Endometriosis: Causes, Symptoms and Treatment

Endometriosis: Causes, Symptoms and Treatment

Endometriosis is a chronic inflammatory condition in which tissue resembling the endometrium (the lining of the uterus) grows outside the uterus — in the pelvis, on the ovaries, fallopian tubes, peritoneum, bowel, bladder, and — rarely — beyond the pelvis. It affects approximately 10% of women of reproductive age, equivalent to approximately 190 million women worldwide.

Despite its prevalence, endometriosis remains dramatically underdiagnosed: the average time from first symptom to confirmed diagnosis is 7–10 years in most countries. Delayed diagnosis can prolong the burden of pain and psychological distress; it does not establish that earlier diagnosis would have prevented infertility in an individual. Endometriosis is one of the leading causes of female infertility and chronic pelvic pain, and yet it remains poorly understood, under-researched, and often dismissed by healthcare providers.

What Is Endometriosis?

Mechanism

Endometriotic lesions contain endometrial-like glands and stroma outside the uterus and are usually associated with local inflammation. The disease can involve:

• Inflammation — cyclical bleeding triggers intense local inflammatory response
• Adhesions — fibrous scar tissue forms between pelvic organs (bowel adheres to ovary, fallopian tube to pelvic wall)
• Endometriomas — blood-filled cysts on the ovaries ("chocolate cysts" — dark brown old blood) that compress and damage ovarian tissue
• Nerve infiltration — deep lesions penetrate pelvic nerves, causing neuropathic pain

The Retrograde Menstruation Theory

The most widely accepted mechanism (Sampson's theory): during menstruation, some menstrual blood flows retrograde through the fallopian tubes into the peritoneal cavity; this endometrial tissue implants and proliferates. However, retrograde menstruation occurs in 90% of women, yet only 10% develop endometriosis — suggesting additional genetic, immunological, and microenvironmental factors determine whether implants survive and proliferate.

Endometriosis vs Adenomyosis

Adenomyosis — endometrial glands and stroma within the myometrium (muscle wall of the uterus); causes a diffusely enlarged, tender uterus; symptoms of heavy bleeding and dysmenorrhoea; diagnosed by MRI; frequently coexists with endometriosis. Management differs from endometriosis and depends on symptoms and pregnancy plans. Options include medicines and, when appropriate, surgery; discuss the suitable approach with a gynaecologist.

Classification of Endometriosis

The rASRM (revised American Society for Reproductive Medicine) staging system classifies endometriosis I–IV by lesion number, size, and adhesion extent — but this does not correlate well with pain severity. The Endometriosis Fertility Index (EFI) better predicts fertility outcomes. The ENZIAN classification describes deep infiltrating endometriosis (DIE) lesions by anatomical compartment.

Type	Description	Key Features
Peritoneal (superficial)	Flat or slightly raised lesions on pelvic peritoneum	Powder-burn, red flame lesions; painful; may be subtle
Ovarian endometrioma	Endometriotic cyst within the ovary	Chocolate cyst; damages ovarian reserve
Deep infiltrating endometriosis (DIE)	Penetrates >5 mm below peritoneal surface	Uterosacral ligaments, rectovaginal septum, bowel, bladder; pain and symptom severity vary

Symptoms

Dysmenorrhoea (Painful Periods)

The cardinal symptom — but critically, not all painful periods indicate endometriosis, and not all endometriosis causes painful periods. Features that raise suspicion:

• Pain begins 1–2 days before menstruation (primary dysmenorrhoea is usually only on day 1–2)
• Pain is severe — interfering with school, work, or daily activities; not adequately controlled by standard NSAIDs
• Pain is progressive — worsening over years (unlike primary dysmenorrhoea which often improves with age/OCP)
• Associated with dyschezia (painful bowel movements) at menstruation — suggests posterior DIE

Chronic Pelvic Pain (CPP)

Pain outside of menstruation — present throughout the cycle; dull, aching pelvic and lower back pain; worse with standing, intercourse, or physical exertion. Central sensitisation contributes — chronic nociceptive input from endometriotic lesions sensitises the central nervous system, leading to widespread pain hypersensitivity.

