Which tumor classically shows perivascular pseudorosette formation?

• A. Ependymoma
• B. Medulloblastoma
• C. Astrocytoma
• D. Oligodendroglioma

Answer: (A)

Perivascular pseudorosette formation is a pattern that reflects ependymal differentiation, where tumor cells arrange around a central blood vessel with processes directed toward the vessel, creating a rosette-like appearance around the vascular core. This is most characteristic of ependymoma, a tumor arising from ependymal cells lining the ventricles and central canal. The pattern helps distinguish it from other glial tumors: medulloblastoma typically shows Homer Wright rosettes—tumor cells encircling a central tangle of neuritic processes rather than vessels; oligodendroglioma features a fried-egg cell appearance with a delicate capillary network and often calcifications; astrocytoma shows astrocytic, GFAP-positive fibrillary background without perivascular rosettes. Thus the perivascular pseudorosette pattern points to ependymoma.