Surgery for Pediatric Anorectal Malformation (Imperforate Anus) Treatment & Management

Indications for surgical treatment (colostomy vs anoplasty) of anorectal malformations (ARMs) are discussed more fully elsewhere (see Presentation). No absolute contraindications for surgery exist.

The presence of associated malformations, such as prematurity and congenital cardiac disease, often postpones definitive colorectal reconstruction. As discussed previously, the surgeon must decide in the newborn period whether the child requires fecal diversion with a colostomy or if a primary repair procedure is possible. In certain circumstances, this primary repair can be delayed by performing dilations of the fistula.

Potential methods of evaluation for ARMs, including antenatal diagnosis and genetic karyotyping to reveal familial disposition, are areas of rapid advance.

Genitourinary defects

Approximately 50% of all patients with ARMs have an associated urogenital anomaly, which commonly varies with the type of anorectal defect. The complexity of these anorectal defects varies with the incidence of associated urogenital anomalies.

All patients must be examined at birth for these defects; the most valuable screening test is abdominal and pelvic ultrasonography (US). Urologic evaluation prior to colostomy provides the surgeon with the information required to address the urologic problem (if necessary).

Tethered cord

A tethered spinal cord refers to the intravertebral fixation of the phylum terminale. ^[14] Tethered cord has a known association with ARM: Approximately 25% of patients with an ARM have a tethered spinal cord. The prevalence of this anomaly increases with increasing 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 an ARM and tethered cord may 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 at present but is the subject of ongoing study.

The neurosurgical literature indicates that untethering the cord avoids motor and sensory problems. No evidence suggests that this operation affects the functional prognosis (in terms of stooling) for patients with an ARM, but it may improve bladder emptying and capacity.

Spinal US in the first 3 months of life and magnetic resonance imaging (MRI) thereafter are useful radiologic modalities for establishing 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. An objective assessment of the sacrum may be obtained by calculating the 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 0.4. Hemisacrum can be 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.

A descending colostomy with separated stomas is recommended (see the image below). 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 infection (UTI)
• Prolapse with this technique is uncommon ^[15] ; although 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, the distal stoma is in a mobile portion of the colon and thus may prolapse; to avoid this, the distal stoma must intentionally be made small and a portion of the closed-off lumen kept below the fascia
• There is some evidence to suggest that loop stomas are as effective as end stomas in preventing UTI ^[16] ; however, it is technically more difficult to perform a completely diverting loop stoma, and thus, most colorectal surgeons suggest using an end divided stoma

When a colostomy is performed in a newborn, the distal bowel should be irrigated to remove all the meconium. This prevents formation of a megasigmoid, ^[17]  which may lead to constipation after the colostomy is ultimately closed.

Colostomy errors include the following ^{[18, 19]} :

• Too-distal sigmoidostomy - In this most common error, the colostomy is placed too distally in the sigmoid colon 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 ARM requires a meticulous, delicate technique and a surgeon with experience in treating these defects. The posterior sagittal approach (posterior sagittal anorectoplasty [PSARP]) is ideal for defining and repairing the majority of anorectal anomalies.

In 90% of newborn boys, ARMs may be repaired with a posterior sagittal approach alone, whereas 10% require an additional abdominal component (with laparotomy or laparoscopy ^{[20, 21, 22]} ) to mobilize a very high rectum. All ARMs in newborn girls may be repaired via the posterior sagittal approach, with the exception of approximately 30% of cloacas. In these 30%, the rectum or vagina is high enough that an abdominal approach is also required.

Posterior sagittal anorectoplasty

To perform the anorectal reconstruction, ^[23]  the patient is placed in a prone position with the pelvis raised and the operating table in Trendelenburg position. An electrical stimulator is used to map the sphincter before and during the operation (see the images below).

The length of the incision varies according to the degree of exposure needed for safe repair of the specific ARM. Thus, a perineal fistula requires only a minimal posterior sagittal incision (2 cm), whereas more complex defects may require a full posterior sagittal incision that runs from the lower sacrum towards the base of the scrotum in males or to the single perineal orifice in females with a cloacal malformation.

