Chordoid glioma of the third ventricle - An ultrastructural study of threecases with a histogenetic hypothesis

Chordoid glioma is a rare neoplasm occurring in the third ventricle and, as the name implies, having a chordoid appearance. It is currently considered a glial neoplasm of uncertain histogenesis with distinct clinicopathologic features. We report three cases of chordoid glioma with a focus on the ult rastructural appearance. The patients were two men and one woman aged, resp ectively, 34, 40, and 43 years. Immunohistochemically, all tumors showed st rong and diffuse reactivity for glial fibrillary acidic protein and vimenti n, whereas immunoreactivity for epithelial membrane antigen and cytokeratin was focal. Ultrastructurally, they showed features of ependymal differenti ation for the presence of an apical pole with microvilli and a basal pole c haracterized, as in normal ependyma, by many hemidesmosomelike structures c onnecting cell membranes to the underlying basal lamina. Constant features were a submicroscopic cell body zonation (i.e., perinuclear, intermediate, subapical, and apical regions) and the presence of secretory granules. Thes e findings were similar to those described for the secretory ependymal cell s of the subcommissural organ, a small structure located in a dorsocaudal r egion of the third ventricle that undergoes regression after birth in human s. Our observations suggest that chordoid glioma may represent a subtype of ependymoma whose cells resemble the highly specialized ependyma of the sub commissural organ.