Endometriosis is a chronic gynecological condition in which endometrial-like tissue grows outside the uterine cavity, commonly on the ovaries, fallopian tubes, and pelvic peritoneum, causing inflammation, pain, and potential infertility.

Endometriosis

Epidemiology

Risk Factors

Understanding risk factors requires understanding the core principle: anything that increases cumulative oestrogen exposure or retrograde menstruation increases risk.

Risk Factor	Mechanism / Explanation
Early menarche (< 11 years)	More total lifetime menstrual cycles → more retrograde menstruation episodes → more ectopic seeding
Late menopause	Same principle — prolonged oestrogen exposure
Short menstrual cycles (< 27 days)	More frequent menstruation → more retrograde flow
Heavy menstrual flow (menorrhagia)	Greater volume of retrograde menstruation → more ectopic implantation
Nulliparity / low parity	Pregnancy is a "break" from menstruation (9 months amenorrhoea + breastfeeding); fewer pregnancies → more cycles
Late first pregnancy	More uninterrupted cycles before first pregnancy
Müllerian anomalies (e.g., obstructive uterine anomalies, cervical stenosis)	Any obstruction to antegrade menstrual flow increases retrograde menstruation
Family history (first-degree relative)	6–10× increased risk; heritable component (polygenic)
Tall, thin body habitus / low BMI	Paradoxical — lean women have higher SHBG but also altered immune surveillance; exact mechanism debated
Exposure to endocrine disruptors (e.g., dioxins)	Dioxins are immunomodulatory and oestrogenic, promoting ectopic endometrial survival

Protective Factor	Mechanism
Multiparity	Fewer total menstrual cycles
Prolonged breastfeeding	Lactational amenorrhoea → fewer cycles
Late menarche	Fewer lifetime cycles
Combined oral contraceptive pill (COCP) use	Suppresses ovulation, thins endometrium, reduces menstrual flow
Exercise	Lowers circulating oestrogen, can cause relative amenorrhoea

High Yield Exam Point

The risk factor pattern for endometriosis is essentially the SAME as for endometrial cancer and breast cancer — anything that increases cumulative unopposed oestrogen exposure. The key difference is that endometriosis is a benign inflammatory condition, not a malignancy (though rare malignant transformation can occur, particularly to endometrioid or clear cell ovarian carcinoma).

Anatomy and Key Anatomical Sites

To understand endometriosis, you must understand the anatomy of the female pelvis and why certain sites are preferentially affected.

Lesion Type	Appearance	Significance
Red/flame-like lesions	Active, vascularised, early implants	Most hormonally active; earliest stage
Black/powder-burn lesions	Pigmented, contain haemosiderin deposits	Classic "chocolate" lesions; represent older, less active implants
White lesions	Scarred, fibrotic	Burnt-out, inactive disease; fibrosis predominates
Endometrioma	Cystic ovarian mass filled with dark "chocolate" fluid	Can grow very large (> 10 cm); risk of rupture, torsion, or malignant transformation
Deep infiltrating endometriosis (DIE)	Solid nodules penetrating > 5 mm below the peritoneal surface	Most symptomatic form; involves rectovaginal septum, uterosacral ligaments, bowel, bladder

Aetiology and Pathophysiology

The aetiology of endometriosis is multifactorial and not completely understood. Multiple theories exist, and the current consensus is that no single theory explains all cases — multiple mechanisms likely act synergistically.

The "Second Hit" — Why Only Some Women Develop Disease

Retrograde menstruation is nearly universal, so additional factors must be present for disease to establish. Think of it as a "two-hit" model:

Endometriosis accounts for approximately 25% of female factor infertility ^[2]^[3]. Multiple mechanisms contribute:

Mechanism	Explanation
Anatomical distortion	Adhesions distort tubo-ovarian relationships → impaired ovum pick-up by the fimbriae
Tubal damage	Endometriotic implants on/in tubes → inflammation → fibrosis → tubal occlusion
Ovarian dysfunction	Endometriomas destroy normal ovarian cortex → reduced ovarian reserve; altered folliculogenesis
Hostile peritoneal environment	Increased peritoneal fluid cytokines, macrophages → toxic to sperm, ova, and embryos; impaired sperm motility and sperm-oocyte interaction
Defective implantation	Eutopic endometrium in women with endometriosis has altered expression of implantation markers (e.g., αvβ3 integrin, HOXA10) → reduced endometrial receptivity
Hormonal abnormalities	Progesterone resistance in the endometrium → inadequate luteal phase support
Altered oocyte quality	Oocytes retrieved from follicles adjacent to endometriomas show reduced fertilisation and embryo quality

Classification

The American Society for Reproductive Medicine (ASRM) revised classification (formerly the American Fertility Society, rAFS) is the most widely used staging system. It is a surgical staging system based on findings at laparoscopy.

Stage	Points	Description
Stage I: Minimal	1–5	Few superficial implants
Stage II: Mild	6–15	More implants, some deep; no significant adhesions
Stage III: Moderate	16–40	Deep implants; small endometriomas on one/both ovaries; filmy adhesions
Stage IV: Severe	> 40	Large endometriomas; dense adhesions; obliteration of Pouch of Douglas; rectovaginal disease

Scoring is based on:

Size, depth, and location of implants
Presence and extent of adhesions (filmy vs. dense)
Presence of endometriomas

Limitations of rAFS/ASRM Classification

The ASRM classification has significant limitations:

Does NOT correlate with pain severity (a Stage I patient can have worse pain than Stage IV)
Poorly predicts fertility outcomes (a Stage II patient may be more infertile than a Stage III)
Does NOT account for deep infiltrating endometriosis (DIE) adequately
Inter-observer variability is high

Despite these limitations, it remains the standard classification because no superior alternative has been universally adopted for staging. However, for surgical planning, the ENZIAN classification (below) is increasingly used.

Clinical Features

Symptoms

Signs (Physical Examination Findings)

Important: Physical examination may be completely normal in mild/early endometriosis. Signs are more likely in moderate-to-severe disease, especially deep infiltrating endometriosis. Examination is best performed during menstruation when implants are maximal in size and tenderness.

Sign	Pathophysiological Basis
Tenderness in the posterior fornix	Endometriotic implants on uterosacral ligaments / Pouch of Douglas
Nodularity of the uterosacral ligaments	Palpable deep infiltrating endometriotic nodules — this is a highly specific finding
Fixed, retroverted uterus	Dense adhesions tether the uterus posteriorly to the rectum/rectovaginal septum → uterus cannot be anteverted on examination ("frozen pelvis")
Adnexal mass (tender, fixed)	Endometrioma — typically fixed due to surrounding adhesions (cf. functional cysts which are mobile)
Restricted uterine mobility	Adhesions restrict normal uterine movement in all directions
Thickening of the rectovaginal septum	Palpable nodularity between the posterior vaginal wall and the anterior rectal wall — indicates deep infiltrating endometriosis

System	Symptom	Sign	Pathophysiology
Gynaecological	Dysmenorrhoea, CPP, dyspareunia, infertility	Uterosacral nodularity, fixed retroverted uterus, adnexal mass	Ectopic implants on pelvic structures, adhesions
GI	Dyschezia, cyclical rectal bleeding, bloating, nausea	Rectovaginal nodularity, anterior rectal tenderness	Bowel wall infiltration, adhesions
Urological	Dysuria, cyclical haematuria, frequency	Usually none on exam	Bladder wall implants
Respiratory	Catamenial pneumothorax, haemoptysis	Reduced breath sounds (if pneumothorax)	Pleural/diaphragmatic implants
Scar	Cyclical scar pain/swelling	Tender nodule in scar	Iatrogenic implantation

High Yield Summary

Endometriosis — Key Points for Exams:

Definition: Endometrial-like tissue (glands + stroma) outside the uterine cavity
Prevalence: 10–15% of reproductive-age women; 25–50% of infertile women
Endometriosis accounts for ~25% of female factor infertility and is one of the five important causes of infertility (ovulatory dysfunction, tubal problems, endometriosis, male factors, unexplained)
Pathophysiology: Sampson's retrograde menstruation theory (most accepted) + immune dysfunction + altered endometrial biology + genetic susceptibility
Pain does NOT correlate with disease stage — depth of infiltration and nerve involvement matter more
Classic triad: Dysmenorrhoea + dyspareunia + infertility
Cyclical symptoms are the hallmark — any cyclical symptom in a reproductive-age woman should raise suspicion
Examination: Uterosacral nodularity and a fixed retroverted uterus are highly suggestive signs
Most common site: Ovaries → endometriomas ("chocolate cysts") with "ground glass" appearance on ultrasound
ASRM Classification: Stages I–IV (surgical staging); poorly correlates with symptoms or fertility
Distinguish from adenomyosis: Endometriosis = ectopic endometrium OUTSIDE the uterus; adenomyosis = endometrium invading INTO the myometrium

Active Recall - Endometriosis (Definition, Epidemiology, Aetiology, Classification, Clinical Features)

Differential Diagnosis of Endometriosis

A. Differential Diagnosis of Chronic Pelvic Pain / Dysmenorrhoea

This is the most common clinical scenario: a reproductive-age woman presenting with pelvic pain, often cyclical, with or without dyspareunia and bowel/bladder symptoms.

