MICROSCOPIC DESCRIPTION:
Sections show multiple fragments of tissue which is largely replaced by a cellular tumour. Tumour consists predominantly of small undifferentiated cells which have high nuclear to cytoplasmic ratios. The cells are primitive in nature with a stippled chromatin pattern with occasional mitoses. Tumour cells are embedded in a fibrillary background. No nodularity or areas of high grade anaplasia is seen in the biopsy.
Immunohistochemistry shows the tumour cells stain positive with CD56 and synaptophysin. S-100 is positive.
Staining for GFAP is present but this appears to be staining background astrocytic processes rather than the tumour.
P53 stains approximately 10% of nuclei (considered wild type).
CD3, CD20, CD45 are negative.
GAB - YAP - Beta-catenin -Nuclear negative.
FINAL DIAGNOSIS: medulloblastoma, classic histologic subtype, most likely non-SHH/non-WNT subtype. WHO Grade IV.