eMedicine Specialties > Pediatrics: Surgery > General Surgery

Imperforate Anus: Surgical Perspective: Treatment

Author: Marc A Levitt, MD, Assistant Professor of Surgery and Pediatrics, University of Cincinnati; Associate Director, Colorectal Center for Children, Department of Pediatric Surgery, Cincinnati Children's Hospital Medical Center
Coauthor(s): Alberto Pena, MD, Consulting Surgeon, Colorectal Center for Children, Department of Pediatric Surgery, Cincinnati Children's Hospital Medical Center
Contributor Information and Disclosures

Updated: Aug 10, 2007

Treatment

Medical Therapy

Associated malformations

• Genitourinary defects
  • Approximately 50% of all patients with anorectal malformations have an associated urogenital anomaly, which commonly varies with the type of anorectal defect.
  • A list of anorectal defects and the percentages of patients with associated urogenital anomalies is as follows:¹
    • Cloaca - 81%
    • Rectovesical defect - 52%
    • Rectoprostatic - 40%
    • Rectovestibular - 9%
    • Rectobulbar - 4%
    • Rectoperineal - 0%
    • Overall - 48%
  • All patients must be examined at birth for these defects; the most valuable screening test is abdominal and pelvic ultrasonography.
  • Urologic evaluation prior to colostomy provides the surgeon the necessary information to address the urologic problem at colostomy. The surgeon must be prepared to perform a urologic diversion, if necessary.
• Tethered cord
  • A tethered spinal cord refers to the intravertebral fixation of the phylum terminale.
  • Tethered cord has a known association with anorectal malformation; approximately 25% of patients with anorectal malformation have a tethered spinal cord.
  • The prevalence of this anomaly increases with increasing height and complexity of the anorectal anomaly. In addition, patients with a hypodeveloped sacrum and associated urologic problems are more likely to have tethered cord.
  • Motor and sensory disturbances of the lower extremities may result.
  • Patients with anorectal malformations and tethered cord have a poorer prognosis for bowel and urinary function; they also have higher anorectal defects, less-developed sacra, associated spinal problems, and less-developed perineal musculature. The actual impact of tethered cord alone on functional prognosis remains unclear.
  • The neurosurgical literature indicates that untethering the cord avoids motor and sensory problems. No evidence suggests that this operation affects the functional prognosis of patients with anorectal malformation.
  • Spinal ultrasonography in the first 3 months of life and MRI thereafter are useful radiologic modalities to establish the diagnosis.
• Sacral and spinal defects
  • The sacrum is the most commonly affected bony structure. Traditionally, the number of sacral vertebral bodies was counted to evaluate the degree of sacral deficiency. A more objective assessment of the sacrum may be obtained by calculating a sacral ratio. The sacrum is measured and its length is compared with bony parameters of the pelvis (see Image 8). The lateral view is more accurate than the anteroposterior view because its calculation is not affected by pelvic tilt.
  • Assessment of sacral hypodevelopment correlates with the patient's functional prognosis. Normal sacra have a calculated sacral ratio of 0.77. Bowel control has never been observed in patients with calculated sacral ratios of less than 0.3.
  • Hemisacrum is always associated with a presacral mass, which commonly includes dermoids, teratomas, or anterior meningoceles.
  • Hemivertebrae may also affect the lumbar and thoracic spine, leading to scoliosis.
  • Patients may have spinal anomalies other than tethered cord, such as syringomyelia and myelomeningocele.

Surgical Therapy

As discussed above, the surgeon must decide in the newborn period whether the child requires fecal diversion with a colostomy or if a primary procedure is possible.

