Answer: Extracranial sinonasal meningioma

Histology: Extracranial sinonasal meningiomas are rare neoplasms of primary extracalvarial (ectopic) origin. Although morphologically identical to their intracalvarial counterparts, they can lead to diagnostic difficulties considering their rarity in such locations. The origin of extracalvarial meningiomas is though to be from ectopic arachnoid cells or arachnoid cells exiting the cranium along cranial nerves and vessels.

Discussion: In the largest reported series of 30 cases, sinonasal meningiomas occurred equally in both genders and were most frequently present in the nasal cavity as well as frontal and sphenoid sinuses. Hiistologic features of “atypical” meningioma were only rarely encountered and did not predict recurrence. The diagnosis of extracranial meningiomas can be confirmed by their positive reactivity to EMA and vimentin. Finally, primary cranial menigiomas can involve the sinonasal tract by direct extension, or very rarely, as a metastatic lesion from a malignant cranial primary.

Reference(s):
– Thompson L et al. Ectracranial Sinonasal Tract Meningiomas: A clinicopathologic study of 30 cases with a review of the literature. Am J Surg Pathol 2000: 640.