ABSTRACT
ВМ morphology: The ВМ aspirate is usually a “dry tap,” due to reticulin fibro sis. In the BM biopsy, the pattern of involvement is interstitial or patchy and there is usually preservation of some of the fat and hematopoietic cells. The neoplastic cells are slighdy larger than normal lymphocytes with oval or reniform nuclei and abundant cytoplasm with distinct cell borders imparting a “fried egg” appearance to the individual cells or a “honeycomb appearance” to groups of cells viewed on low power. Mitoses are scant. W hen the BM is involved by small amounts of tumor in an interstitial pattern, the neoplastic cells can blend imperceptibly with normal BM elements. IH C stains such as CD20 are invaluable in such situations. Reticulin fibrosis is common and may be seen using special stains such as Snooks reticulin stain. Advanced cases may show diffuse solid involvement of the BM. In 20% of cases the BM is markedly hypocellular, making differentiation from aplastic anemia quite difficult. A CD20 immunostain should be done on the BM biopsy specimen in all cases of suspected aplastic anemia. The decrease in the hematopoietic cells in such cases is theorized to be due to cytokines produced by the neoplastic lymphocytes.
