Myeloblastoma of the brain.

Two patients developed intraparenchymal myeloblastomas (granulocytic sarcomas) of the brain. One patient with acute myelogenous leukemia in hematological remission had multiple myeloblastomas in the cerebrum and thalamus. The second patient, who had Philadelphia-chromosome-positive chronic myelogenous leukemia, developed a solitary lesion of the cerebrum without systemic evidence of blastic transformation of leukemia. By light microscopy, each biopsy specimen revealed a tendency for the malignant cells to appear in perivascular locations, and the presence of cytoplasmic naphthol AS-D chloroacetate esterase activity in some cells. Ultrastructural analysis demonstrated the presence of primary granule-like lysosomal structures in these cells, confirming their granulocytic origin. The lack of continuity of the myeloblastomas with the dura mater and the perivascular clusters of blast cells suggest that the pathogenesis of these lesions in the present cases could best be accounted for by the direct, hematogenous spread of mitotically competent leukemic cells to brain parenchyma.