid and middle fossa surgical approach exposed the tumor and allowed complete resection. A hypoglossal nerve–to–facial nerve anastomosis was then created. Histologic analysis of the resected specimen confirmed the diagnosis of benign schwannoma.
The surgical approach to facial nerve schwannoma is dictated by which segments of the facial nerve are involved by tumor and by the patient's hearing status (17). A transmastoid approach generally is used, although additional middle fossa or parotid approaches or both may be added as necessary. Although some very small tumors can be dissected from the facial nerve, the removal of most facial nerve schwannomas requires sectioning of the facial nerve and nerve grafting. Some degree of permanent facial weakness is to be expected following resection, even if a hypoglossal nerve–to–facial nerve anastomosis is created (17).
Our congratulations to the 89 individuals who submitted the most likely diagnosis (facial nerve schwannoma with middle cranial fossa involvement) for Diagnosis Please, Case 16. The names and locations of the individuals, as submitted, are as follows:
- Gholamali Afshang, MD, Tinley Park, Ill
- Edward L. Baker, MD, San Francisco, Calif
- Zubin N. Balsara, MD, Fort Smith, Ark
- Grazia T. Bitti, Cagliari, Italy
- Jeffrey L. Black, Lafeyette, Calif
- Dr. A. J. Booth, Cambridgeshire, United Kingdom
- Kamel Boubagra, Grenoble, France
- Giuseppe Brancatelli, MD, Palermo, Italy
- Eric L. Bressler, MD, Minnetonka, Minn
- Douglas C. Brown, MD, Norfolk, Va
- Michael P. Buetow, MD, Okemos, Mich
- Dr. Wiluck Chu-Ongsakul, Bangkok, Thailand
- Y-S Cordoliani, MD, Paris, France
- M. G. de Baets, MD, Lugano, Switzerland
- Manuel de Juan-Delago, MD, Barcelona, Spain
- Dr. Ravi V. Desai, Chandigarh, India
- Dra. Estela Di Nella, Buenos Aires, Argentina
- Keith D. Epperson, MD, Milwaukee, Wis
- Steven Fagan, DO, Iron River, Mich
- Akifumi Fujita, Tochigi-ken, Japan
- Nestor Gonzalez, Los Angeles, Calif
- Athanassios D. Gouliamos, MD Walter O. Grauer, MD, Zürich, Switzerland
- Flavius Guglielmo, MD, Basking Ridge, NJ
- H. Paul Hatten, Jr, MD, Vero Beach, Fla
- Geum Joo Hwang, MD, New York, NY
- Waleed M. Ibrahim, MD, Detroit, Mich
- Christophe Ide, MD, Namur, Belgium
- Kenji Kachi, MD, Tokyo, Japan
- Ercan Karaarslan, Istanbul, Turkey
- Douglas S. Katz, MD, Mineola, NY
- Albert Kujas, MD, Paris, France
- Stephanos Lachanis, MD, Athens, Greece
- Jeffrey Neal Lang, MD, New York, NY
- Virginie Lefournier, Grenoble, France
- James W. Lester, Jr, Marietta, Ga
- Joseph H. Lock, Jr, MD, Mankato, Minn
- N. B. S. Mani, MD, Chandigarh, India
- K. Marsot-Dupuch, Paris, France
- Andrew J. McDonnell, MD, Corning, NY
- Edward Menges, MD, Aptos, Calif
- Leslie J. Miller, MD, Mineola, NY
- Manabu Minami, MD, Tokyo, Japan
- Hidetoshi Miyake, MD, Oita, Japan
- Sergio J. Moguillansky, Rio Negro, Argentina
- Peter Mollet, MD, Gent, Belgium
- Eduardo Mondello, MD, Buenos Aires, Argentina
- Kirk Moon, MD, San Francisco, Calif
- Toshio Moritani, Rochester, NY
- Dana Murakami, MD, Las Vegas, Nev
- Shinji Naganawa, MD, Nagoya, Japan
- Kanokporn Oranratanachai, CMU, Thailand
- Teresa Peltz, MD, Cagliari, Italy
- Victor Pérez-Candela, MD, Las Palmas de Gran Canaria, Spain
- John M. Plotke, Naperville, Ill
- Henry Pribram, MD, Orange, Calif
- Donald B. Price, MD, Mineola, NY
- Shawn P. Quillin, MD, Charlotte, NC
- M. R. Ramakrishnan, MD, Big Stone Gap, Va
- Enrique Remartinez Escobar, Melilla, Spain
- Nancy Richert, MD, PhD, Bethesda, Md
- Caroline D. Robson, MB, ChB, Boston, Mass
- Eric J. Russell, MD, Chicago, Ill
- Janet Scheraga, Syracuse, NY
- Steven M. Schultz, MD, Ft Worth, Tex
- Joel M. Schwart, MD, Irvington, NY
- S. Shankar, MD, Chandigarh, India
- Matt Shapiro, MD, Boxborough, Mass
- Huiping Shi, MD, PhD, Beijing, China
- Laila Shita, MD, Brussels, Belgium
- Paolo Siotto, MD, Cagliari, Italy
- Michael S. Stecker, MD, Carmel, Ind
- Irving Stein, DO, Long Branch, NJ
- Marius Stellmann, MD, Stade, Germany
- Stacy Stevens, San Antonio, Tex
- Peter M. Stroz, MD, Toronto, Ontario, Canada
- Eugenio L. Suran, MD, Framingham, Mass
- J. Takasugi, Mercer Island, Wash
- Dr. Tiong Yong Tan, Republic of Singapore
- Douglas L. Teich, MD, Brookline, Mass
- Shendee Teng, MD, Alhambra, Calif
- John To, MD, Iron Mountain, Mich
- Sunil S. Trasi, MD, New York, NY
- Carlos E. Triana Rodriguez, Santafe de Bogota, Colombia
- Juan Antonio Valdez, Miami, Fla
- H. Wouter van Es, MD, Nieuwegein, the Netherlands
- Pamela Van Tassel, MD, Charleston, SC
- Richard B. Yow, MD, Winston-Salem, NC
- Joe Yut, MD, Olathe, Kan
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HISTORY
IMAGING FINDINGS
