NQ-033 Answer: (B) Papillary ependymoma

Pathology of this case: In essence, this is a papillary tumor. The tumor cells are polarized and have a smooth luminal surface. The cytoplasm is fine, fibrillary, and point towards blood vessels in a coronary fashion with a mantle of cytoplasm without nuclei. There is no basement membrane. These features can be well recognized in the medium-magnification photo but is better appreciated in high-magnification. With all of these features taken into consideration, this is an ependymoma.

Immunohistochemically, expression of epithelial membrane antigen (EMA) can be seen on the luminal surface and ependymomas almost always patchy to diffusely positive for glial fibrillary acidic protein (GFAP). [click here to see immunohistochemistry]

Myxopapillary ependymoma: There is no myxoid change in this case. Myxopapillary ependymoma typically occur in the cauda equine but not in the brain.

Choroid plexus papilloma: Choroid plexus papillomas have basement membrane and a fibrovascular core. None of the two features are here.

Angiocentric glioma: This entity is mainly seen in children and young adults. Histologically, these tumors are featured by an angiocentric pattern of growth pattern with remarkably monomorphous bipolar, spindle cells. Their cytoplasmic processes tend to arrange around blood vessels and give a vague resemblance to ependymomal pseudorosettes or astroblastomas. Similar to ependymoma, dot like positive immunoreactivity for EMA can be seen in tumor cells. Angiocentric glioma and ependymoma has overlap in histopathologic and immunohistochemical features. However, angiocentric gliomas do not form papillary structure with smooth luminal border.

Astroblastoma: This is another tumor that can be confused with ependymoma. In general, astroblastoma also has perivascular orientation but in contrast to ependymoma, the cytoplasmic contact with blood vessels is composed of broad cytoplasmic processes. In ependymoma, it is composed of fine fibrillary cytoplasmic processes. In addition, astroblastomas do not form true papillary structure with a smooth luminal surface.