Infratentorial medulloepithelioma with divergent differentiation: Possibly a predictor of poor outcome.

Medulloepitheliomas (WHO grade IV) are rare, malignant embryonal tumors of pediatric population, classified under the central nervous system (CNS) primitive neuroectodermal tumors (PNET). Histologically, these tumors are characterized by neoplastic neuroepithelium recapitulating the embryonic neural tube. We describe a rare case of infratentorial medulloepithelioma with divergent differentiation in a 1-year-old male child who presented with headache, vomiting, and seizures. Histopathologic examination of the excised tumor revealed the characteristic neuroepithelium, along with other areas showing primitive neuroectodermal (blastemal) cells in sheets, ependymoblastic rosettes, and nodular areas of neuronal differentiation. Possibly, this proliferating immature neuroepithelium is the cause of poor outcome in medulloepitheliomas. Due to the rarity of these tumors, it remains to be established whether infratentorial location or tumors with divergent differentiation are also predictors of adverse prognosis.