Subependymoma of the spinal cord and review of the literature.

Subependymoma is a tumor of the central nervous system, which frequently occurs in the ventricles and rarely in the spinal cord. Most of the intraventricular subependymomas are subclinical and thus incidentally encountered at autopsy, whereas the spinal ones are inevitably accompanied by myelopathy and are often diagnosed clinically as ependymomas or astrocytomas. Two cases of spinal cord subependymomas are reported, one of which recurred 9 years after the initial operation. All specimens of both cases showed similar microscopic features. Within a highly fibrillary background, round to ovoid tumor cells were unevenly distributed and arranged in cell clusters. Mitoses were rarely encountered. No necrosis was demonstrated in any of the specimens. Ultrastructural examination demonstrated many slender processes containing abundant intermediate filaments and occasional small lumen-like structures with many microvillous projections and cell junctions. Subependymomas arising in the spinal cord should be distinguished from other more aggressive gliomas, such as diffuse astrocytomas and ependymomas. Characteristic microscopic features and the ultrastructural studies support the diagnosis.