Endometriosis is a chronic, estrogen-dependent condition in which tissue similar to the uterine lining grows outside the uterus — on the ovaries, fallopian tubes, bladder, bowel, pelvic ligaments, and beyond. This ectopic tissue responds to monthly hormonal cycling by proliferating and bleeding, generating progressive inflammation, fibrosis, and adhesions. Endometriosis affects approximately 10% of reproductive-age women — an estimated 190 million women worldwide — and is one of the leading causes of chronic pelvic pain and infertility.
Endometriosis is both a systemic and a pelvic disease whose manifestations span multiple organ systems and multiple related diagnoses. When endometrial tissue implants on the ovary and forms a blood-filled cyst, the result is an endometrioma — the most common pelvic cystic manifestation of endometriosis and a dedicated condition with its own management considerations. Endometriosis in the uterine wall is called adenomyosis, which frequently coexists and shares the same hormonal dependency. The chronic pelvic pain of endometriosis overlaps extensively with that of pelvic congestion syndrome and uterine fibroids — all three are common causes of chronic pelvic pain in reproductive-age women that require imaging to differentiate. Endometriosis is also an independent risk factor for ovarian cancer — specifically the endometrioid and clear cell subtypes.
Causes
Theories of origin.
The exact mechanism by which endometriosis develops remains incompletely understood — no single theory fully explains all clinical presentations. The retrograde menstruation theory — the most widely accepted — proposes that menstrual blood carrying viable endometrial cells flows backward through the fallopian tubes into the pelvis, where cells implant on peritoneal surfaces and establish ectopic colonies. However, retrograde menstruation occurs in up to 90% of menstruating women while endometriosis develops in only 10%, which demonstrates that retrograde flow alone is insufficient — immune surveillance failure is a necessary co-factor. The coelomic metaplasia theory proposes that peritoneal mesothelial cells transform into endometrial-like tissue under hormonal stimulation, which may explain endometriosis at distant sites including the pleura and diaphragm where retrograde flow cannot reach. Lymphovascular spread and embryonic müllerian remnants are additional mechanisms explaining extra-pelvic disease. Most current evidence supports a multifactorial model in which retrograde menstruation, immune dysfunction, and genetic susceptibility act together to produce the full clinical syndrome.
Other contributing factors.
Genetics play a major role — first-degree relatives of affected women have a 7–10 times higher risk. Endometriosis is strongly hereditary with multiple susceptibility loci identified by GWAS studies. Immune dysfunction — including reduced NK cell activity, elevated peritoneal macrophage levels, and impaired clearance of ectopic endometrial cells — is central to disease establishment. Early menarche, short menstrual cycles (under 27 days), heavy or prolonged periods (increased retrograde flow volume), and congenital outflow obstruction (which maximizes retrograde flow) all increase risk. Tall stature and low BMI are additional epidemiologic associations. Oral contraceptive use reduces risk by suppressing ovulation and retrograde flow. Endometriosis predominantly affects women in their 20s and 30s but can occur throughout the reproductive years and, in rare cases, after menopause in women on estrogen replacement.
Symptoms
Endometriosis is one of the most symptomatically heterogeneous conditions in gynecology. The hallmark symptom is severely painful periods (dysmenorrhea) that worsen progressively over time — this worsening trajectory is the single most important clinical clue, distinguishing endometriosis from primary dysmenorrhea, which typically remains stable or improves with age and OCP use. Chronic non-cyclical pelvic pain affects the majority of patients with moderate to severe disease. Dyspareunia (pain with intercourse, especially deep penetration) reflects posterior compartment disease involving the uterosacral ligaments and rectovaginal septum. Dyschezia (pain with defecation, particularly during menstruation) and dysuria (pain with urination) indicate bowel or bladder involvement respectively. Heavy or irregular periods, bloating, and gastrointestinal symptoms — often misattributed to irritable bowel syndrome for years — are common. Infertility affects approximately 30–50% of women with endometriosis, from mechanisms including tubal distortion by adhesions, impaired oocyte quality, altered peritoneal environment, reduced ovarian reserve from endometriomas, and disrupted implantation. The symptom severity does not reliably predict disease extent — a woman with Stage I endometriosis may have debilitating pain, while Stage IV disease with extensive peritoneal involvement may be nearly asymptomatic.