Colostomy

• A descending colostomy with separated stomas is recommended. The advantages of this type of colostomy include the following:
  • Only a small portion of distal colon is defunctionalized.
  • In patients with large rectourinary fistulae who pass urine into the bowel, the urine comes out easily through the mucous fistula, avoiding the problems of hyperchloremic acidosis caused by urine absorption. Urinary tract infections are also avoided.
  • Washing and cleaning the portion of the colon distal to the colostomy is relatively easy.
  • Distal colostography is easy to perform.
  • The sigmoid loop is kept distal to the colostomy, which provides enough length to reach the perineum during the definitive pull-through procedure.
  • The separated stomas prevent spillage of stool from proximal to distal bowel, which avoids impacted distal stool and urinary tract infections.
  • Prolapse with this technique is uncommon. Proximal stoma prolapse in a normally rotated colon should not occur with this technique because the colon is well fixed to the retroperitoneum just before the colostomy rises to skin level. Because the distal stoma is in a mobile portion of the colon, it may prolapse. The distal stoma must intentionally be made small, both to avoid prolapse and because it is used only for irrigations and radiologic studies.
• When performing a colostomy in the newborn, the distal bowel should be irrigated to remove all the meconium. This prevents formation of a megasigmoid, which may cause constipation.
• Colostomy errors include the following:
  • Too-distal sigmoidostomy: In this most common error, the colostomy is placed too distal and interferes with the pull-through procedure.
  • Right upper sigmoidostomy: Instances of inadvertent sigmoid colostomy placed in the right upper quadrant during attempts to perform a transverse colostomy have been reported. Anchoring of the sigmoid in the right upper quadrant interferes with the pull-through procedure.
  • Incomplete diverting of stool: An error occurs when a loop colostomy does not divert the stool completely and allows for distal stool impaction and urinary tract infections.
  • Megarectum: Transverse colostomies may produce megarectum.

