Intraventricular Pilocytic Astrocytoma With KIAA1549/BRAF Fusion Arising in a 44-Year Old.

Rare pilocytic astrocytomas (PA) have been described to arise in the ventricles of children. They are even less common in this location for the adult population. We present the case of a 44-year old man presenting with vision and mental status changes. Brain imaging revealed an intraventricular mass within the right ventricular atrium, most consistent with a meningioma. Microscopic examination revealed a neoplasm composed of elongated to plump bipolar astrocytes arranged in a fascicular architecture, accompanied by foci containing numerous Rosenthal fibers. By immunohistochemistry, the tumor cells were positive for vimentin and glial fibrillary acid protein, whereas negative for epithelial membrane antigen. Isocitrate dehydrogenase 1 (R132H) was also negative. By fluorescence in situ hybridization, we detected a KIAA1549/BRAF fusion gene. These findings supported the diagnosis of intraventricular PA arising in an adult.