Congenital Uterine & Mullerian Anomalies

Mullerian (paramesonephric) duct anomalies are structural defects arising from failure of formation, fusion, or septal resorption of the Mullerian ducts. They are high-yield for distinguishing the septate (resorption defect, surgically correctable) from the bicornuate (fusion defect, usually not surgical) uterus — a classic NEET PG vignette.

Embryology — the basis of every anomaly

The female genital tract develops from the paired Mullerian (paramesonephric) ducts, which give rise to the fallopian tubes, uterus, cervix, and upper two-thirds of the vagina. The lower one-third of the vagina is derived from the urogenital sinus (sinovaginal bulbs → vaginal plate).

Three sequential embryological steps occur, and anomalies are classified by which step fails:

1. Organogenesis / formation → failure produces agenesis or hypoplasia (one or both ducts fail to develop). Unilateral failure → unicornuate uterus.
2. Fusion → the two ducts fuse in the midline. Failure of fusion → didelphys (no fusion) or bicornuate (incomplete fusion of the upper segment).
3. Septal resorption → the midline septum between the fused ducts is resorbed. Failure → septate uterus; incomplete resorption with a near-normal fundus → arcuate uterus.

High-yield: Mullerian ducts form the upper vagina, cervix, uterus and tubes; the ovaries are NOT Mullerian (they arise from the genital ridge). Hence ovarian function and secondary sexual characters are normal in Mullerian agenesis (MRKH), and karyotype is 46,XX.

Because the Mullerian ducts develop adjacent to the mesonephric (Wolffian) ducts and the metanephros (kidney), Mullerian anomalies are strongly associated with renal tract anomalies — most commonly unilateral renal agenesis, ipsilateral to the affected/obstructed side.

High-yield: Always image the urinary tract in any Mullerian anomaly. Up to 30–40% (highest with unicornuate and didelphys) have associated renal anomalies, classically renal agenesis on the side of the rudimentary/obstructed horn.

Classification systems

Two systems are tested. The ASRM (American Society for Reproductive Medicine, originally AFS 1988, revised 2021) classification is the most exam-relevant; the ESHRE/ESGE 2013 system is the European alternative.

ASRM / AFS Class	Anomaly	Embryological defect
Class I	Hypoplasia / Agenesis (incl. MRKH)	Formation failure
Class II	Unicornuate (± rudimentary horn)	Unilateral formation failure
Class III	Uterus didelphys	Complete fusion failure
Class IV	Bicornuate (partial/complete)	Partial fusion failure
Class V	Septate (partial/complete)	Septal resorption failure
Class VI	Arcuate	Near-complete resorption (mild)
Class VII	DES-related (T-shaped)	Diethylstilbestrol exposure in utero

High-yield: The septate uterus (Class V) is the most common Mullerian anomaly and is the one most strongly associated with recurrent pregnancy loss — and it is the most correctable (hysteroscopic resection). Arcuate is the mildest and generally a normal variant.

The ESHRE/ESGE system classifies by uterus (U0–U6), cervix (C0–C4) and vagina (V0–V4), which allows combined coding (e.g. septate uterus with cervical and vaginal septa).

Individual anomalies — features and clinical pearls

Septate uterus (Class V)

• External fundal contour is normal/convex (the key distinguishing feature).
• A fibrous (occasionally muscular) midline septum divides the cavity — partial (subseptate) or complete (to the cervix/vagina).
• Worst reproductive prognosis: highest rates of recurrent first-trimester miscarriage, due to implantation on the poorly vascularised fibrous septum.
• Management: hysteroscopic septal resection (metroplasty / septoplasty) — minimally invasive, leaves no abdominal scar, and allows subsequent vaginal delivery.

Bicornuate uterus (Class IV)

• External fundal contour shows a deep midline cleft/indentation (>1 cm) — two divergent horns.
• Two endometrial cavities communicating at a single cervix (bicornuate unicollis) or two cervices (bicollis).
• Reproductive issues: second-trimester loss, preterm labour, malpresentation rather than early miscarriage.
• Surgery is rarely needed; if indicated, abdominal metroplasty (Strassman) is done.

Uterus didelphys (Class III)

• Complete duplication: two uteri, two cervices, often a longitudinal vaginal septum.
• Classic presentation: dyspareunia, "double" tampon insertion problems, or an obstructed hemivagina with ipsilateral renal agenesis (OHVIRA / Herlyn–Werner–Wunderlich syndrome) — presents post-menarche with cyclical pelvic pain and a paravaginal mass (haematocolpos).
• Generally the best obstetric outcome among major fusion anomalies; surgery usually unnecessary except resecting an obstructing vaginal septum.

