Microscopic Report - Samples consist of a cellular tumour composed of densely packed small cells with scant cytoplasm. Nuclei are mostly round or oval and quite hyperchromatic. There is vague nodularity on low-power but no desmoplasia. Some tumour cell nuclei are large and very pleomorphic; however they are not very common. Mitoses are frequent and a small area of necrosis is present. There is also microvascular proliferation. No rhabdoid cells are present. Most tumour cells express synaptophysin and show preserved nuclear INI-1 staining. Tumour cells are negative with EMA and Cam5.2 antibodies. Beta-catenin shows no nuclear translocation. MIB-1 expression reflects the vague nodularity and is approximately 20% overall.
Comment: Features are those of a medulloblastoma with metastatic disease without evidence of Wnt pathway activation and morphology of classical type rather than anaplastic large cell variant or desmoplastic/nodular variant.
Diagnosis: Medulloblastoma, WHO Grade IV, classical subtype with no WNT Pathway Activation.
Post Operative MRI Report - There has been a gross total macroscopic resection of the tumour; there may be a very small portion present inferiorly within the right side of the fourth ventricle. Extensive metastatic dissemination is again noted to within the cranial cavity and I think the small focus of nodular enhancement related to the left superior vermis is metastatic disease rather than residual disease related to the fourth ventricular tumour.