Breast Oil Cysts Causes, Diagnosis, and Treatment

self-breast exam
What are breast oil cysts?. Ian Hootan, Getty Images

What are breast oil cysts, how and why do they occur, and can they be dangerous? After breast surgery or an injury, many women note the appearance of small flexible lumps that feel squishy and smooth, similar to the feeling of a small water balloon. what causes the to occur, and how is it treated?

Breast oil cysts are benign breast lumps that usually don't require treatment. Similar to simple breast cysts, oil cysts are fluid-filled sacs that may feel smooth and squishy. If you've recently had breast surgery, the last thing you want to find is a new lump in your breast. Don't panic -- but get any breast lumps checked out no matter what they feel like. Let's take a look at oil cysts, and how you can deal with them.

How an Oil Cyst Forms 

Breast oil cysts may occur after breast surgery, along with other breast conditions, or even occur spontaneously.

They are called oil cysts because they contain a liquid form of body fat.

If you have a lumpectomy or mastectomy, fat tissue may die as your body is healing and attempting to form a scar. Breast fat necrosis (the breakdown of fatty tissue in the breast) can form into hard scar tissue, or it can "melt."

When "melted fat" collects in one area, your body may cause a thin layer of calcium to form around it. This eggshell calcification (the appearance of oil cysts on a mammogram) gives your doctor a clear idea of your diagnosis. Simple and complex cysts do not have the calcium layer, but oil cysts are usually enclosed partially or totally by calcium.

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

  • Breast cancer surgery or reconstruction
  • Trauma to the breast
  • Breast augmentation or breast reduction
  • Radiation therapy to the breast after a lumpectomy
  • Breast biopsy or cyst aspiration
  • Duct ectasia
  • Mastitis (a breast infection)
  • Conditions in which bleeding occurs easily, such as during Coumadin (warfarin) therapy, with heparin, or with bleeding disorders
  • In association with uncommon conditions such as polyarteritis nodosa


An oil cyst can show up on a mammogram, but an ultrasound will give you a clearer picture.

A breast ultrasound will use sound waves bouncing off breast tissues to create an image of masses, lumps, and cysts. Because cysts are filled with fluid, gas, or semisolid substances, they appear on ultrasound as dark, smooth-edged circular or oval areas. These cysts have a clear outline that distinguishes them from surrounding tissues. Other types of breast lumps will appear on ultrasound with different characteristics. Oil cysts will also show up on a breast MRI.

Treatment Options

Oil cysts are benign—they are not cancerous and they don't cause breast cancer. If you develop a cyst after a procedure such as a lumpectomy, however, it will be important to distinguish and oil cyst from a possible recurrence.

If you are diagnosed with an oil cyst, you have some options for dealing with it. An oil cyst may be left alone, as many of these will shrink on its own. But if case your oil cyst becomes physically painful or causes you worry or distress, it can be aspirated. Your doctor can use a very fine needle to suction the fluid out of the cyst, which will deflate it. Aspirated fluid from an oil cyst will be evaluated to see if it looks bloody. If the cyst is large or has a coarse calcium layer, your doctor might recommend surgical removal.

Bottom Line 

Breast oil cysts are benign, yet since they often show up after breast surgery—whether the surgery was just a scare or instead, a confirmation of breast cancer—they can cause a lot of anxiety. Mammography is the most specific test for breast oil cysts, but breast ultrasound or breast MRI may be helpful in making the diagnosis at times. Treatment options include "watchful waiting" or aspirating the cyst. While treatment is not usually needed, many women (and men, since men can experience this as well) feel more comfortable with aspiration. With cyst aspiration, the oil cysts usually deflate, both resolving the cyst and the anxiety that can accompany having these cysts.

Also Known As: oil cyst, mammary oil cyst, oil cyst of breast

Similar ​To: lipoma (fatty lump under the skin), hematomaseroma

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