ABSTRACT
The bone marrow (BM) in adults occupies the medullary spaces of large bones such as the femur, the hip, the sternum, and the humerus. The primary function of the BM is to produce blood cells, in which early progenitor cells progressively differentiate into intermediate and mature elements. The BM contains progenitor cells called stem cells. The normal BM shows myeloid and erythroid cells at different stages of maturation as well as scattered megakaryocytes, lymphocytes, and rare eosinophils. Lymphoid cells are normally present in the BM and account for approximately 10%–20% of marrow cells in adults. Blood smear or BM aspirate shows benign histiocytes with phagocytized erythrocytes, platelets, and occasionally granulocytes and lymphocytes. Histologic evaluation of the BM core biopsy is an integral part of comprehensive marrow evaluation. Lymphomas can display different histologic patterns of BM involvement: diffuse, nodular, interstitial, paratrabecular, intrasinusoidal, and mixed.