Unicornuate uterus (Class II)

• Single banana-shaped horn from one duct; the other duct fails → may leave a rudimentary horn, which can be communicating or non-communicating, and with or without functional endometrium.
• Most associated with renal agenesis (ipsilateral) — image the kidneys.
• A non-communicating rudimentary horn with functional endometrium → haematometra, cyclical pain, and risk of ectopic (cornual/horn) pregnancy which can rupture catastrophically → excise the rudimentary horn.

Mullerian agenesis — MRKH syndrome (Class I)

• Mayer–Rokitansky–Küster–Hauser syndrome: congenital absence of the uterus and upper vagina.
• 46,XX, normal ovaries, normal secondary sexual characters, normal testosterone.
• Second most common cause of primary amenorrhoea (after gonadal dysgenesis/Turner).
• Type I (isolated) vs Type II / MURCS association (Mullerian aplasia, Renal aplasia, Cervicothoracic Somite dysplasia).
• Management: vaginal dilatation (Frank's method — first line) or vaginoplasty (e.g. McIndoe, Vecchietti).

High-yield differential of primary amenorrhoea with normal breasts + absent uterus: MRKH (46,XX, raised body/pubic hair, normal testosterone) vs Androgen Insensitivity Syndrome (46,XY, scanty/absent pubic & axillary hair, male-range testosterone, testes present).

Arcuate uterus (Class VI)

• Mild concave fundal indentation; essentially a normal variant with near-normal obstetric outcomes. No treatment.

DES-related / T-shaped uterus (Class VII)

• In utero diethylstilbestrol exposure → T-shaped cavity, hypoplasia, cervical hood; linked to clear cell adenocarcinoma of the vagina/cervix. Historic, but examinable.

Septate vs Bicornuate — the most important distinction

This is the single most asked clinical discrimination because the management differs completely (hysteroscopic vs abdominal/none).

Feature	Septate uterus	Bicornuate uterus
Defect	Resorption failure	Fusion failure
External fundal contour	Normal / convex / flat	Deep cleft (cornua diverge)
Intercornual distance	Normal (<4 cm)	Wide (>4 cm)
Fundal indentation depth	—	>1 cm cleft
Reproductive impact	Recurrent early miscarriage (worst)	2nd-trimester loss, preterm
Treatment	Hysteroscopic metroplasty	Usually none / Strassman if needed

The discriminating measurement (ESHRE/ASRM-type morphometric criteria): the key is the fundal external contour and the angle/depth of the internal indentation.

Diagnostic flow: Internal fundal indentation present → look at the external fundal contour → Smooth/convex fundus = SEPTATE → Deep notch (>1 cm cleft) = BICORNUATE.

High-yield: You cannot reliably tell septate from bicornuate on 2D ultrasound or HSG alone, because HSG only shows the cavity, not the external contour. Both can show a "two-horned" cavity. The external fundal contour is the deciding feature.

Diagnosis & investigation of choice

Investigations move from screening to definitive:

1. 2D transvaginal ultrasound → screening; suggests an anomaly.
2. Hysterosalpingography (HSG) → shows cavity shape and tubal patency, but cannot assess external contour (so cannot separate septate from bicornuate).
3. 3D transvaginal ultrasound → excellent; shows coronal plane with both cavity and fundal contour; high accuracy, now often first-line in expert hands.
4. MRI → gold standard / investigation of choice for definitive characterisation, mapping cervical/vaginal involvement, and detecting rudimentary horns and renal anomalies in one study.
5. Combined laparoscopy + hysteroscopy → historical gold standard; allows simultaneous diagnosis (external + internal) and treatment.

High-yield: MRI is the gold-standard (non-invasive) investigation for Mullerian anomalies — it shows internal cavity, external fundal contour, cervix, vagina and the kidneys simultaneously. 3D ultrasound is the best initial accurate modality.

Management & procedures of choice

• Septate uterus → Hysteroscopic septal resection (metroplasty) is the procedure of choice — incision of the septum under hysteroscopic vision (scissors, resectoscope, or laser). Low morbidity, no uterine scar, subsequent vaginal delivery permitted.
• Bicornuate uterus (if intervention warranted after recurrent loss) → Strassman metroplasty (abdominal unification).
• Septate uterus, historical abdominal approaches: Jones (Jones & Jones) — wedge excision of the septum; Tompkins — midline incision without tissue excision.
• Didelphys / obstructing vaginal septum / OHVIRA → resection of the obstructing septum, drainage of haematocolpos.
• Unicornuate with symptomatic/functional non-communicating rudimentary horn → laparoscopic excision of the horn (prevents haematometra and horn-pregnancy rupture).
• MRKH → vaginal dilatation (Frank's, first line); surgical neovagina (McIndoe graft, Vecchietti, Davydov) if dilatation fails.