Dyspareunia (Painful Intercourse)

Pain during or after deep vaginal penetration (deep dyspareunia) — highly suggestive of posterior DIE involving the uterosacral ligaments, rectovaginal septum, or pouch of Douglas. Severe dyspareunia profoundly impacts intimate relationships and quality of life.

Cyclical Bowel and Bladder Symptoms

• Dyschezia — painful defaecation, particularly at menstruation; rectal urgency; altered bowel habit; from posterior DIE involving the rectum or recto-sigmoid
• Cyclical rectal bleeding — from bowel endometriosis mucosa penetration
• Cyclical dysuria / haematuria — bladder endometriosis; cyclical urinary frequency and urgency; voiding difficulty
• Cyclical shoulder tip pain — diaphragmatic endometriosis (rare); pleural endometriosis with catamenial pneumothorax

Infertility

Among women with infertility, an estimated 25–50% have endometriosis. This is an association and prevalence estimate, not the proportion of infertility proved to be caused by endometriosis. Potential mechanisms include:

• Endometriomas — bilateral ovarian cysts damage follicular reserve (primordial follicle loss); reduce AMH; impair oocyte quality; respond poorly to ovarian stimulation
• Pelvic adhesions — fallopian tube distortion and obstruction; impaired ovum pick-up
• Peritoneal environment — inflammatory mediators, activated macrophages, and prostaglandins in peritoneal fluid impair sperm function and embryo implantation
• Implantation defect — endometriosis alters endometrial receptivity

Fatigue

Profound, disabling fatigue is consistently reported by women with endometriosis — partly from chronic pain and disrupted sleep, and partly from the systemic inflammatory burden of the disease.

Diagnosis

The Diagnostic Delay Problem

The average 7–10 year diagnostic delay results from multiple factors:

• Symptoms normalised by both patients and clinicians ("bad periods are normal")
• Endometriosis has no reliable non-invasive diagnostic biomarker (CA125 is unreliable)
• Definitive diagnosis historically required laparoscopy with histological confirmation
• Symptoms overlap with IBS, UTI, and primary dysmenorrhoea — leading to misdiagnosis

Clinical Diagnosis

A thorough history (symptom pattern, severity, relationship to cycle) and examination (vaginal tenderness, uterosacral nodularity on bimanual examination) are essential. Clinical suspicion warrants investigation — empirical medical treatment is appropriate without laparoscopic confirmation if clinical suspicion is high.

Transvaginal Ultrasound (TVUS)

Ovarian endometriomas may have a characteristic homogeneous ground-glass appearance on ultrasound. Diagnostic accuracy depends on the lesion, technique and operator; no single sensitivity or specificity applies to every scan. TVUS with bowel preparation by an experienced operator (IOTA/IDEA consensus approach) can reliably detect posterior deep endometriosis (rectosigmoid, rectovaginal septum).

MRI Pelvis

Specialist pelvic MRI can help assess the extent of suspected deep endometriosis and plan treatment. Specialist transvaginal ultrasound is another option; imaging should be selected and interpreted by clinicians with appropriate expertise. A normal MRI does not exclude endometriosis, particularly superficial peritoneal disease.

Diagnostic Laparoscopy

The historical gold standard — direct visualisation of endometriotic lesions (red, blue/black, or white lesions; endometriomas; adhesions; deeply infiltrating disease) with biopsy and histological confirmation. Enables simultaneous surgical treatment. Modern guidelines acknowledge that empirical medical treatment may be initiated on clinical grounds alone without laparoscopy, reserving surgery for diagnostic uncertainty, treatment failure, or women seeking surgical management.

Treatment

Endometriosis is a chronic disease. Treatment aims to relieve symptoms and support quality of life and fertility goals. Menopause and hysterectomy do not guarantee that symptoms or disease will disappear permanently.

