Anorectal Malformations

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Original Author(s): Matthew Brazkiewicz and Vikrant Kumbhar (Senior Reviewer)
Last updated: 6th June 2024
Revisions: 7

Original Author(s): Matthew Brazkiewicz and Vikrant Kumbhar (Senior Reviewer)
Last updated: 6th June 2024
Revisions: 7

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Anorectal malformations (ARMs) comprise a wide spectrum of diseases, which involve the anus and rectum as well as the urinary and genital tracts. Defects range from the very minor and easily treated with an excellent functional prognosis, to those that are complex, difficult to manage and often have a poor functional prognosis.


ARM occur in 1 in 3,000-5,000 babies and affects slightly more boys than girls (1.2:1).


The precise cause of ARM’s is unknown.

ARMs have historically categorised into two groups: low and high defects.

Features of low-ARMs include where the anus is closed over, in a slightly different position or narrower than usual, with or without a fistula.

Features of high-ARMs include where the bowel has a closed end at a high level and do not connect with the anus or it connects with another part of the body (bladder, urethra, or vagina) via a fistula.

This classification is outdated, with movement to instead group ARMs according to Krickenbecks classification (2005) into major clinical groups and rarer/regional variants of ARMs1.

Risk Factors

Risk factors for ARM are a family history of ARM or certain genetic conditions:

Approximately 50% are associated with other defects or as part of a syndrome including VACTERL (Vertebral, Anal, Cardiac, Tracheal, Oesophageal, Renal and Limb abnormalities), Down’s syndrome and Hirchsprung’s Disease.

This means genetic counselling may be appropriate as risk of ARM for a sibling of someone with an ARM can reach 1%2.

Clinical Features

Signs of ARM can rarely be detected on antenatal scans or linked to polyhydramnios in pregnancy. More commonly, ARMs are detected in the neonatal period, during the NIPE (Newborn and Infant Physical Examination), which should be performed within the first 72 hours of life.

The signs of an ARM will depend on the type of ARM but may include the following:

  • Failure to pass meconium within 48 hours
  • Absence of an anal opening or abnormal looking perineum*
  • The anal opening is in a different place to where it should be (closer to the vagina or scrotum)
  • Faeces may pass via fistulae** (from the penis or the area around the vagina)
  • Faeces may be mixed with the urine
  • Vomiting (may be bilious)
  • Abdominal distention
  • Drooling of saliva (if coexistent oesophageal atresia present)
  • Signs of genetic syndromes (dysmorphic features, limb abnormalities etc)

* The importance of thorough inspection of the anus during the NIPE was highlighted by a 2010 paper which found 1 in 5 babies with imperforate anuses were not detected early, leading to delayed diagnosis and worse prognostic outcomes3

**For this reason, meconium present in a new-born’s nappy does NOT rule out presence of an ARM. To avoid this serious error, the perineum should always be cleaned and inspected for a normally sited anus4.

Differential Diagnosis

Occasionally a patient may present with an anal opening that appears to be more anterior than is typical in most patients, which is a normal variant if the anal opening sizes appropriately and is in the centre of the anal muscle complex5.

Other potential causes of failure of pass meconium included cystic fibrosis, Hirschsprung’s disease, meconium plug syndrome, motility disorders, hypothyroidism, sepsis, and electrolyte abnormalities.


Suspected ARMs should be investigated by:

  • Placement of a nasogastric or orogastric tube
  • Plain abdominal and chest radiographs
  • Abdominal and pelvic ultrasound
  • Rarely MRI scans may be used to guide management
  • Spinal imaging (ultrasound in the first three months of life and magnetic resonance imaging thereafter)


Initial steps

If there are any signs of shock or dehydration adequate fluid resuscitation should be given immediately.

The patient should be kept nil by mouth and a size 8-10 Fr nasogastric tube should be inserted with 4 hourly aspirates to empty the stomach.

IV cannula should be inserted at which point blood tests including pre-operative bloods such as clotting, and blood group should be obtained. Maintenance intravenous fluids and broad-spectrum antibiotics should be started, and nasogastric losses should be replaced with an appropriate crystalloid fluid.

All patients should receive IV or IM Vitamin K. Oral vitamin K is unreliably absorbed in bowel obstruction.

