Diagnosis: Peripheral blood, bone marrow aspirate and biopsy: WHO classification - Acute myeloid leukemia with inversion of chromosome 16.

Left frontal mass, biopsies: Acute myeloid leukemic infiltrates in cerebral white matter consistent with granulocytic sarcoma (Chloroma).

Microscopy: Sections A1-A4 show small fragments of gray and white matter. In sections A1, A3, and A4, the white matter is partly invaded by a dense malignant cell infiltrate composed of immature granulocytic cells displaying round cells with hyperchromatic nuclei and high nuclear:cytoplasmic ratio. Some tumor cells have more abundant cytoplasm filled with eosinophilic granules. The leukemic cells are distributed around blood vessels and are also diffusely infiltrating the white matter. In addition, tumor cells are seen within the lumen of cerebral microvessels. In section A1, small foci of early tumor necrosis are seen. Apoptotic nuclei are frequent. By immunohistochemistry, the leukemic cells show strong membrane staining for leukocyte common antigen (CD45) and strong cytoplasmic staining for myeloperoxidase and CD43, consistent with the diagnosis of granulocytic sarcoma (chloroma). Rare reactive CD3-positive T-lymphocytes are present. The neoplastic cells are negative for CD20. Reactive astrocytes are seen in sections A1, A3, and A4 in association with the malignant cell infltrates, as well as in the adjacent white matter.