Condition	Key Distinguishing Features	Why It Can Mimic Endometriosis
Primary dysmenorrhoea ^[1]	Onset within 6 months–2 years of menarche; pain limited to menses (starts day 0–2, resolves by 12–72 hours); NO pain between periods; responds well to NSAIDs/COCP; no demonstrable disease accounting for symptoms ^[1]; due to prostaglandin release (esp PGF2α) → uterine contractions → intrauterine pressure > systolic BP → arterial ischaemia → "uterine angina" ^[1]	Both cause cyclical pelvic pain. However, primary dysmenorrhoea classically starts early after menarche, is limited to menses, and improves after first childbirth. Endometriosis pain typically starts BEFORE menses, persists AFTER, and worsens progressively over years.
Adenomyosis ^[2]	Diffusely enlarged, globular, boggy uterus ^[2]; heavy menstrual bleeding (60%) ^[2]; dysmenorrhoea limited to menses (25%) ^[2]; generally NOT associated with dyspareunia ^[2]; peak age 35–50 years; pathogenetically distinct from endometriosis although it commonly co-occurs ^[2]	Both cause dysmenorrhoea and infertility. Key differences: adenomyosis → enlarged uterus, HMB predominates; endometriosis → normal-sized uterus, dyspareunia predominates. TVUS shows junctional zone thickening in adenomyosis vs. endometriomas/peritoneal deposits in endometriosis.
PID (Pelvic Inflammatory Disease) ^[3]	Bilateral lower abdominal pain, deep dyspareunia, abnormal vaginal or cervical discharge, cervical excitation and adnexal tenderness, fever (> 38.3°C) ^[3]; sexually active with risk factors for STIs; acute/subacute onset	Both cause pelvic pain and dyspareunia. PID is typically acute/subacute with fever, discharge, and raised inflammatory markers. Endometriosis is chronic and cyclical without fever or discharge. However, chronic PID can mimic chronic endometriosis.
Leiomyomas (Fibroids) ^[1]	More common for > 35 years, usually associated with heavy flow with clots ^[1]; enlarged, irregularly-shaped, non-tender uterus ^[1]; pain is usually related to mass effect, degeneration, or torsion of pedunculated fibroid rather than cyclical	Both can cause pelvic pain and infertility. Fibroids → irregular uterine enlargement; endometriosis → uterosacral nodularity. Uterine enlargement in fibroids is irregular and focal ^[2] while adenomyosis is diffuse.
Ovarian cyst complications ^[3]	Sudden onset of severe pain ^[3]; torsion causes acute colicky pain with nausea/vomiting; rupture causes acute peritonism with free fluid; haemorrhage causes acute pain with adnexal mass	Endometriomas themselves can undergo these acute complications. Other functional cysts can mimic endometriosis-related adnexal pain. The key is the acuity — acute onset suggests complication, chronic cyclical pain suggests endometriosis.
Tubal ectopic pregnancy ^[3]	ALWAYS excluded by pregnancy test ^[3]; LMP classically 6–8 weeks ago (amenorrhoea); pain starts unilaterally; ± signs of haemoperitoneum and shock: syncope episodes, shoulder tip pain ^[3]	Ectopic pregnancy can cause acute pelvic pain mimicking an acute complication of endometriosis. Pregnancy test is the critical discriminator.
Adhesions	History of previous pelvic/abdominal surgery or PID; constant traction-type pain, not necessarily cyclical; no specific imaging findings	Adhesions cause chronic pelvic pain by tethering of organs. Endometriosis itself causes adhesions, so the two frequently coexist.
Developmental anomalies	Outflow tract obstruction (e.g., imperforate hymen, transverse vaginal septum) → obstructed menstruation → severe cyclical pain; typically presents soon after menarche with primary amenorrhoea + cyclical pain	Obstructive anomalies actually CAUSE endometriosis (by forcing retrograde menstruation). Must be excluded in young girls with early-onset severe dysmenorrhoea and no menses.

Exam Favourite: Primary vs. Secondary Dysmenorrhoea

Endometriosis is the most common cause of secondary dysmenorrhoea ^[1]. The key distinguishing features are:

Primary: onset within 6 months–2 years of menarche, pain limited to menses, responds to NSAIDs/COCP, no demonstrable pathology
Secondary (endometriosis): onset later (or progressive worsening), pain starts BEFORE menses and continues AFTER, associated dyspareunia/dyschezia/infertility, may NOT fully respond to NSAIDs
Features suggestive of secondary cause: onset < 6 months or > 2 years from menarche; or late onset with history of freedom from dysmenorrhoea; pain during non-menstrual phase of cycle; associating symptoms: dyspareunia, vaginal discharge, AUB ^[1]

Condition	Key Distinguishing Features	Why It Can Mimic Endometriosis
Irritable Bowel Syndrome (IBS)	Chronic abdominal pain with altered bowel habit (constipation/diarrhoea/alternating); relieved by defaecation; no alarm features; Rome IV criteria; no structural abnormality	IBS and endometriosis have HUGE symptom overlap — bloating, abdominal cramps, dyschezia, altered bowel habit. Up to 50–80% of endometriosis patients meet IBS criteria. Key difference: IBS is not cyclical with menses. Many patients carry BOTH diagnoses.
Inflammatory Bowel Disease (IBD) — Crohn's disease	RLQ pain, diarrhoea (may be bloody), weight loss, perianal disease; raised inflammatory markers; endoscopic/histological confirmation	Crohn's affecting the terminal ileum/caecum can cause RLQ pain mimicking endometriosis. Rectal endometriosis can mimic Crohn's proctitis. Key: IBD is not cyclical; systemic features (fever, weight loss, extra-intestinal manifestations) are suggestive.
Acute appendicitis ^[4]	Periumbilical pain migrating to RLQ; low-grade fever, vomiting, anorexia; McBurney's point tenderness, Rovsing's sign, psoas sign, obturator sign ^[4]	Acute presentation of right-sided endometriosis or right ovarian endometrioma can mimic appendicitis. Appendicitis is acute and progressive; endometriosis is chronic and cyclical.
Diverticulitis ^[4]	LLQ pain (sigmoid diverticulitis); fever; raised WCC/CRP; CT shows pericolic inflammation	Left-sided pelvic endometriosis can mimic sigmoid diverticulitis, especially in older women.

Condition	Key Distinguishing Features	Why It Can Mimic Endometriosis
Interstitial Cystitis / Bladder Pain Syndrome	Chronic suprapubic pain, urgency, frequency; pain relieved by voiding; negative urine cultures; cystoscopy may show Hunner's lesions	Bladder endometriosis causes identical symptoms. Key: interstitial cystitis is NOT cyclical. Bladder endometriosis worsens with menses. The two can coexist (viscero-visceral cross-talk).
UTI ^[3]	Urinary symptoms should be present; rarely associated with peritoneal signs ^[3]; dysuria, frequency, positive urine culture	Recurrent UTI-like symptoms in a young woman without positive cultures should raise suspicion for bladder endometriosis.
Ureteric colic	Colicky flank pain, haematuria, unilateral; CT KUB shows stone	Ureteric endometriosis can cause identical symptoms including hydronephrosis. Key: cyclical pattern and absence of stone on imaging.

Condition	Key Distinguishing Features
Myofascial pelvic pain / pelvic floor dysfunction	Tender trigger points in pelvic floor muscles on digital examination; often secondary to chronic endometriosis (central sensitisation)
Nerve entrapment (e.g., pudendal neuralgia)	Burning/shooting pain in pudendal nerve distribution; worsened by sitting; positive Tinel's sign at ischial spine
Psychological / central pain syndromes	Fibromyalgia, chronic fatigue syndrome — comorbid with endometriosis in up to 30% of cases; reflects central sensitisation

B. Differential Diagnosis of Pelvic Mass (Endometrioma)

When endometriosis presents as an adnexal mass (endometrioma), the DDx is that of any pelvic mass ^[5].

The differential diagnosis for a pelvic mass should be classified according to gynaecological and non-gynaecological causes ^[5]. Non-gynaecological causes are separated into gastrointestinal, urological, and retroperitoneal ^[5].

Don't Forget!

Don't forget about pregnancy → especially for teenage girls ^[5]. Pseudocyst related to previous surgeries ^[5] must also be considered. ALWAYS do a pregnancy test before any investigation of a pelvic mass.

Category	Conditions	Key Features Distinguishing from Endometrioma
Functional ovarian cysts	Follicular cyst, corpus luteum cyst	Usually < 6 cm, thin-walled, anechoic on USS (not ground-glass), resolve spontaneously within 2–3 cycles
Benign ovarian neoplasms	Mature cystic teratoma (dermoid), serous cystadenoma, mucinous cystadenoma	Dermoid: echogenic foci with shadowing (fat, hair, teeth). Serous: thin-walled, unilocular, anechoic. Mucinous: multilocular with fine septations.
Ovarian malignancy ^[6]	Epithelial ovarian cancer (serous, mucinous, endometrioid, clear cell)	Complex mass with solid components, thick septa, papillary projections, ascites, elevated CA125 (but CA125 is also elevated in endometriosis!). CA125 > 35 U/mL as cutoff but low specificity in pre-menopausal women (pregnant, menstruation, benign ovarian tumors, endometriosis, cirrhosis, pancreatitis) ^[6].
Hydrosalpinx / Tubo-ovarian abscess	Hydrosalpinx (dilated, fluid-filled tube), TOA (complex adnexal mass with debris/septations)	Hydrosalpinx: tubular shape ("incomplete septation" or "cogwheel" sign). TOA: fever, leucocytosis, associated PID features.
Ectopic pregnancy	Adnexal mass + positive β-hCG + empty uterus	Always exclude with pregnancy test
Paraovarian cyst	Arises from mesosalpinx (broad ligament remnants), separate from ovary on USS	Typically unilocular, anechoic; ovary visualised separately

Category	Conditions
Gastrointestinal	Appendiceal mass/abscess, diverticular abscess, colorectal carcinoma, Crohn's inflammatory mass
Urological	Pelvic kidney, distended bladder, bladder tumour
Retroperitoneal	Lymphoma, sarcoma, nerve sheath tumour
Pregnancy ^[5]	Especially in teenage girls ^[5] — gravid uterus
Pseudocyst ^[5]	Related to previous surgeries ^[5]

Endometrioma vs. Ovarian Malignancy — The Critical Distinction

Both endometriomas and ovarian cancer can present as a pelvic mass with elevated CA125. Key differences:

Endometrioma:

Young reproductive-age woman
Cyclical pain
USS: homogeneous ground-glass echoes, no solid components, no papillary projections
CA125 mildly elevated (usually < 200 U/mL)
No ascites

Ovarian cancer:

Typically postmenopausal (but can occur in young women)
Non-cyclical, progressive symptoms
USS: complex mass with solid components, thick irregular septa, papillary projections, ascites
CA125 often markedly elevated
Weight loss, abdominal distension

Remember: endometriomas carry a small (1–2.5%) risk of malignant transformation (to endometrioid or clear cell carcinoma), so persistent or enlarging endometriomas warrant surveillance.

The five important causes of infertility are ^[7]^[8]:

Ovulatory dysfunction / anovulation
Tubal problems
Endometriosis
Male factors
Unexplained

Endometriosis accounts for approximately 25% of female factor infertility ^[7]^[8].

