What are the Forms of Endometriosis?

Reviewed by: HU Medical Review Board | Last reviewed: June 2018

There are a variety of ways endometriosis can present for those who have the condition. Each case can vary in severity, classification, symptoms, and defining characteristics. Some of the most recognized forms of endometriosis are superficial peritoneal endometriosis, ovarian endometriomas, endometriotic nodules, and deep infiltrating endometriosis, however, this is not an exhaustive list of all of the ways endometriosis can present. These classifications are most associated with where endometriosis is located within the body, as well as its severity from a pathological standpoint (what the tissue looks like and how deep it infiltrates). One thing that is important to note, however, is that the type of endometriosis present does not always correlate to the symptoms an individual experiences. For example, someone with superficial peritoneal endometriosis may experience more pain or physical symptoms than someone else with deep infiltrating endometriosis.1,2

Superficial peritoneal endometriosis

In superficial peritoneal endometriosis, thin, often surface-level lesions are found on the peritoneum or the surface of the pelvic organs. The peritoneum is the membrane that surrounds the pelvic cavity and the individual organs within it. This sac-like covering nourishes and protects the organs in the pelvis. Endometriosis lesions of this type are often blue or blue-black in color. Some experts categorize endometriosis into stages based on severity. In the staging classification system, this type of endometriosis would be considered mild, and would generally be classified as stage I or stage II. Endometriomas are typically not present in this type of endometriosis.2,3

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Ovarian endometriomas

Ovarian endometriomas, also called endometriosis cysts or chocolate cysts, are filled with old blood, giving them a dark brown-colored inside. This is why they are called chocolate cysts. The walls of the cyst have areas of endometriosis, and in some cases, these cysts can grow and pose a threat to a woman's fertility. They can also rupture and cause extreme pain. If a woman has endometriomas, her endometriosis is considered to be more severe, and may be classified as stage III or IV.

Endometriomas are associated with an increased risk of developing ovarian cancer. Cysts that are growing or that could become cancerous are often surgically removed. Although endometriomas may affect fertility, many women who possess these cysts can still become pregnant, especially when utilizing assisted reproductive technologies like in vitro fertilization. Endometriomas can also attach via adhesions to other organs or structures around the ovaries. They are often found and diagnosed during an ultrasound exam.2-6

Deep infiltrating endometriosis

Deep infiltrating endometriosis is characterized by endometriosis lesions that have invaded the peritoneum five or more millimeters beyond the surface, into the retroperitoneal space that leads further into the abdomen. If an individual has deep infiltrating endometriosis, their endometriosis is thought to be more severe, and is classified as stage III or IV. Deep infiltrating endometriosis lesions are often found in the ligaments that support the uterus, the bladder, or the rectovaginal space near the rectum. Because of the location of these deep infiltrating lesions, individuals who have them may experience deep pain during sex, chronic pelvic pain, and various bowel issues, including straining or pain when having a bowel movement, as well as diarrhea.2,3,7

Endometriotic nodules

Endometriotic nodules are often considered the most severe type of deep infiltrating endometriosis, however, their exact classification is currently up for debate. They are hard masses composed of various tissue types (including endometrial, fat, and fibrous muscular tissue) that can be found between the rectum and vagina, among other nearby places. Rectovaginal endometriotic nodules are considered to be the most severe, and often look like superficial peritoneal lesions during laparoscopy (minimally-invasive investigational surgery), which can make them very difficult to diagnose. These nodules can cause chronic pelvic pain, deep pain during sex, and bowel issues. These issues can increase in severity as a nodule grows. Surgical removal of these nodules is considered the most effective treatment option for symptom relief.7,8