Posterior fossa ependymoma

An enhancing lesion arises from the inferior 4th ventricle, distorting the medulla and displacing it anteriorly. No hydrocephalus. Rare and sparse chronic small vessel ischemic white matter changes are present, in a number acceptable for the age group. The remainder brain is unremarkable.

Conclusion: 4th ventricle mass which may correspond to an ependymoma or a choroid plexus papilloma. 

The sections show fragments of a moderately hypercellular ependymoma. Tumor cells have mildly pleomorphic vesicular nuclei with a finely granular chromatin. Well formed perivascular pseudorosettes are noted throughout all fragments submitted. Annotated Figure 1: A) tumor cells B) 'clear area' and C) central vessel. 

A very occasional mitotic figure is identified (1/20 HPF). There is no microvascular proliferation. Two small areas of bland infarct-like necrosis are noted.

Immunohistochemistry shows prominent perinuclear dot staining for epithelial membrane antigen (EMA) in tumor cells as well as strong staining for GFAP. The topoisomerase labeling index is approximately 10%.

DIAGNOSIS: Posterior fossa ependymoma (WHO Grade 2).

Note: as molecular profiling is unavailable in this case, it would have the diagnosis of posterior fossa ependymoma not otherwise specified (NOS).