Pediatric Imperforate Anus (Anorectal Malformation)

Background

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.

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Pathophysiology

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).

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Etiology

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.

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Epidemiology

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.

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Prognosis

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.

Morbidity/mortality

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.

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History

Prenatal ultrasonography examination findings are often normal, although the polyhydramnios or intraabdominal cysts may suggest imperforate anus with associated hydrocolpos or hydronephrosis.

Newborns with imperforate anus are usually identified upon the first physical examination. Malformations in newborns that are missed upon initial examination are often discovered within 24 hours when the newborn is observed to have distention and has failed to pass meconium and a more thorough examination is performed.

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Physical Examination

During a thorough physical examination, attention should be focused on the abdomen, genitals, rectum, and lower spine.^[4]

The umbilicus should be examined for the absence of an umbilical artery (two-vessel cord), which may suggest an absent kidney. The abdomen should be palpated for masses, which may include a dilated kidney, bladder, hydrocolpos, ectopic kidney, duplication, or other cystic structure.

In males, the testicles must be palpated in the scrotum. The perineum is then examined. Perineal fistulas are diagnosed upon discovery of openings on the perineum, meconium or mucus in a small strip running up into the scrotal median raphe, a perineal groove, or a bucket-handle malformation in the anal dimple skin. If no opening is present, urine is obtained for study, and the child is observed for 24 hours.

In females, a perineal fistula can be directly identified as a small opening on the perineum. If none is present, the labia are separated to search for a vestibular fistula. A fourchette fistula is a type of vestibular fistula that straddles the spectrum of malformation between perineal and vestibular; it is characterized by wet mucosa of the vestibule anteriorly and a dry anoderm posteriorly at the junction of the vestibule and perineum (see the image below).

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Pediatric imperforate anus (anorectal malformation). Fourchette fistula. This malformation is about half way between a perineal fistula and vestibular....

If no fistula is visible and only one opening between shortened labia is observed, the child has a cloaca (see image below).

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Pediatric imperforate anus (anorectal malformation). Cloaca. This is the classic appearance of a female infant with a cloacal malformation with a sing....

If the child has a normal urethra and no vestibular fistula, she may have imperforate anus without fistula. If she appears to have trisomy 21, the likelihood increases that she does not have a fistula. Girls with normal urethra and no visible fistula are observed for 24 hours to allow a perineal fistula to present before operation is required. This waiting period is beneficial in differentiating between children with perineal fistula who may be effectively treated using only a minimal anoplasty from those who require colostomy with further evaluation using distal colostography. Examples of colostography findings are shown in the images below.

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Pediatric imperforate anus (anorectal malformation). Distal colostogram, posteroanterior view. The initial phase of augmented-pressure distal colostog....

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Pediatric imperforate anus (anorectal malformation). Distal colostogram, lateral view. This image shows the second phase of distal colostography, in w....

The remainder of physical examination is focused associated malformations. Cardiovascular malformations occur in 12-22% of patients. The most common lesions are tetralogy of Fallot and ventricular septal defects. Transposition of the great arteries and hypoplastic left heart syndrome have been reported but are rare.

Many gastrointestinal malformations have been described in association with imperforate anus. As many as 10% of patients have tracheoesophageal abnormalities.^[5]  Duodenal obstruction due to annular pancreas or duodenal atresia occurs in a small percentage of patients. Malrotation with Ladd bands that causes obstruction has also been described. Hirschsprung disease has been well described in association with imperforate anus, although the incidence of this combined condition is unknown. Constipation is common.

The association of imperforate anus and vertebral anomalies has been recognized for many years. Patients with high lesions have an increased risk of this association. Lumbosacral anomalies predominate and occur in approximately one third of patients with imperforate anus.^[6]

The frequency of spinal dysraphism (evaluated with ultrasonography or MRI) had been thought to increase with the severity of the lesion, with higher malformations having greater frequency than lower malformations. Several studies have disputed this and have even shown higher incidence of spinal malformations in children with low malformations. The most common type of dysraphism is tethered spinal cord, which is present in as many as 35% of patients. The normal spinal cord terminates between the first and second lumbar vertebral bodies. In patients with a tethered spinal cord, the cord ends lower in the lumbar spine. Cord lipomas and syringohydromyelia are also common. All lumbosacral spinal malformations negatively affect the child's prognosis with respect to urinary and fecal incontinence.

Currarino described a triad of sacral defect, presacral mass, and imperforate anus.^[7]  All patients with an anorectal malformation must be screened for these vertebral abnormalities in the newborn period using sacral radiography and lumbosacral spinal ultrasonography. As many as one half of patients with anorectal malformations have urologic abnormalities. Urinary anomalies are more common in patients with more complex lesions. Improved imaging studies have provided the ability to document an increased range of abnormalities. Mild hydronephrosis is the most common abnormal ultrasonography finding. Vesicoureteric reflux is also a frequent finding, followed by renal agenesis and dysplasia. Cryptorchidism reportedly occurs in 3-19% of males.

