Central neurocytoma with remarkably large rosette formation and rapid malignant progression: a clinicopathological follow-up study with autopsy report

Abstract

Small fibrillary areas mimicking neuropils are known to be one of the histological features of ordinary central neurocytomas. It is known that Ki-67 labeling indices are an indicator for prognosis of central neurocytomas. A tumor arising from the lateral ventricle of a 42-year-old man was almost completely resected. The mass resembled an aneurysm-like hematoma at the septum pellucidum. Histologically, the tumor mainly consisted of synaptophysin-positive small round cells displaying prominent rosette formation and calcification. The Ki-67 labeling index of the tumor was zero. Adjacent glial components were not neoplastic. Two years later, the tumor underwent meningeal dissemination. The patient died and an autopsy was performed. Histologically, proliferation of small round cells with a high Ki-67 labeling index was observed. In the present case, clinical tumor onset was marked by intracerebral hemorrhage. Rosette formation is a characteristic histological finding of neurocytic tumors including central neurocytomas. However, in the present case, rosette formation and calcification were remarkably prominent. In addition, this case demonstrates that malignant transformation may also occur in central neurocytomas that show very low initial Ki-67 labeling indices.