NQ-036 Answer: (D) This tumor is unlikely to spread through the cerebral spinal fluid or metastasize outside the brain

Diagnosis: Medulloblastoma, WHO grade IV

Pathology of this case: With the location of the tumor in the cerebellum, the patient is a child, and the histologic features of a small blue cell tumor with fibrillary cytoplasmic processes that point to an imaginary center (C) forming rosettes (these are Homer Wright rosettes), this is a medulloblastoma, WHO grade IV.

Homer Wright rosettes are not rare but not really common in medulloblastomas. In contrast, it is frequently seen in neuroblastomas arising in the adrenal gland. In contrast, Flexner-Wintersteiner rosettes form a tubule like structure due to the presence of the limiting membrane, a feature that recapitulate the structure of photoreceptors. Flexner-Wintersteiner rosettes are typical for retinoblastoma but can also be occasionally seen in medulloblastomas.

In contrast to many other neuroepithelial tumor of the central nervous system, medulloblastoma has a strong tendency to disseminate through cerebral spinal fluid. In uncommon but not rare situations, medulloblastoma can metastasize outside the central nervous system with bone as the most common site of metastasis.