Medical Management (Hormonal Suppression)

Medicines can help control pain and hormone-related disease activity; they do not all work by suppressing ovarian hormone production:

Combined Oral Contraceptive Pill (COCP)

First-line medical treatment — continuous (no pill-free break) or cyclical; reduces dysmenorrhoea in approximately 70–80% of women. Well-tolerated, inexpensive, reversible. Does not eliminate endometriosis; it can help control endometriosis-associated pain while taken, but it does not guarantee prevention of new lesions.

Progestogens

• Norethisterone, medroxyprogesterone acetate, dydrogesterone — oral progestogens; suppress endometrial tissue; effective for pain
• Levonorgestrel IUS (Mirena) — intrauterine system providing local progestogen; induces endometrial atrophy; effective for dysmenorrhoea and CPP; reduces period volume; can reduce endometriosis-associated pain, but symptom relief does not establish removal or resolution of ovarian endometriomas or deep lesions
• Desogestrel (progestogen-only pill) — continuous pill; induces amenorrhoea; effective pain control

GnRH Agonists (Leuprorelin, Goserelin, Buserelin)

GnRH agonists may relieve pain but can cause low-oestrogen symptoms and bone loss. Add-back therapy, duration and monitoring require an individual prescription.

Oral GnRH Antagonists (Elagolix, Linzagolix, Relugolix)

Oral GnRH antagonists are another hormonal option. Dose, duration, add-back requirements and authorisation depend on the specific product and jurisdiction; they are not interchangeable regimens.

Dienogest

Selective progestogen with anti-androgenic properties — approved for endometriosis in Europe and Asia; continuous administration; effective pain control; induces endometrial atrophy; good tolerability; widely used in China and Japan.

Surgical Management

Surgery may be considered after individual assessment of persistent symptoms despite medical treatment, diagnostic uncertainty, lesion characteristics, and bowel or bladder involvement. A desire to preserve or improve fertility is not a standalone indication: the decision should account for pain, age, ovarian reserve, previous surgery, other infertility factors and patient preferences, including discussion of assisted reproduction where appropriate.

Laparoscopic Excision of Endometriosis

Excision (cutting out) may be considered instead of ablation (burning/vaporising) for endometriosis-associated pain. Removal of deep endometriosis may improve pain and quality of life, but the approach should be individualised with a specialist discussion of benefits and risks. Specialist endometriosis surgeons excise peritoneal lesions, uterosacral ligament DIE, and deep rectovaginal and bladder disease.

For rectosigmoid endometriosis, the surgical team selects the technique according to the depth, extent and location of disease:

• Rectal shaving — separates the lesion from the rectal wall, aiming to avoid opening the bowel lumen; it may leave residual disease with deeper muscular involvement
• Disc excision — removes a localised full-thickness area of bowel wall and closes the defect; it is not simply a superficial shave
• Segmental bowel resection — removes an affected bowel segment with anastomosis when appropriate; planning may involve a combined gynaecologist and colorectal surgical team

Laparoscopic excision may improve pain, but the degree and durability of benefit vary; recurrence rates approximately 20–30% over 5 years.

Laparoscopic Cystectomy for Ovarian Endometrioma

Cystectomy removes the endometrioma cyst wall and can reduce recurrence and pain compared with drainage and coagulation. Carbon-dioxide laser vaporisation is another option; the choice should take account of ovarian reserve, fertility priorities and the benefits and risks of each technique. Important consideration: cystectomy can remove healthy ovarian tissue and reduce ovarian reserve; the degree of risk varies, so tissue-sparing technique and an individual discussion of benefits, risks and fertility priorities are important. Bilateral ovarian cystectomies carry particular risk of irreversible ovarian failure.

Hysterectomy and the Decision About Ovary Removal

Hysterectomy with removal of visible lesions may be considered when conservative treatments have failed and future pregnancy is not desired. It is not a guaranteed cure. Removing the ovaries is a separate decision: discuss symptom and recurrence risks, the long-term effects of early menopause, and the possible need for hormone replacement therapy with the specialist.

