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Adenomyosis

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Adenomyosis

Definition

Adenomyosis is the presence of endometrial glands and/or stroma within the myometrium (uterine wall), with secondary smooth muscle hyperplasia. The ectopic tissue remains in continuity with the endometrium, representing presumed downward invasion of endometrial tissue between smooth muscle fascicles. This distinguishes it from endometriosis, where endometrial tissue is outside the uterus entirely. — Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 929; Robbins & Kumar Basic Pathology, p. 689

Epidemiology

  • Found in 10–88% of hysterectomy specimens (wide range due to variable diagnostic thresholds)
  • Occurs in up to 20% of uteri on microscopic examination
  • Prevalence ~30% in reproductive-age patients, rising in later reproductive years
  • More common in multiparous women
  • ~33% are asymptomatic — Grainger & Allison's Diagnostic Radiology, p. 898; Sabiston Textbook of Surgery

Pathogenesis

Not fully understood. Adenomyosis likely shares some pathophysiology with endometriosis. The leading hypothesis is invagination/downward growth of the basalis layer of the endometrium into the myometrium. It frequently coexists with uterine leiomyomata.

Pathology / Morphology

On microscopy: irregular nests of endometrial stroma with or without glands, arranged within the myometrium. The ectopic endometrial tissue induces reactive hypertrophy of the surrounding myometrium, resulting in:
  • Enlarged, globular uterus
  • Thickened uterine wall
The tissue may respond to hormonal cycling, causing localised haemorrhage. — Robbins & Kumar Basic Pathology, p. 689

Clinical Features

FeatureDetail
DysmenorrheaSecondary, colicky; worsens premenstrually
Menorrhagia / menometrorrhagiaHeavy and/or irregular menses
DyspareuniaPelvic pain with intercourse
Pelvic painEspecially premenstrual
Uterine enlargementDiffuse, globular — found on examination
InfertilityAssociated but less primary than endometriosis
Symptoms correlate with the extent and depth of myometrial involvement. Can coexist with endometriosis. — Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 929

Diagnosis

Definitive diagnosis is histological — traditionally confirmed only after hysterectomy. However, imaging allows pre-operative diagnosis.

Transvaginal Ultrasound (TVUS)

Accuracy 68–86% for diffuse disease; lower accuracy when coexisting fibroids or focal adenomyosis are present.
Ultrasound features:
  • Enlarged uterus with globular configuration
  • Asymmetry of anterior and posterior uterine walls
  • Diffuse echogenic nodules and subendometrial echogenic linear striations
  • 2–6 mm subendometrial cysts (haemorrhagic foci) in ~50%
  • Poor definition of the endomyometrial interface
  • "Rain shower" appearance — multiple fine areas of attenuation
  • Colour Doppler: speckled pattern of increased vascularity
Ultrasound of adenomyosis showing asymmetric wall thickness and hyperechoic islands
TVS measurement of uterine walls and 3D junctional zone assessment

MRI

MRI is superior for distinguishing adenomyosis from fibroids — clinically important for management planning.
MRI features (T2-weighted):
  • Ill-defined areas of low myometrial signal intensity — smooth muscle hyperplasia
  • Focal or diffuse thickening of the junctional zone (JZ):
    • JZ ≥ 12 mm → predicts adenomyosis with high accuracy
    • JZ ≤ 8 mm → excludes adenomyosis with high accuracy
    • JZ 8–12 mm → indeterminate; use ancillary criteria
  • High T2 signal foci within low-signal myometrium = islands of ectopic endometrial tissue
  • High T1 signal foci = punctate haemorrhage within ectopic tissue (95% positive predictive value)
  • High T2 linear striations ("finger-like projections") extending from endometrium into myometrium
  • Rarely: cystic adenomyosis with high T1 / intermediate-low T2 signal
MRI mimics: myometrial contractions, endometrial carcinoma, fibroids. — Grainger & Allison's Diagnostic Radiology, p. 898

Management

Management is guided by age, severity of symptoms, and desire for future fertility.
ApproachOptions
AnalgesiaNSAIDs
Hormonal suppressionCombined oral contraceptives, progestins (oral, IM injection, or LNG-IUS), GnRH agonists
Minimally invasiveUterine artery embolization (effective)
DefinitiveHysterectomy — guarantees relief of dysmenorrhea; reserved for completed family or treatment failure
Management follows the same protocol as endometriosis treatment. The levonorgestrel intrauterine system (LNG-IUS) is often first-line for those wishing to preserve the uterus. — Berek & Novak's Gynecology, p. 581–582

Key Points

  • Adenomyosis = endometrial tissue within the myometrium (vs. endometriosis = outside the uterus)
  • Classic triad: dysmenorrhea, menorrhagia, enlarged globular uterus
  • Histological confirmation remains the gold standard, but MRI with JZ ≥12 mm is highly predictive
  • Often coexists with fibroids and endometriosis
  • Definitive treatment is hysterectomy; hormonal therapies provide symptom control
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