Fat necrosis can affect any area of fatty tissue. However, it often occurs in the breast. Where there was previously fatty tissue, there may now be scar tissue or a cyst, which appears as a lump.

Necrosis happens when fat cells become inflamed and die due to a lack of oxygen supply. When this happens, the oily contents of the fat cells that are no longer functioning replace the fatty tissue.

In 70% of cases, there is no clear cause. However, it can result from:

  • trauma or surgery
  • the use of blood thinning drugs
  • some infections and diseases
  • radiation therapy

Areas of necrosis or oil cysts can feel like a round, firm lump, and there may also be dimpling, bruising, or changes in color on nearby skin. This can be worrying. However, fat necrosis and oil cysts are not cancerous.

Fat necrosis can occur anywhere that fatty tissue is present. However, it commonly affects the breast. Around 2.75% of all breast lesions are due to fat necrosis.

This article will look at how fat necrosis can affect the breast, what oil cysts are, and what to do if these conditions occur.

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When a person experiences damage to breast tissue, the damaged cells die, and the body usually replaces them with scar tissue.

However, sometimes the fat cells die due to a lack of oxygen supply. When this happens, they release their oily contents as a liquid. Around the liquid fat, a calcified rim can form, resulting in an oil cyst.

The most common causes of fat necrosis are:

It occurs on average at the age of 50 years.

What is breast reconstruction surgery?

Breast reconstruction surgery is an option for people who undergo a full or partial removal of the breast during treatment for breast cancer. A surgeon can reconstruct the breast immediately after the original procedure or even years later.

Not everyone who has a lumpectomy or mastectomy will opt for reconstruction, and the choice will be individual. Depending on the extent of surgery, a reconstructed breast may not have the same sensations as the breast before surgery.

What is breast augmentation surgery?

Breast augmentation surgery aims to increase the size of one or both breasts. A surgeon may do this using an implant or transplanting fat from another part of the body.

A person may opt for augmentation surgery:

  • following surgery to remove cancer from the breast
  • because the size of their breasts is affecting their mental or physical wellbeing
  • as part of gender transition

With any of these surgeries, there is a risk of fat necrosis.

What is breast reduction surgery?

Breast reduction aims to reduce the overall volume of the breasts.

It can benefit those who:

  • have large or heavy breasts that are affecting their health or quality of life
  • have asymmetrical breasts due to previous surgery
  • are undergoing gender transition

People with large breasts can experience physical health problems, such as pain and skin infections. Large breasts can interfere with their ability to exercise and carry out other daily functions. They can also affect a person’s mental health, for example, due to self-consciousness about their breast size.

Breast reduction surgery can lead to fat necrosis. In addition, there may be a risk of infection and other complications, especially for people with a body mass index (BMI) over 30 and those who smoke.

Fat necrosis in the breast may occur without symptoms. If symptoms appear, a person will usually notice lumps under the skin. These are often, but not always, around the areola, the part that surrounds the nipple.

Fat necrosis and oil cysts are not usually painful. However, they can be.

If a lump or oil cyst develops, it may appear as:

  • a single smooth lump
  • several smooth, round nodules
  • fixed, irregular masses

There may also be:

  • changes in skin color
  • bruising
  • dimpling
  • thickening or retraction of the skin
  • nipple retraction
  • swelling in the lymph nodes

Fat necrosis occurs in stages:

  1. The fat cells die and release their contents.
  2. The released oil forms a sac of greasy liquid, called an oil cyst.
  3. In time, calcium builds up around the outside, forming a hard lump visible on a mammogram.
  4. The body repairs the damaged tissue, and thicker scar tissue forms.

The symptoms of fat necrosis do not usually show up immediately after a trauma or surgery. They can take weeks or months to appear.

Fat necrosis in the abdomen, buttocks, arms, and legs

Fat necrosis usually affects the breasts. However, it can occur anywhere there is fat tissue.

  • In the abdomen, it can sometimes result in acute or sudden pain. In this case, it can affect the internal organs and visceral areas.
  • It can affect the buttocks after surgery to increase buttock size by transferring fat from elsewhere in the body.
  • Following a trauma, it can occur on the shins, thighs, and arms.

According to the American Cancer Society, fat necrosis and oil cysts are not cancerous and do not increase the risk of breast cancer.

However, the symptoms can resemble those of breast cancer. For this reason, a doctor may recommend testing and follow-up screening for breast cancer if a person seeks advice for a breast lump, even if it is most likely due to fat necrosis.

