الملخص

ABSTRACT Atypical teratoid/rhabdoid tumor (AT/RTs) is a highly malignant nervous system tumor, occurs primarily in very young children. These tumors are distinctive, malignant neoplasms of uncertain histogenesis. They are thought to be embryonal and are usually composed of varying amounts of rhabdoid cells, small primitive neuroepithelial cells, epithelial tissue and neoplastic mesenchymal components. This is a case of AT/RT in a four years male patient who presented to the department of neurosurgery at Ibn-Sena Teaching Hospital, complaining of headache, nausea and vomiting for the last two months, progressed to visual disturbance and limbs weakness. Computerized tomography showed an ill-defined large mixed density posterior fossa tumor associated with hydrocephalus. Urgent ventriculoperitonial shunt followed by craniectomy and excision of the cerebellar tumor were performed. Histologically, according to the complex heterogeneity of cell types and tissue components, tumor was diagnosed as AT/RT and confirmed by immunohistochemical study. Keywords: Atypical teratoid/rhabdoid tumor, posterior fossa tumor.