Fat necrosis is a condition that occurs when a person experiences an injury to an area of fatty tissue. This can result in the fat being replaced with the oily contents of fat cells.

The term “necrosis” means the cells have died. Potential causes of fat necrosis include blunt trauma, surgeries, or radiation to a particular area of the body.

Areas of fat necrosis can feel like small, hard tumors but they are not cancerous tissue.

The appearance of fat necrosis can cause a person significant concern until a doctor examines the lesion.

While fat necrosis can occur anywhere on the body where there is fatty tissue, the most common location for it to appear is the breast.

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One of the most common causes of fat necrosis is injury or damage to fatty tissue. In particular, this can occur in car accidents, when the seatbelt restrains the person wearing it.

Typically, when a person experiences damage to the breast tissue, the damaged cells die, and the body replaces them with scar tissue. However, sometimes the fat cells die, and they release their oily contents. As a result, a lump can form. Doctors call this lump an oil cyst.

The most common causes of fat necrosis are:

  • physical trauma, often to the breast area in a car accident when a person is restrained by a seatbelt
  • history of radiation to a particular area of tissue
  • history of surgery to a particular area
  • history of removal of breast implants

Women who are obese and have very large breasts are more likely to have fat necrosis of the breast.

Sometimes the lumps may be painful although this is not always the case. Other characteristics of an area or areas of fat necrosis include:

  • lumps with a red area around them
  • lumps that appear bruised around them
  • skin around the lump that appears thicker than the unaffected area
  • nipple retraction due to fat necrosis in the breast

Areas of fat necrosis may appear red or bruised because the destruction of the fat cells causes the release of inflammatory compounds. According to the journal Radiology Research and Practice, the average time it takes for a fat necrosis lump to present after an injury is about 68.5 weeks.

While doctors usually associate fat necrosis with the breasts, the masses can occur anywhere a person has fat tissue. Examples could include the abdomen, buttocks and thighs.

According to the American Cancer Society, areas of fat necrosis in the breast do not increase a woman’s risk of breast cancer. However, fat necrosis areas in the breast can closely resemble breast cancer tumors, and they can cause changes to the breast that are similar to cancer-related inflammation.

As a result, the appearance of fat necrosis can be very frightening for a woman who is unfamiliar with fat necrosis.

According to the same 2015 article in the journal Radiology Research and Practice, an estimated 2.75 percent of all breast lesions are due to fat necrosis. The average age a woman might experience fat necrosis is at 50 years.

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Fat necrosis may be diagnosed using an MRI machine.

If a person feels a lump that is suspected of being fat necrosis, a doctor will usually recommend an imaging scan. This will identify if the lump could be cancerous or due to another underlying cause.

A doctor will probably take a health history also, and perform a physical examination. If someone has a history of trauma or radiation to the body, it could help a doctor identify that the area of concern may be fat necrosis.

Examples of the imaging tools a doctor may use include:

  • X-ray: X-rays, such as mammography, can be used to visualize areas of fat necrosis. Sometimes, oil content can have a distinctive appearance that makes fat necrosis easy for a doctor to identify. However, some people may have a degree of scarring or other unusual appearance, and a doctor may recommend other imaging studies.
  • Ultrasound: Ultrasound technology uses sound waves to re-create an image of the underlying tissues. Ultrasound can be especially helpful in identifying cysts that are not fully solid and may have oily contents.
  • MRI: MRI uses a powerful magnet to generate magnetic waves that recreate images inside the body. Sometimes, a doctor will recommend using intravenous contrast to make areas of fat necrosis show up more easily.

Fat necrosis can have a variety of different appearances when imaging is done. In some instances, a doctor may not be able to definitively say an area or areas of fat necrosis are not cancerous.

When this is the case, a doctor may recommend a biopsy, which involves taking tissue samples from the affected area and testing the cells for the presence of cancer.

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Surgery may be required to remove larger lumps of fat necrosis, although in many cases invasive procedures are uneccessary.

An area of fat necrosis can go away without any treatment. Massaging the area firmly can help resolve some of the firmness.

However, if an area or areas of fat necrosis are particularly bothersome to a person, a doctor can perform several removal options:

  • Needle aspiration: This procedure involves inserting a thin, hollow needle into the area of fat necrosis to drain the oily contents. This will usually cause the lump to disappear.
  • Surgical removal: If the lump is larger or in a difficult place to access with a needle aspiration procedure, a doctor may recommend removing the lump surgically.

Fat necrosis is a benign yet sometimes bothersome occurrence in the breasts and, less commonly, in other areas of the body.

Because fat necrosis can closely resemble the symptoms of breast cancer, it can be cause for concern.

Although fat necrosis areas can change over time, they also can go away with time, as well. If a person is very bothered by fat necrosis lumps, they should talk to their doctor about options for surgical removal.