The patient went on to have a resection and made an unremarkable recovery.
There are portions of a hypercellular glial neoplasm showing perivascular pseudo-rosetting with anucleated zones of fibrillary matrix. The neoplastic cells have round to elongated relatively small nuclei with salt and pepper chromatin pattern. Focal geographic necrosis is present but features of anaplasia are not identified. There is no endothelial proliferation, no palisaded necrosis and no brisk mitotic activity. Immunohistochemistry shows positive labelling of the anucleated perivascular fibrillary zones for GFAP. Occasional peri-nuclear labelling is noted for EMA.
FINAL DIAGNOSIS: posterior fossa ependymoma (WHO grade2).