Unification procedure	Approach	Key feature
Strassman	Abdominal	Unification of bicornuate uterus; transverse fundal incision, vertical closure
Jones (Jones & Jones)	Abdominal	Wedge excision of septum (septate)
Tompkins	Abdominal	Midline incision, no tissue excised (septate)
Hysteroscopic metroplasty	Hysteroscopic	Modern treatment of choice for septate

High-yield mnemonic — septate metroplasties: "Just The Septum" → Jones (wedge), Tompkins (no excision), Septum hysteroscopic resection. Strassman is for the Structurally Split (bicornuate) uterus.

Clinical features & how patients present

• Often asymptomatic — discovered incidentally on imaging or during fertility/recurrent-loss workup.
• Recurrent pregnancy loss (especially septate).
• Preterm labour, malpresentation (breech/transverse), IUGR, retained placenta, increased caesarean rate (fusion anomalies).
• Primary amenorrhoea with normal secondary sexual characters → MRKH.
• Cyclical/cryptic pelvic pain with a normal external genital exam → obstructed system (non-communicating horn, OHVIRA) → haematometra/haematocolpos.
• Dyspareunia / longitudinal vaginal septum → didelphys.
• Infertility is not strongly increased by most anomalies except via miscarriage; conception rates are often near normal.

Complications

• Obstetric: recurrent miscarriage (septate worst), mid-trimester loss, preterm birth, malpresentation, cervical insufficiency, abnormal placentation, increased caesarean and postpartum haemorrhage.
• Gynaecological: haematometra/haematocolpos and endometriosis (retrograde menstruation in obstructed systems), dysmenorrhoea.
• Obstetric emergency: rudimentary-horn (cornual) ectopic pregnancy → late presentation, often ruptures at ~mid-pregnancy with massive haemorrhage.
• Surgical: uterine perforation, intrauterine adhesions (Asherman's) and rarely uterine rupture in subsequent pregnancy after deep metroplasty.

Key differentials

• Primary amenorrhoea with absent uterus: MRKH vs Androgen Insensitivity Syndrome vs isolated transverse vaginal septum/imperforate hymen (the latter present with cyclical pain and a bulging membrane, uterus present).
• Recurrent miscarriage: septate uterus vs antiphospholipid syndrome, cervical insufficiency, chromosomal, endocrine (thyroid, PCOS), Asherman's.
• Cyclical pelvic pain post-menarche, patent lower tract: non-communicating functional rudimentary horn vs OHVIRA vs endometrioma.
• Two cavities on HSG: septate vs bicornuate vs didelphys — resolved by external contour on 3D USG/MRI.

Recently asked / exam angle

• "Patient with recurrent first-trimester abortions, normal external fundal contour, midline cavity division — diagnosis and treatment?" → Septate uterus → hysteroscopic metroplasty.
• "Strassman operation is done for?" → Bicornuate uterus (unification).
• "Most common Mullerian anomaly?" → Septate uterus.
• "Investigation of choice / gold standard for uterine anomaly?" → MRI (with 3D USG as best initial accurate tool).
• "Post-menarche girl with cyclical pain, mass, and unilateral renal agenesis?" → OHVIRA / Herlyn–Werner–Wunderlich (obstructed hemivagina, ipsilateral renal agenesis) in uterus didelphys.
• "46,XX, primary amenorrhoea, normal breasts and pubic hair, absent uterus?" → MRKH; differentiate from AIS (46,XY, scanty pubic hair).
• "Anomaly most associated with renal agenesis?" → Unicornuate (and didelphys); image the urinary tract.
• "Tompkins vs Jones" → both for septate (Tompkins = no tissue excision; Jones = wedge excision).
• "HSG cannot distinguish?" → septate from bicornuate (no external contour view).

Rapid revision

• Mullerian ducts → tubes, uterus, cervix, upper 2/3 vagina; ovaries are NOT Mullerian.
• Defects: formation → agenesis/unicornuate; fusion → bicornuate/didelphys; resorption → septate/arcuate.
• Septate = most common anomaly and worst for recurrent early miscarriage; arcuate = mildest/normal variant.
• Septate vs bicornuate = external fundal contour: smooth/convex = septate; deep cleft (>1 cm) = bicornuate.
• HSG cannot separate septate from bicornuate; MRI = gold standard, 3D USG = best initial accurate test.
• Septate → hysteroscopic metroplasty (procedure of choice; vaginal delivery allowed).
• Bicornuate → Strassman abdominal unification (if needed); septate abdominal → Jones (wedge) / Tompkins (no excision).
• Unicornuate = strongest link to ipsilateral renal agenesis; excise functional non-communicating rudimentary horn (ectopic-rupture risk).
• Didelphys = complete duplication, longitudinal vaginal septum, best obstetric outcome; watch for OHVIRA.
• MRKH: 46,XX, normal ovaries, absent uterus/upper vagina, 2nd commonest cause of primary amenorrhoea; treat with dilatation first (Frank's).
• Always image the kidneys in any Mullerian anomaly (renal agenesis association).
• Rudimentary-horn pregnancy ruptures late with catastrophic bleeding — a surgical emergency.