What Is Endometriosis? Symptoms, Diagnosis, and Treatment

What Is Endometriosis?

Endometriosis is a chronic inflammatory disease characterized by the presence of tissue histologically resembling endometrium (the lining of the uterus) at sites outside the uterine cavity. These ectopic lesions most commonly occur on the peritoneum (the lining of the abdominal and pelvic cavity), the ovaries (forming endometriomas, or 'chocolate cysts'—cysts filled with old dark blood), and the rectovaginal septum. Less commonly, endometriosis affects the bladder, bowel, appendix, diaphragm, and in rare cases, distant sites including the lungs and brain.

Like the uterine endometrium, endometriotic lesions respond to cyclical hormonal fluctuations: they proliferate under the influence of estrogen and attempt to shed during menstruation. However, because the shed material has no path out of the body, it becomes trapped, inducing a local inflammatory response that causes adhesion formation, scarring, and the chronic pain that is the hallmark of the disease. Endometriosis is classified into stages (I–IV) based on the American Society for Reproductive Medicine (ASRM) scoring system, which assesses lesion extent, depth, and adhesion severity—though stage does not reliably predict symptom severity or fertility impact.

Prevalence and the Diagnostic Delay Crisis

Endometriosis affects an estimated 10–15% of reproductive-age individuals assigned female at birth—approximately 190 million people worldwide. Despite its prevalence and the significant suffering it causes, endometriosis is chronically underdiagnosed: the average time from symptom onset to diagnosis is 7–10 years in most countries, a delay rooted in multiple interconnected failures. Symptoms are frequently dismissed as 'normal period pain'; the medical curriculum historically underemphasized endometriosis; and definitive diagnosis requires surgery, creating a significant diagnostic barrier.

The diagnostic delay has profound consequences. For individuals in pain, years of undiagnosis mean years of inadequately managed suffering, disrupted education, employment, and relationships. It also allows disease to progress: a condition that might have been detected at Stage I or II may have advanced to Stage III or IV by the time a diagnosis is made, with far greater impact on fertility and organ function. Advocacy organizations and specialist endometriosis centers have pushed for greater awareness, symptom education for clinicians, and non-surgical diagnostic approaches to reduce this delay.

Symptoms and How They Present

The dominant symptom is pain—but endometriosis pain is heterogeneous and does not conform neatly to a single pattern. Dysmenorrhea (painful periods) is the most common symptom, often described as more severe than typical menstrual cramps—colicky, stabbing, or constant pelvic pain beginning before menstrual flow and lasting through or beyond the period. Deep dyspareunia (pain with deep penetration during sexual intercourse) affects over half of those with endometriosis and is often a key diagnostic pointer, particularly when it is position-dependent and related to lesion location. Chronic pelvic pain (non-menstrual pelvic pain lasting over six months) and cyclical bowel or bladder symptoms (painful defecation, diarrhea, constipation, blood in stool or urine worsening during menstruation) suggest bowel or bladder endometriosis.

Paradoxically, some individuals with extensive endometriosis have minimal symptoms, while those with minimal disease may have severe pain—a disconnect that likely reflects individual variation in pain sensitization, inflammation levels, and lesion characteristics. Fatigue—often profound and disproportionate to the observable disease—is an underrecognized but extremely common and impactful symptom, present in up to 50% of individuals with endometriosis. Endometriosis is also strongly associated with other chronic pain conditions (fibromyalgia, irritable bowel syndrome, interstitial cystitis), suggesting shared mechanisms of central sensitization.

Diagnosis: The Surgical Gold Standard

Laparoscopy—a minimally invasive surgical procedure in which a camera is inserted into the abdominal cavity—with histological confirmation of biopsied lesions is the definitive diagnostic gold standard. During laparoscopy, a surgeon can visualize lesions (which may appear as black spots, blue lesions, clear vesicles, or various colored powder-burn lesions), assess adhesions, and simultaneously treat the disease by excising or ablating lesions. However, requiring surgery for diagnosis creates a significant barrier and cannot ethically be performed on everyone with pelvic pain.

Non-invasive diagnostic approaches are advancing but remain imperfect. Transvaginal ultrasound (TVUS) by an experienced sonographer can reliably detect ovarian endometriomas (sensitivity and specificity both exceeding 90%) and deep infiltrating endometriosis of the rectovaginal septum, bladder, and bowel. MRI offers superior soft tissue characterization and is useful for mapping the extent of deep infiltrating disease before surgery. Neither ultrasound nor MRI reliably detect superficial peritoneal lesions. Blood biomarkers, including CA-125 (an ovarian cancer marker), are insufficiently sensitive and specific for endometriosis diagnosis. The development of a reliable non-invasive biomarker test (from blood, urine, or endometrial biopsy) is an active research priority.

Hormonal and Surgical Treatments

Hormonal therapies are the cornerstone of medical management and work by suppressing estrogen production and/or menstrual cycling, thereby reducing the estrogen-dependent growth and inflammation of endometriotic lesions. The combined oral contraceptive pill (OCP), taken continuously (without a pill-free interval) to prevent breakthrough bleeding, is often a first-line approach for symptom management—affordable, reversible, and generally well-tolerated. Progestins (norethisterone, dienogest, the levonorgestrel-releasing IUD) suppress endometriotic tissue directly and effectively reduce pain. GnRH agonists (leuprolide, nafarelin) and GnRH antagonists (elagolix, relugolix) induce a temporary medical menopause by dramatically reducing estrogen, effectively treating pain but causing menopausal side effects (hot flashes, bone loss) that limit long-term use.

Surgical treatment—ideally performed laparoscopically by a specialist with expertise in endometriosis—involves excision (cutting out lesions with margins) or ablation (destroying lesions with heat or laser). Excision is generally preferred for complete removal of deep-infiltrating disease and improved long-term outcomes. Surgery provides significant pain relief and can improve fertility, but endometriosis recurs after surgery in 20–40% of patients within five years, reflecting the systemic nature of the disease. Endometriosis-associated infertility affects 30–50% of individuals with the condition through multiple mechanisms: distorted pelvic anatomy from adhesions, inflammatory effects on gametes and embryos, ovarian reserve reduction from endometrioma, and impaired implantation. Referral to reproductive medicine specialists and assisted reproductive technologies (IVF) is recommended for those struggling to conceive. Pain management often requires a multidisciplinary approach, including physiotherapy (particularly pelvic floor therapy), pain psychology, and in specialist centers, multidisciplinary teams including colorectal surgeons and urologists for complex disease.