Referral to Specialist Paediatric Surgical Team is key as there is a serious risk of bowel perforation which can lead to significant morbidity and mortality. The decision around potential Total Parenteral Nutrition (TPN) should be made by the specialist surgical team4.

Surgical management

Most ARMs require invasive definitive surgery.

The operation will be dependent on the patient’s clinical condition, type of ARM and surgeon experience/preference.

Most commonly faecal diversion with a colostomy is the treatment of choice, which requires three separate operations, if not more.

First operation (Stoma formation):

A life-saving operation that should happen in the first days of life to allow passage of stool. Parents will be taught stoma management prior to discharge.

diagram showing how a loop stoma is formed

Creation of loop stoma (divided stoma are also an option)

Second operation (Posterior sagittal anorectoplasty (PSARP)):

A delicate operation to reconstruct the anatomy in the correct position. Following the operation, the new anus in most of the cases will need to be dilated to prevent stenosis.

If the ARM is too high abdominal surgical approach may be required6.

A special x-ray using contrast dye inserted through the stoma called a loopogram is performed prior to the second operation to better assess the ARM6.

Third operation (Closure of stoma):

This operation involves assessing the reconstructed anus and if everything is fine the stoma will be closed so that the baby will be able to pass stool normally. It happens when the reconstruction has healed, and the anus has been stretched to a normal size by a few months of outpatient serial dilatations of the neoanus.

The goals of surgical treatment are to achieve bowel control, urinary control, and normal sexual function.

Post-op patients should have regular check-ups with the specialist medical or surgical team.


Untreated ARMs will lead to bowel perforation and death.

Other complications include:

  • Standard surgical risks including risks of anaesthesia, bleeding, infection, damage to nearby organs/structures and breakdown of the wound.
  • Anal stenosis and rectal prolapse.
  • Bowel can leak into the abdominal cavity leading to peritonitis.

Long term problems will depend upon the type of ARM.

  • Constipation is the most common long-term problem for children following ARM repair. This needs to be prompt treatment with laxatives, education on good fluid intake and diet and/or rectal washouts.
  • Associated bladder problems may require further interventions to help achieve bladder control.
  • Girls may be better having a caesarean section rather than vaginal childbirth. This will put less strain on the operation site and is less likely to cause problems in the future7.
  • ARMs affect childhood behaviour, educational attainment, and quality of life. It is therefore important that parents are offered psychological support. A referral after surgery to clinical psychology should be encouraged8.


The outlook for children with ARMs depends on the type of abnormality. Many children go on to lead normal lives, working and raising a family. However, some children continue to have bowel problems for many years after the operations.

Faecal continence depends on three main factors: voluntary sphincter muscles, anal canal sensation, and colonic motility. All three of these may be adversely affected by ARMs or surgical treatment of ARM. Approximately 75% of all patients with ARM have voluntary bowel movements, but about 50% of these will soil their underwear occasionally6.

The overwhelming majority of male patients have urinary control, females less so.


1. Singh M, Mehra K. Imperforate Anus. [Updated 2022 May 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:
2. Non-syndromic anorectal malformation
3. Turowski C, Dingemann J, Gillick J. Delayed diagnosis of imperforate anus: an unacceptable morbidity. Pediatr Surg Int. 2010 Nov;26(11):1083-6. doi: 10.1007/s00383-010-2691-5. PMID: 20714730.
4. Management of Ano-Rectal Malformation in the NNU prior to transfer to a Surgical Centre. SOUTHERN WEST MIDLANDS NEWBORN NETWORK. Jan 2012 Version no. SWMNN – draft 1
5. Smith CA, Avansino J. Anorectal Malformations. [Updated 2021 Aug 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:
6. Levitt, M.A., Peña, A. Anorectal malformations. Orphanet J Rare Dis 2, 33 (2007).
7. Great Ormond Street Hospital for Children NHS Foundation Trust: Information for Families – Anorectal anomaly. Specialist Neonatal and Paediatric Surgery department in collaboration with the Child and Family Information Group. Ref: 2016F0652. GOSH NHS Foundation Trust August 2016.
8. Jenny Lind Children’s Hospital Trust Guideline for the Management of Anorectal Malformations in Neonates and Infants. Norfolk and Norwich University Hospitals NHS Foundation Trust. Mr Richard England. 10/11/2021. Trust Doc ID 10836 Version 3.