What Is Endometriosis: Causes, Diagnosis, and Treatment

Understanding Endometriosis

Endometriosis is a chronic inflammatory condition in which tissue similar to the lining of the uterus grows outside of it, most commonly on the ovaries, fallopian tubes, and pelvic peritoneum. Less frequently, it can be found on the bowel, bladder, appendix, and in rare cases even the lungs or other distant sites. This misplaced tissue behaves like the endometrium — it thickens and bleeds in response to hormonal fluctuations during the menstrual cycle — but because it has no way to exit the body, it becomes trapped, causing inflammation, scarring, and the formation of adhesions.

Endometriosis affects an estimated 190 million people worldwide who have been assigned female at birth, roughly 10 percent of the reproductive-age population. Despite its prevalence, the average time from symptom onset to diagnosis is seven to ten years in many countries, largely due to its highly variable presentation and the normalization of period pain in many cultures.

The condition is staged from one to four based on the extent and depth of lesions and the presence of adhesions. However, stage does not reliably predict symptom severity — some individuals with stage one disease experience severe pain while others with stage four have few symptoms. This disconnect makes endometriosis challenging to understand and treat.

Theories on the Causes of Endometriosis

The exact cause of endometriosis remains debated, and it is likely that multiple mechanisms contribute. The most widely accepted theory is retrograde menstruation, in which menstrual blood flows backward through the fallopian tubes into the pelvic cavity rather than exiting through the cervix. This occurs to some extent in most people who menstruate, but in those with endometriosis, the shed endometrial cells implant and grow on pelvic structures rather than being cleared by the immune system.

Immune dysfunction is thought to play a significant role. In individuals with endometriosis, the immune system appears unable to recognize and destroy the misplaced tissue. Elevated levels of inflammatory cytokines, natural killer cell dysfunction, and altered macrophage activity have all been documented, suggesting that the immune environment of the pelvis is different in those with endometriosis. Genetic factors also contribute, as the condition runs in families — first-degree relatives of those with endometriosis have a significantly higher risk.

Other proposed mechanisms include the metaplasia theory (normal pelvic cells transform into endometrial-like cells in response to inflammation or hormones), stem cell dissemination via blood or lymphatic vessels, and the influence of environmental toxins such as dioxins. It is increasingly viewed as a systemic disease rather than simply a pelvic disorder.

Symptoms: More Than Painful Periods

The hallmark symptom of endometriosis is dysmenorrhea — painful menstruation — that is often severe enough to interfere with daily activities. Unlike typical menstrual cramps that improve after the first day or two, endometriosis-related pain often persists throughout the period and may continue for days after it ends. The pain can range from a deep, aching sensation to acute, stabbing discomfort.

Pelvic pain outside of menstruation is also common and may be chronic. Deep dyspareunia, pain during or after sexual intercourse, particularly with deep penetration, is another characteristic symptom caused by lesions on the uterosacral ligaments or posterior cul-de-sac. Dyschezia (painful bowel movements) and dysuria (painful urination) can occur if the bowel or bladder is involved, and these symptoms often worsen around menstruation.

Infertility affects approximately 30 to 50 percent of those with endometriosis. The mechanisms include distorted pelvic anatomy from adhesions, impaired egg quality, inflammation that creates a hostile environment for fertilization and implantation, and in severe cases, blocked fallopian tubes. Fatigue is a pervasive but often overlooked symptom, with research indicating levels of fatigue comparable to those seen in chronic inflammatory diseases. Nausea, bloating, and mood disturbances are also frequently reported.

Diagnosis: The Ongoing Challenge

Definitive diagnosis of endometriosis has traditionally required laparoscopic surgery with histological confirmation of biopsy samples. This remains the gold standard, but it represents a significant barrier since surgery carries risks, costs, and recovery time. No blood test or imaging study can definitively diagnose endometriosis, though these tools are useful for ruling out other conditions and identifying endometriomas (ovarian cysts containing old blood, often called chocolate cysts).

Transvaginal ultrasound performed by an experienced sonographer can identify endometriomas and deep infiltrating lesions with reasonable accuracy but is less effective at detecting superficial peritoneal lesions. MRI provides better soft-tissue detail and is useful for surgical planning when deep infiltrating endometriosis involving the bowel, bladder, or ureter is suspected.

The long delay in diagnosis is driven by multiple factors: the variable and often dismissed nature of symptoms, the normalization of pelvic pain, lack of awareness among both patients and some healthcare providers, and the absence of a non-invasive diagnostic test. Advocacy organizations have worked to reduce this delay through education campaigns and updated clinical guidelines that recommend empirical treatment based on clinical presentation.

Medical Treatment Options

Medical treatments for endometriosis aim primarily to reduce pain by suppressing the hormones that drive lesion activity. Combined oral contraceptives (the pill), taken continuously to avoid monthly bleeding, are often the first-line treatment. Progestin-only options, including the levonorgestrel IUD, implant, and oral progestins, suppress endometrial tissue growth and are effective for pain management in many individuals.

GnRH agonists and antagonists create a temporary pseudo-menopause by dramatically reducing estrogen levels. They are highly effective at reducing lesion activity but cause significant side effects including hot flashes, bone loss with long-term use, and mood changes. Add-back therapy — low-dose estrogen and progesterone given alongside GnRH agonists — can mitigate side effects while preserving most of the pain relief. These treatments do not eliminate lesions permanently and symptoms often recur after stopping.

Anti-inflammatory medications such as NSAIDs (ibuprofen, naproxen) address pain but do not treat the underlying disease. Research into disease-modifying treatments, including targeted approaches to inflammation and immune function, is ongoing. Complementary approaches including acupuncture, dietary changes, and physical therapy for pelvic floor dysfunction provide additional symptom relief for some individuals.

Surgical Treatment and Fertility Considerations

Excision surgery, in which endometriosis lesions are cut out rather than burned, is considered the most effective surgical approach. When performed by experienced surgeons specializing in endometriosis, excision can provide significant and durable pain relief. Ablation (burning or vaporizing lesions) is a less complete approach that may leave disease behind. Surgery does not cure endometriosis — recurrence rates vary but can be substantial, particularly with ablation.

For those wishing to conceive, surgery to remove endometriomas and clear adhesions can improve fertility outcomes. Assisted reproductive technologies, particularly IVF, are effective options when surgery has not restored fertility or when other factors are also present. The decision to proceed with surgery versus IVF first depends on the individual's age, ovarian reserve, the nature of lesions, and preferences.

Endometriosis is a complex, lifelong condition that requires ongoing management. Living well with endometriosis involves building a knowledgeable medical team, tracking symptoms to identify patterns and triggers, and accessing support from specialist nurses, mental health professionals, and peer communities. Advances in research are gradually improving understanding of the disease's mechanisms and pointing toward better diagnostic and therapeutic tools for the future.