Morphologic and ultrastructural characteristics of T-cell acute lymphoblastic leukemia.

The morphology, ultrastructure, and acid phosphatase activity of the leukemic cells of 11 cases of T-cell acute lymphoblastic leukemia (T-ALL) were studied. Distinctive small cells with markedly hyperchromatic convoluted nuclei comprised from 2 to 25% of the leukemic cells in the blood and bone marrow smears of 10 of the 11 patients. Similar cells were found in only four of 47 cases on non-T, non-B-ALL. Many of these small leukemic cells exhibited ultrastructurally nuclear membrane reduplication and nuclear blebs and splits. The presence of these small leukemic cells with markedly hyperchromatic convoluted nuclei in ALL is strongly suggestive of T-ALL. This cytomorphologic finding, when combined with the presence of strong focal acid phosphatase activity, lends even greater predictability of a T-cell process.