What is the typical demographic of patients with medulloblastomas?
They usually present in childhood with 77% of cases before the age of 19. The median age of diagnosis is 9 years. When diagnosed in adulthood, they typically present in the 3rd and 4th decades.
Where do they typically arise?
Typically in the mid vermis, protruding into the 4th ventricle.
When arising in adults, does their location change?
Although they continue to arise in the cerebellum, they more commonly arise from unusual locations, such as the cerebellar hemispheres.
The patient went on to have a craniotomy and resection of the tumour.
Histology
The sections show a densely cellular malignant tumour, forming mainly diffuse sheets. Scattered interspersed pale islands and nests of cells are present. Within these islands, the tumour has more linear and cord-like arrangement. The stroma is somewhat more fibrillary. Occasional poorly formed rosettes are identified elsewhere. The tumour cells have high N/C ratio with enlarged round nuclei, small nucleoli, granular chromatin and scanty cytoplasm. No mature neurons are present. Sparse mitoses are seen (0-1 mitosis per 10 high power fields). There are scattered apoptotic bodies throughout the tumour. No endothelial cell hyperplasia is identified. The background is rich in reticulin fibres, apart from the pale islands. The tumour cells are synaptophysin and B-tubulin positive. There is focal GFAP positivity. The Ki-67 index is about 15%. Neurofilament, chromogranin and CAM5.2
are negative.
The presence of reticulin-poor pale islands has only be described in medulloblastoma and not in pineal parenchymal tumour.
FINAL DIAGNOSIS:
Posterior fossa tumour: Desmoplastic / nodular medulloblastoma (WHO Grade IV).