The average diagnostic delay from symptom onset to diagnosis is 7–10 years — one of the longest diagnostic delays of any chronic disease — reflecting the normalization of period pain in clinical culture, misattribution of symptoms to IBS or anxiety, and the absence until recently of a reliable noninvasive diagnostic test. MRI has fundamentally changed this by enabling confident noninvasive diagnosis in many cases.
Diagnosis
Clinical suspicion based on the symptom history — particularly progressive dysmenorrhea, deep dyspareunia, and dyschezia — is the foundation of diagnosis. Pelvic examination may reveal uterosacral nodularity, a fixed retroverted uterus (from posterior adhesions), or adnexal masses from endometriomas. Transvaginal ultrasound identifies endometriomas but is limited for superficial peritoneal disease and deep infiltrating lesions — particularly rectovaginal and ureteral endometriosis — because it cannot reliably characterize soft tissue implants in the cul-de-sac and posterior compartment.
An MRI of the pelvis with dedicated endometriosis protocol sequences has become the imaging gold standard for mapping pelvic endometriosis — particularly deep infiltrating disease — and has largely replaced diagnostic laparoscopy in many centers for preoperative planning. MRI systematically evaluates each anatomic compartment: the ovaries for endometriomas (T1-bright, T2-shading); the posterior compartment for uterosacral ligament thickening, rectovaginal nodules, and rectal wall infiltration — the most important and commonly missed deep endometriosis locations; the anterior compartment for bladder wall involvement and vesicouterine pouch obliteration; and the ureters for extrinsic compression causing hydronephrosis. MRI also evaluates the uterus for concurrent adenomyosis, identifies "kissing ovaries" (bilateral endometriomas adherent in the posterior cul-de-sac), and maps the degree of posterior cul-de-sac obliteration — the single most important surgical planning finding that determines whether standard laparoscopy or specialized colorectal involvement is required. Serum CA-125 may be elevated in moderate to severe endometriosis but lacks diagnostic specificity. Definitive histologic confirmation can be obtained at laparoscopy when needed, but MRI-guided management avoids unnecessary surgery in many patients.
Classification
Endometriosis is classified both by the revised American Society for Reproductive Medicine (rASRM) staging system and by lesion type — the two systems capture different clinically important aspects of the disease.
rASRM staging (I–IV):
- Stage I (Minimal): Few superficial peritoneal implants with minimal adhesions. May cause significant pain despite limited anatomic extent.
- Stage II (Mild): More implants, some slightly deeper, with mild adhesions. Fertility impact begins to emerge.
- Stage III (Moderate): Many deep implants, small endometriomas on one or both ovaries, filmy peritubal or periovarian adhesions. Significant fertility impact.
- Stage IV (Severe): Many deep implants, large endometriomas (over 3 cm), extensive dense adhesions distorting pelvic anatomy. Most severe fertility and pain burden. MRI mapping is essential before surgery at this stage.
By lesion type:
- Superficial peritoneal endometriosis: Implants on the surface of the pelvic peritoneum. Variable MRI visibility — active lesions appear as subtle T2-hypointense foci on the peritoneal surface; hemorrhagic foci may show T1-hyperintensity.
- Ovarian endometriosis (endometriomas): Blood-filled cysts with the characteristic T1-bright, T2-shading MRI appearance. The most reliably detected form on imaging. Detailed on the Endometrioma page.
- Deep infiltrating endometriosis (DIE): Lesions extending more than 5 mm beneath the peritoneal surface into the rectovaginal septum, uterosacral ligaments, bowel wall, bladder wall, or ureters. The most clinically significant form — responsible for the most severe pain and requiring the most complex surgery. MRI is the only imaging study that reliably maps DIE extent for preoperative planning.
