11 - Nerve Sheath Tumors

Abstract

Nerve sheath and neuroectodermal tumors are derived from the neuroectoderm or neural crest tissue of the developing embryo. Normal nerve consists centrally of axons, surrounded by Schwann cells. The connective tissue of the axons, including the Schwann cells, fibroblasts, mast cells, capillaries, and collagen, is called the endoneurium. Groups of these axons with their Schwann cells are surrounded by perineurium. Any one of these components may give rise to a neoplasm. Schwannomas are benign nerve sheath tumors composed of Schwann cells, while neurofibromas consist of a mixed population of Schwann cells, perineurial cells, and fibroblasts. Other variants of nerve sheath tumors, including granular cell tumor, perineurioma, and dermal nerve sheath myxoma, have specific clinicopathologic features. The most important aspect of making a diagnosis of nerve sheath tumors is to determine whether the lesion is benign or malignant, and in doing so, to determine whether the patient has an associated syndrome, neurofibromatosis type 1 (NF1) or NF2.