The incision includes the skin and subcutaneous tissue and separates the parasagittal fibers, muscle complex, and levator muscles in the midline. In less complex defects (perineal and vestibular), the incision separates only the parasagittal fibers and the muscle complex in the midline. The levator muscle is not seen. (See the image below.)

Once the sphincter mechanism has been divided, the key step is separating the rectum from the urogenital structures. With perineal and vestibular fistulas, the rectum is immediately visible, and multiple silk sutures are placed on the rectum to apply uniform traction and thereby facilitate safe separation from adjacent structures. Even in these more minor ARMs, care must be taken to separate the rectum completely from its anterior attachments to either the urethra or vagina. Failure to do this will leave the anoplasty under tension and is the cause of many failed repairs. ^[8]

Once the rectum is fully mobilized in the correct plane, it should be reconstructed in the middle of the muscle complex, which is accurately mapped with an electrical stimulator. Interrupted long-term absorbable sutures are used to repair the perineal body. The posterior edge of the muscle complex is tacked to the posterior rectal wall. Thus, the posterior muscle complex surrounds the rectum and helps prevent rectal prolapse. ^[24]  (See the images below.)

The parasagittal fibers are then reapproximated, the posterior incision is closed (see the image below), and an anoplasty is performed to complete the repair.

Repair of a rectourethral fistula in a male follows many of the same basic principles but also has a number of fundamental differences. A urinary catheter must be inserted at the start of the procedure, and a Coude tip catheter helps prevent inadvertent insertion into the rectal fistula.

First, the rectum is located via the posterior sagittal incision. It is essential that the surgeon know exactly where to expect to find the rectum before starting the procedure. Therefore, the importance of an accurate distal colostogram to avoid injuries to adjacent structures cannot be overstated. ^[25]  In the case of a bulbar urethral fistula, the rectum will lie just beneath the levator muscles, and in the case of a prostatic urethral fistula, it will lie much higher, under the coccyx.

Once the parasagittal fibers, muscle complex, and levators are opened, the surgeon should attempt to find the rectum. Once the rectum has been confidently identified, it should be mobilized laterally and posteriorly. Then, with silk traction sutures in place, the rectum should be opened in the midline. Multiple stitches are then placed on the edges of the rectum as it is opened in an inferior direction, precisely in the midline. The fistula is then identified, and a line of silk sutures is placed proximal to the fistula.

The common wall between the rectum and the urethra is then carefully separated. The initial 1-2 mm of the separation should be done in a submucosal rectal plane in order to prevent a urethral injury. The dissection is facilitated by completing the lateral dissection of the rectum before attempting the anterior plane. Once the rectum is completely separated from the urethra, the site of the fistula can be closed with long-term absorbable sutures, and the rectum can be further mobilized to allow a tension-free anoplasty.

Laparoscopic-assisted anorectoplasty

About 90% of defects in males can be repaired via a posterior sagittal approach alone. Only with rectourethral (bladderneck) fistulas or high prostatic fistulas is it necessary to approach the rectum through the abdominal cavity by means of either laparoscopy ^{[26, 27, 28, 29, 30]}  or laparotomy.

The repair is always performed with a urethral catheter in place. In patients with bladderneck fistula, the rectum is separated from the urethra through the abdomen laparoscopically (or with a laparotomy), and the fistula is closed. In these defects, the rectum enters the urethra at a right angle. Once the rectum is freed and sufficient length is achieved, a limited posterior sagittal incision can be used to split the muscle complex accurately. This can be performed with the patient supine and the legs lifted up.

The levator muscles are opened sufficiently, and the rectum is passed through the pelvic floor and repaired in the standard manner, with tacking of the posterior rectal wall to the posterior edge of the muscle complex.

In anomalies such as rectourethral (bulbar) fistulae, there is a long common wall between the rectum and the urethra, which makes dissection from an abdominal approach extremely difficult and can result either in urethral injury or in a portion of the original rectum being left behind. The residual portion may grow over time and produce an outpouching on the back of the urethra. This condition was previously known as a posterior urethral diverticulum (PUD); however, given that it is neither urethral nor a diverticulum, we prefer to call it a remnant of the original fistula (ROOF). A posterior sagittal–only approach is easier and safer in such cases.

