Fluid-filled sacs produced inside the breast are called​ breast cysts​. They are usually benign, meaning noncancerous. You may feel one or more cysts in either one of the breasts, and it is possible to have cysts in both breasts at the same time. The cysts are mostly oval or round lumps with defined edges. They are usually soft but it is possible for them to be firm. The size of a breast cyst can be anywhere from as small as a pea to as large as a water-filled balloon. Some can be easily felt with a physical examination, while others require an imaging test to reach a diagnosis.

Breast cyst can be observed at any age, but they most commonly afflict women over the age of 40. In over 50% of the cases, women will develop multiple cysts at one time. Breast cysts can cause tenderness, pain, and the lumpiness in the breast. Symptoms vary and may get better or worse at different stages of the menstrual cycle.

Breast cysts can be broken down into a few different categories, which may help determine the nature and treatment method of the cyst.

Simple Cysts​.These are fluid-filled sacs that are covered by thin, smooth, and evenly shaped walls. Ultrasound tests can easily detect them. These cysts are benign.

Complex Cysts​.These cysts occur when debris or a solid object exists inside the cystic fluid. These cysts are surrounded by thick walls, and have scalloped borders. The ultrasound test can detect the solid mass inside of the cysts, thus making them easily diagnosable. These cysts typically require drainage using a fine needle. The resulting fluid is tested and evaluated in order to determine whether the cyst is malignant, or cancerous.

Complicated Cysts​.These fall between simple and complex cysts. Though they resemble simple cysts, an ultrasound test can still detect solid masses inside of them. Due to the lack of thick walls and more prominent solid components characteristic of complex cysts, a complicated cyst falls somewhere between simple and complex.

You should always seek medical advice when you notice physical abnormalities in your breasts. Proper testing may be required to ensure that the lumps or cysts are benign. Talk to your doctor if you experience:

• A lump that you can feel inside of your breast – round or oval.

• Discharge from one or both the nipples. It can be clear, yellow or dark brown.

• Pain on or near your breasts.

• Pain inside the lump you’ve felt.

• Growth of the breast lump.

• Breast tenderness resembling premenstrual syndrome (PMS).