When a woman presents with infertility, endometriosis must be differentiated from these other causes:

Cause	Proportion	Key Differentiating Features
Ovulatory dysfunction ^[7]^[8]	15%	Irregular/absent periods, anovulatory cycles; confirmed by day 21 progesterone < 30 nmol/L; causes include PCOS (most common), hyperprolactinaemia, thyroid disease, hypothalamic amenorrhoea
Tubal problems ^[7]^[8]	20%	History of PID, ectopic pregnancy, pelvic surgery; confirmed by HSG or laparoscopy showing tubal occlusion; may coexist with endometriosis (which itself causes tubal damage)
Endometriosis ^[7]^[8]	25%	Cyclical pain, dyspareunia, dyschezia; may be asymptomatic; confirmed by laparoscopy
Male factors ^[7]^[8]	30%	Abnormal semen due to production defects (e.g., idiopathic, endocrine, trauma, genetic); no sperm due to obstructive defects (e.g., absent vas, vasectomy); coital factors ^[7]^[8]; semen analysis is the key investigation
Unexplained ^[7]^[8]	By exclusion	By exclusion in the presence of ovulation, patent tubes, and normal semen ^[7]^[8]

Important Clinical Point

Infertility evaluation is a couple-based assessment. Even when endometriosis is found in the female partner, male factors must be concurrently evaluated (semen analysis) because 30% of infertility involves male factors ^[7]^[8], and combined male + female factors are common.

This summary table maps each presenting symptom to the relevant DDx:

Presenting Symptom	Endometriosis Mechanism	Key DDx to Exclude
Cyclical dysmenorrhoea	Ectopic implant bleeding + prostaglandin release	Primary dysmenorrhoea, adenomyosis, fibroids
Chronic pelvic pain	Adhesions, central sensitisation, neurotropism	IBS, IBD, interstitial cystitis, pelvic floor dysfunction, adhesions
Deep dyspareunia	DIE in uterosacral ligaments / rectovaginal septum	PID, ovarian cyst, retroverted uterus (non-pathological)
Dyschezia	Rectovaginal / rectal endometriosis	IBS, IBD (Crohn's proctitis), rectal carcinoma
Cyclical rectal bleeding	Transmural bowel endometriosis	IBD, colorectal carcinoma, haemorrhoids
Cyclical haematuria	Bladder endometriosis	UTI, bladder carcinoma, renal stone
Catamenial pneumothorax	Diaphragmatic/pleural endometriosis	Spontaneous pneumothorax, LAM (lymphangioleiomyomatosis)
Adnexal mass	Endometrioma	Functional cyst, dermoid, cystadenoma, ovarian cancer, ectopic pregnancy
Infertility	Multifactorial (see above)	Anovulation, tubal factor, male factor, unexplained
Scar nodule	Iatrogenic implantation at surgical sites	Incisional hernia, suture granuloma, desmoid tumour, metastatic deposit

Feature	Endometriosis	Primary Dysmenorrhoea	Adenomyosis	PID	IBS
Age at onset	25–35 years	Within 2 years of menarche	35–50 years	Any sexually active age	Any age
Pain timing	Premenstrual → menstrual → postmenstrual	Menstrual only (day 0–3)	Menstrual only	Constant / subacute	Not cyclical
Dyspareunia	Deep, common	Uncommon	Generally absent	Deep (acute PID)	Uncommon
Discharge	None	None	None	Purulent	None
Fever	Absent	Absent	Absent	Present	Absent
Uterine size	Normal	Normal	Diffusely enlarged, boggy	Normal/tender	Normal
Examination	Uterosacral nodularity, fixed uterus	Normal	Globular tender uterus	Cervical excitation, adnexal tenderness	Normal
NSAID response	Partial	Usually excellent	Partial	No (needs antibiotics)	Variable
Infertility	Yes (25%)	No	Controversial	Yes (tubal damage)	No

High Yield Summary

Differential Diagnosis of Endometriosis — Key Exam Points:

Think by presenting complaint: chronic pelvic pain → DDx includes primary dysmenorrhoea, adenomyosis, PID, IBS, interstitial cystitis; pelvic mass → DDx includes functional cysts, dermoid, ovarian cancer; infertility → DDx includes anovulation, tubal factor, male factor, unexplained
Endometriosis is the most common cause of secondary dysmenorrhoea ^[1]
Primary vs. secondary dysmenorrhoea ^[1]: primary = no pathology, onset near menarche, pain limited to menses, responds to NSAIDs; secondary = demonstrable cause, pain extends beyond menses, progressive
Adenomyosis is pathogenetically distinct from endometriosis but commonly co-occurs ^[2]; adenomyosis → enlarged boggy uterus + HMB; endometriosis → normal uterus + dyspareunia
Always exclude pregnancy (especially ectopic) with a pregnancy test ^[3]^[5]
CA125 has low specificity in pre-menopausal women ^[6] — elevated in endometriosis, pregnancy, menstruation, PID, cirrhosis → cannot reliably distinguish endometrioma from ovarian cancer
Five causes of infertility: ovulatory dysfunction, tubal problems, endometriosis (25%), male factors (30%), unexplained ^[7]^[8]
Cyclical pattern is the key discriminator — endometriosis symptoms are cyclical (tied to menses); most DDx conditions are not cyclical (IBS, interstitial cystitis, adhesions)
Symptom overlap with IBS is enormous — up to 50–80% of endometriosis patients meet IBS criteria; always consider endometriosis in a young woman "diagnosed" with IBS

Active Recall - Differential Diagnosis of Endometriosis

References

^[1] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.1 Approach to Dysmenorrhoea, p43–44) ^[2] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.3 Adenomyosis, p50–51) ^[3] Senior notes: Adrian Lui Gynecology Notes.pdf (Section on PID diagnosis and DDx, p66) ^[4] Senior notes: Maksim Surgery Notes.pdf (Section 4.6 Acute appendicitis, p89) ^[5] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p17) ^[6] Senior notes: Adrian Lui Gynecology Notes.pdf (Section on ovarian cancer evaluation, p84) ^[7] Lecture slides: GC 117. I want to have a baby male and female infertility.pdf (p8–9) ^[8] Lecture slides: Block C - I want to have a baby_ male and female infertility.pdf (p3)

Diagnostic Criteria and Investigations for Endometriosis

Diagnostic Criteria

Unlike many conditions, endometriosis does not have a single universally accepted set of diagnostic criteria (like the Jones criteria for rheumatic fever or the McDonald criteria for MS). Instead, diagnosis operates at two levels:

Investigation Modalities — Detailed Breakdown

TVUS is the first-line imaging modality for endometriosis ^[1].

Why TVUS?

Non-invasive, widely available, no radiation, relatively inexpensive
Excellent for detecting endometriomas and deep infiltrating endometriosis
Can be performed in the outpatient clinic
Operator-dependent — expertise matters significantly

Key TVUS Findings in Endometriosis:

Finding	Description	Significance
Endometrioma ^[1]^[9]	Unilocular cyst with homogeneous low-level internal echoes ("ground-glass" appearance) ^[1]; thick wall; no internal vascularity on Doppler; may have wall nodularity	Highly specific for endometrioma. The "ground-glass" appearance is due to thick, old haemolysed blood (haemosiderin). Usually separated from uterus; less mobile if adhesions, endometriosis ^[9]
Negative sliding sign ^[1]	Loss of normal sliding movement between the anterior rectosigmoid and the posterior uterus during real-time TVUS with gentle pressure	Indicates obliteration of the Pouch of Douglas due to endometriosis ^[1]. Normally, the rectum slides freely over the posterior uterus; adhesions from DIE fix these structures together. This is a dynamic assessment unique to ultrasound.
Deep infiltrating endometriotic nodules	Hypoechoic, irregularly marginated, solid lesions in the rectovaginal septum, uterosacral ligaments, bladder, or bowel wall	Can identify DIE with high specificity when performed by an experienced sonographer. Peritoneal deposits appear as hypoechoic, vascular and/or solid mass with irregular spiculated margins ^[1]
"Kissing ovaries"	Both ovaries adherent to each other behind the uterus in the Pouch of Douglas	Suggests dense adhesions pulling the ovaries into the POD — marker of severe disease
Adenomyosis features	Asymmetric myometrial thickening, subendometrial echogenic linear striations/cysts, increased vascularity	Adenomyosis frequently coexists with endometriosis; TVUS has moderate sensitivity for adenomyosis

Critical Limitation of TVUS

TVUS has poor sensitivity (~11%) for superficial peritoneal implants ^[1]. This means a normal TVUS does NOT exclude endometriosis. It can only reliably detect endometriomas (> 1–2 cm) and some forms of DIE. Superficial peritoneal disease — which may be the ONLY form present in Stage I–II endometriosis — is invisible on ultrasound.

MRI has increased specificity and sensitivity compared to TVUS, but is not considered first-line (ESHRE 2022) ^[1].

When to use MRI:

Suspected DIE — to map the extent of disease before surgery (especially bowel, bladder, ureteric involvement)
Indeterminate adnexal mass — to characterise when TVUS is inconclusive
Surgical planning — to help surgeons anticipate the need for bowel resection, ureteric stenting, etc.
Research / specialist centres — for comprehensive disease mapping

Key MRI Findings:

Finding	MRI Appearance	Significance
Endometrioma	High signal on T1-weighted images (blood products); "shading" sign = loss of signal on T2-weighted images (due to high iron/protein content of old blood)	The T1-high / T2-shading combination is highly specific for endometrioma (distinguishes from other haemorrhagic cysts)
DIE nodules	Low signal on both T1 and T2 (fibrous tissue) ± foci of high T1 signal (haemorrhagic foci)	Identifies DIE in uterosacral ligaments, rectovaginal septum, bladder, bowel wall
Adenomyosis	Thickening of the junctional zone > 12 mm ± foci of high T1/T2 signal density ^[2]	Confirms coexisting adenomyosis
Adhesions	Indirect signs — angulation of bowel loops, distortion of anatomy, "tethering" of ovaries	MRI is not excellent at detecting adhesions directly

5. Blood Tests

Test	Role	Interpretation
CBC	Assess for anaemia (if heavy menstrual bleeding coexists — adenomyosis/fibroids)	Iron deficiency anaemia with microcytic indices suggests chronic blood loss
CRP / ESR	Non-specific inflammatory markers	Usually normal or mildly elevated; significant elevation suggests infection (PID) rather than endometriosis
TSH, Prolactin	Part of infertility workup	Exclude thyroid dysfunction and hyperprolactinaemia as causes of anovulation
Day 2–5 FSH, LH, E2, AMH	Ovarian reserve assessment in infertility context	AMH may be reduced if endometriomas have destroyed ovarian cortex (reduced ovarian reserve)

There Is No Reliable Biomarker for Endometriosis

Despite decades of research, no single blood or urine biomarker has sufficient sensitivity and specificity to diagnose endometriosis non-invasively. CA125, CA19-9, IL-6, and various experimental markers (e.g., microRNAs, cell-free DNA) have all been studied but none are recommended for clinical diagnosis (ESHRE 2022, NICE 2024). This is why the diagnosis still relies on the clinical–imaging–surgical triad.

