pathology_of_human_tumor:h&e stained slides show a small round blue cell neoplasm growing in sheets without distinct architecture. the cells have irregular nuclei with vacuolated chromatin and prominent nucleoli along with sparse, indistinct basophilic cytoplasm. no rosettes are identified. there are readily identifiable mitoses and karryorhectic debris. immunoperoxidase staining for ini-1 shows diffuse nuclear expression. sections that contain cerebellar tissue demonstrate the neoplasm invading white matter and growing prominently within the leptomeninges.