Repair of imperforate anus without fistula

In these cases, the blind end of the rectum is usually located at the level of the bulbar urethra and is easily reachable via the posterior sagittal approach. The rectum must be carefully separated from the urethra because the two structures share a common wall, even though no fistula is present. The rest of the repair is performed in the same way as that for a rectourethral fistula defect.

Repair of rectal atresia and rectal stenosis

The posterior sagittal approach is also suitable for repair of these malformations. The upper rectal pouch is opened, and the distal anal canal is split in the posterior midline. An end-to-end anastomosis is performed under direct visualization, with the dentate line left intact. ^[31]  If a presacral mass (which occurs in 30% of these patients) is identified on preoperative MRI, ^[32]  it is removed with presacral dissection at the same time—unless it is connected to the dural elements, in which case the neurosurgical part is done separately.

Patients with rectal atresia undergo a colostomy at birth and thus are always repaired under colostomy cover. All patients with anal stenosis should also be repaired with a colostomy in place to protect the repair. Because of the way in which PSARP is performed for this particular malformation, there is some tension on the posterior corner of this repair, which leads to the high incidence of wound complications when the repair is done without a stoma.

General management

Pain control after a posterior sagittal incision is relatively straightforward.

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 after the operation. If a laparotomy or laparoscopy was necessary, the patient may require a period of fasting and nasogastric decompression.

Anal dilatations with a dilator that fits easily into the anus are started 2 weeks after the repair to avoid a skin-level stricture. Dilations are performed twice daily by the parents at home, and the size of the dilator is increased weekly until the rectum reaches the desired size (based on the patient’s age). Once this desired size is reached, the colostomy can be closed. Once there is no longer resistance with insertion of the final dilator, the dilations can be tapered over the subsequent 3-4 months.

Significant anal strictures occur in cases where the blood supply of the distal rectum is insufficient or when the anoplasty is performed under tension. Skin-level (1-2 mm) strictures occur in some patients who do not undergo recommended dilations. There is some question about the need for postoperative anal dilations after PSARP, and this question is currently being addressed in several studies; however, until new evidence emerges, anal dilations remain the postoperative standard of care for patients who have undergone PSARP.

After colostomy closure, severe diaper rash is common, because the perineal skin has never before been exposed to stool. This can be prevented by the use of waterproof barrier treatments, which should be started in the operating room at the time of the colostomy closure. Surgeons are advised to work closely with wound ostomy specialists to help to prevent this well-known occurrence.

Management of functional disorders

Constipation is the most common problem encountered after treatment for imperforate anus. ^{[33, 34]} 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, those with the most benign defects (ie, the least amount of perirectal dissection) have 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 circle. 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 daily soiling. These patients are often referred to as having fecal incontinence. ^{[35, 36, 37]}  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 and its blood supply must 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 bowel control. The risk of dehiscence, which has been shown to be low (8-10%) with primary repair, ^[38] must be balanced against the risk of colostomy, which may approach 50% if one includes colostomy formation and closure. The care of each patient should be individualized, and the experience of the individual surgeon must be taken into account.

With inadequate preoperative anatomic information, the urinary tract is at considerable risk because the surgeon does not know the precise anorectal defect. If, for example, the surgeon approaches a low rectum transabdominally, there is a risk of leaving behind the very distal rectum, which becomes an ROOF. Many of these patients will develop urologic symptoms (eg, recurrent UTI or postvoid dribbling); they may also report passing mucus from the urethra.

The key in these patients is to treat constipation proactively and, if possible, avoid it after the reconstructive 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 complex ARMs or in those with poor muscles and an abnormal sacrum or spinal cord. These patients require a bowel management program (see Bowel Management). However, in a patient with a good prognosis, soiling may represent overflow pseudoincontinence, 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 2-year-old child who has undergone definitive repair of an ARM 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. A child with true fecal incontinence should not be expected to achieve fecal continence.