Diagnostic laparoscopy ± biopsy is the gold standard for definitive diagnosis of endometriosis ^[1].

Procedure:

Under general anaesthesia, pneumoperitoneum is established (CO₂ insufflation)
A laparoscope is inserted through an umbilical port
Systematic inspection of the pelvis: peritoneal surfaces, ovaries, tubes, uterosacral ligaments, Pouch of Douglas, bladder peritoneum, bowel surfaces
Identification and documentation of lesions
Biopsy of suspicious lesions for histological confirmation
Staging using the rAFS/ASRM classification
Chromopertubation (dye test): methylene blue injected through the cervix → observed spilling from the fimbrial ends → confirms tubal patency. This is the gold standard for assessing tubal patency and is routinely performed during diagnostic laparoscopy for infertility.
Simultaneous therapeutic intervention if appropriate (excision/ablation of implants, adhesiolysis, ovarian cystectomy)

Visual appearances at laparoscopy:

Lesion Type	Appearance	Clinical Significance
Red/flame-like lesions	Bright red, petechia-like, vascularised	Early, active disease; most metabolically active
Black/powder-burn lesions	Dark brown/black, puckered	Classic appearance; older, less active; haemosiderin deposits
White lesions	Pale, scarred, fibrotic	Burnt-out disease; mostly fibrosis
Endometrioma	Smooth-walled ovarian cyst; dark "chocolate" fluid drains when opened	Ovarian endometriosis
DIE nodules	Hard, fibrous nodules > 5 mm deep, invading into organs	Most severe form; rectovaginal, uterosacral, bladder, bowel
Adhesions	Filmy (thin, translucent) or dense (thick, opaque, vascularised)	Indicate chronicity; dense adhesions distort anatomy
Obliterated Pouch of Douglas	Rectum densely adherent to posterior uterus; no free space	Hallmark of severe disease

Histological confirmation — what the pathologist looks for:

Endometrial glands — columnar epithelium resembling uterine glands
Endometrial stroma — spindle cells surrounding the glands
Haemosiderin-laden macrophages — evidence of old haemorrhage
At least two of the three features should be present for definitive histological diagnosis

Investigation	Role	When to Use
CT Abdomen/Pelvis	NOT routinely used for endometriosis (poor soft tissue contrast compared to MRI); useful for excluding other pathology (appendicitis, diverticulitis, bowel obstruction)	When alternative diagnoses are suspected; NOT for endometriosis characterisation
Colonoscopy	Assess for mucosal invasion of bowel endometriosis; also to exclude colorectal carcinoma or IBD	When cyclical rectal bleeding is present and bowel endometriosis is suspected
Cystoscopy	Assess for bladder mucosal endometriotic implants	Cyclical haematuria; suspected bladder endometriosis
IVP / CT Urogram	Assess for ureteric involvement (hydronephrosis, ureteric stricture)	Suspected ureteric endometriosis; flank pain; pre-operative planning for DIE surgery
Renal ultrasound	Screen for hydronephrosis	Should be performed when severe DIE is suspected, as ureteric involvement can be silent and cause progressive renal damage
Chest X-ray / CT Thorax	Assess for catamenial pneumothorax or pleural endometriosis	Cyclical chest symptoms

When a woman with suspected endometriosis presents with infertility, the investigation workup must address all five causes of infertility ^[7]^[8], not just endometriosis:

Investigation	What It Assesses	Expected Finding in Endometriosis
Semen analysis	Male factor (30% of cases)	Normal (unless concurrent male factor)
Day 21 progesterone	Ovulation	Usually normal (endometriosis does not typically cause anovulation, unless large endometriomas disrupt ovarian function)
Day 2–5 FSH, LH, E2	Ovarian reserve	May be abnormal if bilateral endometriomas have destroyed ovarian cortex
AMH	Ovarian reserve	Often reduced in bilateral endometriomas
TVUS	Endometriomas, antral follicle count, uterine pathology	Endometrioma with ground-glass echoes; reduced AFC if ovarian reserve compromised
HSG or HyCoSy ^[11]	Tubal patency	May show tubal occlusion from adhesions
Diagnostic laparoscopy with chromopertubation ^[11]	Direct visualisation of pelvic disease + tubal patency	Endometriotic lesions, adhesions, tubal occlusion confirmed by failed dye spill
TSH, Prolactin	Thyroid / hyperprolactinaemia	Usually normal
Karyotype	Chromosomal abnormalities	Not routinely recommended ^[11]

The following investigations are NOT routinely recommended in the standard infertility workup ^[11]:

Advanced sperm function testing (e.g., DNA fragmentation testing)
Postcoital testing
Thrombophilia testing
Immunological testing
Karyotype
Endometrial biopsy

Modality	What It Detects	Sensitivity for Peritoneal Disease	Sensitivity for Endometriomas	Sensitivity for DIE	Invasiveness
Clinical examination	Uterosacral nodularity, fixed uterus, adnexal mass	Low	Moderate	Moderate-High	Non-invasive
TVUS	Endometriomas, DIE, negative sliding sign	Very low (~11%)	High (> 90%)	Moderate-High (operator-dependent)	Non-invasive
MRI	Endometriomas, DIE, adenomyosis	Low	High (> 95%)	High (> 90%)	Non-invasive
CA125	Non-specific inflammation	Very low	Low-Moderate	Low	Non-invasive (blood test)
HSG	Tubal patency (indirect)	Not applicable	Not applicable	Not applicable	Minimally invasive
Laparoscopy ± biopsy	All forms of endometriosis	High (gold standard)	High	High	Invasive (GA required)

The current ESHRE guideline (2022 update) recommends the following approach:

Suspect endometriosis based on symptoms (cyclical pain, dyspareunia, dyschezia, infertility) + signs (uterosacral nodularity, adnexal mass)
Perform TVUS (preferably by an experienced sonographer) — look for endometriomas, DIE, negative sliding sign
Consider MRI if TVUS is inconclusive or for pre-surgical mapping of DIE
Do NOT use CA125 as a diagnostic test (insufficient accuracy)
Consider empirical medical treatment if clinical suspicion is high and imaging is supportive or normal — response to treatment supports the diagnosis
Perform diagnostic laparoscopy only if:
- Medical treatment fails
- Surgical treatment is planned
- Infertility assessment requires direct visualisation
- Histological confirmation is needed for diagnostic certainty

High Yield Summary

Diagnosis of Endometriosis — Key Exam Points:

Diagnostic laparoscopy ± biopsy is the gold standard ^[1], but it is no longer mandatory before starting treatment (ESHRE 2022)
Presumed diagnosis can be made on clinical grounds + imaging + response to empirical treatment ^[1]
TVUS is first-line imaging — excellent for endometriomas (ground-glass echoes) and DIE (negative sliding sign), but poor for peritoneal implants (~11% sensitivity) ^[1]. A normal TVUS does NOT exclude endometriosis.
MRI is second-line — superior for mapping DIE and pre-surgical planning; classic finding is T1 hyperintensity with T2 shading in endometriomas
CA125 has low specificity in pre-menopausal women ^[6] and is NOT recommended for diagnosis
HSG assesses tubal patency in infertility workup ^[11]; laparoscopy with chromopertubation is more accurate and allows simultaneous treatment ^[11]
Histological confirmation requires at least two of: endometrial glands, endometrial stroma, haemosiderin-laden macrophages
Pelvic examination should assess the Pouch of Douglas for nodularity, thickening, and tenderness ^[10] — highly specific for DIE
At laparoscopy, lesions appear as red (early active), black/powder-burn (classic), or white (fibrotic/burnt-out) — biopsy is recommended for confirmation
In infertility workup, evaluate all five causes simultaneously — do not assume endometriosis is the sole cause

Active Recall - Diagnosis of Endometriosis

References

^[1] Senior notes: Adrian Lui Gynecology Notes.pdf (Section on Endometriosis — Approach to Evaluation and Diagnosis, p46) ^[2] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.3 Adenomyosis, p50) ^[3] Senior notes: Adrian Lui Gynecology Notes.pdf (Section on PID DDx, p66) ^[5] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p17) ^[6] Senior notes: Adrian Lui Gynecology Notes.pdf (Section on ovarian cancer evaluation — CA125, p84) ^[7] Lecture slides: GC 117. I want to have a baby male and female infertility.pdf (p8–9) ^[8] Lecture slides: Block C - I want to have a baby_ male and female infertility.pdf (p3) ^[9] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p18, p20) ^[10] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p18) ^[11] Lecture slides: Block C - I want to have a baby_ male and female infertility.pdf (p13)

Management of Endometriosis

A. Medical Treatment — Detailed Breakdown

The fundamental principle behind ALL medical treatments for endometriosis is the same: suppress oestrogen-driven proliferation and cyclic bleeding of ectopic endometrial tissue. This is achieved by:

Suppressing ovulation
Creating a pseudo-pregnant state (high progesterone → decidualisation → atrophy)
Creating a pseudo-menopausal state (low oestrogen → atrophy)
Directly inhibiting endometrial proliferation

Important: Medical treatments are suppressive, not curative — symptoms recur after discontinuation. They are also contraceptive (suppress ovulation), so they are contraindicated when the patient desires immediate conception.

NSAIDs and other analgesics are commonly used ^[12].

Agent	Dose Example	Mechanism	Notes
Mefenamic acid (Ponstan)	250–500 mg TDS PRN	Inhibits cyclooxygenase (COX) → reduces prostaglandin synthesis (PGE2, PGF2α) → reduces inflammation, uterine contractions, and nociceptor sensitisation	Fenamates have a slight advantage as they also block prostaglandin receptor action in addition to inhibiting synthesis
Naproxen	250–500 mg BD PRN	Same as above	Longer half-life than ibuprofen; good for sustained relief
Ibuprofen	400 mg TDS PRN	Same as above	Widely available OTC
Paracetamol	500 mg–1 g QID PRN	Central analgesic (exact mechanism debated — likely involves COX-3 inhibition and endocannabinoid pathway modulation)	Less effective than NSAIDs for dysmenorrhoea but useful as adjunct

Contraindications to NSAIDs: peptic ulcer disease, NSAID allergy, renal impairment, aspirin-exacerbated respiratory disease, late pregnancy, concurrent anticoagulant use.

