Infratentorial dysembryoplastic neuroepithelial tumor (DNT) associated with Arnold-Chiari malformation.

Dysembryoplastic neuroepithelial tumor (DNT), a benign neoplasm, is now a well recognized clinicopathological entity. We report the second case of DNT in the cerebellum occurring in a 20-year-old male presenting with ataxia. He also had Arnold-Chiari malformation of the adult type. Histologically the tumor was a "simple" DNT having the specific "glioneuronal" element, namely oligodendrocyte-like cells (OLCs), mucoid change and floating neurons (Purkinje cells). A striking feature was the perpendicular arrangement of the neuropil columns extending from the pial surface to white matter similar to those seen in supratentorial examples. On immunstaining some of the OLCs were positive for synaptophysin and negative for glial fibrillary acidic protein (GFAP), glucocerebroside, tau and MAP-2. The neuropil was synaptophysin-positive and focally positive for MAP-2 and GFAP as well. The Purkinje cells were morphologically normal but malaligned and were positive for phosphorylated neurofilament suggesting secondary dysplastic changes. A transition of the lesion into relatively normal cerebellum preserving the folial architecture was observed. The histological and immunochemical features of the DNT in cerebellum suggests its possible origin from the pluripotential external granular layer.