The Stages of Endometriosis

Staging endometriosis can be a useful tool for healthcare providers and patients, but it has drawbacks.

A woman meets with her gynecologist.

The uterus, also called the womb, is a pear-shaped female reproductive organ located between the bladder and rectum. The uterus is hollow, muscular, and lined with tissue. This lining inside the uterus is where a fertilized egg implants when a woman becomes pregnant. This lining is also what is shed during menstruation, when a woman is not pregnant.

Endometriosis is a disorder that affects women of reproductive age. It involves tissue that is similar to the tissue that lines the womb. When a woman has endometriosis, this tissue grows outside the womb. Most often, endometrial implants occur on sites in the pelvic area—the outer surface of the uterus, the ovaries, and the fallopian tubes, as well as the bowel. Endometrial implants can also occur in more distant sites, though this is rare.

Symptoms include painful periods, heavy menstrual bleeding, and pain during sex. Other symptoms can include nausea, diarrhea, constipation, bloating, fatigue, lower abdominal pain, and lower back pain. Endometriosis has also been associated with fertility problems.

Stages of endometriosis

If you are researching endometriosis you will likely come across mention of the phrase “stages of endometriosis.” This comes from a classification system developed by the American Society of Reproductive Medicine (ASRM). This system classifies endometriosis into stages based on the amount of endometrial tissue that is present, whether implants are superficial or deep, the density of the endometrial adhesions, and the pelvic organs and structures that are affected.

Adhesions refer to intrauterine adhesions (IUA), which are bands of scar tissue that can form between structures inside the pelvis that are not normally connected and should glide against one another. For example, an IUA can bind an ovary to the pelvic wall, which can result in significant pain and also damage to the ovaries. Adhesions that are described as “filmy” are thin and transparent. At more advanced stages of endometriosis adhesions can be thicker and denser.

This classification system has a few drawbacks (which we will get to in a moment) but for now, the stages are:

  • Stage I (minimal): At this stage, there are only a few superficial endometrial implants.
  • Stage II (mild): At this stage, there are a greater number of implants, and the implants are deeper.
  • Stage III (moderate): At this stage, there are many deep endometrial implants, cysts on one or both ovaries, and filmy adhesions.
  • Stage IV (severe): At this stage, there are many deep endometrial implants, large cysts on one or both ovaries, and adhesions are thicker and denser.

Note that these descriptions of the stages are not absolute, and there is overlap between the stages (for example, endometriosis can be staged at I or II even with filmy adhesions present). Categorization is based on findings during diagnostic surgery, which in most cases will be laparoscopic surgery, which uses a small incision and a long flexible camera.

Staging can be a useful tool for healthcare providers, especially when making treatment decisions and evaluating if a treatment has been effective. However, staging has its drawbacks.

Drawbacks of staging

Staging does not account for the level of pain being caused by endometriosis, when the level of pain does not always correlate with the stage of the disease. For example, a woman with stage I endometriosis may experience severe pain, and a woman with stage III endometriosis may only have minimal pain.

Staging also does not take into account the impact endometriosis has on fertility, which again, does not always correlate with the stage of the disease. For this reason, staging is sometimes complemented by something called the endometriosis fertility index (EFI), which takes into account other fertility factors such as age and medical history, including prior history of pregnancy and infertility.

This staging system also does not take into account deeply infiltrating endometriosis (DIE), a subtype of endometriosis that has implanted deeper than 5mm into the tissues that line the pelvic cavity, though this is addressed in another complementary classification system called the Enzian proposal.

Individualized approach

While staging can be useful, it is only one way to look at a diagnosis. Endometriosis is different for everyone, and requires an individualized approach to treatment. If you have endometriosis or symptoms of endometriosis, it is important to work with a healthcare provider who understands the disorder and can guide you through treatment.

Article sources open article sources

MedicineNet. "Medical Definition Of Uterus."
UpToDate. "Patient education: Endometriosis (Beyond the Basics)."
Merck Manual Consumer Version. "Endometriosis."
Luciana P. Chamie, MD, PhD, Duarte Miguel Ferreira Rodrigues Ribeiro, MD, Dario A. Tiferes, MD, PhD, Augusto Cesar de Macedo Neto, MD, and Paulo C. Serafini, MD, PhD. "Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings." RadioGraphics, 2018. Vol. 38, No. 1.
Mayo Clinic. "Endometriosis."
Cynthia Farquhar. "Endometriosis." The BMJ, Feb 2007.
John Hopkins Medicine. "Endometriosis."
Edgardo Rolla. "Endometriosis: advances and controversies in classification, pathogenesis, diagnosis, and treatment." F1000 Research, April 2019. Vol. 8. "Adhesions."
Rosanne M. Kho, MD and  Mauricio S. Abrao, MD. "Deep infiltrating endometriosis: Evaluation and management." OBG Management, May 2018. Vol. 30, No. 5.

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