Endometriosis is a chronic, oestrogen-dependent inflammatory condition in which tissue histologically resembling endometrium (the lining of the uterus) grows outside the uterine cavity — most commonly on the ovaries (endometrioma or 'chocolate cyst'), the uterosacral ligaments, the pouch of Douglas, the bladder, and the bowel. Affecting approximately 10% of women of reproductive age (roughly 190 million women worldwide), it is one of the most common causes of chronic pelvic pain, dysmenorrhoea (painful periods), dyspareunia (deep pain during intercourse), dyschezia (pain during defaecation), and subfertility. Diagnosis is typically delayed by 7–10 years from symptom onset, largely because symptoms are commonly attributed to 'normal' menstrual pain, and no reliable non-invasive diagnostic biomarker exists. CA-125 (cancer antigen 125) is elevated in severe endometriosis (rASRM stage III–IV) but has poor sensitivity and specificity for early-stage or minimal disease. Clinical classification systems include the revised American Society for Reproductive Medicine (rASRM) staging system (Stage I minimal through Stage IV severe, based on extent and depth of disease), and the ENZIAN classification, a surgical staging system developed specifically to describe deep infiltrating endometriosis (DIE) more accurately than rASRM. Both require laparoscopy (direct surgical visualisation with histological confirmation) for definitive diagnosis. The gold standard diagnostic method remains diagnostic laparoscopy with biopsy, though specialist pelvic MRI can identify deep infiltrating disease before surgery.
No validated numerical risk score; clinical diagnosis based on symptom pattern + examination + USS/MRI + definitive laparoscopy. rASRM Score: Stage I (1-5 points), Stage II (6-15), Stage III (16-40), Stage IV (>40)
- 1Take a detailed menstrual and pain history: onset of dysmenorrhoea, whether pain is cyclical or continuous, site and radiation, relationship to defaecation and intercourse, impact on quality of life and work, duration of symptoms before presentation.
- 2Perform a systematic gynaecological examination: assess for uterine tenderness and retroversion, fixed retroverted uterus on bimanual examination, tenderness of the uterosacral ligaments, adnexal mass (endometrioma), nodularity on recto-vaginal examination.
- 3Request a transvaginal ultrasound (TVUS) by a specialist experienced in endometriosis: look for ovarian endometriomata (ground-glass or homogeneous low-level echo pattern), sliding sign of the rectosigmoid, bladder or ureteric involvement.
- 4Consider specialist pelvic MRI if deep infiltrating endometriosis (DIE) is suspected — particularly bowel, bladder, or ureteral involvement — to map disease before surgery.
- 5Measure serum CA-125: significantly elevated levels (>200 U/mL) may support the diagnosis in context but a normal CA-125 does not exclude endometriosis.
- 6Confirm diagnosis by diagnostic laparoscopy with visual inspection and biopsy of suspicious lesions for histological confirmation of endometrial glands and stroma.
- 7Apply rASRM or ENZIAN classification intraoperatively to stage the disease and document findings systematically; this guides treatment planning and prognostic counselling.
NICE NG73: empirical hormonal treatment is appropriate without laparoscopy in typical presentation
NICE and ESHRE guidelines support a trial of hormonal treatment (combined oral contraceptive pill or progestogens) without requiring diagnostic laparoscopy in women with typical symptoms. Laparoscopy is recommended if treatment fails, if there is an adnexal mass, or if infertility is a concern.
Cystectomy reduces recurrence vs. drainage alone; but each surgery risks normal ovarian tissue removal
A homogeneous low-level echo cyst without internal papillae or septations in a symptomatic woman of reproductive age has a >95% probability of being an endometrioma. MRI can confirm. Laparoscopic cystectomy is preferred over aspiration, though ovarian reserve (AMH) should be measured beforehand.
Surgery for rectovaginal DIE requires colorectal surgeon involvement; risk of bowel resection, ureteral injury, and bladder dysfunction
Rectal invasion by endometriosis (ENZIAN C-class) requires surgical excision for definitive treatment if medical management fails. Surgery must be performed at a specialist centre with colorectal and urological support due to the complexity and complication risk.
ESHRE guideline: laparoscopic excision of minimal-mild endometriosis improves spontaneous pregnancy rates vs. diagnostic laparoscopy alone
Endometriosis-associated infertility is mediated by peritoneal inflammation, altered tubal and ovarian function, and endometrial receptivity changes. IVF is the most effective treatment for infertility in Stage III-IV disease. In Stage I-II, surgical excision followed by a timed natural conception period of 6–12 months is reasonable.
Professionals in relevant industries use Endometriosis Risk as part of their standard analytical workflow to verify calculations, reduce arithmetic errors, and produce consistent results that can be documented and shared with colleagues, clients, or regulatory bodies.
University professors and instructors incorporate Endometriosis Risk into course materials and homework assignments, allowing students to check their manual calculations, build intuition about how input changes affect outputs, and focus on conceptual understanding rather than arithmetic.
Consultants and advisors use Endometriosis Risk to quickly model different scenarios during client meetings, enabling real-time exploration of what-if questions that would otherwise require returning to the office for spreadsheet-based analysis.
Individual users rely on Endometriosis Risk for personal planning decisions — comparing options, verifying quotes received from service providers, and building confidence that the numbers behind an important decision have been calculated correctly.
