Ependymoma

Higher magnification of perivascular pseudorosettes. They consist of a collar of tumor cells arranged around blood vessels creating a nucleus-free zone immediately around the vascular lumen. True rosettes with a central lumen and canals lined by ependymal cells and resembling small ventricles are seen in about 10% of cases. Most typical ependymomas are considered WHO Grade II tumors (although the Myxopapillary variant is, by definition, WHO Grade I tumor). The anaplastic variant (discussed later) is WHO Grade III tumor.