Pediatric Imperforate Anus Surgery

Updated: Dec 01, 2015
  • Author: Marc A Levitt, MD; Chief Editor: Eugene S Kim, MD, FACS, FAAP  more...
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Overview

Background

Anorectal malformations comprise a wide spectrum of diseases that affect boys and girls and can involve malformations of the distal anus and rectum, as well as the urinary and genital tracts. Malformations range from minor, easily treated defects that carry an excellent functional prognosis, to complex defects that are difficult to treat, are often associated with other anomalies, and carry a poor functional prognosis.

Throughout the centuries, doctors have seen and attempted to treat infants born with imperforate anus. Because few patients have been described in the early literature, most are assumed to have died without treatment. Paulus Aegineta recorded the earliest account of successful surgery for imperforate anus. He suggested rupturing an obstructing membrane with the finger or knifepoint and then dilating the tract until healing was complete. This approach was used for many years.

Almost 1000 years later, in 1660, Scultet used dilatation to treat an infant with anal stenosis. In 1676, Cooke used incision and dilatation and advised care of the sphincter muscles. In 1787, Bell suggested using a midline perineal incision to find the bowel. In 1783, acting on Littre's suggestion from 1710, Dubois performed an inguinal colostomy for imperforate anus. Other surgeons followed suit, but almost all of the infants died; thus, colostomy remained unpopular and a procedure only of last resort.

In 1835, Amussat described formal perineal proctoplasty (ie, mobilization of the bowel through a perineal incision and suturing to the skin). This technique gained rapid acceptance. Strictures were less common than observed in earlier procedures. In addition to Amussat, Dieffenbach described anal transposition (1826); Chassaignac used a probe through a stoma to guide the perineal dissection (1856); and Leisrink (1872), McLeod (1880), and Hadra (1884) recommended opening the peritoneum if the bowel was not encountered from below.

In 1930, Wangensteen and Rice first advocated imaging to delineate the abnormality. Single-stage abdominoperineal procedures became widely used after reports by Rhoads, Pipes, Randall, Norris, Brophy, and Brayton (1948-1949). In 1953, Stephens described this procedure with specific emphasis on preservation of the puborectalis muscle. This surgery and its modifications were the standard approach until 1980.

In 1980, the surgical approach to repairing anorectal malformations altered dramatically with the introduction of the posterior sagittal approach, because it allowed pediatric surgeons to clearly view the anatomy of anorectal malformations and to repair them under direct vision, with better visualization and understanding of the anatomic relationships than previous approaches allowed.

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Pathophysiology and Etiology

Understanding the true anatomy is helpful to prevent damage to important structures during surgical repair and to preserve the best potential for bowel control.

Anatomic visualization has allowed surgeons to eliminate many previous misconceptions. For instance, the previous classification of these defects into high, intermediate, and low malformations was a misleading oversimplification that did not adequately describe the spectrum of anorectal anomalies.

Improved imaging techniques and a more thorough knowledge of the anatomy of the pelvic structures at birth have refined diagnosis and early treatment. Analysis of large series of patients has allowed better prediction of associated anomalies and functional prognosis.

The surgeon’s primary concern in correcting these anomalies is bowel control. Problems with urinary control and sexual function must also be considered.

Early diagnosis, treatment of associated anomalies, and efficient and meticulous surgical repair provide patients the best chance for a good functional outcome.

Some patients experience fecal and occasional urinary incontinence despite excellent anatomic repair. Associated problems such as a poorly developed sacrum and tethered cord and/or myelomeningocele likely contribute to an inability to achieve continence. For patients with fecal incontinence, an effective bowel management program has been devised to improve quality of life (see Bowel Management).

Although the etiology remains unknown, a slight genetic predisposition appears to exist.

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Epidemiology

Anorectal malformations occur in approximately 1 per 5000 live births.

