Medulloblastoma

Discussion:

The patient went on to have a resection. 

Histology

MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of a densely hypercellular tumor. Tumor is seen to expand cerebellar white matter and extend through cerebellar cortex in specimen 2. Prominence of an external granular layer containing atypical cells is also noted. Tumor cells have overlapping and molded pleomorphic hyperchromatic nuclei and delicate processes. Moderately well-formed Homer-Wright rosettes are identified in many areas. There are frequent mitotic figures. No necrosis is seen.

Immunohistochemistry shows strong diffuse staining in tumor cells for synaptophysin and beta-tubulin. No staining for GFAP or epithelial membrane antigen (EMA) is seen in tumor cells. The topoisomerase labeling index is approximately 60%. Patchy moderate nuclear staining in tumor cells for YAP-1, moderate cytoplasmic staining for GAB1 and strong perinuclear and membrane staining for beta-Catenin. No nuclear staining for beta-Catenin is seen. Nuclear staining for INI-1 is preserved.

This immunophenotype is most consistent with Group 2 (Sonic Hedgehog; SHH) medulloblastoma.

FINAL DIAGNOSIS: Medulloblastoma (WHO Grade IV) Group 2 (Sonic Hedgehog; SHH) 

 

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