Breast Oil Cysts: Causes, Diagnosis, and Treatment

Breast oil cysts are benign (noncancerous) breast lumps. They often feel similar to the lumps common to breast cancer. They may be diagnosed on ultrasound or other breast imaging. Oil cysts in the breast commonly occur due to injury to the chest or medical procedures.

Cysts are the most commonly found type of breast mass, especially for those aged 35 to 50. Cysts are pockets filled with fluid, pus, air, or other substances. They have an outer wall or barrier that keeps the inside contents of the cyst inside the sac.

Breast oil cysts are filled with an oil-like fluid that results from the breakdown of the fat cells of the breast. They often feel soft and squishy. They typically don't require treatment.

Breast oil cysts do not become cancerous, and they do not increase the risk of developing breast cancer. However, in rare cases, they may occur in association with underlying cancer. Any mass that can be felt or is concerning on imaging tests should be evaluated by your healthcare team.

This article discusses the symptoms, causes, diagnosis, and treatment of breast oil cysts.

Symptoms

When breast oil cysts are small, they often go unnoticed. As a cyst gets larger, it may be found during a self-breast exam. Sometimes cysts are found when they are seen on a mammogram or other imaging tests.

Some breast cysts can grow larger over time. Bigger cysts can be felt on a breast exam as soft, squishy, and smooth lumps. They can be painful or painless. If they occur after surgery or trauma, there may also be bruising associated with the cyst.

Causes

Breast oil cysts may occur after breast surgery, along with other breast conditions, or can occur spontaneously. They are called oil cysts because they contain a liquid form of body fat.

How They Develop

During a lumpectomy or mastectomy, there can be damage to the fat cells of the breast. As the fat cells break down (breast fat necrosis), their structure changes. The damaged fat cells can form into hard scar tissue or an oily liquid.

When liquid fat collects in one area, a thin layer of calcium can form a wall around it. This eggshell calcification describes the appearance of oil cysts on a mammogram. Simple and complex cysts are different than oil cysts—they do not have the calcium layer. Typically, oil cysts are usually partially or totally enclosed by calcium.

Risk Factors

Oil cysts often develop after breast surgery. They can also occur after a breast biopsy or cancer removal (mastectomy). Because they may appear during cancer diagnosis and treatment, some people are alarmed to learn that they have one.

Conditions in which fat necrosis and oil cysts may occur include:

• Breast cancer surgery or reconstruction
• Trauma to the breast
• Breast reduction surgery
• Radiation therapy to the breast after a lumpectomy
• Breast biopsy or fine-needle aspiration
• Breast cyst aspiration
• Mastitis (a breast infection)
• Uncommon conditions such as polyarteritis nodosa or steatocystoma multiplex

After breast augmentation surgery, oil cysts are more common when autologous fat grafting (fat taken from another region of the body and placed in the breast) is used.

Diagnosis

If you have noticed a lump in your breast, your doctor will likely recommend further testing. Your treatment team will help determine if additional imaging is required or if a breast biopsy should be performed. Mammogram, ultrasound, and breast MRI (magnetic resonance imaging) are all potential tests your team may recommend.

Mammogram

An oil cyst often shows up on a mammogram as a well-defined mass that appears fatty, and eggshell calcifications may be present. The calcifications of an oil cyst are different than the type of breast calcifications that tend to be associated with breast cancer.

Breast Ultrasound

A breast ultrasound often gives a clearer picture of oil cysts than a mammogram. Ultrasounds use sound waves bounced off of breast tissues to create an image of masses, lumps, and cysts.

Cysts are filled with fluid, gas, or semisolid substances. This causes them to appear on ultrasound as dark, smooth-edged circular or oval areas. The cysts have a clear outline that distinguishes them from surrounding tissues.

A seroma (fluid-filled cyst) can appear identical to an oil cyst on ultrasound. However, other types of breast lumps will typically appear on ultrasound with different characteristics. This difference in appearance helps the provider to determine what structures are within the breast.

Breast MRI

At times, benign breast lumps can look very similar to cancer on imaging tests. The radiologist will compare any concerning areas to the surrounding tissue to help determine if further testing is needed.

Generally, breast MRI is used for diagnosis and staging of breast cancer, rather than as a screening tool. However, your provider may recommend it to get the very detailed internal pictures that MRI can produce. Oil cysts will show up on a breast MRI but are best diagnosed using breast ultrasound.

Differential Diagnosis

Conditions that may appear similar to a breast oil cyst include:

• Simple cysts
• Fat necrosis
  
• Galactocele (collection of milk)
• Hematomas
• Papillomas
• Breast abscess
• Seromas (also common after breast surgery)
• Lipomas

Very rarely, breast oil cysts can have a similar appearance to a tumor that is breaking down (medically called necrotizing malignancy). The cell death and inflammation may look similar to an oil cyst on some imaging.

Treatment Options

Breast oil cysts are benign—they are not cancerous. They do not cause breast cancer or increase your risk of developing breast cancer. Therefore, an oil cyst may be left alone. This is often called "watchful waiting.” Many times, these will shrink or go away on their own without treatment.

If it appears that you have developed a cyst after a procedure to treat or remove cancer (such as a lumpectomy), it will be important for your provider to determine what the lump might be. Your team will work to distinguish an oil cyst from a possible cancer recurrence.

There are several treatment options if you are diagnosed with a breast oil cyst:

• Aspiration: If your oil cyst becomes physically painful or causes you to worry, it can be drained with a small needle (aspirated).The aspirated fluid will be evaluated in a lab to make sure the lump is simply an oil cyst. 
• Surgery: If the oil cyst is large, painful, or continues to recur, your provider might recommend surgical removal of the cyst.
• Home remedies: If your oil cyst is painful, medications such as Advil (ibuprofen) may be helpful. You should also wear a comfortable bra or camisole. Using an ice pack may also reduce your discomfort.

Summary

Breast oil cysts are common benign breast conditions. They most often develop after trauma or damage to the breast. Cysts may be seen on a mammogram, breast ultrasound, or MRI. Breast oil cysts can usually be left alone. The fluid can be aspirated for removal and to confirm the diagnosis. If a cyst is large, painful, or if the diagnosis is in doubt, surgery may be done to completely remove it.

A Word From Verywell 

Breast oil cysts are benign, yet since they often show up after breast surgery, they can cause a lot of anxiety. While treatment is not usually needed, many women and men who develop breast oil cysts feel more comfortable with aspiration. With aspiration, the oil cysts usually deflate—both resolving the cyst and the anxiety that can accompany having them.