Pediatric Imperforate Anus (Anorectal Malformation)

Updated: Dec 30, 2019
  • Author: Nelson G Rosen, MD, FACS, FAAP; Chief Editor: Carmen Cuffari, MD  more...
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Anorectal malformations include a wide spectrum of defects in the development of the lowest portion of the intestinal and urogenital tracts. Many children with these malformations are said to have an imperforate anus because they have no opening where the anus should be. Although the term may accurately describe a child's outward appearance, it often belies the true complexity of the malformation beneath. When a malformation of the anus is present, the muscles and nerves associated with the anus often have a similar degree of malformation. The spine and urogenital tract may also be involved.

The position and nature of these malformations made repair difficult for early surgeons. The affected organs are located deep in the pelvis and are not well visualized through abdominal incisions. Traditional surgical dictum did not allow for division of the posterior midline because this division of the muscle was believed, somewhat erroneously, to cause incontinence in the child. Therefore, surgeons approached these malformations using a combined abdominal, sacral, and perineal approach, with limited visibility. Such approaches have put continence, and surrounding genitourinary structures, at greater risk than simply cutting sphincter muscles because of the difficulty of adequately visualizing the malformation through limited incisions. This principle was central to the development of the surgical techniques currently used to repair these malformations.

In 1982, Peña et al reported the results of the use of a posterior sagittal surgical repair approach. [1] Peña et al used the traditional approach with a sacral incision and made the incisions progressively larger in an attempt to adequately visualize the anatomy. Eventually, the entire posterior sagittal plane was opened, affording a full view of the complete malformation. This technique, referred to as posterior sagittal anorectoplasty (PSARP) or posterior sagittal anorectovaginourethroplasty (PSARVUP), has led to a more complete understanding of the anatomy of these children and of what is required to repair the malformations with optimal results.

After reconstructive surgery for the malformation, many children still experience effects in the form of urinary or fecal incontinence. Despite optimal surgical management, no adequate repair for poorly developed muscles or nerves has been developed. Bowel-management regimens can provide an excellent quality of life for these children when primary continence is not achievable.



The embryogenesis of these malformations remains unclear. The rectum and anus are believed to develop from the dorsal potion of the hindgut or cloacal cavity when lateral ingrowth of the mesenchyme forms the urorectal septum in the midline. This septum separates the rectum and anal canal dorsally from the bladder and urethra. The cloacal duct is a small communication between the two portions of the hindgut. Downgrowth of the urorectal septum is believed to close this duct by 7 weeks' gestation. During this time, the ventral urogenital portion acquires an external opening; the dorsal anal membrane opens later. The anus develops by a fusion of the anal tubercles and an external invagination, known as the proctodeum, which deepens toward the rectum but is separated from it by the anal membrane. This separating membrane should disintegrate at 8 weeks' gestation.

Interference with anorectal structure development at varying stages leads to various anomalies, ranging from anal stenosis, incomplete rupture of the anal membrane, or anal agenesis to complete failure of the upper portion of the cloaca to descend and failure of the proctodeum to invaginate. Continued communication between the urogenital tract and rectal portions of the cloacal plate causes rectourethral fistulas or rectovestibular fistulas.

The external anal sphincter, derived from exterior mesoderm, is usually present but has varying degrees of formation, ranging from robust muscle (perineal or vestibular fistula) to virtually no muscle (complex long–common-channel cloaca, prostatic or bladder-neck fistula).



Although the precise embryologic defect that causes anorectal malformations has not been determined, cloacal membrane formation and subsequent breakdown into urogenital and anal openings should occur by 8 weeks' gestation. Defects in the formation or shape of the posterior urorectal septum account for many of the described abnormalities of imperforate anus. Müllerian ducts appear after this critical period; how they are incorporated into this development is unclear.

No known risk factors predispose a person to have a child with imperforate anus, which should be clearly emphasized to parents of affected children who may harbor feelings of guilt. A genetic linkage is sometimes present. Most cases of imperforate anus are sporadic without a family history of the condition, but some families have several children with malformations. Genetic studies are ongoing.



Anorectal malformations occur in approximately 1 newborn per 5000 live US births.

Race-, sex-, and age-related demographics

No known racial or sex predilection has been reported.

Most children with an anorectal malformation are identified upon routine newborn physical examination. Delayed presentation is often the result of incomplete initial examination. Newborn anorectal and urogenital examination can be technically challenging and makes many practitioners uncomfortable.

