Fine Needle Aspiration Appearances of Enoxaparin Induced Fat Necrosis

Background: Low molecular weight heparin such as enoxaparin is widely used in the prevention and treatment of deep vein thrombosis or pulmonary embolism. The drug is administered as a subcutaneous injection. Tissue damage in the form of hemorrhage and necrosis can occur at sites of injection leading to the development of subcutaneous masses. These masses can be clinically confused with other conditions such as infection or cancer.
Case Report: The fine needle aspiration (FNA) cytology of 2 cases of fat necrosis at site of injection of enoxaparin is presented. One of the cases also had a core biopsy, presenting an opportunity to describe the histological changes. Large irregularly shaped weakly refractile material was observed in a background typical of fat necrosis. The material was either orangeophilic or basophilic in the Papanicolaou stained material and was blue in the Quik Diff stained smears. The histological appearances mirrored the FNA findings. The drug Enoxaparin was placed on a slide, allowed to dry and examined under the microscope. This showed colorless but crystalline material, similar to that seen in the samples obtained from both patients.
Conclusions: Enoxaparin produces characteristic cytological changes. Awareness of this reaction should avoid confusing it with other conditions.

Keywords: Biopsy, Fine-Needle, enoxaparin, Fat Necrosis