What Is Endometriosis?
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Medically reviewed by Renita White, MD
Endometriosis is a chronic disease in which inflammatory tissue similar to the lining of the uterus grows outside the uterus. The presence of endometriosis lesions can lead to severe pain, infertility, debilitating bowel and bladder symptoms, and more. The physical and mental symptoms of endometriosis can significantly impact your quality of life.
One in 10 people born with a uterus has endometriosis, yet it is known for a long diagnostic delay, frequent misdiagnosis, and many myths and misinformation surrounding it.
In this article, learn more about endometriosis.
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Where Does Endometriosis Occur?
By definition, endometriosis occurs anywhere in the body that is outside the uterus.
Body locations where endometriosis may occur include:
Ovaries
Fallopian tubes
Uterus
Peritoneum (inner lining of the abdomen)
Uterosacral ligaments (the connective tissue that supports the uterus)
Pouch of Douglas (area between the uterus and rectum)
Appendix
Rectovaginal space (a structure between the vagina and the rectum)
Diaphragm (a muscle that helps you inhale and exhale)
Ureters (a tube that transports urine from the kidneys to the bladder)
Kidneys
Liver
Lungs
Experts once believed that endometriosis only occurred on and near reproductive organs. Though this theory has been disproved, the myth persists and can inhibit proper diagnosis.
Endometriosis has been found in every organ, including the heart, brain, lungs, liver, and eyes. For many years, the spleen was the only organ where endometriosis had not been observed, but in 2022, researchers discovered the first case of endometriosis of the spleen.
Bowel endometriosis may occur in up to 12% of cases, most commonly in the rectum and sigmoid colon (parts of the large intestine).
Urinary tract endometriosis occurs in approximately 1% of cases and is more common in the bladder than the ureters.
Endometriosis within the pelvic cavity is more common than extra-pelvic endometriosis (endometriosis outside the pelvis).
What Causes Endometriosis?
The cause of endometriosis is currently unknown, but there are two primary theories: metaplasia and retrograde menstruation.
Metaplasia
Metaplasia is when a mature cell turns into another type of cell. Theories based on metaplasia are the current leader among endometriosis experts.
One such theory, which David Redwine, MD, advanced, suggests that endometriosis is caused by abnormalities in the development of the Müllerian duct (a structure that forms the female reproductive anatomy) in embryos.
The coelomic theory of endometriosis suggests that specialized cells in the body's inner cavity turn into endometrial lesions.
Both theories could explain why endometriosis has been found in fetuses, people assigned male at birth, prepubescent girls, and outside the pelvis.
Retrograde Menstruation
This theory of endometriosis was proposed in 1927 by gynecologist John Sampson. According to his theory, endometriosis is caused by retrograde menstruation, the backflow of menstrual blood and tissue into the pelvic cavity, with eventual tissue implantation.
Most endometriosis specialists have moved away from this theory in recent decades due to various issues, including:
Most menstruating people have retrograde menstruation, yet only 10% have endometriosis.
Endometriosis lesions also have characteristics that are different from those of the endometrium (lining of the uterus).
This theory does not explain endometriosis lesions that occur outside the pelvis or those that have been found in non-menstruating individuals such as children, fetuses, and men.
Is Endometriosis Genetic?
Most scientists agree that genetics do contribute to endometriosis. You are at greater risk of endometriosis if you have a first-degree relative (e.g., mother, sister, daughter) with endometriosis. Family history increases the risk for endometriosis and the severity of symptoms and is linked to earlier symptom onset.
According to the largest-ever study on the genetics of endometriosis, published in Nature in 2023, there is a genetic link between endometriosis and 11 other inflammatory pain conditions, including:
Additional Theories
Other theories include genetics and epigenetics, immune system dysfunction, involvement of hormones, oxidative stress, stem cells, direct transplantation, and more.
Researchers and medical professionals don't unanimously agree on one theory. Some believe that there is more than one cause of endometriosis, which could explain the different presentations and subtypes of the disease.
Related: Causes and Risk Factors of Endometriosis
Endometriosis Symptoms
Endometriosis can feel different to each person. Pain is the most common endometriosis symptom. Over 60% of people with endometriosis have chronic pelvic pain.
Symptoms of endometriosis include:
Pelvic pain (cyclical or non-cyclical)
Painful sex
Painful bowel movements
Painful urination
Infertility
Fatigue
Depression or anxiety
Constipation or diarrhea
Nausea
Severe bloating (also called endo belly)
Stages of Endometriosis
There are four endometriosis stages based on the extent and location of endometriosis lesions and how they affect fertility. The endometriosis stage is not related to symptoms. For example, someone with stage 1 endometriosis can have severe symptoms, whereas someone with stage 4 can have no symptoms.
When to See a Healthcare Provider
If you experience any endometriosis symptoms, contact a trusted healthcare provider. Discuss your symptoms and note when they occur or show signs of any possible triggers. Also, mention if you have any family history of endometriosis or unexplained infertility.
