Histologic changes: The bluish material in these small vessels (A) probably represents necrotic bone marrow although no fat or cellular details are seen.
An oil red O stain for neutral fat (B) shows a globule of fat in a capillary. Several alveolar macrophages also stain, but the stain is slightly browner and in small granules. This granular pigment corresponds to the lipochrome pigment just described, which appears brown on H&E stain. Lipochrome pigment must be distinguished from the homogeneous red of fat embolism, as seen in the capillary wall.
For comparison, a bone marrow embolus (C) from another patient who had CPR shows viable marrow fragments in a medium-sized artery. Such emboli are common postmortem findings. None was found in our patient. However, it is possible that small fatty emboli as seen in B are also present after CPR, but they are not sought in routine autopsies. Thus, the fat embolus in B could be a result of resuscitation. The presence of lipid-laden macrophages in BAL fluid during an acute chest episode, however, supports the idea that fat embolism occurs as a part of the episode (see discussion).
Clinical summary Image 7
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