Benign schwannoma with perineurioma-like areas: A clinicopathologic study of 11 cases.

Eleven schwannomas are described. All tumors were well demarcated and surrounded by a true capsule or pseudocapsule and manifested Antoni A and Antoni B areas, Verocay bodies, and hyalinized vessels. In addition to typical schwannoma, there were clear cell areas composed of spindled cells arranged either in parallel sheets or in loops within the myxoid matrix, morphologically identical to retiform (reticular) perineurioma. The Schwann cells in the conventional schwannomatous areas displayed typical ultrastructural features. Those comprising the perineurioma-like areas revealed a primitive morphology. They were slender or polygonal and were devoid of an external lamina, pinocytic vesicles, or junctions. These findings suggest that the perineurioma-like areas consist of primitive or modified Schwann cells, or, alternatively, these perineurioma-like areas represent true, but incomplete perineurial differentiation within otherwise ordinary benign schwannomas. These neoplasms represent a morphologic variant of schwannoma having distinctive perineurial-like areas, a pattern which may elicit diagnostic difficulties.