The nuclear chromatin is condensed with one or more nucleoli. The cytoplasm is abundant, blue to purple in color and contains reddish-purple granules. Osteoclasts are normal cells that are involved in bone resorption. Morphologically they may closely resemble megakaryocytes, but megakaryoctes possess nuclei with multiple overlapping lobes and nucleoli are usually absent. Megakaryocyte cytoplasm is granular but the granules are usually smaller and more uniform in appearance than in osteoclasts.
Mast cells are normal constituents of bone marrow.
They are usually present in low numbers but may become more prominent in hypocellular or aplastic states, myeloproliferative disorders, chronic lymphoproliferative disorders and when the marrow is involved by systemic mastocytosis. Mast cells have round to oval nuclei that may be obscured by abundant, small, round densely stained blue-black granules throughout the cytoplasm. Mast cells are usually round, but may be elliptical or spindle-shaped with cytoplasmic extensions. They resemble basophils morphologically but mast cell granules are usually smaller, rounder and more uniform in appearance than basophil granules and mast cell nuclei are single rather than lobated. Large foamy macrophages, however, are more characteristic of Neimann-Pick disease.