Chapter 25 – Bone Marrow

The bone marrow consists of hematopoietic tissue and the organized stroma that supports the proliferation and differentiation of the hematopoietic cells. In routine toxicology studies, peripheral blood hematology and histological sections of bone marrow are the primary means of evaluating this tissue; however, the spleen, and, in some cases, the liver, may also be included in the overall assessment of the hematopoietic system. Histopathology provides information about bone marrow architecture, overall cellularity, megakaryocyte numbers and morphology, an estimation of the myeloid to erythroid (M:E) ratio and iron stores, and can demonstrate focal or subtle lesions. This chapter discusses the common spontaneous and chemically related changes or lesions observed in histological sections of bone marrow as well as normal bone marrow development and histology.