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

Background: Small fibrillary ar- eas 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. Case report: A tumor arising from the lateral ventricle of a 42-year-old man was almost completely resected. The mass re- sembled 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 label- ing index of the tumor was zero. Adjacent glial components were not neoplastic. Two years later, the tumor underwent meningeal dissemi- nation. The patient died and an autopsy was performed. Histologically, proliferation of small round cells with a high Ki-67 labeling in- dex was observed. Conclusion: In the present case, clinical tumor onset was marked by intra- cerebral hemorrhage. Rosette formation is a characteristic histological finding of neuro- cytic tumors including central neurocytomas. However, in the present case, rosette formation and calcification were remarkably prominent. In addition, this case demonstrates that malig- nant transformation may also occur in central neurocytomas that show very low initial Ki-67 labeling indices.