Extraventricular neurocytoma (EVN) is a rare brain tumor that poses diagnostic difficulty. Described herein is a case of atypical EVN arising in a 35-year-old man. A well circumscribed lesion in the right frontal lobe showed diffuse proliferation of monotonous tumor cells with perinuclear clearing and salt and pepper chromatin within a delicate fibrillary matrix. Tumor also showed vascular proliferation and high mitotic activity. Immunohistochemically, these tumor cells were strongly positive for synaptophysin and CD56 in the perinuclear cytoplasm, and negative for epithelial membrane antigen (EMA) and vimentin. Ki- 67 labeling index was 25-30% in the most stained areas. These findings were compatible with those of atypical EVN. EVN should be considered as a candidate in the differential diagnosis of parenchymal brain tumor, especially oligodendroglioma. Keywords: Atypical, extraventricular, immunohistochemistry, neurocytoma, synaptophysin
Corresponding Author: Nagpal R.