Bone marrow cores allow for the best evaluation of bone marrow cellularity, cellular distribution, and cellular relationships and elements. These cores also allow for evaluation of disease involvement and distribution. Bone marrow core biopsies should be 1-2 cm in length for evaluation of anemia. For evaluation of lymphoma or metastatic carcinoma, a larger core is desirable.
It is imperative that core biopsies be well fixed prior to exposure to a decalcifier to ensure optimal morphology. Cellular morphology in core specimens is optimized when a mercurial fixative, such as B5 is utilized. However, due to the carcinogenic hazards associated with mercury-based fixatives, many laboratories employ zinc-based fixatives as a substitute.
After fixation, decalcification, and paraffin processing, bone marrow cores are thinly sectioned, usually at 3 microns in thickness and H&E stained. Cutting thin sections allows for appreciation of cellular detail. Five levels are customarily prepared for pathologist evaluation as well as an additional slide stained with Prussian blue for iron storage evaluation. These additional levels allow for successful visualization of focal disease processes.
Immunohistochemical staining of core sections can be performed, but weak to mild acid-based decalcification solutions must be used to avoid degeneration of antigens. Immunohistochemical staining of bone marrow cores help to determine the extent of tumor involvement and the presence of post-treatment residual disease.