Key point: NSAIDs treat symptoms (pain) but do NOT suppress disease progression. They are first-line for pain relief but must be combined with hormonal therapy for disease control.

Progestin-only therapy is an alternative to COCP ^[12].

Mechanism:

Creates a pseudo-pregnant state — high progesterone → decidualisation of ectopic endometrium → eventual atrophy
Suppresses HPO axis (at sufficient doses) → anovulation
Direct anti-proliferative effect on endometrial tissue
Anti-inflammatory effects in the pelvic environment

Examples ^[12]:

Agent	Route	Dose	Specific Notes
Medroxyprogesterone acetate (Provera) ^[12]	Oral or depot injection	Oral: 10–30 mg/day; Depot: 150 mg IM every 12 weeks	Depot form (Depo-Provera) provides 3-month coverage; causes amenorrhoea in ~50% by 1 year. Disadvantage: irregular bleeding initially, weight gain, delayed return of fertility (up to 12 months after last injection), bone density loss with prolonged use.
Norethisterone acetate (Primolut N) ^[12]	Oral	5–15 mg/day continuously	Effective but can cause androgenic side effects (acne, hirsutism). Also used cyclically for AUB (different context).
Cyproterone acetate ^[12]	Oral	10–50 mg/day	Anti-androgen + progestogenic; useful if patient also has acne/hirsutism. Risk of hepatotoxicity with prolonged use at high doses.
Dienogest (Visanne)	Oral	2 mg/day	Specifically developed for endometriosis; selective progestogenic effect on endometrial tissue with minimal androgenic or oestrogenic effects. Increasingly popular. Well-studied with good long-term safety data.
Levonorgestrel-releasing IUCD (Mirena) ^[12]	Intrauterine	52 mg device, releases ~20 mcg/day	Local progestogenic effect on endometrium → profound endometrial atrophy; particularly useful for dysmenorrhoea and as post-operative preventive therapy ^[13]. Minimal systemic side effects. Does NOT suppress ovulation reliably (not a treatment for endometriomas).

Contraindications to progestins (fewer than COCP):

Current breast cancer
Severe liver disease / liver tumours
Unexplained vaginal bleeding (must be investigated first)
Active VTE (relative CI for some formulations)

Side effects: Irregular bleeding (especially initially), weight gain, bloating, mood changes, acne (depends on specific progestin), reduced libido, bone density loss (depot preparations with prolonged use).

What are they? GnRH agonists (e.g., leuprolide/Lupron, goserelin/Zoladex, nafarelin, triptorelin) are synthetic analogues of GnRH that, paradoxically, suppress the HPO axis when given continuously.

Mechanism — explained from first principles:

Normal physiology: GnRH is released from the hypothalamus in a pulsatile fashion → stimulates anterior pituitary to release FSH and LH → stimulates ovaries to produce oestrogen and progesterone
GnRH agonist effect: Continuous (non-pulsatile) exposure to a GnRH agonist initially causes a "flare" effect (transient increase in FSH/LH for 1–2 weeks → transient increase in oestrogen) → then the pituitary GnRH receptors become desensitised/downregulated → FSH/LH secretion drops to near zero → ovaries stop producing oestrogen → medical menopause
This creates a profoundly hypo-oestrogenic environment → ectopic endometrial tissue atrophies → symptoms improve

Clinical use:

Second-line therapy when COCP / progestins have failed
Pre-operative adjunct to reduce disease bulk before surgery
Maximum duration without add-back therapy: 6 months — because prolonged hypo-oestrogenaemia causes:
- Hot flushes, night sweats (vasomotor symptoms)
- Vaginal dryness, decreased libido
- Accelerated bone density loss (osteoporosis risk)
- Mood disturbance, depression

Add-back therapy: To mitigate hypo-oestrogenic side effects while maintaining efficacy, low-dose oestrogen + progestin "add-back" is co-administered. The principle (Barbieri's "oestrogen threshold hypothesis") is that there is a therapeutic window: endometriotic tissue requires higher oestrogen levels to proliferate than bone and cardiovascular tissue require for protection. So adding back a small amount of oestrogen protects bone/cardiovascular health WITHOUT reactivating endometriosis.

Typical add-back: norethisterone 5 mg/day ± conjugated oestrogen 0.625 mg/day; or tibolone 2.5 mg/day
With add-back, GnRH agonists can be used for longer durations (up to 2 years)

Contraindications: Pregnancy, breastfeeding, undiagnosed vaginal bleeding, metabolic bone disease (osteoporosis — already has low bone density).

Agent	Line	Mechanism	Duration	Key Advantages	Key Disadvantages	CI for Fertility?
NSAIDs	Adjunct	↓ Prostaglandin synthesis	PRN	Rapid pain relief	No disease suppression; GI side effects	No
COCP ^[12]	1st	Suppress HPO axis, decidualise endometrium	Long-term (continuous)	Well-tolerated, cheap, contraception	VTE risk; CI if migraine with aura	Yes (contraceptive)
Progestins ^[12]	1st (alternative)	Decidualisation → atrophy	Long-term	Fewer CI than COCP; Mirena is local	Irregular bleeding, weight gain	Yes (most suppress ovulation)
GnRH agonists	2nd	Pituitary downregulation → medical menopause	6 months (without add-back); longer with add-back	Very effective for pain	Bone loss, menopausal symptoms	Yes
GnRH antagonists	2nd (newer)	Pituitary blockade → dose-dependent E2 suppression	Long-term possible	Oral, no flare, dose-titratable	Cost; availability	Yes
Aromatase inhibitors	3rd / specialist	Block androgen → oestrogen conversion	Variable	Targets local E2 production	Must combine with COCP/progestin; bone loss	Yes

B. Surgical Treatment — Detailed Breakdown

Surgery in endometriosis serves two purposes: diagnostic (confirming the disease) and therapeutic (treating the disease). The concept of "see and treat" ^[13] — performing diagnostic laparoscopy and simultaneously treating any disease found — is the standard approach.

Conservative surgery is first line for surgical treatment, usually done together with diagnostic laparoscopy ("see and treat") ^[13].

Involves ^[13]:

Excision or ablation of endometriotic lesions — no significant difference in outcome between excision and ablation ^[13] for superficial peritoneal disease (though excision is preferred for DIE and for histological confirmation)
Ovarian cystectomy if ovarian endometrioma ^[13] — stripping of the endometrioma wall (pseudocapsule) from the ovarian cortex; preserves remaining ovarian tissue. Preferable to simple drainage (which has near-100% recurrence rate)
Adhesiolysis if adhesions seen intra-operatively ^[13] — restoring normal tubo-ovarian anatomy to improve fertility potential

Outcomes ^[13]:

Decreased overall pain: 73% vs. 21% compared to diagnostic laparoscopy alone
Increased live birth or ongoing pregnancy: 30% vs. 18% compared to diagnostic laparoscopy alone
However, higher rate of recurrent symptoms compared to definitive surgery: 58% vs. 19% re-operation rate over 7 years

Excision vs. Ablation — What's the Difference?

Technique	Method	Pros	Cons
Excision	Cutting out the lesion completely	Provides tissue for histology; removes full depth of disease; preferred for DIE	More technically demanding; risk of damaging underlying structures
Ablation	Destroying lesion surface with heat (diathermy/laser)	Faster, simpler, less technical skill needed	No histological specimen; may not destroy deep lesions; higher recurrence theoretically

Special Considerations for Endometrioma Surgery:

Cystectomy (stripping the cyst wall) is preferred over drainage + ablation — lower recurrence, better fertility outcomes
However, cystectomy inevitably destroys some healthy ovarian cortex → reduces ovarian reserve (lower AMH, lower antral follicle count)
Must balance: removing disease vs. preserving ovarian reserve — especially important in women planning IVF
General recommendation: cystectomy for endometriomas > 4 cm; smaller ones may be observed or drained + ablated

Endometrioma and Ovarian Reserve

Every cystectomy removes some normal ovarian tissue. In women with bilateral endometriomas or repeated surgeries, this can cause premature ovarian insufficiency. Always check AMH and antral follicle count before surgery and counsel the patient about the risk to fertility. In some cases, proceeding directly to IVF without surgery may be preferable to preserve ovarian reserve.

The management of endometriosis-related infertility differs fundamentally from pain management because hormonal suppressive therapies are contraceptive and must NOT be used when the patient is trying to conceive ^[13].

Treatment for infertility ^[13]:

Clinical Scenario	Management	Rationale
ASRM Stage I/II endometriosis ^[13]	Laparoscopic excision/ablation + adhesiolysis	Removes disease, restores anatomy → improves natural conception rates. Live birth rate: 30% vs. 18% with diagnostic laparoscopy alone ^[13]
ASRM Stage I/II, not conceived after surgery ^[13]	Intrauterine insemination (IUI) with controlled ovarian stimulation (COS)	COS with clomifene or gonadotrophins → multiple follicular development → increases chance of ovulation and fertilisation; IUI bypasses cervical factor and places sperm closer to oocyte
Severe endometriosis (Stage III/IV) ^[13]	IVF/ICSI	Bypasses all anatomical barriers (tubal damage, adhesions, hostile peritoneal environment); allows direct oocyte retrieval from ovaries; ICSI overcomes any impaired sperm-oocyte interaction

Key points on IVF in endometriosis:

Endometriosis patients undergoing IVF have slightly lower success rates compared to tubal factor infertility (due to reduced oocyte quality, lower ovarian reserve if endometriomas present, and possible implantation defects)
Pre-treatment with 3–6 months of GnRH agonist before IVF has been shown to improve IVF outcomes in endometriosis (suppresses disease activity, improves oocyte quality) — this is a unique situation where GnRH agonist is used IN the fertility pathway
Large endometriomas (> 4 cm) may need cystectomy before IVF to:
- Improve access to follicles for oocyte retrieval
- Reduce infection risk (aspirating through an endometrioma can seed bacteria)
- Improve response to ovarian stimulation

Key Point: Hormonal Suppression Does NOT Improve Natural Fertility

This is a common misconception. Medical treatments (COCP, progestins, GnRH agonists) used to suppress endometriosis do NOT improve subsequent natural fertility after discontinuation. The time spent on medical suppression is "lost" reproductive time. Fertility treatment should proceed directly to surgery and/or assisted reproduction — not prolonged medical suppression. The exception is the specific use of GnRH agonist as a pre-treatment before IVF.

