Fat Embolus - Oil Red O

Fractures can cause displacement of bone marrow into the bloodstream and eventually, the lungs, called fat emboli.

Fat emboli are a common consequence of blunt impact injuries, bone fractures, and cardiopulmonary resuscitation (CPR). Fat is a component of bone marrow, the tissue within the pelvis, sternum, vertebrae, and ribs of adults that produces the cellular elements of blood. Bony fractures may cause the embolization (inappropriate movement) of bone marrow into the bloodstream. The vast majority of fat emboli are asymptomatic and without consequence; however, a small percentage are clinically relevant and potentially fatal. Known as fat embolism syndrome, this phenomenon occurs 24 to 72 hours after blunt impact injury and is characterized by sudden-onset shortness of breath, a fine red rash, mental status changes and, in some cases, death. The precise mechanism with which fat embolism syndrome causes death is, as yet, unclear.

Oil Red O is a fat-soluble dye that colors fat (normally white on histologic section) a brilliant red hue. The application of Oil Red O to lung tissue identifies and highlights the fast cells in intravascular bone marrow emboli if they have migrated to the lungs. The presence of fat emboli in the lungs in conjunction with a clinical history of skeletal fractures and sudden death is consistent with fat emboli syndrome.