Early, the lesion is hemorrhagic. Later central liquefaction necrosis of fat occurs. Still later, the lesion will contain chalky white or hemorrhagic debris. Histologically we see disruption of adipose cells, with inflammation and fibrosis.
Calcification can occur.
This specimen demonstrates necrotic fat cells with an intense neutrophilic infiltration. Note the fibrosis present in the lower left quadrant of the specimen. Lipid laden macrophages may also be seen, but are not appreciated in this specimen.