Definitive repair

• Repair of an anorectal malformation requires a meticulous, delicate technique and a surgeon with experience in treating these defects.
• The posterior sagittal approach is ideal for defining and repairing anorectal anomalies.
• Anorectal abnormalities in 90% of newborn boys may be repaired solely with a posterior sagittal approach, whereas 10% require an additional abdominal component (with laparotomy or laparoscopy) to mobilize a very high rectum.
• All anorectal malformations in newborn girls may be repaired with the posterior sagittal approach, with the exception of approximately 30% of instances of persistent cloaca. In this 30%, the rectum or vagina is high enough to also require an abdominal approach.
• A Foley catheter is placed first; then, patients are placed in the prone position with the pelvis elevated.
• The posterior sagittal incision length varies depending on the anorectal defect. Perineal fistulas are repaired with a minimal posterior sagittal incision that is large enough to divide the external sphincter and to mobilize the anus back to the center of the external sphincter. The sphincter mechanism is always located posterior to the fistula site. This operation may be performed in the neonatal period without a protective colostomy.
• The posterior sagittal approach is based on the fact that nerves do not cross the midline. Remaining exactly in the midline, the surgeon preserves the innervation of all the important pelvic structures.
• An electrical stimulator helps reveal the location of the sphincteric mechanism. The parasagittal fibers, the muscle complex, and the levators are identified during the dissection. The external sphincter is represented by muscle fibers that run parallel to the midline in a parasagittal fashion. A muscle structure termed the levator mechanism lies medial to these fibers and represents the lower end of the funnel-like voluntary muscle.
• The levator mechanism extends in continuum down to the skin, but this was not known prior to the use of the posterior sagittal approach. Electrically stimulated, the parasagittal fibers elicit a contraction that results in shortening of the same fibers. The rectum pushes forward toward the pubic bone when the upper portion of the levators are stimulated. Stimulating the lower part of the funnel-like muscle structure elevates the anal dimple. This group of muscle fibers, termed the muscle complex, extends from the levator mechanism down to the skin and is located immediately medial to the parasagittal fibers.
• The surgeon opens the posterior sagittally. The skin and subcutaneous tissue are divided, and the parasagittal fibers below are divided in the midline, as is the muscle complex.
• The levator muscle is then opened, and the rectum is found, except in patients with a true supralevator malformation (10% of cases), in whom the surgeon finds a genitourinary structure.
• When the rectum is located, its posterior wall is opened in the midline to demonstrate the presence of a fistula. This posterior incision in the rectum is carried down to the fistula site.
• The rectum and urethra share a common wall. Meticulous dissection is required to separate the distal rectum from the urethra. A submucosal dissection must be performed in the first 5 mm above the fistula site.
• The rectum is separated from the urinary tract. This dissection is facilitated through placing multiple 6-0 silk sutures in the rectal mucosa to exert uniform traction.
• The opening in the urethra is then closed with absorbable suture.
• Once the rectum is separated, it is then mobilized down to reach the perineum by circumferentially dividing the bands and vessels that hold the rectum up in the pelvis. The intramural blood supply of the rectum is excellent; therefore, the rectum remains viable. Because the newborn depends on this intramural blood supply, preventing damage to the rectal wall is vital.
• Once the rectum is fully mobilized, the size of the rectum and the available space must be assessed. The rectum occasionally requires tapering to fit the limits of the sphincteric mechanism. The tapering should take place on the posterior wall so that the suture lines of the tapered rectum and the closed urethral fistula do not lie next to each other.
• The rectum is placed in the limits of the sphincter mechanism, which is reconstructed in the midline. The rectum is sutured to the perineal skin (anoplasty).
• In 10% of newborn boys with this defect, the rectum enters the urinary tract at the bladder neck level.  The repair of this malformation involves a posterior sagittal incision and an abdominal component. All the muscle structures are divided in the midline, leaving the urinary tract untouched. The pathway just under the coccyx and sacrum is identified, and the abdomen is entered in this area of the pelvic retroperitoneum.  The rectum is pulled through this space, and the sphincter mechanism is reconstructed around it. 
• To mobilize the rectum off of the bladder neck, an abdominal component is required via laparoscopy or laparotomy.  The fistula is ligated with great care to avoid injuring the ureters and vas deferens:  the plane of dissection must be made close to the bowel wall of the rectosigmoid, 2-3 cm above the peritoneal reflection. The rectum is then mobilized for adequate length to reach the perineum without tension.
• The fistula is divided and sutured with absorbable material. The rectum is passed through to the posterior sagittal incision and an anoplasty is performed.
• In patients with imperforate anus without fistula, the same meticulous dissection is required to separate the distal rectum from the urinary tract as in patients with rectourinary fistulae, because the rectum and urethra still share a common wall.
• In patients with rectovestibular fistula, the posterior sagittal incision may be shorter than in newborn boys with rectourethral fistulae. Often, the entire levator mechanism does not need to be divided; only the external sphincter, muscle complex, and part of the lower portion of the levator mechanism require division. The rectum and posterior vagina share a common wall; this separation is the most difficult part of the operation. Once the rectum is completely mobilized, a perineal body is constructed, and the rectum is placed within the limits of the sphincter mechanism.
• A rare malformation, rectal atresia, occurs in 1% of patients. The anal canal is normal, and, externally, the anus appears typical. However, a blockage exists 1-2 cm from the anal skin and is usually found when the nurse tries to pass a thermometer. These babies should undergo colostomy at birth; definitive repair involves a posterior sagittal approach and an end-to-end anastomosis between the upper rectal pouch and the anal canal.

Postoperative Details

Postoperative management

The posterior sagittal incision is relatively painless.

In patients with a rectourethral fistula, the Foley catheter usually stays in place for approximately 5-7 days. Occasionally, a longer period is required.

If the colostomy is untouched during the operation and laparotomy was not necessary, oral feedings may be started immediately postoperatively. If a laparotomy was necessary, the patient may require a period of fasting and nasogastric decompression.

At 2 weeks' postsurgery, anal calibration is performed, followed by a program of anal dilatations. The anus must be dilated twice daily, and the size of the dilator is increased every week. The final size to be reached depends on the patient’s age.

Once the desired size is reached, the colostomy may be closed.

