Relapse of acute myelogenous leukemia as a cerebellar myeloblastoma showing megakaryoblastic differentiation

Myeloblastomas (granulocytic sarcomas) occurring within the central nervous system (CNS) are extremely rare lesions that may develop in patients with acute or chronic myeloproliferative disorders. The majority of such lesions involve brain or spinal cord by contiguous spread from meningeal or bony s ites, rather than originating within the CNS parenchyma We describe a patie nt with acute myelogenous leukemia in remission, who developed a purely int raparenchymal cerebellar myeloblastoma with megakaryocytic differentiation. The neoplastic cells expressed the megakaryocytic markers factor VIII-rela ted antigen and platelet glycoprotein IIIa (CD61), and showed ultrastructur al features that were indicative of megakaryocytic differentiation. Clinica lly, myeloblastomas of the CNS invoke a broad differential diagnosis that i ncludes abscess, hemorrhage, and metastatic neoplasms because of their intr aparenchymal location and radiologic features. Although they are rare, myel oblastomas should be included in the histopathologic differential diagnosis of a poorly differentiated neoplasm occurring within the CNS, particularly in a patient with a history of myeloproliferative or myelodysplastic disea se.