Peripheral nerve sheath neoplasms

Published on 20/03/2015 by admin

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Last modified 20/03/2015

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42

Peripheral nerve sheath neoplasms

Neoplasms derived from cells that surround peripheral nerves may present with central nervous system (CNS) symptoms and signs when they arise at a proximal site. The three main groups of these nerve sheath neoplasms are schwannomas (neurilemmomas), neurofibromas, and malignant peripheral nerve sheath tumors (MPNSTs; neurofibrosarcomas). Nearly all cranial nerve sheath tumors and most peripheral nerve sheath tumors in the spinal canal are schwannomas. All three groups show an association with neurofibromatosis (NF).

SCHWANNOMAS

Schwannomas are slowly growing neoplasms composed of Schwann cells. Solitary schwannomas with effects on the CNS occur on cranial (Table 42.1, Fig. 42.1) and spinal nerve roots; rarely they are found in the substance of the brain or spinal cord. Melanotic schwannomas have a predilection for spinal nerve roots. The plexiform schwannoma is rare and occurs in the skin. Unlike the plexiform neurofibroma, it is not associated with NF.

Table 42.1

The commonest neoplasm of the cerebellopontine angle is a schwannoma of the vestibulocochlear nerve

Cerebellopontine angle neoplasm %
Schwannoma 85
Meningioma 10
Others (cholesteatoma, glioma, medulloblastoma, metastatic carcinoma, paraganglioma, hemangioma, AT/RT)  5

MACROSCOPIC APPEARANCES

Schwannomas are composed of nodular rubbery tissue, which has a variegated cut surface. Yellow and gray areas may be interspersed with hemorrhagic foci or cysts. The neoplasm has a capsule and the nerve from which the schwannoma arises may be splayed over the surface of the neoplasm (Figs 42.2, 42.3).

MICROSCOPIC APPEARANCES

Two histologic patterns predominate (Figs 42.442.6):

image NF2

Neoplasms associated with NF2

image Schwannomas.

image Neurofibromas.

image Ependymomas.

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