The large cell indicated by the arrow is a reticulum cell. Reticulum cells are fixed tissue cells but are included in the differential. Most clinical hematologists include under this classification the hemocytoblasts and hemohistioblasts. The cell commonly called a reticulum cell is 20-30 microns in diameter. Its most distinguishing feature is heavy, ropy chromatin that is loosely hung together. Dispersed in the loose chromatin are two or three small, sky-blue nucleoli. The cytoplasm is the color of mature lymphocyte cytoplasm, sometimes with a mixture of pink. The cell outline is irregular. Some reticulum cells contain azurophilic granules and others, like the one shown here, do not. Reticulum cells are usually increased, perhaps as high as 20%, in the bone marrow of a patient with acute leukemia.
Course Section: 06. Microscopic Examination of the Bone Marrow
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