Severe DIE involving bowel, bladder, or ureters requires a multidisciplinary team (MDT) approach:

Specialist	Role
Gynaecologist (endometriosis specialist)	Overall management, pelvic surgery, ovarian cystectomy
Colorectal surgeon	Bowel resection (segmental resection, disc excision, or shaving of rectal nodules)
Urologist	Ureteric reimplantation, ureteric stenting, bladder partial cystectomy
Radiologist	Pre-operative MRI mapping of disease extent
Pain specialist / anaesthetist	Management of chronic pain, nerve blocks, central sensitisation
Psychologist / psychiatrist	Management of chronic pain-related anxiety, depression, relationship issues
Fertility specialist	IVF/ICSI when applicable

Measure	Evidence	Mechanism
Physiotherapy / pelvic floor rehabilitation	Moderate evidence	Addresses secondary pelvic floor muscle dysfunction and myofascial pain
Psychological support / CBT	Good evidence for chronic pain	Addresses catastrophising, central sensitisation, anxiety, depression
Exercise	Moderate evidence	Reduces circulating oestrogen, endorphin release, improves mood
Heat therapy	RCT evidence for dysmenorrhoea	Local vasodilation, muscle relaxation
Dietary modification	Limited evidence	Anti-inflammatory diet (omega-3 fatty acids); reduce red meat, increase fruit/vegetables
Acupuncture	Weak/conflicting evidence	May modulate pain perception; used widely in HK/Chinese medicine context

Scenario	First Line	Second Line	Third Line
Pain, wants future fertility	NSAIDs + COCP (continuous) or progestins	GnRH agonist + add-back (6 months)	Conservative laparoscopic surgery + post-op Mirena
Pain, family complete	NSAIDs + COCP or progestins	GnRH agonist + add-back	Definitive surgery (TAH + BSO + excision of all lesions)
Endometrioma, wants fertility	Observe if < 4 cm and asymptomatic	Cystectomy if > 4 cm or symptomatic (balance ovarian reserve)	IVF if ovarian reserve compromised
Stage I/II infertility	Laparoscopic excision + adhesiolysis	IUI + controlled ovarian stimulation	IVF/ICSI
Stage III/IV infertility	IVF/ICSI (± pre-treatment GnRH agonist × 3–6 months)	Consider surgery for large endometriomas pre-IVF	—
Incidental asymptomatic	Observation	—	—

High Yield Summary

Management of Endometriosis — Key Exam Points:

The fundamental question: Does the patient want to conceive NOW? → If yes, medical hormonal suppression is contraindicated; proceed to surgery ± assisted reproduction. If no, use long-term medical suppression.
COCP (continuous regimen) is first line for pain ^[12] — suppresses HPO axis, decidualises endometrium, well-tolerated
Progestin-only therapy (Mirena, depot Provera, dienogest, norethisterone) is an alternative first line ^[12]
GnRH agonists are second-line — cause medical menopause via pituitary downregulation; limit to 6 months without add-back (bone density loss); add-back HRT allows longer use
Conservative surgery: excision/ablation + cystectomy + adhesiolysis ("see and treat") ^[13] — decreases pain (73% vs. 21%) and increases live birth (30% vs. 18%) ^[13]
Definitive surgery (TAH + BSO + excision of all lesions): for completed family + failed conservative Tx ^[13] — less recurrence but does NOT necessarily cure symptoms ^[13]
Post-operative preventive therapy: Mirena IUCD for ≥ 18–24 months ^[13] — decreases recurrence of dysmenorrhoea
Infertility treatment: Stage I/II → laparoscopic surgery ± IUI with COS; Stage III/IV → IVF/ICSI ^[13]
Medical suppression does NOT improve natural fertility — don't waste reproductive time on hormonal therapy when the goal is conception
Endometriomas have 1% (premenopausal) and 1–2.5% (postmenopausal) risk of malignant transformation, but there is no evidence for decreased risk with prophylactic surgical removal ^[1]

Active Recall - Management of Endometriosis

References

^[1] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.2 Endometriosis — natural history and malignant transformation, p46) ^[7] Lecture slides: GC 117. I want to have a baby male and female infertility.pdf (p8–9) ^[8] Lecture slides: Block C - I want to have a baby_ male and female infertility.pdf (p3) ^[12] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.2 Endometriosis — Medical Treatment, p47) ^[13] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.2 Endometriosis — Surgical Treatment and Treatment for Infertility, p49)

Complications of Endometriosis

A. Reproductive Complications

Infertility affects approximately 25% of women with endometriosis ^[1]^[7]^[8] and is the second most common presentation after pain.

The pathophysiology of infertility has been detailed previously but, summarised as a complication, the mechanisms are:

Mechanism	How It Causes Infertility
Pelvic adhesions → distortion of anatomy → impaired oocyte transport ^[1]	Adhesions between the ovary, fallopian tube, and pelvic sidewall prevent the fimbria from capturing the released oocyte
Tubal damage and occlusion	Endometriotic implants on or within the tubes → inflammation → fibrosis → luminal obstruction
Ovarian reserve depletion	Endometriomas destroy normal ovarian cortex; repeated cystectomies further deplete follicles → reduced AMH, reduced antral follicle count
Hostile peritoneal environment	Increased peritoneal cytokines (IL-1, IL-6, TNF-α), activated macrophages → toxic to sperm, impair sperm motility, impair fertilisation
Defective endometrial receptivity	Altered expression of implantation markers (αvβ3 integrin, HOXA10), progesterone resistance → failed implantation
Impaired oocyte quality	Follicles adjacent to endometriomas produce oocytes with reduced fertilisation potential and poorer embryo development

Impact: Even after surgical treatment, only 30% achieve live birth or ongoing pregnancy (vs. 18% with diagnostic laparoscopy alone) ^[13]. Many patients ultimately require IVF/ICSI.

Women with endometriosis who do conceive have higher rates of certain pregnancy complications:

Complication	Mechanism	Evidence
Ectopic pregnancy	Tubal damage from adhesions/inflammation → impaired tubal transport → embryo implants in the tube	Risk approximately 2–3× increased
Miscarriage	Defective endometrial receptivity, progesterone resistance, increased uterine contractility, altered immune milieu	Modest increase in risk (OR ~1.5)
Preterm birth	Chronic pelvic inflammation, uterine irritability, concurrent adenomyosis (which itself increases preterm risk)	OR ~1.5–2.0
Placenta praevia	Possibly due to altered endometrial vascularity and implantation in non-optimal uterine locations	OR ~1.5–3.0
Small for gestational age (SGA)	Impaired placentation from altered endometrial biology	Modest increase
Pre-eclampsia	Shared inflammatory and vascular pathology; altered spiral artery remodelling	Controversial; some meta-analyses show modest increase
Caesarean section rate	Higher rates partly due to adhesions (altered pelvic anatomy), partly due to obstetrician awareness, and higher rates of placenta praevia	Significantly increased

Clinical Pearl

Symptoms tend to improve during pregnancy due to decidualisation of ectopic endometrial epithelium ^[1]. This is because the sustained high progesterone of pregnancy causes the ectopic endometrial tissue to undergo decidualisation (transformation into pregnancy-type tissue) → atrophy and quiescence. However, this is a temporary reprieve — symptoms typically recur after delivery and cessation of breastfeeding.

Ovarian mass is present in 20% of endometriosis cases due to endometriotic cyst formation, and may be detected incidentally or associated with ovarian cyst complications (rupture, haemorrhage, RARELY torsion) ^[1].

Ovarian endometriomas are associated with a 1% (premenopausal) and 1–2.5% (postmenopausal) risk for malignant transformation (mainly endometrioid and clear cell types) ^[1].

However, there is no evidence for decreased risk with prophylactic surgical removal ^[1].

The Endometriosis–Ovarian Cancer Link

Cancer Type	Association with Endometriosis	Notes
Endometrioid ovarian carcinoma ^[14]	Associated with endometriosis in up to 42% of cases ^[14]; often identified at an earlier stage → associated with better prognosis ^[14]	Endometrioid carcinoma ("endometrioid" = resembles endometrial tissue) can arise directly from endometriotic implants on the ovary through a metaplasia → dysplasia → carcinoma sequence
Clear cell ovarian carcinoma ^[14]	Most common ovarian cancer type associated with endometriosis ^[14]; more common in East Asians, especially Japanese ^[14]; often identified at an earlier stage → associated with better prognosis (but poorer prognosis if discovered late) ^[14]	The iron-rich, oxidative environment within an endometrioma (haemosiderin, reactive oxygen species) is thought to drive DNA damage → malignant transformation into clear cell carcinoma
Uterine endometrial stromal sarcoma ^[15]	Can be found in association with endometriosis ^[15]	Rare; arises from endometrial stroma; can occur at ectopic endometriotic sites

Mechanism of malignant transformation — the oxidative stress hypothesis:

Endometriomas contain trapped haemolysed blood → free iron (from haemoglobin breakdown) generates reactive oxygen species (ROS) via the Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + OH•)
ROS cause oxidative DNA damage in the endometriotic epithelium
Accumulation of mutations (ARID1A loss-of-function mutations are particularly common in endometriosis-associated clear cell and endometrioid ovarian cancers, occurring in ~50% of cases)
Progressive dysplasia → carcinoma in situ → invasive carcinoma

Risk factors for malignant transformation:

Larger endometrioma size (> 9 cm)
Postmenopausal status (oestrogen from HRT may drive transformation)
Prolonged duration of endometriosis
Rapid growth or change in imaging characteristics (new solid components, papillary projections, loss of ground-glass pattern)

When to Suspect Malignant Transformation in an Endometrioma

Be suspicious of malignant transformation if:

An endometrioma changes in character on serial imaging — development of solid mural nodules, papillary projections, or loss of the homogeneous ground-glass pattern
Rapid increase in size, especially in a postmenopausal woman
New ascites in a woman with known endometrioma
Rising CA125 (though CA125 is already mildly elevated in endometriosis, a significant rise should prompt concern)
New symptoms: weight loss, abdominal distension, early satiety

These features warrant urgent surgical evaluation with intraoperative frozen section.

D. Organ-Specific Complications from Deep Infiltrating Endometriosis (DIE)

Deep infiltrating endometriosis (defined as endometriotic implants penetrating > 5 mm below the peritoneal surface) causes complications through direct invasion of adjacent organs.

