Perineurioma (localized hypertrophic neuropathy).

Three patients with localized hypertrophic neuropathy ( LHN ) had a painless, slowly progressive mononeuropathy over many years, resulting in severe focal neurologic deficit. Grossly, the affected nerves showed a fusiform enlargement. Histologically, there was loss of nerve fibers, disorganization of the fascicular pattern, and proliferation of elongated cells with whorl formation. These cells exhibited no immunoreactivity for S-100 protein, and ultrastructural features set them apart from Schwann's cells. We conclude that LHN is not a disorder caused by hyperplasia of Schwann's cells but a benign peripheral nerve tumor of perineurial cell origin. This study also suggests that perineurial and Schwann's cells may not derive from the same precursor element.