Distinctive cytoplasmic surface activity in benign and leukemic bone marrow cells: ultrastructural definition and clinicopathologic correlation

A distinctive ultrastructural finding, observed in a case of acute lymphoblastic leukemia (ALL) and previously unreported on the surface of bone marrow cells, is described. The alteration is referred to as distinctive cytoplasmic surface activity (DCSA). For further delineation, study of 130 consecutively submitted bone marrow specimens was undertaken. All samples were obtained from children and included diverse myeloid leukemias, acute lymphoblastic leukemia, normal marrows, and abnormal but non-neoplastic conditions. The DCSA was composed of simple and complex interconnected tubular elements in continuity with the cytoplasmic membrane, probably, sharing its glycocalyx. The intensity of the DCSA varied but, its presence was detected in one third of the 130 cases. Except for rare marrows (three cases) with DCSA bearing polymorphs, all positive cells were lymphoid in origin, usually originating from non-B, non-T ALL patients. In very few non-neoplastic cases, DCSA-positive lymphocytes also were found. Review of the literature shed little light on the subject but disclosed rare instances in which DCSA was illustrated in benign as well as malignant lymphoid cells. Based on this information and the observations made throughout the study, it is surmised that DCSA may be the morphologic expression of a cellular function, probably a form of micropinocytosis. Despite its prevalence in ALL cases, it appears to be nondiagnostic and nonspecific to a cell line.