An unusual presentation of a case of myeloblastoma (granulocystic sarcoma, chloroma) as demonstrated by computed tomography (CT) and selective angiography is reported. Our patient, who presented with acute hydrocephalus due to a large posterior fossa myeloblastoma, had no evidence of systemic disease in either peripheral blood smear, bone marrow aspiration, lumbar puncture or further metastatic workup. While no evidence for generalized disease was seen, systemic chemotherapy may help to prevent overt systemic leukemia.