The patient went on to have excision of the intraventricular mass.
Sections show a tumor comprised of cells with small round nuclei with stippled neoplasm. Occasional cells have a small nucleolus. Many of the cells have a perinuclear halo and on smears and touch preparations, the cytoplasm is a thin rim of eosinophilia. Within the sheets of tumor cells there are areas where there are delicate eosinophilic processes giving a fibrillar appearance. No mitoses are seen. There are occasional thrombosed vessels associated with hemosiderin deposition. Occasional calcospherites are present.
Immunocytochemistry shows that the tumor is positive for neuron specific enolase and synaptophysin. It is negative for chromogranin and phosphorylated neurofilament. Immunocytochemistry for glial fibrillary acidic protein (GFAP) shows focal areas of positivity; many of the cells with perinuclear halos are negative. Electron microscopy shows that the cells contain dense granules consistent with dense core vesicles.
FINAL DIAGNOSIS: Central neurocytoma.