Extraneural relapse of medulloblastoma mimicking acute leukemia: A diagnostic challenge in adult patient

Abstract Medulloblastoma is the most frequent malignant tumor of the central nervous system (CNS) in children, but it can rarely occur in adults. Extraneural relapse of medulloblastoma occurs very rarely and it is usually associated with dismal prognosis. We present a case of young adult with relapsed medulloblastoma with extraneural metastases in the bone marrow and expression of terminal deoxynucleotidyl transferase (TdT) on the malignant cells mimicking acute leukemia. To the best of our knowledge, this is the first report of medulloblastoma exhibiting expression of the TdT in adult. We would like to emphasize that in cases like this, differential diagnosis of anemia and thrombocytopenia in adults should include a consideration of primary or secondary bone marrow involvement by medulloblastoma or other rare malignancy.