Ultrasonographic Presentation of Nodular Cystic Fat Necrosis after a Low-velocity Trauma: A Case Report

Abstract

Objective: Morel-Lavallée lesion is a well-known entity after a high-energy, shearing trauma. Another form of lesion in the subcutaneous tissue is fat necrosis, presenting as a palpable mass. The most common presentation of fat necrosis is oil cysts, which occur mainly in the breast. However, in the lower extremities fat necrosis appears as nodular cystic fat necrosis. We report here a case of a patient with multiple injuries after a low-velocity trauma, who developed fat necrosis.
Results: Six months after the traumatic event the patient reported multiple subcutaneous lumps on the right knee. On ultrasonography, the probable diagnosis of post-traumatic fat necrosis with consequent development of nodular cystic fat necrosis was seen. The diagnosis was confirmed based on magnetic resonance imaging (MRI).
Discussion: Fat necrosis should be included in the differential diagnosis in cases of tissue injuries after a trauma. Fat necrosis can present months or years after the initial injury. It is a benign entity and is the result of an organized haemorrhage, swelling and oedema that progresses with fibrosis. There is no absolute need for surgical treatment.

LAY ABSTRACT
Nodular cystic fat necrosis presents as palpable lumps, most commonly on the lower extremities after a trauma. Patients may report these cystic structures many months after the trauma. This case report illustrates the ultrasonographic appearance of nodular cystic fat necrosis. This is a benign finding that does not require treatment or removal if no pain or aesthetic discomfort is present.