Bone Marrow

The marrow biopsy specimen is usually taken from the iliac bone. It consists of bony trabeculae surrounded by a mixture of fat and hematopoietic cells. The percent cellularity (non-fat) should be roughly [100 – the patient’s age]. The hematopoietic cells consist of megakaryocytes, erythroid precursors, and myeloid precursors. There may also be assorted plasma cells, lymphocytes, and histiocytes. The bone marrow is considered a reflection of what is in the peripheral blood, so the disorders of marrow affect blood counts. Lymphomas can involve the marrow, but generally the primary malignancies of the marrow are the leukemias.

Technically, all three of the basic “trilineage hematopoiesis” lines (megakaryocytes, erythroids, and granulocytic cells) are of the myeloid lineage, which differentiates them from the lymphoid lineage (B and T cells). The myeloproliferative diseases and myeloid leukemias refer to this broad classification. However, the word myeloid, as used at the microscope, generally refers to those cells in the granulocyte/monocyte pathway only.