A case of acute megakaryocytic leukemia with hematogones.

A case of an infant male with Down's syndrome, pancytopenia, and a relative lymphocytosis is presented. A bone marrow aspirate and crushed marrow biopsy were evaluated by microscopy and flow cytometry. A population of immature lymphoid cells positive for CD10 (CALLA) and CD19 (Leu 12) was initially interpreted as suggestive of an acute lymphoblastic leukemia (ALL). However, a second bone marrow biopsy revealed morphologic features consistent with acute megakaryocytic leukemia (AMKL) with fibrosis. This diagnosis was supported by the flow cytometric study showing increased myeloid and megakaryocytic antigen-positive cells in the bone marrow and peripheral blood obtained after chemotherapy for ALL. This report presents evidence that the original lymphoid population represented hematogones, which were preferentially aspirated due to marrow fibrosis. There are no previous reports of hematogones identified at the presentation of an acute leukemia. It also emphasizes that the presence of hematogones with the resultant marker findings can be misleading. The diagnosis of ALL in pediatric patients should not be based solely on the presence of increased CD10-positive cells.