Fat necrosis

Fat necrosis is a condition that happens when fat tissue in the body is damaged and the fat cells (adipose cells) die. The body responds by breaking down the dead cells and often replacing them with scar tissue. This process can result in firm, rounded, or irregular lumps in the affected area. These lumps may feel rubbery and can sometimes be tender or painful. Fat necrosis can develop in many parts of the body but is most commonly seen in the breast.

What causes fat necrosis?

There are several reasons why fat necrosis may occur. The most common causes include trauma or injury, surgical procedures, radiation therapy, inflammatory conditions, and pancreatitis.

What does fat necrosis feel or look like?

Fat necrosis usually appears as a lump under the skin or in deeper tissues. These lumps are often firm, round, or irregular in shape. In the breast, they may feel very similar to a cancerous lump, which is why additional tests are usually needed. Sometimes, the overlying skin may look red, bruised, or dimpled. In other cases, fat necrosis may not cause any symptoms and may only be found by chance during imaging studies.

Is fat necrosis serious?

Fat necrosis itself is benign, which means it is not cancer and does not spread. In many cases, it may shrink and go away on its own as the body reabsorbs the damaged fat tissue. However, because fat necrosis can look and feel like cancer—especially in the breast—it often requires further evaluation with imaging, and sometimes a biopsy, to rule out more serious conditions.

How is this diagnosis made?

Doctors usually start with imaging such as ultrasound, mammogram, or CT scan to evaluate the lump. Fat necrosis has some features that suggest the diagnosis, but in many cases a biopsy is needed to confirm it. During a biopsy, a small piece of tissue is removed and examined under the microscope by a pathologist.

What does fat necrosis look like under the microscope?

When examined under the microscope, fat necrosis shows dead or damaged fat cells that have lost their normal shape. These areas are often surrounded by inflammatory cells such as macrophages, which help clean up dead tissue. Over time, scar tissue may form, and the damaged fat can be replaced by firm fibrous tissue. Sometimes the fat cells release their contents, leading to chalky deposits of calcium that can also be seen under the microscope. These changes explain why fat necrosis can feel firm or appear irregular on imaging tests.

What is the prognosis?

The outlook for fat necrosis is excellent. It is a harmless condition that often improves with time. Treatment is usually not required unless the lump is painful or bothersome. In rare cases, surgery may be performed to remove the area if symptoms are severe or if the diagnosis is uncertain.

Questions to ask your doctor

• Does this finding explain the lump or symptoms I noticed?
• Could fat necrosis come back or happen again in the same area?
• How long will it take for the lump to shrink or go away?
• Do I need any follow-up tests or imaging to monitor the area?
• If the lump changes in size or becomes painful, what should I do?