Anyone who notices a new breast lump should seek medical attention, as it is important to rule out the possibility of breast cancer.

Learn more about different types of breast lumps.

If anyone seeks advice for a lump in the breast, a doctor will most likely:

  • ask about their health status and medical history
  • ask about their family medical history
  • ask about any recent events, such as surgery, radiation therapy, or an injury to the breast
  • carry out a physical examination
  • suggest an imaging scan to help identify if the lump is due to fat necrosis or another cause.

Examples of the imaging tools a doctor may use include:

Mammogram

X-rays, such as mammography, can help identify areas of fat necrosis or an oil cyst.

If fat necrosis is present, a mammogram may show:

  • no change if it is in the early stage
  • a lump with a smooth border that appears to give off light
  • a collection of microcalcifications

How changes appear can depend on the stage of necrosis. The image may also share features with scarring or a cancerous tumor. If the result does not clearly show fat necrosis, the doctor may recommend other tests.

Breast ultrasound

Ultrasound technology uses sound waves to re-create an image of the underlying tissues. Ultrasound can help identify cysts that are not fully solid and may have oily contents.

Fat necrosis can show up in various ways on ultrasound, including:

  • no change
  • changes in tissue just under the skin
  • a cyst or other mass
  • a solid mass
  • whether there is blood supply to a lesion, which could indicate cancer

In some cases, ultrasound can show clearly if a person has an oil cyst due to fat necrosis. However, the results may not be specific enough to identify fat necrosis, in which case a doctor may recommend other tests.

MRI

MRI uses magnetic waves to produce images. It can help identify fat necrosis in the later stages and distinguish it from a cancerous tumor. However, it may not be able to show if early-stage changes are due to an oil cyst or fat necrosis. The result can vary depending on the level of inflammation.

On a fat saturation image — a technique that focuses specifically on fatty tissue — an oil cyst most commonly shows up as a round or oval mass if fat necrosis is present.

Sometimes, a doctor will recommend using intravenous contrast to make areas of fat necrosis show up more easily, although this is not always helpful.

In some instances, more tests may be necessary to find out if changes are cancerous or not.

Which imaging type is best?

Breast fat necrosis may appear differently on the various imaging types. The choice of imaging technology may depend on the stage of fat necrosis.

Some research suggests that:

  • a mammogram most clearly shows calcifications
  • ultrasound more effectively shows oil cysts
  • MRI gives the clearest image of fat necrosis

If the results are unclear, a doctor may recommend a biopsy, which involves taking tissue samples from the affected area and testing the cells for the presence of cancer. They may also recommend a CT scan if there is a possibility that cancer may be present.

Learn more about a breast biopsy.

An area of breast fat necrosis may remain unchanged or go away on its own. Often, no treatment is necessary.

However, if an area of fat necrosis gets bigger or is otherwise troublesome, a doctor may recommend:

Needle aspiration

To treat a fluid-filled mass, the doctor can insert a thin, hollow needle into the cyst to drain the contents. This will usually cause the lump to disappear.

If a biopsy is necessary, the doctor may aspirate the contents at the same time.

Surgery

In the case of a solid mass or more extensive changes, a doctor may recommend surgery.

Options include:

  • removing the lump surgically, possibly with a fat graft from elsewhere in the body
  • debridement, which involves removing the affected tissue
  • further reconstruction, possibly with a different technique, such as an implant
  • surgery on the other breast to improve symmetry

The outlook for breast fat necrosis and oil cysts is good. They are not cancerous and do not increase the risk of cancer. They often go away without treatment or remain unchanged. However, some can increase in size.

Although fat necrosis is benign, a doctor may recommend regular screening to ensure they have correctly identified a lump as fat necrosis, because it can be difficult to distinguish oil cysts from other types of lumps.

Fat necrosis happens when inflammation affects the supply of blood and oxygen to body fat, causing fat cells to die. It can happen after an injury, surgery, or radiation treatment.

Fat necrosis commonly affects the breasts, where it can lead to lumps, skin changes, and oil cysts.

These changes are not cancerous. However, the symptoms can resemble those of cancer. For this reason, a doctor may recommend tests to rule out cancer.

The symptoms of fat necrosis can change over time. However, they often disappear without treatment. If they persist or are troublesome, a doctor may use fine needle aspiration to remove the fluid.

In some cases, they may suggest removing a lump or further reconstructive surgery.