Dysembryoplastic neuroepithelial tumor. A tumor with small neuronal cells resembling oligodendroglioma.

Dysembryoplastic neuroepithelial tumor (DNT) is a clinicopathologically unique group of tumors, mostly located in the temporal lobe, associated with intractable complex partial seizure in young patients. We report two unusual cases with multifocal involvement of diverse sites in the central nervous system. Case 1 is that of a 50-year-old man with 9-year history of grand mal seizures, who died of acute myocardial infarction. Case 2 is that of a 10-year-old girl with intractable complex partial seizures and behavioral disorder. Postmortem examination in case 1 showed multifocal tumor in the left temporal lobe, third ventricle, and basal ganglia. Magnetic resonance imaging in case 2 showed tumor in the right temporal lobe, both thalami, right cerebellar hemisphere, and pons. Histologically, both tumors were characterized by a multinodular appearance with a predominant component of alveolar arrangement of oligodendroglial-like cells around delicate capillaries, with mucoid matrix containing floating ganglion cells. There were also astrocytic nodules resembling pilocytic astrocytoma in case 1, and a gangliocytoma-like area merging with surrounding cortical dysplasia in case 2. Ultrastructural examination showed ganglionic differentiation in the oligodendroglial-like cells in case 2. They possessed dense core neurosecretory granules and many slender neuritic processes with microtubules arranged in parallel and terminating in synaptic junctions. The periventricularly located tumor with nodular extension to the periphery suggests an origin from subependymal germinal matrix with nests of primitive neuroblasts arrested in their embryonal migration. DNTs are related to ganglioglioma based on their common location and clinical behavior and on the presence of both ganglionic and astrocytic cells. They are also related to pilocytic astrocytoma by morphological and behavioral similarity. Together with cerebral neuroblastoma and central neurocytoma, they form a spectrum of tumors harboring small neuronal cells. The differentiation of DNT from oligodendroglioma is important so as to avoid unnecessarily aggressive therapy.