Fertility Treatment

For women with endometriosis-related infertility:

• IUI (intrauterine insemination): may be tried in mild-moderate endometriosis without tubal factor; limited efficacy
• IVF (in vitro fertilisation): the most effective fertility treatment for endometriosis — particularly stage III–IV, bilateral endometriomas, or tubal disease; live birth rates comparable to tubo-peritoneal factor infertility if ovarian reserve is adequate

Surgery before IVF: ovarian endometrioma surgery is not routinely recommended solely to improve live-birth rates; evidence has not shown a benefit and surgery may reduce ovarian reserve. Surgery may be considered for pain or to make follicles accessible for egg retrieval. The decision should be individualised with the fertility and surgical teams.

Holistic Management

Pain management beyond hormonal therapy:

• NSAIDs: mefenamic acid, ibuprofen — first-line for dysmenorrhoea
• Neuropathic pain medicines: gabapentin or amitriptyline may be considered after individual assessment when a neuropathic pain component is identified. They are not routine treatment for all endometriosis-associated pain or for central sensitisation alone; suitability, adverse effects and response require review.
• Physiotherapy: pelvic floor physiotherapy for hypertonic pelvic floor (common in chronic pelvic pain); significantly reduces musculoskeletal pain contribution
• Psychological support: CBT, mindfulness, pain psychology — essential for managing chronic pain; reduces pain catastrophising and improves coping

Endometriosis Care in China

China's gynaecology centres offer:

Before arranging endometriosis care in China, ask the receiving team to confirm:

• Appropriate ultrasound or MRI assessment and whether multidisciplinary input is needed.
• The exact medicine, prescribing restrictions, monitoring and local availability.
• Surgical goals, risks and the experience required for deep or bowel disease.
• Ovarian-reserve assessment and the potential impact of cyst surgery before treatment decisions.
• Fertility options and an individual plan, without a promised IVF outcome.
• An itemised hospital quote and the separately agreed scope of PriumCare coordination.

Contact a PriumCare care navigator to arrange an endometriosis assessment, laparoscopy consultation, or IVF programme.

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Source for this targeted correction

• ESHRE guideline: endometriosis (2022).

• NHS adenomyosis information.

Editorial source correction: 25 October 2026. This targeted check addressed the flagged treatment, surveillance, product and availability claims, and removed unsupported numerical or comparative promises. It is not a clinical review of the whole article. No named medical reviewer is claimed. Original publication date is retained.

Targeted endometriosis treatment clarification

Editorial source check: 26 October 2026. This update checks only the distinction between LNG-IUS symptom control and lesion removal, individual fertility-related surgical decisions, and the difference between bowel shaving and disc excision. It is not a whole-article medical review, adds no named clinical reviewer, and retains the original publication date.

• ESHRE 2022 endometriosis guideline
• ESGE/ESHRE/WES deep endometriosis surgical recommendations

Targeted endometriosis evidence clarification

Editorial source check: 26 October 2026. This update checks only the diagnostic-delay and infertility association, imaging limitations, contraceptive symptom-control wording and selected neuropathic-pain medicine use. It is not a whole-article medical review, adds no named clinical reviewer, and retains the original publication date.

• ESHRE: endometriosis guideline
• WHO: endometriosis
• NICE: endometriosis diagnosis and management
• NICE: neuropathic pain medicine selection and review

Targeted editorial source check — 26 October 2026: only the lesion-cycle explanation, surgical-technique comparison, unqualified pain-improvement percentage and certainty of ovarian-reserve damage were reassessed using ESHRE 2022, WHO and NICE NG73. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date. Other figures and treatment details were not re-certified.

Targeted editorial source check — 26 October 2026: only the deep-lesion pain ranking and endometrioma cystectomy-versus-ablation comparison were reassessed using ESHRE, NICE NG73 and WHO. Technique and symptom assessment remain individual. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.