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Prognosis

When evaluating the results of treatment of anorectal defects, patients should not be grouped into the traditional high, intermediate, and low categories. For instance, within the traditional high group, malformations have different treatments and carry different prognoses (eg, rectoprostatic fistula compared with rectobladderneck fistula). Both of these would be considered high in the traditional nomenclature; however, the malformations are so different they should not be grouped together. An anatomic classification is of more clinical value.

The functional results of repair of anorectal anomalies have improved significantly since the advent of the posterior sagittal approach. However, the results of this approach are difficult to compare with those of other methods because terminology and classification are inconsistent.

Approximately 75% of all patients with anorectal malformations have voluntary bowel movements. Approximately 50% have occasional soiling accidents. Episodes of soiling are usually related to constipation; when constipation is treated properly, the soiling usually disappears. Approximately 40% of all patients have voluntary bowel movements and no soiling.

About 25% of patients with anorectal malformations have fecal incontinence and must receive a bowel management regimen with a daily enema to keep clean (see Bowel Management).

Apart from the anorectal anomaly, the status of the sacrum, spine, and muscles greatly affects a patient's fecal continence. Even with a perfect reconstruction, a patient with a poor sacrum or spine may not achieve bowel control.

Bowel control must be evaluated when the child is older than 3 years.

Patients with low defects (eg, rectoperineal fistula, rectal atresia) have excellent outcomes. Girls with rectovestibular fistulas have very good outcomes, except for a tendency to develop constipation. Approximately 60% of boys with rectourethral fistulae and normal sacra have good outcomes. More than 80% of patients with persistent cloaca and a normal sacrum have bowel control. Patients with very high malformations (eg, rectobladderneck fistula in boys) have poor outcomes.

The sacrum is a good predictor of outcome. Patients with a normal sacrum are much more likely to have fecal continence. Patients with a hypodeveloped sacrum are much more likely to be incontinent. A sacral ratio has been developed to allow for a more objective assessment of the sacrum (see the image below). Patients with a sacral ratio less than 0.3 only rarely achieve continence. A hypodeveloped sacrum is also a good predictor of associated spinal problems, such as tethered cord.

Calculation of the sacral ratio. Calculation of the sacral ratio.

A child's outcome may be predicted. Parents can be realistically informed of their child's potential for bowel control, even in the newborn period. This avoids a great deal of frustration later in life. Establishing the functional prognosis early is vital to avoid raising false expectations in the parents.

Once the diagnosis of the specific defect is established, the functional prognosis can be predicted. The status of the spine, sacrum, and perineal musculature are all factors that affect the counseling given to the parents.

If a given defect carries a good prognosis, such as rectovestibular fistula, rectoperineal fistula, rectal atresia, rectourethral bulbar fistula, or imperforate anus without fistula, expect the child to have voluntary bowel movements by age 3 years. Such children require supervision to avoid fecal impaction, constipation, and soiling.

Certain defects indicate a poor prognosis, such as a high cloaca (common channel >3 cm) or a rectobladderneck fistula. Parents should be informed that the child may require a bowel management program to remain clean. The program should be implemented at age 3-4 years (see Bowel Management).

Patients with rectoprostatic fistulas carry an almost equal chance of voluntary bowel movements or incontinence. Toilet training should be attempted at age 3 years, and if unsuccessful, a bowel management program should be initiated. Each year, during vacation, bowel control should be attempted, and if unsuccessful, the bowel management should be restarted. As the child grows older and more cooperative, the likelihood of achieving bowel control improves. Once it is determined that a daily enema is needed, those can be given antegrade via a Malone appendicostomy.

Urinary incontinence occurs in boys with anorectal malformations only when they have an extremely defective or absent sacrum, an abnormal spine, or when the basic principles of surgical repair are not followed and important nerves are damaged during the operation. The vast majority of boys have urinary control. This is also true for girls, not including the group with persistent cloaca who not infrequently need intermittent catheterization (see Cloacal Malformations). Careful, regular observation is necessary in these patients to accurately reassess their prognosis and to avoid problems that can dramatically affect their ultimate functional results.

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