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OG34.6 | Endometriosis-Adenomyosis Spectrum — SDL Guide

Learning Objectives

• Describe the etiopathogenesis of endometriosis and adenomyosis, including Sampson's retrograde menstruation theory and the adenomyosis endometrial-myometrial disruption model.
• Identify the clinical features distinguishing endometriosis (dysmenorrhoea, dyspareunia, infertility) from adenomyosis (menorrhagia, bulky tender uterus).
• Select and interpret appropriate investigations: transvaginal ultrasound, MRI pelvis, diagnostic laparoscopy, and CA-125.
• Outline medical and surgical management options for both conditions, including fertility-preserving and definitive approaches.
• Explain the implications of endometriosis and adenomyosis on reproductive health and long-term fertility.

INSTRUCTIONS

Endometriosis and adenomyosis are the two most clinically important conditions caused by ectopic endometrial tissue, together accounting for a substantial burden of pelvic pain, dysmenorrhoea, and female infertility. They are frequently encountered in gynaecological outpatient practice and are tested prominently in final MBBS examinations. This module guides you through the clinical presentation, pathological basis, diagnostic approach, and management of both conditions, with an emphasis on the key features that allow a clinician to distinguish them and choose appropriate therapy. A comparison framework is used throughout to solidify understanding of where these two conditions overlap and where they diverge.

References

• DC Dutta's Textbook of Gynecology, 9th ed., Ch. 14 — Endometriosis and Adenomyosis (textbook)
• Shaw's Textbook of Gynaecology, 17th ed., Ch. 21 — Endometriosis (textbook)
• ESHRE Guideline: Management of Women with Endometriosis, 2022 (guideline)
• FOGSI Good Clinical Practice Recommendations: Endometriosis, 2021 (guideline)

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Version 2.0 | NMC CBUC 2024

Clinical Presentation: When to Suspect the Endometriosis-Adenomyosis Spectrum

Recognising the clinical presentation of endometriosis and adenomyosis is the essential first step, since both are diagnoses that can only be confirmed by imaging or histology but are first suspected on clinical grounds. The two conditions have distinct symptom profiles, though they may co-exist in the same patient.

Endometriosis classically presents with the triad of secondary dysmenorrhoea, dyspareunia (deep), and subfertility. The dysmenorrhoea is characteristically secondary — meaning it begins in a patient who previously had painless periods — and progressive (worsening with each cycle). Pain typically starts 1–3 days before the period and continues throughout menstruation; in advanced disease it may become non-cyclical and persist through the cycle. Deep dyspareunia is particularly suggestive of endometriosis involving the posterior fornix, Pouch of Douglas, or uterosacral ligaments. Defaecatory pain during menstruation ('dyschezia') suggests bowel involvement. Cyclical haematuria may indicate bladder endometriosis. The absence of dysmenorrhoea does not exclude endometriosis — some patients present primarily with infertility or a pelvic mass (endometrioma).

On examination, endometriosis may produce fixed retroversion of the uterus (due to adhesions in the Pouch of Douglas), tender nodularity in the posterior fornix or along the uterosacral ligaments (palpable implants), reduced uterine mobility, and occasionally an adnexal mass (endometrioma). Clinical examination can be entirely normal in mild endometriosis.

Adenomyosis presents predominantly with menorrhagia (heavy periods), secondary dysmenorrhoea (often starting a few days before menstruation), and a uniformly enlarged, boggy, tender uterus. The uterine enlargement in adenomyosis is typically symmetrical and smooth (likened to a '12–14 week gravid uterus' in severe cases), in contrast to the irregular, non-tender enlargement of fibroids. The tenderness is characteristic and maximal just before and during menstruation. Dyspareunia may occur but is less prominent than in endometriosis. Many women with adenomyosis are multiparous and in the 35–50-year age group.

A useful clinical distinction: in endometriosis, the uterus may feel fixed (due to adhesions) but is not uniformly enlarged; in adenomyosis, the uterus is uniformly soft and boggy but mobile. The dominant symptom differs: pain dominates in endometriosis; bleeding dominates in adenomyosis.

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Pathophysiology and Basis of Disease

Understanding the pathophysiology of endometriosis and adenomyosis illuminates why each condition behaves as it does clinically and why management strategies differ.

Endometriosis — pathophysiology. The most widely accepted theory is Sampson's retrograde menstruation theory (1927): during menstruation, viable endometrial cells reflux through the fallopian tubes into the peritoneal cavity, where they implant on peritoneal surfaces, the ovary, and pelvic organs. Evidence supporting this theory includes the demonstration of retrograde menstruation in 70–90% of women with patent tubes (via laparoscopy at the time of menstruation) and the predominance of lesions in the dependent parts of the pelvis (Pouch of Douglas, ovarian fossae). However, retrograde menstruation is nearly universal, yet endometriosis develops in only 10–15% of women, implying that additional factors — immune dysregulation, altered peritoneal macrophage activity, and genetic susceptibility — determine whether implanted cells survive, proliferate, and evade immune clearance.

