Endometriosis is a condition in which cells that are similar to the ones that line your uterus start growing in other areas of your body. These growths are more commonly known as endometrial implants or lesions.
Endometriosis is commonly found on the lining of the abdominal cavity, called the peritoneum. It can also grow on almost any organ but is usually found on the pelvic organs. Endometriosis will generally remain contained within your pelvis or abdominal cavity. Although rare, it can grow in other parts of your body, such as your heart, brain, and lungs.
Implants or lesions that grow in the pelvic cavity can react to hormones. These are the same hormones that regulate your menstrual cycle. Lesions can also cause inflammation and scarring, which leads to pain and other symptoms. In some cases, scarring can cause your organs and pelvic tissue to stick together.