Treatments
Treatment is individualized based on symptom burden, disease extent on MRI, fertility goals, age, and response to prior therapies. No treatment is curative — endometriosis is a chronic disease requiring long-term management strategy.
Medical management: First-line treatment centers on hormonal suppression of the estrogen-driven menstrual cycle — eliminating monthly bleeding that feeds ectopic implants. Combined oral contraceptives taken continuously (suppressing periods entirely) reduce pain effectively and are well-tolerated for long-term use. Progestins — including norethindrone, dienogest, and the levonorgestrel IUD — provide strong endometrial suppression and are particularly effective for pain; dienogest has the strongest evidence base specifically for endometriosis pain reduction among oral progestins. GnRH agonists (leuprolide) induce a temporary menopausal state and provide substantial symptom relief but cause bone density loss and vasomotor symptoms limiting long-term use without add-back estrogen therapy. GnRH antagonists (elagolix, relugolix) offer a rapidly reversible oral option with dose-adjustable estrogen suppression. NSAIDs manage pain as an adjunct. None of these treatments eliminate established endometriosis — they suppress its activity and slow progression while being taken.
Surgery.
Laparoscopic excision (rather than ablation/fulguration) of endometriosis implants is the surgical standard of care — excision removes the full depth of the lesion including its deep root, while ablation only destroys the surface and leaves viable deep disease, which is why recurrence rates are higher after ablation. Excision provides superior and more durable pain relief and is the appropriate approach for all deep infiltrating endometriosis. For deep endometriosis involving the rectum — the most challenging surgical scenario — a multidisciplinary approach with gynecologic and colorectal surgery produces the best outcomes, with options ranging from disc excision (removing the infiltrated bowel wall segment while preserving the bowel lumen) to segmental bowel resection for extensive involvement. Bladder and ureteral endometriosis similarly requires urologic surgical collaboration. Associated endometriomas are removed by cystectomy at the same procedure. Surgery improves fertility — particularly by removing endometriomas that impair oocyte retrieval and restoring normal tubal and ovarian anatomy — but carries the risk of reducing ovarian reserve, particularly with repeat procedures on the same ovary.
Fertility treatment.
Endometriosis is a major cause of infertility, and many affected women require assisted reproduction. The decision between surgical treatment and proceeding directly to IVF depends on disease stage, ovarian reserve, partner fertility, and patient age — and should be made in consultation with a reproductive endocrinologist. IVF bypasses many of the mechanisms by which endometriosis impairs natural fertility. Preoperative MRI mapping of the full disease extent is essential before any fertility-motivated surgical intervention to ensure the planned procedure will improve rather than worsen reproductive outcomes.
Definitive surgery.
For women with severe, refractory symptoms who have completed childbearing, total hysterectomy with bilateral salpingo-oophorectomy and complete excision of all visible endometriosis is the most effective definitive treatment. Even after this procedure, residual implants in bowel or bladder can theoretically persist, and small quantities of estrogen from adipose tissue may sustain residual disease — making complete surgical excision of all visible implants at the time of hysterectomy essential. Postoperative estrogen replacement is appropriate in younger women following bilateral oophorectomy given the cardiovascular, bone, and quality-of-life consequences of surgical menopause, but should be managed carefully.
Multidisciplinary care.
Endometriosis is a chronic disease requiring a long-term management partnership. Many women benefit from multidisciplinary care including gynecology, colorectal and urologic surgery when DIE is present, pain management, pelvic floor physical therapy (which addresses the secondary pelvic floor hypertonicity that frequently develops from years of pain guarding), nutritional support, and psychological care. Patient-centered education about the chronic nature of endometriosis — and realistic expectations about what medical and surgical treatment can and cannot achieve — is a critical and often underemphasized component of care.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Pelvis MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.