Immunohistochemical and electron microscopic study of subependymal giant cell astrocytoma.

Six cases of subependymal giant cell astrocytoma (SGCA), five associated with tuberous sclerosis (TS), were reviewed by light microscopy, electron microscopy and immunohistochemistry. Histologically, all cases showed features typical of SGCA. GFAP and neurofilament expression were found in all cases. Synaptophysin and myelin basic protein were positive in single different cases. The MIB-1 positive rate was 0% in 4 cases, 3% in a case with recurrence after a partial resection, and 6.4% in another case with a rapid growing tumor. By electron microscope, glial filament was identified in the tumor cells of all cases, whereas none of them showed any ultrastructural evidence of a neuronal origin. We therefore suggest that SGCA is a glial origin tumor, arising from the astrocytic part of a subependymal nodule--the most common cerebral lesion of tuberous sclerosis caused by distorted migration of the germinal mantle-the neuronal part of which remains as entrapped remnants of dysgenetic, incompletely expressed neuronal cells.