Complication	Mechanism	Presentation
Cyclical rectal bleeding	Endometriotic implants penetrate through the muscularis into the bowel mucosa → cyclic mucosal bleeding during menstruation	Haematochezia timed with menses
Bowel stenosis / stricture	Chronic inflammation and fibrosis of the muscularis propria → progressive luminal narrowing	Constipation, incomplete evacuation, obstructive symptoms; may mimic colorectal carcinoma on imaging
Bowel obstruction	Severe stricture or extrinsic compression from adhesions → partial or complete obstruction	Colicky abdominal pain, distension, vomiting, absolute constipation; surgical emergency
Dyschezia	Especially with posterior POD or rectovaginal septum endometriosis ^[1] → pain on defaecation due to mechanical stimulation of implants	Cyclical painful defaecation

Complication	Mechanism	Presentation
Bladder endometriosis	Implants on or within the detrusor muscle → cyclic swelling, bleeding, inflammation	Frequency and urgency, pain at micturition ^[1]; cyclical haematuria if mucosa is invaded
Ureteric endometriosis	Extrinsic compression (from parametrial/uterosacral disease) or intrinsic invasion of the ureteric wall → progressive ureteric obstruction	Colicky flank pain, gross haematuria ^[1]; may be silent → progressive hydronephrosis → loss of renal function
Hydroureter / Hydronephrosis	Ureteric obstruction (as above) → back-pressure dilation of ureter and renal pelvis	May be asymptomatic until renal function is significantly impaired; bilateral disease can cause renal failure

Silent Ureteric Obstruction — A Dangerous Complication

Ureteric endometriosis is particularly insidious because it can cause progressive, painless hydronephrosis leading to irreversible renal damage. The ureter has minimal sensory innervation compared to the renal pelvis, so obstruction may not cause pain until very late. This is why renal ultrasound should be performed in all patients with suspected severe or deep infiltrating endometriosis to screen for hydronephrosis.

Thoracic endometriosis may cause chest pain, scapular pain, neck pain, pneumothorax, haemothorax, and haemoptysis ^[1].

Manifestation	Mechanism	Frequency within Thoracic Endometriosis
Catamenial pneumothorax	Endometriotic implants on the diaphragm create fenestrations → air enters the pleural space during menstruation; OR implants on the visceral pleura rupture → air leak	~73% of cases (most common)
Catamenial haemothorax	Implants on the pleura bleed cyclically → blood accumulates in the pleural space	~14%
Catamenial haemoptysis	Parenchymal lung endometriosis → cyclic bleeding into airways	~7%
Pulmonary nodules	Parenchymal implants form discrete nodules	~6%

Characteristically right-sided (> 90% of catamenial pneumothorax occur on the right) — thought to be because retrograde peritoneal fluid preferentially flows to the right paracolic gutter and reaches the right hemidiaphragm via clockwise peritoneal circulation
Diagnosis requires high index of suspicion — any young woman with recurrent right-sided pneumothorax timed with menstruation should be evaluated for thoracic endometriosis

Adhesions are one of the most significant sequelae of endometriosis, arising from the chronic inflammatory and fibrotic process:

Complication	Mechanism
Chronic pelvic pain	Adhesions tether pelvic organs → traction pain with movement, intercourse, defaecation, bladder filling
"Frozen pelvis"	Extensive dense adhesions obliterate the Pouch of Douglas and fix the uterus, ovaries, tubes, and bowel into an immobile mass
Bowel obstruction	Adhesive bands across bowel loops → partial or complete small bowel obstruction
Infertility	Distortion of tubo-ovarian anatomy → impaired oocyte capture
Surgical difficulty	Adhesions make subsequent pelvic surgery more difficult and increase the risk of inadvertent bowel, bladder, or ureteric injury

Endometriosis-related chronic pelvic pain has profound impacts beyond the physical:

Complication	Mechanism / Explanation
Central sensitisation	Chronic peripheral nociceptive input from endometriotic implants → spinal cord "wind-up" → amplification of pain signals → hyperalgesia and allodynia. Pain may persist even after surgical removal of disease because the central nervous system has been reprogrammed.
Depression and anxiety	Chronic pain, infertility, disruption of sexual and social life → psychological morbidity. Prevalence of depression in endometriosis: ~30–50%
Sexual dysfunction	Deep dyspareunia → avoidance of intercourse → relationship strain
Impaired quality of life	Missed work/school, social isolation, fatigue, reduced physical activity
Opioid dependence	Chronic pain management with opioids → tolerance → dependence. This is increasingly recognised as a significant iatrogenic complication
Comorbid pain syndromes	Central sensitisation drives development of IBS, interstitial cystitis/bladder pain syndrome, fibromyalgia, migraine — these comorbidities are significantly more common in endometriosis patients

Complication	Context	Mechanism
Damage to ovarian reserve	Ovarian cystectomy for endometriomas	Stripping the cyst wall inevitably removes some healthy ovarian cortex → reduced AMH, reduced AFC → premature ovarian insufficiency (especially with bilateral or repeated surgery)
Bowel injury / anastomotic leak	DIE surgery with bowel resection	Complex surgery in a fibrotic, distorted pelvis increases risk of inadvertent bowel perforation; anastomotic leak is a life-threatening complication requiring emergency re-operation
Ureteric injury	DIE surgery near parametrium/uterosacral ligaments	Ureters may be encased in endometriotic tissue → risk of transection or thermal injury during excision
Bladder injury	Excision of vesicouterine endometriosis	Full-thickness excision of bladder wall may cause fistula
Adhesion reformation	Any pelvic surgery	Surgical trauma → inflammation → new adhesion formation (paradoxically, surgery for adhesions can create new adhesions)
Recurrence after conservative surgery ^[13]	Conservative surgery	58% re-operation rate over 7 years ^[13] — disease regrows from residual microscopic implants under continued oestrogen stimulation

Treatment	Complication	Mechanism
GnRH agonists (without add-back)	Bone density loss (osteoporosis), vasomotor symptoms, vaginal atrophy, mood disturbance, cognitive changes	Prolonged hypo-oestrogenaemia → accelerated bone resorption, loss of oestrogen's protective effects on bone, cardiovascular system, and CNS
Depot medroxyprogesterone acetate	Bone density loss, weight gain, delayed return of fertility	Prolonged progesterone dominance suppresses oestrogen; effect on bone is reversible but slow
NSAIDs (long-term)	Peptic ulcer disease, GI bleeding, renal impairment, cardiovascular risk	COX inhibition → reduced mucosal prostaglandin protection (GI); reduced renal prostaglandin-mediated vasodilation (renal)
COCP	VTE, mood changes, migraine	Exogenous oestrogen increases hepatic synthesis of clotting factors; progestogenic effects on mood

Complication	Mechanism	Notes
Scar endometriosis	Iatrogenic implantation after surgery, e.g., Caesarean section ^[1]	Cyclically painful nodule in surgical scar; may bleed. Requires wide local excision.
Spontaneous haemoperitoneum in pregnancy (SHiP)	Decidualised endometriotic implants on the uterine surface or peritoneum can rupture in late pregnancy → massive intra-abdominal bleeding	Rare but life-threatening; presents as acute abdominal pain ± haemodynamic instability in the third trimester
Catamenial appendicitis	Endometriotic implants on the appendix → cyclic inflammation mimicking appendicitis	Rare; appendicectomy specimen reveals endometriosis histologically

High Yield Summary

Complications of Endometriosis — Key Exam Points:

Infertility affects ~25% of patients ^[1]^[7]^[8] — via adhesions distorting anatomy, tubal damage, hostile peritoneal environment, impaired oocyte quality, and defective endometrial receptivity
Endometriomas may be associated with ovarian cyst complications: rupture, haemorrhage, RARELY torsion ^[1] — torsion is rare because adhesions fix the ovary
Malignant transformation: 1% premenopausal, 1–2.5% postmenopausal → mainly endometrioid and clear cell ovarian carcinoma ^[1] — but no evidence that prophylactic removal reduces risk ^[1]
Clear cell ovarian carcinoma is the most common type associated with endometriosis ^[14]; endometrioid carcinoma is associated with endometriosis in up to 42% of cases ^[14]
Ureteric endometriosis can cause silent hydronephrosis → screen with renal ultrasound in severe/DIE cases
Thoracic endometriosis: catamenial pneumothorax (classically right-sided), haemothorax, haemoptysis
Central sensitisation: explains why pain may persist after complete surgical excision — the CNS has been reprogrammed
Conservative surgery has 58% re-operation rate at 7 years ^[13] — post-operative hormonal suppression with Mirena is essential to reduce recurrence
Repeated ovarian cystectomy → progressive loss of ovarian reserve → risk of premature ovarian insufficiency
Psychosocial impact is enormous: 30–50% depression prevalence, sexual dysfunction, relationship strain, impaired work productivity — must be addressed as part of holistic management

Active Recall - Complications of Endometriosis

References

^[1] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.2 Endometriosis — Clinical features, natural history, p45–46) ^[7] Lecture slides: GC 117. I want to have a baby male and female infertility.pdf (p8–9) ^[8] Lecture slides: Block C - I want to have a baby_ male and female infertility.pdf (p3) ^[13] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 2.3.2 Endometriosis — Surgical Treatment, p49) ^[14] Senior notes: Adrian Lui Gynecology Notes.pdf (Section on Epithelial ovarian tumours — endometrioid and clear cell carcinoma, p83) ^[15] Senior notes: Adrian Lui Gynecology Notes.pdf (Section 4.3.5 Uterine Sarcoma — stromal sarcomas, p105)

High Yield Summary

Definition: Presence of endometrial-like tissue (glands + stroma) outside the uterine cavity — hormonally responsive, cyclic bleeding, inflammation, fibrosis. Not adenomyosis (endometrium within myometrium); they commonly co-occur but are pathogenetically distinct.

Epidemiology: ~10–15% reproductive-age women; 25–50% of infertile women; accounts for ~25% of female factor infertility (one of the five important causes). Peak 25–35 years; regresses after menopause unless HRT/local aromatase. Average diagnostic delay 7–10 years.

Pathophysiology — Sampson + "second hit":

Retrograde menstruation (76–90% of women) seeds ectopic cells into dependent sites (ovaries, Pouch of Douglas, uterosacral ligaments).
Second hit: immune dysfunction (↓NK cytotoxicity, M2 macrophages), altered eutopic endometrium (↑MMPs, ↑integrins, apoptosis resistance, local aromatase), genetic susceptibility (6–10× risk in first-degree relatives).

Common sites: Ovaries (endometrioma) > POD > uterosacral ligaments > bowel/bladder/ureter; rare: diaphragm/pleura (catamenial pneumothorax), C-section scar, umbilicus.

