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anorectal malformations

Friday 3 September 2004

Definition: Anorectal malformations comprise a wide spectrum of diseases, which can affect boys and girls, and involve the distal anus and rectum as well as the urinary and genital tracts. They occur in approximately 1 in 5000 live births.

Defects range from mild anal anomalies to complex cloacal malformations.

They can therefore be classified into the following groups: imperforated anus without fistula, ARM with rectourinary or rectogenital fistula and complex ARM (cloaca).


High anorectal malformations

- anorectal agenesis

  • without fistula
  • with rectovaginal fistula
  • with rectoprostatic fistula
  • with rectourethral fistula
  • with rectovesical fistula

- rectal atresia (high atresia)

Intermediate anorectal malformations

- rectal atresia (intermediate)

  • with rectovestibular fistula
  • with rectovaginal fistula
  • with rectourethral fistula

Low anorectal malformations

- anal agenesis without fistula
- anal agenesis with fistula

  • with anovestibular fistula
  • with anocutaneous fistula

- anal stenosis
- membranous atresia (covered anus)
- anal agenesis

Cloacal malformations

- persistent cloaca


Associated anomalies include genitourinary defects (in approximately 50% of patients) and spinal anomalies. A cloaca is associated with a urological problem (such as obstructive uropathy) in 90% of babies and with hydrocolpos in 50%.

Sacral anomalies (hemisacrum and sacral hemivertebrae) have been described; hemivertebrae may also affect the lumbar and thoracic spine, leading to scoliosis. A tethered spinal cord (in 25% of patients) may result in motor and sensory disturbances of the lower extremities. Syringomyelia and myelomeningocele can occur.

- uninary malformations or urinary anomalies (25-50%) (12778281)

- syndromic ARM

  • Townes-Brocks syndrome
  • Currarino syndrome
  • Pallister-Hall syndrome
  • trisomy 21 (Down syndrome)


The radiological evaluation of a newborn with imperforate anus should include an abdominal and pelvic ultrasound to evaluate for genitourinary defects as they need to be dealt with in the newborn period to avoid serious complications.

Spinal ultrasound in the first three months of life and magnetic resonance imaging thereafter are useful radiological modalities for detecting spinal anomalies. The risk of ARM for a sibling of a patient with ARM can reach 1%.

Patients can either undergo a primary repair procedure (anoplasty) or a protective colostomy and definitive repair at a later date, depending on the malformation.

See also

- digestive malformations


- Levitt MA, Pena A. Anorectal malformations. Orphanet J Rare Dis. 2007 Jul 26;2(1):33. PMID: 17651510