Alternative theories include coelomic metaplasia (Meyer's theory — multipotential peritoneal cells transform into endometrial-type tissue, explaining rare cases in men and pre-menarchal girls) and lymphovascular dissemination (accounting for distant sites such as the pleura, diaphragm, and umbilicus).

Once implanted, ectopic endometrial tissue responds cyclically to ovarian hormones — it proliferates under oestrogen and bleeds under progesterone withdrawal, just as normal endometrium does. This cyclic bleeding releases prostaglandins, interleukins (IL-1β, IL-6), and vascular endothelial growth factor (VEGF), generating local inflammation, adhesion formation, and ultimately fibrosis. The inflammatory milieu also directly impairs oocyte quality and fertilisation, contributing to infertility. Oestrogen dependence is central: endometriotic implants express aromatase (locally synthesising oestrogen) and show relative progesterone resistance, which both drives lesion persistence and explains why hormonal suppression is the cornerstone of medical therapy.

Adenomyosis — pathophysiology. Adenomyosis occurs when endometrial glands and stroma invade the myometrium, typically beyond 2.5 mm from the basal endometrium (some authorities use 1 field of high-power microscopy as the threshold). The disruption of the endometrial-myometrial junction (EMJ) — a specialised zone of smooth muscle — is central to its pathogenesis. Repeated uterine trauma (multiparity, uterine surgery, curettage) or intrinsic EMJ defects allow endometrial cells to migrate into the myometrium. Once established, the ectopic endometrial islands stimulate surrounding myometrial smooth muscle hyperplasia and hypertrophy, producing the characteristic diffuse enlargement of the uterus. Adenomyosis may be diffuse (scattered throughout the myometrium) or focal (adenomyoma — a localised nodule resembling a fibroid but without a capsule). The cyclic hormonal response of ectopic glands — bleeding within the myometrium with each menstrual cycle — causes intense prostaglandin release and myometrial spasm, producing menorrhagia (increased surface area of functional endometrium) and severe dysmenorrhoea.

Pathogenesis of Endometriosis and Adenomyosis: Retrograde Theory and Inflammatory Cascade

Sites and Staging of Endometriosis

Endometriosis can implant on virtually any peritoneal surface, but lesion distribution follows a predictable anatomical pattern based on the dependent parts of the pelvis and the proximity to the fallopian tube openings.

The ovary is the most common site (~80% of cases). When endometrial tissue implants on the ovarian cortex and bleeds cyclically, it forms a cystic structure filled with inspissated, dark-brown old blood — the endometrioma (colloquially, 'chocolate cyst'). Endometriomas are typically unilocular or multilocular, have a thick fibrous wall, and are often adherent to the posterior leaf of the broad ligament and surrounding structures. The Pouch of Douglas and uterosacral ligaments are the next most commonly involved sites, producing the nodular, tender posterior fornix characteristic of endometriosis. The rectosigmoid colon (causing dyschezia and, rarely, rectal bleeding), bladder (cyclical haematuria), uterovesical fold, and fallopian tubes are also commonly affected. Rare sites include the umbilicus (Villar's nodule — cyclical swelling and bleeding at the umbilicus), diaphragm, pleura (catamenial pneumothorax — rare but dramatic), and surgical scars.

Deep infiltrating endometriosis (DIE) refers to lesions that penetrate >5 mm below the peritoneal surface; it is associated with the most severe pain, bowel and bladder symptoms, and the greatest surgical complexity.

The revised American Society for Reproductive Medicine (rASRM) staging system is the most widely used classification:

Stage	Description	Score	Clinical Correlate
I — Minimal	Few superficial implants	1–5	May be asymptomatic or mild pain
II — Mild	More implants, shallow endometrioma <1 cm, limited adhesions	6–15	Pain + early fertility impact
III — Moderate	Bilateral endometriomas ≥1 cm, tubal/ovarian adhesions	16–40	Significant fertility impairment
IV — Severe	Large bilateral endometriomas, dense adhesions, obliterated Pouch of Douglas	>40	Severe pain, infertility common

Importantly, rASRM stage does not correlate well with pain severity — a patient with Stage I disease can have excruciating dysmenorrhoea, while a patient with Stage IV may have minimal pain. Stage does correlate (imperfectly) with fertility outcomes and guides surgical planning.

Endometriosis: Pelvic Implantation Sites and Endometrioma Morphology