Endometriosis

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Endometriosis

Definition

Endometriosis is the presence of endometrial glands and stroma outside the uterine cavity. It is a common chronic inflammatory condition affecting 5-10% of women of reproductive age and nearly 40-50% of women with infertility.

Robbins & Kumar Basic Pathology, p. 689
Bailey and Love's Short Practice of Surgery, p. 1602

Pathogenesis

The exact mechanism remains elusive. Four main theories are proposed:

Theory	Mechanism
Regurgitation (Sampson's)	Retrograde menstruation causes endometrial tissue to implant at ectopic pelvic sites via the fallopian tubes - the most widely accepted theory
Benign metastasis	Endometrial tissue spreads to distant sites (lung, brain, bone) via blood/lymphatics
Metaplastic theory	Coelomic (mesothelial) epithelium undergoes metaplasia into endometrial tissue - explains embryological müllerian remnants
Stem/progenitor cell theory	Bone marrow stem cells differentiate into ectopic endometrial tissue

Endometriotic implants are not simply misplaced cells - they are biologically distinct, exhibiting elevated:

Prostaglandin E2 and COX-2 (inflammation)
VEGF (angiogenesis)
Matrix metalloproteinases (MMPs)
Aromatase - producing excess local estrogen from androgens, reinforcing estrogen dependency

Pathogenesis of Endometriosis - interplay between endometriotic implants and activated macrophages

Fig. 17.9 - Pathogenesis of endometriosis (Robbins & Kumar Basic Pathology)

Classification / Types

Three main types exist:

Superficial peritoneal endometriosis - small lesions on pelvic peritoneum
Ovarian endometriosis (endometriomas) - "chocolate cysts" filled with thick dark fluid, reported in 17-44% of cases; densely adherent to peritoneum
Deep infiltrating endometriosis (DIE) - defined as endometrial-like tissue >5 mm beneath the peritoneum, involving uterosacral ligaments, vagina, bowel, bladder, or ureters; highest risk of malignant transformation

The ASRM classification system (I-IV: minimal, mild, moderate, severe) is commonly used operatively, though it has poor correlation with symptom severity.

Sites of Involvement

Common (pelvic):

Ovaries (most common)
Uterosacral ligaments
Pouch of Douglas
Fallopian tubes
Pelvic peritoneum
Bladder/ureters

Rare (extra-pelvic):

Diaphragm (see laparoscopic image below)
Lungs - causing catamenial haemoptysis or pneumothorax
Bowel/rectosigmoid
Periumbilical tissues and laparotomy scars
Brain, bone (via haematogenous spread)

Endometriosis on the peritoneal surface of the diaphragm seen laparoscopically

Fig. 87.11 - Endometriosis on the peritoneal surface of the diaphragm (Bailey & Love's)

Morphology

Grossly, lesions appear as:

"Powder burn" / "gunshot" lesions - black, dark brown, or blue-black puckered nodules containing old haemorrhage with surrounding fibrosis (classic appearance)
Atypical/subtle lesions - red flame-like, vesicular, polypoid, or haemorrhagic implants; serous/clear vesicles
White plaques or scarring, yellow-brown peritoneal discoloration
Endometriomas - large ovarian cysts containing thick "tar-like" fluid, due to cyclic bleeding into the cyst

Histologically: functioning endometrial glands + stroma undergo cyclic bleeding at ectopic sites, forming red-brown nodules (1-2 mm to 1-2 cm). Organisation of haemorrhage leads to fibrosis and adhesions that obliterate the pouch of Douglas and distort pelvic anatomy.

Clinical Features

Symptoms arise from cyclical bleeding at ectopic sites and inflammation. A significant proportion of women are asymptomatic.

Pain symptoms (most common):

Dysmenorrhoea (cyclic pelvic pain with menstruation)
Deep dyspareunia (pain during intercourse)
Dyschezia (pain on defecation)
Dysuria / haematuria
Chronic non-cyclical pelvic pain

Other symptoms:

Infertility (present in up to 50% of affected women)
Fatigue
Rectal bleeding (haematochezia) - if bowel involvement
Cyclic haemoptysis / pneumothorax - if pulmonary involvement

Examination findings suggestive of endometriosis:

Pelvic tenderness
Fixed retroverted uterus
Tender uterosacral ligaments
Enlarged ovaries
Deeply infiltrating nodules in the pouch of Douglas
Visible blue-domed cystic lesions in the posterior fornix (vaginal DIE)

Note: examination may be entirely normal.

