pathology_of_human_tumor: h&e stained sections show a densely cellular neoplasm which surrounds the cerebellum and appears to infiltrate meninges. the neoplasm is composed of round to oval cells with scant cytoplasm and hyperchromatic nuclei, arranged in nests, cords and sheets. mitotic figures are numerous and there are regions of necrosis, including pseudopalisading. tumor cells frequently abut vessels, which are prominent. foci of larger cells are present with multinucleated forms, but overt anaplasia is not seen. the tumors are largely synaptophysin positive and gfap negative. diffuse ki67 positivity is present.