Gliosis of the eighth nerve transitional region in patients with cerebellopontine angle schwannoma.

The central-peripheral transitional region (TR) of the eighth nerve root was obtained from 8 patients with cerebellopontine angle schwannoma and investigated by light microscopy, electron microscopy, and immunohistochemistry. As a control, the TRs of 6 autopsy patients without any otologic disease were studied. Astrocytic proliferation at the TR was more prominent in the schwannoma patients than in the normal controls. Mild gliosis of the mantle zone of the TR was found in 5 schwannoma patients and moderate gliosis was noted in 3. The distribution of capillaries at the TR differed between the schwannoma patients and the normal controls. In the schwannoma patients, capillaries were rarely found in the mantle zone of the TR but were densely clustered at the glial fringe zone, especially near its border with the peripheral nervous tissue. Stasis of the capillaries in the glial fringe zone was frequently noted. These histological findings may indicate the occurrence of gliosis in response to eighth nerve degeneration. We suggest that there is increased susceptibility of the eighth nerve to injury at the TR in patients with schwannoma.