Fat necrosis is the death of fat tissue, a benign condition that often manifests as a lump beneath the skin. This condition develops when fat cells sustain damage, leading to an inflammatory response and the formation of a firm, palpable mass. Fat necrosis is not associated with an increased risk of developing cancer. The condition is a localized reaction to injury and typically resolves on its own over time.
The Underlying Causes and Biological Mechanism
Fat necrosis is commonly triggered by events that disrupt the blood supply to fatty tissue, causing the cells to die from a lack of oxygen. Frequent causes include blunt trauma, prior surgical procedures (such as breast reduction or reconstruction), and focused radiation therapy used in cancer treatment. The onset of a mass can be significantly delayed, sometimes appearing months or even years after the initial injury.
When fat cells die, they release their oily contents, specifically triglycerides. This release initiates a sterile inflammatory process. Enzymes called lipases break down the released fatty acids, which can then combine with calcium in a process known as saponification, leading to the formation of chalky deposits.
The body’s repair mechanism involves an influx of inflammatory cells, which eventually leads to the formation of scar tissue. In some cases, the released oily liquid pools together, creating a sac of fluid called an oil cyst. This cyst may develop a rim of calcification that makes the lump hard and fixed.
Recognizing the Physical Signs
Fat necrosis most commonly occurs in the breast tissue but can appear anywhere fat is present. The primary sign is a palpable mass under the skin, which can feel firm, round, or sometimes irregularly shaped. Although often painless, the lump may occasionally be tender or cause discomfort.
The skin overlying the necrotic area may also exhibit noticeable changes due to the underlying inflammatory process. These secondary signs include redness, bruising, or a thickened appearance of the skin. In some instances, the scar tissue that forms can pull on the surrounding skin, leading to dimpling or a retraction of the nipple.
Diagnostic Procedures and Differentiation
Because fat necrosis can produce a hard, fixed mass and cause skin changes, its clinical and imaging presentation can sometimes mimic malignant tumors. Distinguishing this benign condition from cancer begins with a thorough medical history, noting any recent trauma, surgery, or radiation exposure.
Imaging techniques are then employed, starting with mammography and ultrasound. On a mammogram, fat necrosis may appear as a characteristic oil cyst—a well-defined, radiolucent lesion with a thin, calcified rim. However, more complex presentations, such as masses with irregular or spiculated margins, can be seen, especially when fibrosis is pronounced.
Ultrasound sometimes reveals a complex cystic mass with internal echoes or anechoic lesions with posterior acoustic enhancement. Magnetic Resonance Imaging (MRI) is often reserved for indeterminate cases, where it can confirm the lesion’s fatty nature by following the signal of fat on specific sequences.
When imaging remains inconclusive or the mass appears suspicious, a tissue sample is necessary. A fine-needle aspiration or core needle biopsy is performed to analyze the cells and definitively rule out malignancy.
Treatment Approaches and Long-Term Outlook
Fat necrosis is a self-limiting condition that frequently requires no medical intervention, as the body gradually breaks down the affected tissue over time. Resolution can take a considerable period, sometimes lasting from several months up to a few years. For localized pain or tenderness, applying warm compresses or using over-the-counter anti-inflammatory medication can provide relief.
If an oil cyst is large and causing significant discomfort, a physician may use fine needle aspiration to drain the oily fluid. Surgery is generally avoided because the procedure itself can sometimes cause new fat necrosis.
However, surgery may be considered if the lump is persistently painful, significantly affects the area’s appearance, or if diagnostic uncertainty remains despite imaging and biopsy. The outlook is excellent, as fat necrosis is not associated with long-term health complications.