Brachial plexus meningioma, report of a case with immunohistochemical and ultrastructural examination.

Peripheral nerve meningiomas are exceedingly rare neoplasms of controversial origin; only four cases have been reported. Proposed origins of ectopic meningiomas include extradural trapping of arachnoid cells during embryogenesis, ectopic migration of arachnoid cell nests with the developing peripheral nerve, and metaplasia of mature peripheral nerve sheath cells or a common progenitor cell. In this report of a meningioma of the brachial plexus, immunohistochemical and ultrastructural examinations of the tumor matched all the criteria of a traditional meningioma but failed to clarify the origins of such neoplasms.