Scanning Electron Microscopy of Peripheral Blood Smears: Comparison of Normal Blood with Some Common Leukemias

Abstract

Peripheral blood smears prepared routinely from nonneoplastic and leukemia cases were studied using the scanning electron microscope (SEM). The peripheral blood glass slide is examined directly in the SEM following application of a thin carbon coat. The morphology of the nonneoplastic and neoplastic smears is described in detail utilizing the SEM secondary electron detector and backscattered electron detectors. Certain cell features are measured as well with the use of the measuring software resident in the SEM. The appearance of the SEM images of peripheral smear slides is compared to that of slides from fixed, processed, and sectioned bone marrow cases previously reported. The problem of cell constituent loss and overall shrinkage in the routinely processed and sectioned material is noted. The lack of these problems in the peripheral blood smear slides and their better appearance is emphasized. The resemblance of neoplastic cells to their normal counterparts is discussed. The monoblast resembles the normal monocyte but both cell size and nuclear size are greater; the moderately reticulated nuclear chromatin distinguishes the monoblast. Neoplastic lymphoid cells maintain the wispy extensions of the cytoplasm perimeter resembling microvilli and thereby differ from myeloid and monocytic cells. The neoplastic lymphoid cell shows coarse clumping of nuclear chromatin and in some instances coarse chromatin anastomoses to distinguish it from the normal lymphocyte. Lymphoid cells of acute lymphoblastic leukemia are 33% larger than those of chronic lymphocytic leukemia and normal lymphocytes. The neoplastic myeloblast has a finely granular nuclear chromatin, maintains a smooth cytoplasmic perimeter, and may show cytoplasmic reticulations. The myeloblast differs from the lymphoblast in that the former has a smooth cytoplasm perimeter. Further, myeloblasts show nuclear lobulations more frequently than lymphoblasts. Comparison of SEM findings with the three case studies by flow cytometry indicates satisfactory correlation. In case 15, flow cytometry indicated a monocyte subset positive for CD14 and CD64 among the neoplastic myeloid forms. A candidate for such a cell is recognized morphologically as well. The availability for SEM ultrastructural study of all the cells, both neoplastic and nonneoplastic, on a routine diagnostic smear slide is emphasized.