Vaginal and uterine abnormalities are common. Females with an imperforate anus must undergo assessment of vaginal patency.^[8] Bicornate uterus and uterus didelphys occur in 35% of female patients with imperforate anus. A vaginal septum is the most common vaginal abnormality and is seen in as many as one half of girls born with a cloacal malformation. Vaginal duplication and agenesis have also been reported. Vaginal agenesis may be associated with ipsilateral absent ovary and kidney.

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Laboratory Studies

Laboratory tests

Complete blood cell (CBC) count, blood typing and screening, and serum electrolyte levels should be measured in all children with imperforate anus who require operation.

Urinalysis should be performed to determine the presence of a rectourinary fistula in all cases in which the diagnosis cannot be made based solely on the physical examination findings. If a child has a perineal fistula, vestibular fistula, or a single perineal orifice, urinalysis is unnecessary. Urinalysis is required in all other affected children.

Other studies

Although anorectal manometry has no role in the newborn period, it may be used in older children who suffer from varying degrees of incontinence. However, the findings are primarily of academic interest.

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Imaging Studies

Imaging studies used in this condition include the following.

Radiography

Sacral radiography

Two views of the sacrum, posteroanterior and lateral, should be obtained to measure sacral ratios and to look for sacral defects, hemivertebrae, and presacral masses. This should be performed before surgery.

Lateral pelvic radiography at 24 hours

Children who could not be diagnosed based solely on physical examination findings, traditionally underwent invertography, which consisted of holding the baby upside down and using lateral radiography to observe the level of gas in the distal rectum. A similar, but more humane, approach is to wait 24 hours after birth to observe for possible maximal pelvic pouch distension and then to use cross-table lateral pelvic radiography with a radio-opaque marker on the anal dimple with the child in the prone position and the hips slightly raised. If the pouch is observed within 1 cm of the marker, some surgeons offer primary repair without colostomy. For pouches farther than 1 cm, colostomy is performed. This 1-cm guideline has been validated only using radiographic measurements and is not directly translatable for measurements made using ultrasonography. Currently, perineal ultrasonography has no role in diagnosis.

Ultrasonography

Prenatal ultrasonography may not always identify an imperforate anus; however, it can be used to identify the type of imperforate anus.^[9] The diagnostic performance of ultrasonography using the pouch-perineum (P-P) distance (suprapubic, infracoccygeal, or perineal approach) to evaluate the type of imperforate anus and any associated anomalies is superior on the day after birth than that on the day of birth,^[10]  particularly for low-type imperforate anus.^[11]  In addition, the diagnostic accuracy of ultrasonography using the P-P distance alone for low-type imperforate anus appears to be comparable to that obtained by prone cross-table radiographic assessment (60% vs 45%, respectively).^[12] However, when using P-P distance and fistula location, there is a significant improvement in the diagnostic accuracy of ultrasonography (90%) over that of prone cross-table radiography (45%).^[12]

There does not appear to be a significant correlation between the distance between the distal rectal pouch and the perineum in low birth weight infants with imperforate anus.^[13]

Abdominal ultrasonography is specifically used to examine the genitourinary tract and to look for any other masses. Hydronephrosis, hydrocolpos, presacral mass, abdominal mass, or any similar finding can profoundly affect management. This study should be performed before surgery and must be repeated after 72 hours because early ultrasonography findings may be insufficient to rule out hydronephrosis due to vesicoureteral reflux.

Spinal ultrasonography or magnetic resonance imaging (MRI)

All children with any form of anorectal malformation, even those considered minor, should undergo screening for spinal malformations. These lesions can be diagnosed using ultrasonography prior to the ossification of the spine. Ultrasonography should be performed as early as possible but is not essential prior to a newborn surgical procedure. Due to ossification, the use of ultrasound diminishes after 3-4 months of age, and by 6 months MRI is usually necessary. MRI may be required any time an ultrasound is suggestive or nondiagnostic.

Augmented-pressure distal colostography

This is the single most important diagnostic test used to clarify the anatomy in all children with malformations who require colostomy. It is personally performed by the colorectal surgeon in many centers. In a fluoroscopy suite, a balloon catheter is placed into the distal stoma, and the balloon is inflated. The catheter is pulled back, and water-soluble contrast is injected by hand. This pressure is required to overcome the pressure of the levator muscles and to allow the contrast to flow into the lowest part of the colon and reveal any fistula. In patients with a fistula to the urinary tract, the bladder often fills, and the study is continued to obtain as much information as is provided with voiding cystourethrography. If no fistula is present, the distal pouch has a rounded appearance, and no urinary extravasation is visible.

Voiding cystourethrography or micturating cystourethrography

These studies are not necessary if comprehensive distal colostography is performed. They are not recommended for primary evaluation of children with anorectal malformations because of poor sensitivity compared with that of distal colostography.

