Adenomyosis versus Endometriosis: What's The Difference?

Last updated: July 2021

The tissue that lines the uterus is known as endometrium. The endometrium changes with your menstrual cycle: During specific phases of the cycle, the endometrium thickens to prepare the uterus to support the implantation of a fertilized egg and the development of a fetus.1 If there is no fertilized egg, during your period, the tissue breaks down and you bleed. This is part of a normal menstrual cycle.

What is endometriosis?

Endometriosis is a chronic condition in which endometrial-like tissue grows outside of the uterus. When you have endometriosis, the tissue that exists outside the uterus becomes inflamed, but there is no way for it to exit the body. Endometriosis can lead to pain and excessive bleeding during periods and it can sometimes lead to infertility.

Endometriosis affects about 10% of reproductive-aged women, 70% of women who have pelvic pain during their period, and 30-40% of patients with infertility.2

Typical symptoms of endometriosis include:1

Adenomyosis versus endometriosis

Adenomyosis is similar to endometriosis in some ways, but adenomyosis has different causes, and behaves differently. As with endometriosis, adenomyosis occurs when endometrial tissue grows abnormally. With endometriosis, endometrial-like tissue grows outside of the uterus (typically on the fallopian tubes, ovaries, and/or outer surface of the uterus); whereas with adenomyosis, endometrial tissue grows abnormally into the muscle wall of the uterus (called the myometrium).

Similar to endometriosis, women with adenomyosis often experience pain (because the abnormal tissue swells and bleeds, but cannot exit the body).4 By growing into the uterine wall, adenomyosis disrupts the normal functioning of the uterus muscle and can also cause heavy bleeding and possibly, infertility.2

Studies show that many women with endometriosis also have adenomyosis. In one study of patients with endometriosis, 78% of women also had adenomyosis.3

Typical symptoms of adenomyosis include:2

  • Heavy or prolonged bleeding during your period
  • Severe cramping or sharp pains during your period
  • Chronic pelvic pain

How is adenomyosis diagnosed?

Previously, adenomyosis could only be diagnosed by examining a uterus after a hysterectomy. More recently, however, researchers have found ways to recognize the disease based on medical imaging, such as by using a trans-vaginal ultrasound, or an MRI. Often during these tests, doctors can see thickening in the tissue, as well as other signals that point to adenomyosis.5 Other signs and symptoms include a tender, enlarged, uterus, which a doctor can feel during a pelvic exam.

Risk factors and research

In the first major study comparing patients with a surgical diagnosis of endometriosis vs. adenomyosis, results showed a variety of differences. For example, in the study population, women with endometriosis were younger than those with adenomyosis, and were more likely to have a mother or sister with endometriosis.

Similarly, the following factors were associated with adenomyosis. Women with adenomyosis...2

  • Had higher parity (delivered more babies).
  • Had early menarche (started their periods earlier).
  • Had shorter menstrual cycles (less than 24 days).
  • Were more likely to be obese.

Does adenomyosis cause infertility?

While adenomyosis may be associated with infertility, research to date has provided conflicting evidence. In one study of women with endometriosis, 90% had adenomyosis, and the researchers suggested that foreign tissue in the uterus might disrupt the normal muscle movements that help sperm travel toward the fallopian tubes to fertilize an egg.3 In other studies, however, adenomyosis was not correlated with infertility.

Due to the high prevalence of co-occurring endometriosis and adenomyosis, many researchers have suggested that it is difficult to attribute infertility to one condition versus the other.6

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