Extreme input values
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in endometriosis risk calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
Assumption violations
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in endometriosis risk calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
Rounding and precision effects
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in endometriosis risk calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
Endometriosis and oestrogen-containing HRT
Women who have had a hysterectomy and bilateral oophorectomy for endometriosis should be offered HRT but, ideally, combined (oestrogen + progestogen) or tibolone rather than oestrogen-only HRT, to minimise the risk of reactivating residual endometriotic deposits and reduce the theoretical risk of malignant transformation.
| Stage | Score | Description |
|---|---|---|
| I — Minimal | 1–5 | Isolated superficial implants; no significant adhesions |
| II — Mild | 6–15 | Superficial and some deep implants; minor adhesions |
| III — Moderate | 16–40 | Multiple deep implants; peritubal/periovarian adhesions; small endometrioma |
| IV — Severe | >40 | Multiple deep implants; large endometriomata; dense adhesions; obliterated pouch of Douglas |
What is the most reliable way to diagnose endometriosis?
The gold standard remains diagnostic laparoscopy with histological confirmation of endometrial glands and stroma in biopsied lesions. However, NICE (NG73) and ESHRE guidelines now support clinical diagnosis and empirical treatment in women with typical symptoms (cyclical pelvic pain, dysmenorrhoea, dyspareunia) without requiring mandatory laparoscopy before treatment. Laparoscopy is indicated if symptoms do not respond to medical treatment, if there is an adnexal mass, or if the presentation is atypical.
What is the ENZIAN classification?
The ENZIAN classification is a surgical staging system designed specifically for deep infiltrating endometriosis (DIE), which is poorly captured by the rASRM system. ENZIAN uses compartments: Compartment A (vagina, recto-vaginal septum), B (uterosacral ligament, parametrium), and C (rectum, sigmoid). Each is graded 1–3 by depth. ENZIAN separately classifies involvement of the adnexa, urinary system, and other organs. It enables precise surgical communication and planning.
Is CA-125 useful for diagnosing endometriosis?
CA-125 has poor sensitivity and specificity for endometriosis diagnosis. It is elevated in only 25–30% of women with minimal-mild disease and in 60–80% of those with severe disease. It is also elevated in other conditions including ovarian cancer, other gynaecological conditions, and even menstruation itself. CA-125 cannot be used alone to diagnose or exclude endometriosis, but markedly elevated levels (>200 U/mL) alongside a suspicious USS or MRI raise suspicion for significant disease or malignancy.
What treatments are available for endometriosis?
Medical treatments include: hormonal suppression (combined oral contraceptive pill, progestogens, Mirena IUS, GnRH agonists/antagonists such as elagolix or relugolix); analgesics (NSAIDs, paracetamol); and add-back HRT during long-term GnRH agonist use to prevent osteoporosis. Surgical treatments include: laparoscopic excision of peritoneal lesions, ovarian cystectomy, and resection of DIE. Surgery for severe or DIE should be performed at specialist centres. Definitive treatment (bilateral salpingo-oophorectomy) is rarely indicated except at menopause.
Can endometriosis become cancerous?
Endometriosis is associated with a small but real increased risk of ovarian cancer, specifically the endometrioid and clear cell subtypes. The absolute risk is low — women with endometriosis have approximately a 2–3-fold increased lifetime risk compared to women without endometriosis, though the absolute lifetime risk remains below 2%. This association is predominantly seen with ovarian endometrioma rather than peritoneal disease.
Does endometriosis always cause infertility?
Not always. Many women with endometriosis conceive naturally. However, endometriosis is found in 25–50% of women investigated for infertility, and even mild peritoneal disease can reduce monthly fecundity rates (natural conception probability per cycle) from approximately 20–25% to 2–10%. Fertility is more significantly affected by ovarian endometrioma (which can damage follicular reserve), tubal disease, and severe adhesions.
What is 'adenomyosis' and how is it related to endometriosis?
Adenomyosis is a condition in which endometrial glands and stroma are present within the myometrium (uterine muscle), causing a bulky, tender uterus with heavy, painful periods. It is distinct from endometriosis (which is outside the uterus) but both conditions frequently coexist and share some pathophysiological mechanisms. Adenomyosis is diagnosed by TVUS (heterogeneous myometrium with cystic spaces) or MRI (junctional zone thickness >12 mm).
What is the typical delay in diagnosis for endometriosis?
Studies from the UK, US, Australia, and Germany consistently show an average diagnostic delay of 7–10 years from first symptom onset to confirmed diagnosis. Reasons include normalisation of period pain by patients and clinicians, the need for laparoscopy for definitive diagnosis, limited endometriosis knowledge in primary care, and the absence of a reliable non-invasive biomarker. This delay significantly impacts quality of life, fertility, and disease progression.
Pro Tip
The combination of dysmenorrhoea, dyspareunia, and dyschezia — the 'three Ds' — is highly suggestive of endometriosis, particularly when accompanied by subfertility. When all three are present, the probability of laparoscopically confirmed endometriosis exceeds 70%.
Did you know?
Endometriosis was first described as a distinct pathological entity by Thomas Cullen in 1896, who found endometrial tissue in the muscle wall of the uterus (adenomyosis) and outside it. Despite affecting 190 million women globally, endometriosis received its first dedicated UK National Institute for Health and Care Excellence guideline (NG73) only in 2017 — 121 years after Cullen's original description.
References
- ›ESHRE — Guideline on Endometriosis (2022)
- ›NICE — Endometriosis: Diagnosis and Management (NG73)
- ›Zondervan KT et al — Endometriosis — Nature Reviews Disease Primers 2018
- ›Revised American Society for Reproductive Medicine classification of endometriosis
- ›Stochino-Loi E et al — ENZIAN classification of deep infiltrating endometriosis