Bone Marrow - Angiectasis

The vascular supply of the bone marrow culminates with capillaries opening into a plexus of sinusoids lined with endothelial cells and an incomplete outer layer of adventitial cells. Angiectasis of the bone marrow is defined as dilatation of these vessels or sinusoids with blood. In some cases, the dilatation can be so severe as to cause the appearance of large lakes of erythrocytes and/or proteinaceous fluid (serum) that should not be confused with hemorrhage (Figure 1 and Figure 2). The presence of a continuous intact endothelial lining helps distinguish angiectasis from hemorrhage. With more severe or chronic congestion of the vasculature, macrophages sometimes containing pigment and/or cholesterol clefts may be seen around the dilated vasculature.

A distinction between angiectasis and hemangioma should be attempted, although the distinction is not always obvious. Hemangiomas tend to be well-circumscribed, unencapsulated masses composed of tightly packed, dilated vascular spaces. Each vascular space is enclosed and lined by a single layer of normal-appearing endothelial cells aligned on collagenous septa, which are usually thin, although some have broad collagenous stroma. Angiectasis does not usually present as a well-circumscribed mass: the dilated vascular channels often course irregularly through the hematopoietic tissue.

Angiectasis has been observed in rodents with severe loss of hematopoietic tissue. It is also observed as a nonspecific finding or in association with inflammation, neoplasia, or vascular/cardiovascular disorders (e.g., thrombi, congestive heart failure).