Subtle malformations, such as those in some children with perineal fistula that may look normal to the casual glance, may present months or years after birth when the child presents to a primary care provider for constipation or urinary tract infection and appears to have a small perineal body upon physical examination.

Anorectal malformations in females with a normal-appearing anus who have absent vagina or persistent urogenital sinus may go undiagnosed for years because of examiner reluctance to separate the labia during physical examination. These malformations can be discovered upon evaluation for urinary tract infection or primary amenorrhea.



All patients who have an anorectal malformation with no significant life-threatening comorbidity should survive. Therefore, prognosis is best determined based on the probability of primary fecal continence.

Continence, defined as voluntary bowel movements with minimal soiling, varies based on primary and associated malformations. A tethered spinal cord or another spinal malformation, such as hemivertebrae or spinal dysraphism, may significantly increase the risk of incontinence.

Surgical complications worsen the chances for primary continence, although this effect is difficult to quantify. Reoperation significantly decreases the opportunity for primarily continence.

All children with a perineal fistula should be continent. Spinal malformations are exceedingly rare in this group.

Approximately 90% of girls with a vestibular fistula have voluntary bowel movements. [2]

Approximately 80% of boys with a bulbar urethral fistula have voluntary bowel movements, whereas 66% of boys with prostatic urethral fistula have voluntary bowel movements. Only 15% of boys with bladder-neck fistulas have voluntary bowel movements. [2]

Children with imperforate anus without fistula have a 76% chance of having voluntary bowel movements. [2]

The chance of fecal and urinary continence in girls with cloaca varies based on the length of the common channel. Girls with a short common channel and no associated urological or spinal malformations can have excellent results, with as many as 75% of girls developing voluntary bowel movements. Urinary or fecal continence is very unlikely in girls with long–common-channel cloacae, sacral malformations, and a tethered spinal cord. [2]

The best determination for future continence is observation of function. A child who constantly leaks stool or urine constantly will probably not improve by school age and may benefit from early bowel management or intermittent catheterization. If a child is able to hold urine, stool, or both, the best course is to observe his or her function.

Regardless of what the child will be capable of in the future, cleanliness of urine and stool must be established before a child enters a school peer group. No child should be allowed to suffer the stigma of being the "smelly" child simply because their physician or parents were unable to accept the child's incontinence or because they were not yet ready to proceed. Even in the worst cases, hope remains. However, the decisions made must be practical and must allow the child to seamlessly fit in with their peer groups.


Anorectal and urogenital malformations are rarely fatal, although some associated anomalies (cardiac, renal) can be life threatening. Intestinal perforation or postoperative septic complications in a newborn with imperforate anus can result in mortality or severe morbidity. [3]

Morbidity generally arises from the following two sources.

Malformation-related morbidity

  • Malformation-related morbidity relates to associated malformations of rectal motility, anorectal innervation, and sphincteric musculature. The most common morbidity in this category is constipation. Most children have mild malformations that commonly result in constipation for reasons that remain unclear. If left untreated, chronic constipation results in rectal dilation, which worsens the constipation. This becomes a vicious cycle, which, if untreated, results in fecal impaction and overflow pseudoincontinence, also known as encopresis.

  • The most severe forms of malformation-associated morbidity are fecal and urinary incontinence. Higher malformations, such as long–common-channel cloacae and prostatic or bladder-neck fistulas, are associated with poorer nerve and muscle formation, all of which increase the likelihood of fecal or urinary incontinence. Malformations that directly involve urinary sphincteric mechanisms, and, specifically, any malformation in which the rectum or vagina joins the urinary tract at the bladder neck, often results in either urinary incontinence or inability to completely void.

Surgery-related morbidity

  • This can include standard complications such as line infections and pneumonia.

  • Wound infections or anastomotic breakdowns can occur in any intestinal surgery.

  • Children with imperforate anus are at greater risk for injury to surrounding pelvic organs because these organs (such as vagina or urethra and seminal vesicles) are located immediately adjacent to the rectum, and may also be involved in the malformation in some unsuspected way.

  • During blind exploration in the pelvis, a dilated ureter can be mistaken for the rectum. Urethras can be opened or transected, and prostates or seminal vesicals can be easily injured. Dissection of these delicate structures can result in ischemia and possible stricture or complete stenosis.