Myelin-containing corpora amylacea in vestibular root entry zone.

The vestibular nerve of patients with Meniere's disease and vascular cross-compression syndrome of the root entry zone due to the antero-inferior cerebellar artery was studied. All patients underwent vestibular neurectomy using the retrosigmoid approach, which permits the removal of a long nerve segment. CA were found in the cytoplasm of astrocytes that had not shown signs of degeneration at the central portion of the vestibular root entry zone. No membrane intervened between CA and the surrounding cytoplasm, which was rich in filaments, in particular near the CA, and poorly equipped with other organelles. CA were round or oval inclusions measuring 10-12 microns in diameter. The matrix of the CA was composed of low-density amorphous material, with irregular masses displaying a medium density. A network of randomly oriented filaments and bilaminar, osmiophilic lipid fragments with the same structure and thickness of myelin layers were embedded in the matrix. The CA rich in bilaminar fragments were recognizable also at low magnification for their high electron density. In the astrocytic cytoplasm, near the CA, round or ovalshaped, electron-dense bodies with a multilamellar structure were often visible. These results confirm the hypothesis that CA may contain degenerating myelin embedded in a microenvironment rich in glucose polymers and that CA could be an indicator of neurodegeneration.