Developmental defects of the female genitourinary tract (Müllerian anomalies)

Overview

The uterus, cervix and upper vagina form from the two Müllerian (paramesonephric) ducts, which must:

1. Form (organogenesis),
2. Fuse in the midline,
3. Canalise (the vaginal plate hollows out), and
4. Absorb the midline septum.

A failure at any step gives a predictable defect. Müllerian anomalies affect up to 6% of women, are often silent, and are linked with infertility, recurrent miscarriage, preterm birth and malpresentation. Renal anomalies occur in up to 30%, because the urinary and genital systems share the mesonephric duct.

Classification by developmental failure

ESHRE/ESGE classification (used in Europe)

The older American (AFS) system numbers the same types I-VII: hypoplasia/agenesis, unicornuate, didelphys, bicornuate, septate, arcuate and DES-related.

Uterine anomalies

Septate uterus

• The septum is not absorbed; the outer shape is normal.
• The commonest major uterine anomaly and the one with the poorest reproductive outcome (recurrent first-trimester miscarriage), because the septum is poorly vascularised for implantation.
• Imaging: smooth or convex fundal outline with a midline septum that may reach the cervix (complete).
• Treatment: hysteroscopic resection of the septum may be offered after recurrent loss, but routine correction is not advised; decide case by case.

Bicornuate uterus

• Partial failure of fusion: one cervix, two horns, with a notched (indented) fundus.
• Pregnancy: malpresentation (breech, transverse lie), preterm labour, retained placenta.
• Surgery is rarely needed.

Uterus didelphys

• Complete failure of fusion: two uteri and two cervices, often with a longitudinal vaginal septum.
• If one hemivagina is blocked, there is cyclical pain and a paravaginal mass, usually with renal agenesis on the same side (obstructed hemivagina with ipsilateral renal anomaly).

Unicornuate uterus and rudimentary horn

• One Müllerian duct fails to develop; a single banana-shaped cavity with one tube.
• Renal agenesis is common, usually on the side of the missing horn.
• A rudimentary horn may be present:
  • if it has functioning endometrium but no connection, blood collects (haematometra), causing cyclical pain and endometriosis;
  • a pregnancy in the rudimentary horn may rupture in the second trimester with severe bleeding.
• A non-communicating functional horn is usually removed.

Arcuate uterus

• A slight fundal dip in the cavity from almost-complete septal absorption; usually of little clinical importance.

DES-related (T-shaped) uterus

• Daughters exposed in utero to diethylstilboestrol (a synthetic oestrogen once given to prevent miscarriage) have a T-shaped cavity, vaginal adenosis and a risk of vaginal and cervical clear cell adenocarcinoma.

Comparison table

Müllerian agenesis (MRKH syndrome)

• Mayer-Rokitansky-Küster-Hauser syndrome: the Müllerian system fails to develop, so the uterus and upper vagina are absent or rudimentary.
• Affects between roughly 1 in 5,000 and 1 in 40,000 girls; cause unknown.
• 46,XX with normal ovaries, so breasts, pubic hair and growth are normal and ovulation occurs.
• Presents with primary amenorrhoea in a girl with otherwise normal puberty; examination shows a short blind-ending vagina (lower part from the urogenital sinus).
• Look for renal and skeletal anomalies.
• Treatment:
  • psychological support and clear explanation;
  • vaginal dilators of increasing size are first line; surgical vaginoplasty only if dilation fails;
  • genetic children are possible by egg collection, IVF and a surrogate; uterine transplant is being studied.

MRKH versus complete androgen insensitivity (CAIS)

Outflow obstruction (canalisation defects)

Imperforate hymen

• The commonest cause of outflow obstruction; the block is at the hymen, at the lower end of the vagina.
• Presents in early adolescence: primary amenorrhoea with normal breasts and pubic hair, cyclical lower abdominal pain, sometimes urinary retention or a lower abdominal mass.
• Old blood fills the vagina (haematocolpos) and later the uterus (haematometra).
• Sign: a tense, bluish, bulging membrane at the introitus, more obvious on straining.
• Treatment: surgical incision of the hymen and drainage (in a Ten Teachers case, about 700 mL of old blood was released).

Transverse vaginal septum

• A horizontal membrane higher in the vagina, from failed fusion or canalisation between the Müllerian part and the sinus part.
• Similar story, but the hymen is normal and no bulge is seen at the introitus; a probe stops short in a blind vagina.
• Ultrasound or MRI shows blood above the block; treat by excision (higher and thicker septa are harder to repair).

Other obstructions

• Longitudinal vaginal septum: often with didelphys; may cause dyspareunia or obstructed delivery.
• Cervical agenesis: rare; obstructed menses with a uterus present.

Urinary tract defects relevant to gynaecology

• Renal agenesis, pelvic kidney and duplex systems are the anomalies most often found with Müllerian defects.
• Ectopic ureter in a girl: in a complete duplex system the upper moiety ureter may open below the bladder neck (urethra or vagina), giving constant dribbling despite normal voiding.
• Urethral diverticulum: dribbling after voiding, dyspareunia, recurrent UTI.
• Congenital weakness of support: prolapse in a young nulliparous woman suggests spina bifida occulta (look for a sacral hair tuft) or a connective tissue disorder (Ehlers-Danlos, Marfan).

Investigations

Effects on pregnancy

• First- and second-trimester miscarriage (especially septate).
• Preterm labour and cervical weakness.
• Malpresentation (breech, transverse), FGR, retained placenta, higher caesarean rate.
• Rupture of a rudimentary horn pregnancy.

Quick revision

• Up to 6% of women; renal anomalies up to 30%.
• No formation: MRKH, unicornuate. No fusion: bicornuate, didelphys. No canalisation: imperforate hymen, transverse septum. No resorption: septate, arcuate.
• Septate: smooth fundus, worst for miscarriage, hysteroscopic resection if indicated.
• Bicornuate: indented fundus, malpresentation.
• Didelphys: two cervices, longitudinal vaginal septum.
• MRKH: 46,XX, normal ovaries, dilators first.
• Imperforate hymen: bluish bulge, haematocolpos, incise and drain.
• DES: T-shaped cavity, vaginal adenosis, clear cell carcinoma.

Written by The House Job from standard references (Gynaecology by Ten Teachers; Obstetrics by Ten Teachers).

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