Key Facts

Endometriosis is defined as the presence of endometrial-like tissue outside the uterine cavity, most commonly on the ovaries, peritoneum, uterosacral ligaments, and rectovaginal septum. It is a chronic, oestrogen-dependent condition causing significant pain and subfertility.

Epidemiology

• Affects approximately 10% of women of reproductive age (176 million worldwide)
• Present in 30-50% of women with infertility
• Present in 70-90% of women with chronic pelvic pain
• Mean diagnostic delay: 7-8 years in the UK
• Peak incidence: 25-35 years

Aetiology

• Sampson's theory (retrograde menstruation): most widely accepted; menstrual blood flows retrograde through fallopian tubes into the pelvis (occurs in 90% of women, but only 10% develop endometriosis)
• Coelomic metaplasia: peritoneal cells undergo metaplastic transformation
• Lymphatic/vascular spread: explains rare extrapelvic endometriosis
• Stem cell theory: bone marrow-derived stem cells may seed endometrial tissue
• Immune dysfunction: failure to clear ectopic endometrial cells
• Genetic: first-degree relatives have 7× increased risk

Pathophysiology

• Ectopic endometrial tissue responds to cyclical oestrogen stimulation
• Monthly proliferation, secretion, and bleeding causes chronic inflammation
• Inflammatory mediators (prostaglandins, cytokines) cause pain and adhesion formation
• Endometriomas ('chocolate cysts') form when endometriosis involves the ovary
• Deep infiltrating endometriosis (DIE) invades >5mm below the peritoneal surface
• Infertility results from tubal distortion, adhesions, impaired folliculogenesis, and altered peritoneal environment

Classic Symptoms

• Dysmenorrhoea: typically progressive, severe, may start before menses
• Chronic pelvic pain: non-cyclical component common in advanced disease
• Deep dyspareunia: particularly with rectovaginal disease
• Dyschezia: painful defaecation, especially during menstruation (suggests rectovaginal/bowel involvement)
• Subfertility: present in 30-50% of women with endometriosis

Site-Specific Symptoms

• Bladder: dysuria, haematuria (cyclical)
• Bowel: cyclical rectal bleeding, diarrhoea, constipation, bloating
• Diaphragm/thoracic: catamenial pneumothorax, shoulder pain (rare)

Red Flags

• Severe pain unresponsive to standard analgesia
• Cyclical haematuria or rectal bleeding (deep infiltrating disease)
• Palpable nodularity in the rectovaginal septum on examination
• Fixed retroverted uterus (adhesions)
• Catamenial pneumothorax (thoracic endometriosis)

Bedside

• Abdominal and bimanual pelvic examination: tenderness, nodularity in POD/uterosacral ligaments, fixed retroverted uterus, adnexal mass (endometrioma)
• Speculum examination: visible endometriotic lesions on cervix/vaginal vault (rare)

Bloods

• CA-125: may be elevated (non-specific; not recommended for diagnosis per NICE NG73)
• FBC (anaemia from associated HMB)

Imaging

• TVS: first-line imaging; can detect endometriomas (ground glass appearance) and deep nodules; operator-dependent
• MRI pelvis: for mapping deep infiltrating endometriosis; helpful for surgical planning
• NICE NG73: normal USS does not exclude endometriosis

Special Tests

• Laparoscopy: gold standard for diagnosis; allows histological confirmation and simultaneous treatment
• rASRM staging at laparoscopy: Stage I (minimal), II (mild), III (moderate), IV (severe)
• Diagnostic laparoscopy is NOT required before starting empirical treatment (NICE NG73)

Non-pharmacological

• Pain management programme: physiotherapy, psychology, TENS
• Dietary modification: some evidence for anti-inflammatory diets
• Exercise: regular physical activity may reduce pain
• Support groups: Endometriosis UK

Pharmacological

• First-line analgesia: paracetamol ± NSAIDs (ibuprofen 400mg TDS, naproxen 250-500mg BD)
• Hormonal therapy (empirical, without need for laparoscopy):
  • COC pill (continuous use to avoid withdrawal bleeds)
  • Desogestrel POP 75mcg OD
  • Mirena IUS
  • Nexplanon implant
  • Depo-Provera (medroxyprogesterone acetate 150mg IM every 12 weeks)
• Second-line: GnRH analogues (goserelin 3.6mg SC monthly or leuprorelin) with add-back HRT (continuous combined) if >6 months; causes medical menopause
• Dienogest 2mg OD: progestogen specifically licensed for endometriosis in some countries
• Neuropathic pain agents: amitriptyline 10-75mg ON, gabapentin 300-1200mg TDS for chronic pain component

Surgical/Interventional

• Laparoscopic excision (preferred) or ablation of endometriotic deposits
• Excision of endometriomas: cystectomy preserves more ovarian tissue than drainage
• Deep infiltrating endometriosis surgery: specialist centres only (colorectal, urological involvement)
• Hysterectomy ± BSO: for women with completed families and severe disease refractory to other treatments
• Presacral neurectomy: adjunct for midline pelvic pain

Referral Criteria

• Suspected endometriosis not responding to empirical treatment: gynaecology referral
• Suspected deep infiltrating endometriosis: refer to BSGE-accredited endometriosis centre
• Subfertility: reproductive medicine referral
• Multidisciplinary pain management if refractory chronic pain

• Endometriosis is a chronic condition; recurrence after surgery is common (40-50% at 5 years)
• Surgical excision provides symptom relief in 60-80% of women
• Fertility: spontaneous pregnancy possible in mild disease; IVF success rates comparable to other causes of subfertility
• Malignant transformation: rare (<1%); endometrioid and clear cell ovarian carcinoma associated with endometriosis
• Symptoms typically improve at menopause (though HRT may reactivate disease)
• Significant impact on quality of life, mental health, and relationships

rASRM Staging System

NICE NG73 Key Recommendations