Clinical features — classic triad: Dysmenorrhoea + deep dyspareunia + infertility. Cyclical pattern is the hallmark (premenstrual onset, may persist after menses). Also: dyschezia, cyclical haematuria/rectal bleeding, chronic pelvic pain. Pain does NOT correlate with ASRM stage — depth/nerve involvement and central sensitisation matter more.

Exam: Uterosacral nodularity, fixed retroverted uterus, tender fixed adnexal mass (endometrioma). Best examined during menstruation. "Frozen pelvis" in severe disease.

Endometrioma: Homogeneous "ground-glass" low-level echoes on TVUS; chocolate fluid; 1% premenopausal / 1–2.5% postmenopausal malignant transformation risk (endometrioid, clear cell CA).

ASRM staging (I–IV): Surgical; poor correlation with pain/fertility. #Enzian for DIE. EFI predicts fertility post-surgery.

Risk factors ↑: Early menarche, short cycles, heavy flow, nulliparity, family history, dioxins. Protective: multiparity, COCP, late menarche.

High Yield Summary — Differential Diagnosis

Think by presentation: chronic pelvic pain / dysmenorrhoea | pelvic mass | infertility.

Primary vs secondary dysmenorrhoea — endometriosis is the most common cause of secondary dysmenorrhoea:

Primary: onset near menarche, pain limited to menses (48–72 h), normal exam, responds to NSAIDs/COCP.
Secondary: late onset/progressive, pain before/after menses, dyspareunia, dyschezia, menorrhagia, subfertility, abnormal exam.

Feature	Endometriosis	Primary dysmenorrhoea	Adenomyosis	PID	IBS
Dyspareunia	Deep, common	Uncommon	Rare	Deep (acute)	Uncommon
Uterine size	Normal	Normal	Diffuse, boggy	Normal/tender	Normal
Exam	POD nodularity	Normal	Globular tender uterus	Cervical excitation	Normal
Cyclical?	Yes	Yes (menses only)	Yes	No (fever/discharge)	No

Pelvic mass (endometrioma) DDx: functional cyst, dermoid, cystadenoma, ovarian cancer, TOA, ectopic — always β-hCG first.

Endometrioma vs ovarian cancer: Young + cyclical pain + ground-glass cyst + mild CA125 vs postmenopausal + solid components/papillae/ascites + marked CA125.

Infertility DDx (five causes): ovulatory dysfunction (15%), tubal (20%), endometriosis (25%), male (30%), unexplained.

Non-gynae mimics: IBS (50–80% overlap — not cyclical), interstitial cystitis, appendicitis, ureteric colic, myofascial pain.

Emergency DDx (acute pain): ruptured ectopic, torsion, ruptured cyst, appendicitis.

High Yield Summary — Diagnosis

Two levels of diagnosis:

Presumed: Typical symptoms + supportive imaging + response to empirical treatment (ESHRE 2022, NICE 2024).
Definitive: Laparoscopy ± biopsy (endometrial glands + stroma ± haemosiderin-laden macrophages). Laparoscopy NOT mandatory before starting treatment.

Indications for laparoscopy: treatment failure, infertility workup, diagnostic uncertainty, DIE surgical planning.

Stepwise algorithm: History/exam → β-hCG → TVUS → consider MRI → empirical medical Rx OR laparoscopy.

Modality	Role	Key findings
TVUS	First-line	Endometrioma (ground-glass); negative sliding sign (POD obliteration); DIE nodules. Sensitivity ~11% for superficial peritoneal disease — normal USS does NOT exclude
MRI	Second-line / pre-op DIE mapping	Endometrioma: T1 high + T2 shading; DIE nodules
CA125	NOT diagnostic	Mildly ↑ in endometriosis; low specificity in premenopausal women
Laparoscopy ± biopsy	Gold standard	Red (active), black/powder-burn, white (fibrotic) lesions; negative laparoscopy reliably excludes

Infertility workup: Semen analysis, day 21 progesterone, AMH, HSG/HyCoSy (if no comorbidities) vs laparoscopy + chromopertubation (if suspected endometriosis/PID/ectopic).

POD exam: Nodularity/thickening/tenderness — highly specific for DIE.

High Yield Summary — Management

Core question: Does she want to conceive now?

No / not now → medical suppression (contraceptive).
Yes → surgery ± assisted reproduction; avoid prolonged suppressive hormones (wastes reproductive time).

Pain — medical (first line):

NSAIDs (symptom only; mefenamic acid blocks PG synthesis + receptors).
COCP continuous regimen (↓ HPO axis, decidualise endometrium).
Progestins: Mirena, dienogest, DMPA, norethisterone.

Pain — second/third line:

GnRH agonist ± add-back (max 6 months without add-back — bone loss).
GnRH antagonists (elagolix), aromatase inhibitors (specialist).
Conservative surgery: excision/ablation + cystectomy + adhesiolysis ("see and treat") — pain 73% vs 21%, live birth 30% vs 18% vs diagnostic lap alone; 58% re-op at 7 years.
Definitive: TAH + BSO + excise all lesions (family complete, failed conservative) — less recurrence but may not cure pain (central sensitisation).
Post-op Mirena ≥18–24 months — ↓ dysmenorrhoea recurrence.

Infertility:

Stage I/II: Laparoscopic excision ± IUI + COS.
Stage III/IV: IVF/ICSI (± pre-treatment GnRH agonist 3–6 months; cystectomy if endometrioma >4 cm — balance ovarian reserve).
Medical suppression does NOT improve natural fertility after discontinuation.

Asymptomatic incidental disease: Observe — treat symptoms, not the scan.

DIE: MDT (colorectal, urology, pain team).

High Yield Summary — Complications

Reproductive:

Infertility (~25%): adhesions, tubal damage, hostile peritoneal fluid, ↓oocyte quality, defective implantation.
Adverse pregnancy: ↑ ectopic, miscarriage, preterm birth, placenta praevia, CS rate. Symptoms often improve in pregnancy (decidualisation).

Endometrioma: Rupture (chemical peritonitis), haemorrhage, torsion RARE (adhesions fix ovary).

Malignant transformation: 1% premenopausal, 1–2.5% postmenopausal → mainly clear cell and endometrioid ovarian CA (oxidative stress/ARID1A); no evidence prophylactic removal reduces risk. Suspect if: new solid components, rapid growth, rising CA125, postmenopausal change.

DIE organ complications:

Bowel: cyclical rectal bleeding, stricture, obstruction.
Ureteric: silent hydronephrosis → screen renal USS in severe/DIE.
Thoracic: catamenial pneumothorax (classically right-sided), haemothorax, haemoptysis.

Adhesions: Frozen pelvis, bowel obstruction, surgical difficulty.

Chronic pain: Central sensitisation → pain persists after excision; comorbid IBS, IC, fibromyalgia.

Treatment-related: GnRH agonist bone loss; cystectomy ↓ ovarian reserve; bowel/ureter injury with DIE surgery; 58% re-op at 7 years without post-op suppression.

Psychosocial: Depression 30–50%, sexual dysfunction, opioid dependence.

Endometriosis

Definition

Epidemiology

Prevalence

Demographics

Hong Kong Context

Risk Factors

Factors that Increase Risk

Factors that Decrease Risk (Protective)

Anatomy and Key Anatomical Sites

Normal Endometrium

Common Sites of Endometriosis (in descending order of frequency)

Extra-pelvic Sites (Rare but Important for Exams)

Gross Morphology of Endometriotic Lesions

Aetiology and Pathophysiology

Theory 1: Retrograde Menstruation (Sampson's Theory, 1927)

Theory 2: Coelomic Metaplasia

Theory 3: Lymphatic and Haematogenous Dissemination

Theory 4: Iatrogenic Transplantation (Direct Implantation)

Theory 5: Stem Cell Theory

The "Second Hit" — Why Only Some Women Develop Disease

1. Immune Dysfunction

2. Altered Endometrial Biology

3. Genetic Susceptibility

The Pathophysiological Cascade

Pathophysiology of Pain in Endometriosis

Pathophysiology of Infertility in Endometriosis

Classification

rAFS/ASRM Revised Classification (1996)

ENZIAN Classification (Updated 2021: #Enzian)

Endometriosis Fertility Index (EFI)

Clinical Features

General Principles

Symptoms

1. Dysmenorrhoea (Painful Periods) — Most Common Symptom

2. Chronic Pelvic Pain (CPP)

3. Deep Dyspareunia (Pain During Deep Intercourse)

4. Infertility

5. Dyschezia (Painful Defaecation)

6. Dysuria (Painful Urination) and Urinary Symptoms

7. Cyclical Rectal Bleeding

8. Catamenial Symptoms at Distant Sites (Rare)

9. Constitutional / Associated Symptoms

Signs (Physical Examination Findings)

Abdominal Examination

Bimanual Vaginal Examination

Speculum Examination

Rectal Examination

Endometrioma ("Chocolate Cyst") — Special Consideration

Summary of Clinical Features by System

Active Recall - Endometriosis (Definition, Epidemiology, Aetiology, Classification, Clinical Features)

References

The Core Problem: Why is DDx Important?

Organising Framework for the Differential Diagnosis

A. Differential Diagnosis of Chronic Pelvic Pain / Dysmenorrhoea

Gynaecological Causes

Gastrointestinal Causes

Urological Causes

Musculoskeletal / Other Causes

B. Differential Diagnosis of Pelvic Mass (Endometrioma)

Gynaecological Causes of Adnexal Mass

Non-Gynaecological Causes of Pelvic Mass

C. Differential Diagnosis of Infertility (Endometriosis as a Cause)

D. Differential Diagnosis by Specific Symptom Presentation

Clinical Approach to Differential Diagnosis — Decision Algorithm

Key Distinguishing Features: Endometriosis vs. Its Main Mimics

Active Recall - Differential Diagnosis of Endometriosis

The Diagnostic Challenge — Why Is Endometriosis So Hard to Diagnose?

Diagnostic Criteria

1. Presumed (Clinical) Diagnosis

2. Definitive (Surgical/Histological) Diagnosis

Diagnostic Algorithm

Investigation Modalities — Detailed Breakdown

1. Pregnancy Test

2. Transvaginal Ultrasound (TVUS) — First-Line Imaging

3. Pelvic Examination Findings (Revisited for Diagnostic Context)

4. Magnetic Resonance Imaging (MRI)

5. Blood Tests

CA125

Other Blood Tests