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Neuroradiology Case of the Week

Case 140

Tanya Tivorsak and PL Westesson MD, DDS, PhD

Clinical Presentation: A 70-year-old male with memory loss and tonic-clonic seizures with no focal neurologic symptoms.

Radiological Findings: Non-contrast enhanced CT demonstrates a mass with subtle increased intensity with a well-defined lateral convex border in the left cavernous sinus region. There is erosion of the tip of the left petrous bone and widening of the foramen ovale through which the mass extends into the infratemporal fossa (Fig. 1).
     MR images demonstrate a well-defined, lobulated hyperintense mass on T2 WI which is intensely and heterogeneously enhanced with gadolinium, measuring 2.0 cm x 3.0 cm x 3.3 cm in transverse, AP, and longitudinal dimensions, respectively. The mass occupies the lateral region of the left cavernous sinus abutting the internal carotid artery, which is patent. It extends superiorly into the middle cerebral fossa, posteriorly into the cerebellopontine region, and inferiorly through the foramen ovale into the infratemporal fossa (Figs. 2 - 4).

Discussion: Trigeminal schwannomas are benign, uncommon tumors that account for 0.07–0.36% of all intracranial tumors and 0.8–8% of intracranial schwannomas. Acoustic schwannomas are the most common cranial nerve schwannoma (> 90%), followed by trigeminal and facial nerve schwannomas. A clinical analysis of 120 cases by McCormick et al. (1988) revealed that the peak incidence of trigeminal schwannomas occurs during the fourth decade of life. Schwannomas arise from Schwann cells, which form the axon myelin sheaths.
     The trigeminal nerve provides sensory innervation to the head and face and motor innervation to the muscles of mastication. Thus, the main symptoms of trigeminal schwannomas are facial numbness, hyperesthesia, and pain, although seizures and memory loss may occur. Trigeminal schwannomas can arise from the root, ganglion, or intracranial portion of the three peripheral divisions of the nerve – ophthalmic (CN V1), maxillary (CN V2), and mandibular (CN V3).
     In terms of the pathway, the nerve exits the brainstem at the mid-pons and proceeds anteriorly toward the trigeminal ganglion in the Meckel’s cave, which is posterolaterally to the cavernous sinus. CN V3 exits inferiorly via the foramen ovale, and CN V1 and V2 course along the lateral wall of the cavernous sinus, with CN V2 exiting through the foramen rotundum and CN V1 entering the orbit via the superior orbital fissure.
     Four distinct types of trigeminal schwannomas have been identified:
     (a) those confined to the cavernous sinus,
     (b) those located within the Meckel’s cave,
     (c) cerebellopontine angle schwannomas, and
     (d) giant trigeminal schwannomas that involve the posterior and the middle cranial fossa (our case).
     MR with gadolinium-based contrast medium is the preferred technique of choice for imaging. The lesions are isointense or mixed iso-/hypointense on T1WI, hyperintense on T2WI, and well-circumscribed with strong enhancement on post-contrast T1 WI.  Trigeminal schwannomas are more likely to contain cystic components and are more varied in appearance than acoustic schwannomas, although their signal intensities are similar. CT is ideal for evaluating the secondary effects on the neural foramen.
     The differential diagnosis includes meningioma, an ICA aneurysm, and less likely metastases, infection, or rheumatic process. Treatment of trigeminal schwannomas is surgical resection.

References:

1. McCormick PC, Bello JA, Post KD. Trigeminal schwannoma. Surgical series of 14 cases with review of the literature. J Neurosurg 1988; 69: 850–860. [Medline]
2. Dolenc VV. Frontotemporal epidural approach to trigeminal neurinomas. Acta Neurochir. (Wien) 1994. 130: 55–65. [Medline]
3. Kamel HA, Toland J. Trigeminal nerve anatomy: illustrated using examples of abnormalities. AJR Am J Roentgenol. 2001; 176:247-251. [Medline]
4. Rigamonti D, Spetzler RF, Shetter A, Drayer BP. Magnetic resonance imaging and trigeminal schwannomas. Surg Neurol 1987; 28: 67-70.[Medline]
5. Som PM and HD Curtin. Head and Neck Imaging, 4th ed. 2003. Mosby. pg.1291-1292.
6. Williams LS, Schmalfuss IM, Sistrom CL, Inoue T, Tanaka R, Seoane ER, Mancuso AA. MR Imaging of the trigeminal ganglion, nerve, and the perineural vascular plexus: normal appearance and variants with correlation to cadaver specimens. AJNR American Journal of Neuroradiology 2003. 24:1317-1323.[Medline]