A cellular tumor formed of sheets of loosely packed rounded, oval or some elongated cells with enlarged hyperchromatic nuclei and scanty cytoplasm. Nuclei mostly display coarse chromatin pattern, but focally some rounded cells show vesicular nuclei. Anaplasia is marked and mitotic activity. Tumor is vascular. Picture is consistent with embryonal tumor, mostly medulloblastoma which is a WHO grade IV tumor. Marker study (GFAP, Synaptophysin, INI-1, LCA, CD20 and Ki-67) is recommended for confirmation of this possibility and exclusion of other less likely ones.
Posterior fossa tumor in the medial cerebellar hemisphere and fourth ventricle causing mild brainstem compression.
Soft tissue fragments collectively measured 2.7x2.3x0.8 cm, totally embedded.
Posterior fossa mass, excision biopsy: