Pediatric Imperforate Anus Surgery Treatment & Management
- Author: Marc A Levitt, MD; Chief Editor: Eugene S Kim, MD, FACS, FAAP more...
Indications for surgical treatment (colostomy vs anoplasty) are discussed more fully elsewhere (see Presentation). No absolute contraindications to surgery exist. The presence of associated malformations, such as prematurity and congenital cardiac disease, often postpones definitive colorectal reconstruction.
Potential methods of evaluation for anorectal malformations, including prenatal diagnosis and genetic karyotyping to reveal familial disposition, are areas of rapid advance.
Associated malformations must be addressed.
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:
Persistent cloaca - 90%
Rectobladderneck fistula - 84%
Rectoprostatic urethral fistula - 63%
Rectovestibular fistula - 47%
Rectobulbar urethral fistula - 46%
Rectoperineal fistula - 26%
Imperforate anus without fistula - 31%
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 if needed.
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, other 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, but may improve bladder emptying capacity.
Spinal ultrasonography in the first 3 months of life and magnetic resonance imaging (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 the image below). 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 greater than 0.7. Bowel control has rarely been observed in patients with calculated sacral ratios of less than 0.3. Hemisacrum is almost always associated with a presacral mass (teratomas or anterior meningoceles). Hemivertebrae may also affect the lumbar and thoracic spine, predisposing to scoliosis.
Patients may have spinal anomalies other than tethered cord, such as syringomyelia and myelomeningocele.
As discussed previously, the surgeon must decide in the newborn period whether the child requires fecal diversion with a colostomy or if a primary procedure is possible.
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, but with an adequate amount of rectosigmoid for the future pullthrough
Washing and cleaning the portion of the colon distal to the colostomy is relatively easy
Distal colostography is easy to perform
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 lead to constipation after the colostomy ultimately gets closed.
Colostomy errors include the following:
Too-distal sigmoidostomy - In this most common error, the colostomy is placed too distal and interferes with the pullthrough procedure
Right upper sigmoidostomy - Instances of inadvertent sigmoid colostomy placed in the right upper quadrant during an attempt to perform a transverse colostomy have occurred. Inadvertent anchoring of the sigmoid in the right upper quadrant interferes with the pullthrough procedure
Incomplete diversion of stool - 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, due to passage and accumulation of mucus
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 sphincter complex. 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 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 will instead find a genitourinary structure with this approach.
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 around it 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 bladderneck level. The repair of this malformation involves a posterior sagittal incision and an abdominal component. The distal rectum is separated from the urinary tract, mobilized, and pulled through to lay within the sphincteric funnel. The pathway is just under the coccyx and sacrum in the area of the pelvic retroperitoneum.
To mobilize the rectum off of the bladderneck, 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. This part can be done with legs lifted up, remaining in supine position.
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, the 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 anastomosis between the posterior rectum and the anal canal. This defect is particularly associated with a presacral mass, which must be sought.
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.
If the colostomy is untouched during the operation and laparotomy or laparoscopy was not necessary, oral feedings may be started immediately postoperatively. If a laparotomy or laparoscopy was necessary, the patient may require a period of fasting and nasogastric decompression.
At 2 weeks after surgery, 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. It is the most important problem to avoid after definitive repair in newborn girls with rectovestibular or rectoperineal fistula and in newborn boys with rectobulbar urethral fistula, imperforate anus without fistula, and rectoperineal fistula. Failure to avoid constipation may result in megarectum and megasigmoid and can lead to fecal impaction and overflow incontinence. See Bowel Management for further discussion.
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 an older operation, an abdominoperineal operation 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 constantly passes (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 normal caliber and motility is anastomosed to the rectum at the peritoneal reflection. This procedure is useful for the select group of patients who require enormous amounts of daily laxatives to keep their colons clean. The rectal reservoir should be preserved to avoid the problem of diarrhea-related incontinence.
Complications of surgery include dehiscence and infection, which may be avoided with colostomy before the main repair. These complications may compromise the chance of achieving typical bowel function.
With inadequate preoperative anatomic information, the urinary tract is at considerable risk because the surgeon does not know the precise anorectal defect and if the surgeon approaches a low rectum transabdominally, they risk leaving behind the very distal rectum, which becomes a posterior urethral diverticulum.
The key in these patients is to treat constipation proactively and, if possible, avoid it after the pull-through procedure altogether. Patients must be regularly monitored, and laxatives and dietary manipulations are begun at the first sign of constipation.
Patients may 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.
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 pullthrough procedure for imperforate anus and has one to three discrete bowel movements per day has good 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. Whereas a child with a typical bowel movement pattern is trainable, a child with the pattern of fecal incontinence likely requires a bowel management program with a daily enema. The child with true fecal incontinence should not be expected to achieve voluntary bowel control.
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