Diagnosis

Method	Role
Laparoscopy + biopsy	Gold standard - direct visualisation and histological confirmation
Transvaginal ultrasound (TVUS)	Reliably detects endometriomas and severe/deep pelvic disease; misses superficial peritoneal lesions
Transrectal ultrasound	Useful for bowel and recto-vaginal endometriosis
MRI pelvis	Detects haemosiderin deposits; useful for DIE mapping, surgical planning
Sigmoidoscopy	Assesses bowel involvement; measures distance of rectal lesion from anal verge (critical for surgical planning)
CA-125	Non-specific; may be elevated but not diagnostic

A clinical diagnosis can be made empirically in women with typical symptoms, and medical treatment commenced without histological confirmation - laparoscopy is reserved for cases not responding to initial management or where infertility is a concern.

Bailey and Love's Short Practice of Surgery, p. 1603

Management

1. Conservative (watchful waiting)

Appropriate for asymptomatic or mildly symptomatic women not seeking fertility.

2. Medical Management

All hormonal therapies aim to suppress ovarian estrogen production, causing endometrial atrophy at ectopic sites. They treat symptoms but do not permanently cure the disease.

Drug	Mechanism	Notes
Combined oral contraceptive pill (COCP)	Suppresses gonadotropins → inhibits estrogen biosynthesis	First-line; well-tolerated
Progestogens (medroxyprogesterone, dienogest)	Decidualization of ectopic tissue, anti-proliferative	Effective for pain; dienogest widely used
Levonorgestrel IUS (Mirena)	Local progestogenic effect	Used off-label; good for menorrhagia + pain
GnRH agonists (leuprolide, goserelin, nafarelin)	Downregulate pituitary GnRH receptors → medical castration	"Add-back" therapy (low-dose oestrogen or norethindrone 5 mg) required if >6 months, to limit hypoestrogenic effects and bone loss
GnRH antagonist - Elagolix	Oral receptor antagonist; suppresses gonadotropins	Effective for dysmenorrhoea and pelvic pain; risk of hot flashes, dyslipidaemia, bone mineral density reduction
Danazol	Synthetic androgen; inhibits pituitary-ovarian axis via feedback	FDA-approved but rarely used - significant androgenic side effects (hirsutism, hepatotoxicity)
NSAIDs	Prostaglandin inhibition	Simple analgesia for pain control

Goodman & Gilman's Pharmacological Basis of Therapeutics, p. 303-307

3. Surgical Management

Conservative surgery (laparoscopic):

Ablation or excision of endometriotic lesions
Adhesiolysis to restore pelvic anatomy
Cystectomy for endometriomas
Aim: remove ectopic tissue while preserving fertility
Bowel integrity testing (methylene blue / air insufflation) should be performed if bowel dissection is needed
Ureteral stents should be considered in bladder/trigonal endometriosis

Definitive surgery:

Hysterectomy + bilateral salpingo-oophorectomy (BSO) + total excision of endometriotic disease - offers best chance of cure; reserved for women who have completed their family

Surgical risks include bowel, bladder, and ureteric injury (~2 in 1000 women); risk is higher in DIE, repeat operations, and cases involving rectal lesions close to the anal verge (5-8 cm) where anastomotic leak risk is elevated.

Endometriosis and Infertility

Infertility present in 25-40% of infertile women
Mechanisms include: tubal involvement, impaired oocyte maturation, pelvic adhesions, altered peritoneal environment (elevated inflammatory cytokines), and possibly impaired implantation
Surgical correction of anatomical distortion may improve natural fertility; IVF is the primary option for tubal-factor infertility

Malignant Transformation

Overall risk is low
Primarily associated with deep infiltrating endometriosis and ovarian endometriomas
Most common histological type arising in endometriosis: endometrioid and clear cell carcinomas of the ovary

Key Points Summary

Common (5-10% of reproductive-age women), estrogen-dependent, chronic inflammatory condition
Leading pathogenic theory: retrograde menstruation
Classic presentation: dysmenorrhoea + dyspareunia + infertility
Gold standard diagnosis: laparoscopy with biopsy
Medical treatment suppresses ovarian function; surgery excises disease
Definitive cure: hysterectomy + BSO in women who have completed childbearing
Recurrence is common after conservative treatment

Sources:

Robbins & Kumar Basic Pathology (9780323790185), p. 689
Bailey and Love's Short Practice of Surgery, 28th Ed. (9780367548117), pp. 1602-1604
Goodman & Gilman's The Pharmacological Basis of Therapeutics (9781264258079), pp. 303-307

Recent evidence note: A 2025 systematic review (PMID 39373298) highlights that the median diagnostic delay for endometriosis remains 4-11 years globally, driven by symptom normalisation and overlap with other conditions. A 2026 meta-analysis (PMID 40705433) demonstrates significant benefit of physiotherapy for endometriosis-associated pelvic pain - an emerging non-pharmacological option not yet reflected in older textbooks.

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