A 26 years old patient was operated for a tumor of cerebellar vermix, and then reoperated for a relapse at the age of 35 years, with a similar histological pattern in both cases. At pathologic examination, the tumor was composed of hypercellular sheets typical of medulloblastoma, containing also sparse large cells with eosinophilic cytoplasm and round nuclei containing voluminous nucleoli. Neuroblastic cells showed expression of neurofilament protein and synaptophysin. The large cells expressed desmin, myogenin, and neurofilament. These morphological and immunohistochemical features are characteristic of medullomyoblastoma. The patient deceased 11 years after the initial surgery. Medullomyoblastoma is a rare variant of medulloblastoma with a rhabdomyoblastic differentiation. The two tumoral populations share the same genetic alterations. The main differential diagnoses are atypical teratoid/rhabdoid tumor, immature teratoma, medulloepithelioma, primitive intracranial rhabdomyosarcoma and myoneurocytoma.
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