By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated July 27, 2026

Endometriosis is a chronic inflammatory condition in which tissue similar to the endometrium grows outside the uterine cavity, most commonly on the ovaries, fallopian tubes, pelvic peritoneum, and uterosacral ligaments. It is common among women of reproductive age and is a significant driver of both pelvic pain and infertility in couples seeking care.¹ Despite its prevalence, the median time from symptom onset to diagnosis often exceeds 7 to 9 years,² a delay driven by normalized dismissal of pelvic pain and dysmenorrhea as routine.³ Endometriosis causes inflammation, adhesion formation, distorted pelvic anatomy, and impaired tubal and implantation function, all of which affect both the woman's health and a couple's fertility.⁴ Laparoscopic excision surgery physically removes established endometriosis lesions; multicenter outcomes data show measurable improvement in pain and quality of life after excision.⁵⁶ After surgery, hormonal suppression can reduce pain and lower the rate of symptom and endometrioma recurrence.⁷ Hormonal suppression does not remove established lesions or restore pelvic anatomy disease has already distorted.⁸ When suppression is stopped, disease activity commonly returns.⁹ Within restorative reproductive medicine, complex or near-frozen pelvic disease may be approached with specialized excision-and-repair techniques that emphasize adhesion prevention and restoration of normal anatomy, including the approaches defined here as PEARS, NARPS, and S-MAP.¹⁰

Where endometriosis comes from remains an open question. The dominant theory, proposed by Sampson in 1927, holds that menstrual tissue flows backward through the fallopian tubes and implants in the pelvis.¹¹ This theory has shaped clinical thinking for nearly a century, but it cannot fully explain the disease.¹² Endometriosis occurs at sites menstrual reflux cannot reach: extrapelvic locations, endometrial tissue identified in human female fetuses at autopsy,¹³ and documented cases in male patients under high-dose estrogen exposure.¹⁴¹⁵ The research literature describes several competing or complementary theories, including coelomic metaplasia, embryonic-rest and Mullerianosis theories, stem-cell seeding, and lymphovascular spread.¹⁶ The retrograde-menstruation theory is best understood as insufficient as a sole explanation, not as a settled account of the disease's origin.¹⁷

Can ultrasound detect endometriosis? It depends on the type of disease. Skilled transvaginal ultrasound can detect endometriomas and deep infiltrating lesions, but it frequently misses the small, superficial peritoneal implants that drive many women's symptoms, so a negative scan cannot rule out endometriosis.¹⁸¹⁹²⁰ Surgical evaluation by laparoscopy remains the most thorough way to map disease and the only route to histologic confirmation.²¹ Imaging guidelines have moved toward diagnosing endometriomas and deep infiltrating disease on expert ultrasound or MRI, but histologic confirmation of superficial disease still requires laparoscopy.²¹ Critically, the severity of symptoms does not correlate with disease stage.²² Severe, debilitating pain can occur with stage I disease.²² Disease stage poorly predicts pain severity: in a multivariate analysis of over 1,000 women, the association between endometriosis stage and pelvic pain was marginal and inconsistent, meaning advanced stage IV disease does not reliably indicate high symptom burden and some women with severe disease present with infertility rather than pain.²² Stage number alone tells a clinician very little about a patient's symptom burden or fertility risk.

Medical therapy suppresses endometriosis but does not eliminate established lesions or cure the disease.⁴ Hormonal suppression can ease symptoms and shrink some lesions while taken, but no drug clears established lesions or permanently reverses the disease.²³ Whether and when to operate is an individual clinical decision based on symptoms, fertility goals, and disease extent. Some comparative data favor excision over ablation for symptom domains such as dysmenorrhea, dyschezia, and chronic pelvic pain, though the trial evidence is limited and clinicians weigh lesion type and depth in choosing technique.⁶ Complete excision by an experienced surgeon is also associated with lower rates of repeat surgery in some published series, though reported recurrence figures vary considerably by disease severity, lesion type, and length of follow-up, so each case must be evaluated individually.²⁴²⁵ Surgery removes existing disease, but recurrence is possible, so it is best understood as durable control rather than a guaranteed permanent cure.²⁶

Endometriosis affects the nervous system, not just the pelvis. The disease can durably remodel sensory nerve pathways, producing peripheral and central sensitization that drives chronic pain.²⁷ Persistent pain after excision can reflect the lasting impact endometriosis has already had on the nervous system rather than residual disease.²⁸ Effective pain management often requires addressing multiple contributors alongside surgery, including pelvic floor physical therapy and lifestyle factors.²⁹ Endometriosis is a whole-body inflammatory condition associated with immune dysregulation³⁰ and with high rates of systemic comorbidities including fibromyalgia, chronic fatigue syndrome, and autoimmune and endocrine disorders; its effects reach well beyond the pelvis.³¹ Endometriosis is associated with reduced ovarian reserve and may affect oocyte quality over time,³² which is one reason couples often benefit from early evaluation rather than delay.³³ The luteal phase can be compromised as well, adding another layer of reproductive dysfunction beyond the structural distortion of the pelvis.³⁴ Women with endometriosis labeled "unexplained infertility" are frequently undiagnosed: systematic laparoscopic evaluation often reveals disease that prior imaging missed.³⁵

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Authoritative References

How other clinical authorities define this term. RRM Academy curates these verbatim or under fair use so the medical consensus is visible alongside our RRM-contextualized definition above.

MeSH D004715

A condition in which functional endometrial tissue is present outside the UTERUS. It is often confined to the PELVIS involving the OVARY, the ligaments, cul-de-sac, and the uterovesical peritoneum.

U.S. National Library of Medicine, Medical Subject Headings (MeSH) Read source →
NCI Thesaurus C3014

The growth of functional endometrial tissue in anatomic sites outside the uterine body. It most often occurs in the pelvic organs.

NCI Thesaurus, National Cancer Institute Read source →
MedlinePlus

Endometriosis is a disease in which tissue like the lining of the uterus grows in other places in your body. These patches of tissue are called "implants," "nodules," or "lesions."

MedlinePlus, U.S. National Library of Medicine Read source →
Wikipedia Endometriosis

Endometriosis is a disease in which tissue similar to the endometrium—the lining of the uterus (womb)—grows elsewhere in the body. The tissue most often grows close to the uterus, such as on the ovaries, fallopian tubes, or the lining of the pelvis.

Wikipedia (CC BY-SA) Read source →

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.