Definition:
The stroma is the supporting tissue of the bone marrow. Stromal cells consist of fibroblasts, endothelial cells, fat cells, osteoblasts, smooth muscle cells, macrophages and mast cells. Only the latter two are clearly recognizable by light microscopy and can occur in increased numbers in different disease processes. The remaining cells are not usually recognized as such by light microscopy. In addition, most are located within the bone marrow spicules, where individual cells are not recognized due to the density of material.