Meningioma

Meningioma is a common intracranial neoplasm with a variety of easily recognizable histomorphologic growth patterns. (1) Primary extracranial or ectopic meningiomas of the middle ear and temporal bone are rare, accounting for only 1% of all meningiomas. (2) The literature is limited to isolated case reports and a few literature reviews. (2-5) The largest study to date included 14 cases. (5) There has been only a single case report in which a primary extracranial meningioma did not have an intracranial component. (5)

Controversies continue to surround the exact origin of middle ear and temporal bone meningiomas. (4) Histologically, meningiomas of the middle ear and temporal bone are identical to their intracranial counterparts. Diagnostic difficulties arise because a meningioma in this location can be misdiagnosed as a paraganglioma, schwannoma, adenoma, carcinoma, or melanoma. (5)

We evaluated a 64-year-old woman who presented with long-standing and progressive left hypoacusis and facial paralysis. Computed tomography (CT) of the temporal bone detected a soft-tissue mass that involved the left epitympanum and mesotympanum and compromised the malleolus of the ossicular chain and the facial nerve (figure 1). Magnetic resonance imaging (MRI) revealed marked homogenous enhancement of the mass in the middle ear and epitympanum; there was no evidence of connection or extension intracranially (figure 2). Based on the clinical and imaging findings, our impression was that the mass represented a schwannoma of the facial nerve. After surgical excision, we identified the mass as a benign myxoid tumor with reactive bone formation, which is an unusual myxoid variant of meningioma that has been described in the literature as a metaplastic meningioma. (5)

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Arachnoid cells line the inner aspect of the arachnoid membrane. Increasing evidence supports the development of meningiomas from arachnoid cap cells, with different mechanisms to suggest how extracranial meningiomas arise. (5) In the middle ear or mastoid portion of the temporal bone, an intracranial meningioma can extend along the path of least resistance through a tegmen tympani to dehiscence, the sulci of the greater and lesser superficial petrosal nerves, the sigmoid sinus plate, the geniculate ganglion area, the internal auditory canal, the lateral semicircular canal, and the perilabyrinthine cell tracts or jugular foramen. (5) In our patient, we saw no evidence that the intratympanic meningioma had any connection with the intracranial structures. However, arachnoidal cells have been identified outside the neural axis, which may give rise to intratympanic or temporal bone meningiomas. (5)

References

(1.) Maniglia AJ. Intra and extracranial meningiomas involving the temporal bone. Laryngoscope 1978;88(Suppl 12):1-58.

(2.) DeWeese DD, Everts EC. Primary intratympanic meningioma. Arch Otolaryngol 1972;96:62-6.

(3.) El-Ghazali TM. Primary intra-tympanic meningioma. J Laryngol Otol 1981;95:849-52.

(4.) Chang CY, Cheung SW, Jackler RK. Meningiomas presenting in the temporal bone: The pathways of spread from an intracranial site of origin. Otolaryngol Head Neck Surg 1998; 119:658-64.

(5.) Thompson LD, Bouffard JP, Sandberg GD, Mena H. Primary ear and temporal bone meningiomas: A clinicopathologic study of 36 cases with a review of the literature. Mod Pathol 2003;16:236-45.

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