Dilatations are continued afterward according to a prescribed protocol.

Dilatations are a vital part of postoperative treatment to avoid an anoplasty stricture.

After colostomy closure, severe diaper rash is common, because the perineal skin has never before been exposed to stool.

Postoperative functional disorders

Constipation is the most common problem encountered after treatment for imperforate anus with rectal preservation.

The origin of the constipation problem is unknown. Originally, the perirectal dissection was believed to cause a degree of denervation that resulted in constipation. However, on careful review of the largest patient series, those with the most benign defects (ie, the least amount of perirectal dissection) experienced the worst constipation.

The presence of a megarectum prior to the pull-through procedure correlates with postoperative constipation. Megarectum is more common in patients who underwent a transverse or loop colostomy during the newborn period.

Constipation appears to be a hypomotility disorder secondary to chronic bowel dilatation; alternatively, the hypomotility may cause the dilatation. Dilatation causes constipation, creating a vicious cycle. Patients who have undergone abdominoperineal operations for imperforate anus that included rectum resection are prone to develop diarrhea because of lack of a rectal reservoir. Incontinence in these patients is much more difficult to treat because stool is constantly passed (see Bowel Management).

Occasionally, constipation becomes so severe that patients develop chronic fecal impaction and constant soiling. These patients are often referred to as having fecal incontinence. However, if the patient has a type of anorectal anomaly with a good prognosis, this incontinence is often overflow pseudoincontinence. Once the constipation is treated, the patient regains continence.

When constipation is severe and the patient has a megasigmoid (and the patient is fecally continent), resection of the sigmoid has been found to dramatically reduce the patient's laxative requirements. The descending colon with typical caliber and motility is anastomosed to the rectum at the peritoneal reflection. This procedure is for the select group of patients who require enormous amounts of daily laxatives to keep their colons clean. A new pull-through operation should be avoided to preserve the rectal reservoir. Loss of the rectal reservoir may lead to the worse problem of diarrhea-related incontinence.

Follow-up

The key in these patients is to treat constipation proactively and avoid it after the pull-through procedure. Patients must be regularly monitored, and laxatives and dietary manipulations are begun at the first sign of constipation.

Less commonly, patients experience soiling. This may represent fecal incontinence in patients with very high imperforate anus or in those with poor muscles and an abnormal sacrum. These patients require a bowel management program (see Bowel Management). However, in a patient with a good prognosis, soiling may represent overflow incontinence, and constipation must be treated. A contrast enema is helpful in differentiating these 2 groups of patients.

The child’s bowel movement pattern before toilet-training may provide important information concerning the potential for continence. For example, a 1-year-old child who has undergone a pull-through procedure for imperforate anus and has 1-3 bowel movements per day with no soiling accidents has high potential for future fecal continence. Signs of feeling are demonstrated while the child is pushing during a bowel movement. On the other end of the spectrum, a child who has fecal incontinence passes stool constantly without evidence of pushing or feeling. A child with a typical bowel movement pattern is trainable, whereas a child with the pattern of fecal incontinence likely requires a bowel-management program. The child with fecal incontinence should not be expected to achieve voluntary bowel control.

Complications

Complications of surgery include dehiscence and infection, which may be avoided with colostomy before the main repair.

Some authors have performed definitive repair in the newborn period. The advantages to this approach include avoiding a colostomy and repairing of the malformation earlier; however, with this practice, the urinary tract is at considerable risk because the surgeon does not know the precise anorectal defect.

The only way to definitively determine the patient's anorectal defect is to perform distal colostography, which requires the presence of a colostomy. Without this information, an operation in the newborn period is, essentially, a blind perineal exploration. The surgeon may not be able to locate the rectum; during the search, he or she may find and damage other unexpected structures, such as the posterior urethra, seminal vesicles, vas deferens, and ectopic ureters.

Finally, without fecal diversion, the risk of dehiscence and infection exists. These complications may compromise the chance of achieving typical bowel function.

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