Patterns in Endometriosis Diagnosis Delays
People with endometriosis often experience diagnosis delays. Current estimates indicate it can take seven to nine years from symptom onset to reach a correct diagnosis.
Various factors can contribute to these delays, including the following:
Healthcare provider attitudes normalizing female pain
Lack of public awareness of the condition
Controlled symptoms from birth control and other hormonal treatments
It is essential that these diagnostic delays be addressed because delays can contribute to the progression of the disease, infertility, deteriorating physical and mental health, financial strain from incorrect treatments or diagnostic methods, and an overall decline in quality of life.
Whom Should You See if You Suspect You Have Endometriosis?
If you suspect that you have endometriosis, see a surgeon specializing in the condition. It would be best if you aimed to see someone who spends most of their time focusing on endometriosis patients.
As in many fields of medicine, there are subspecialists in obstetrics and gynecology (OB-GYN). Though general OB-GYNs are able to treat endometriosis medically and surgically, there are some gynecologists who have chosen to subspecialize in endometriosis and chronic pelvic pain care. Patients should consider seeking care from subspecialists.
Before committing to an endometriosis specialist, ask them questions about how much of their practice is devoted to endometriosis patients (ideally, most or all of it), how frequently they perform endometriosis excision surgery (ideally, multiple surgeries per week), and what their approach is to endometriosis management.
How to Find an Endometriosis Specialist
One way to find endometriosis specialists is through iCareBetter, a directory of video-vetted endometriosis surgeons approved by other top endometriosis specialists worldwide.
Diagnostic Testing vs. Exploratory Laparoscopy for Endometriosis
The only way to officially diagnose endometriosis is through histopathology (looking at the tissue under a microscope) after surgery. During an exploratory laparoscopy (a surgical procedure), a sample of suspected endometriosis is excised (cut out). This tissue sample is then sent to a pathologist (a doctor specializing in finding disease causes), who looks at it under a microscope to confirm a diagnosis.
However, a healthcare provider may recommend one or more diagnostic tests before surgery to rule out other possible diagnoses or help with surgical planning. Additional tests may include:
Blood tests
Colonoscopy
Keep in mind that none of those tests can diagnose endometriosis. Negative results (no signs of endometriosis found) also do not rule out endometriosis.
Because extensive testing can be expensive and time-consuming and does not preclude future surgery, some healthcare providers may recommend surgery without other diagnostic tests.
Related: How to Get an Endometriosis Diagnosis
Endometriosis Treatment
The best available treatment for endometriosis is excision surgery, which is considered the gold standard. During this surgery, endometriosis lesions are cut out and removed. Excision surgery is complex and should be performed by endometriosis specialists.
Depending on your treatment goals, a healthcare provider may try approaches to manage your symptoms and improve your quality of life without surgery. Those treatment approaches include the following:
Pain medications
Birth control
Gonadotropin-releasing hormone (GnRH) agonists
GnRH antagonists
Unlike surgery, these medications help manage your symptoms without affecting the endometriosis lesions. Some medications, particularly the GnRH agonists, have severe and long-lasting side effects and can only be taken for limited periods.
Ablation vs. Excision Surgery for Endometriosis
There are generally two methods of endometriosis surgery: excision or ablation. In excision surgery, the lesions are "excised" or cut out of the body, removing them by the roots. In ablation surgery, the surface of lesions is "ablated" or burned, leaving deeper tissue behind and preventing examination by a pathologist. Endometriosis specialists prefer excision but may use ablation when excision is not possible.
Is Endometriosis Curable?
No, endometriosis is not curable. Some people with endometriosis have experienced lesion recurrence even after excision surgery.
The goals of endometriosis treatment vary from person to person and may include the following:
Easing symptoms
Improving fertility
Preventing disease progression and complications
Complementary and Alternative Treatments
Many people seek out alternative treatments for endometriosis, which may help with symptoms while they wait for surgery or if they decide not to undergo surgery for endometriosis.
Some complementary and alternative treatments for endometriosis include:
Acupuncture
Anti-inflammatory diet
Gentle stretching and exercise
Heating pads
Wearing loose-fitting clothing
Risks and Complications Associated With Endometriosis
Leaving endometriosis untreated can impact your quality of life and lead to complications from disease progression.
As endometriosis progresses, it creates inflammation in the body leading to adhesions (scars) that can pull organs and tissues out of alignment, leading to infertility (difficulty becoming pregnant).
Other possible complications of endometriosis can include:
Pelvic floor dysfunction
Bowel obstruction
Kidney failure
Loss of bowel or bladder function
Higher incidence of ovarian cancer
Related: Endometriosis: What You Need to Know
Summary
Endometriosis is when endometrial-like tissue grows outside the uterus, often causing painful symptoms impacting mental health and overall quality of life. About 10% of people born with a uterus have endometriosis, yet diagnosis takes an average of seven to nine years. Excision surgery is the gold standard treatment for endometriosis. Endometriosis can lead to infertility, poor quality of life, and other complications when left untreated.