MRI

All children who have sacral defects on plain radiographs should undergo spine ultrasonography to rule out associated malformations, such as meningocele or meningomyelocele, teratoma, or mixed lesions. If ultrasonography findings are suggestive or nondiagnostic, MRI should be performed. All children who have suggestion of tethered cord on ultrasound, a nondiagnostic ultrasound, or have not had an ultrasound and are older than 6 months should undergo MRI.

Computed tomography (CT) scanning

CT scanning presently plays no role in the routine evaluation of children with anorectal malformations.

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Staging

Imperforate anus was historically classified based on the position of the distal-most aspect of the colon in relation to the levator ani muscles. Malformations at or above the levator muscle complex were defined as high anomalies. Infralevator lesions were termed low and were considered simpler and were associated with better prognosis. This system was based on the now obsolete Wingspread classification.

Information obtained from the posterior sagittal approach has led to an anatomic classification that lists malformations based on their specific anatomy. The following is a list of the most common malformations:

Perineal fistula

This malformation is associated with good prognosis, occurs in either sex, and involves a closed anus with a small connection opening on the perineal body.

Some babies with this malformation have a small loop of skin at the anal opening that resembles a bucket-handle. This is pathognomonic for perineal fistula.

Some boys may have no visible perineal opening but may accumulate mucous or meconium in the fistula, which can extend up the median raphe of the scrotum and resembles a black cord (meconium) or a string of pearls (mucous).

This malformation is amenable to primary neonatal pull-through.

Healthy girls who have normal-sized anal openings and small-appearing perineal bodies do not have perineal fistula. This is easily determined by measuring the size of the anus using Hegar dilators. The anus of an average-term newborn should be approximately 12 mm but varies with the size of the child. The "correct" size of the perineum is largely a matter of experience.

Vestibular fistula

This malformation is associated with good prognosis and is easily diagnosed upon physical examination based on the appearance of a small opening at the posterior aspect of the vestibule. The opening is external to the hymen and is, therefore, not vaginal.

The term vaginal fistula was commonly and incorrectly used to describe vestibular fistula. True solitary congenital rectovaginal fistula is exceedingly rare.

Vestibular fistula is safely treated with diverting colostomy, although some pediatric colorectal surgeons repair this malformation primarily in the newborn period without using colostomy.

Cloaca

Persistent cloaca is a malformation in females that encompasses a spectrum of defects, including the presence of a common channel that incorporates the urethra, vagina, and rectum.

The length of the common channel correlates with complexity and prognosis. Shorter channels (< 3 cm) have fewer associated malformations and carry a better prognosis. Longer channels have more complex malformations and poorer prognosis.

One half of all girls with this malformation have 2 hemivaginas and many have hydrocolpos.

This malformation is easily diagnosed upon physical examination based on the presence of a solitary perineal orifice. Females with this malformation often have very small-appearing labia.

All children with cloacae should undergo colostomy shortly after birth.

Bulbar urethral fistula

This malformation observed in boys is relatively common.

No fistula is observed upon physical examination, and urinalysis often shows meconium.

Colostomy is essential to relieve obstruction, prevent urinary soiling, and to allow for distal colostography, which clarifies the malformation for definitive surgical repair.

Prostatic urethral fistula

This malformation observed in boys is rarer than bulbar fistula and carries a poorer prognosis.

The diagnosis and treatment algorithm are identical to those of bulbar fistula, although the surgical procedures used differ.

Bladder-neck fistula

This rare malformation observed in males (10% of all malformations in males) carries a very poor prognosis.

Most patients with bladder-neck fistula require bowel-management regimens.

The diagnosis and treatment algorithm are identical to those of bulbar and prostatic fistulas, although the surgical procedures used differ.

This fistula is best approached abdominally.

Absent fistula

This malformation can occur in either sex, is somewhat rare, and is associated with a good prognosis. It is commonly associated with trisomy 21.

Diagnosis is primarily by exclusion.

Lateral pelvic radiography is performed in babies who have no external evidence of fistula, who pass no meconium after 24 hours, and who have no meconium in the urine.

If the pelvic rectal pouch is within 1 cm of the anal dimple, a primary pull-through may be performed. In these instances, a fistula is unlikely but should be definitely excluded using the proper surgical technique.

If the surgeon opts for colostomy, the absence of a fistula is confirmed using distal colostography.

Cloacal exstrophy

This extremely rare malformation can occur in either sex but is most common in boys. It encompasses a spectrum that includes variant forms of covered exstrophy. The classic form is devastatingly complex.

Affected children have an omphalocele and a large extrophied cloacal plate on their lower abdominal wall. They have 2 hemibladders separated by an intestinal plate, often with prolapsed terminal ileum that proceeds distally to include an extrophied urethral plate flanked by 2 hemiphallic or hemiclitoral structures.

All children with cloacal exstrophy have some degree of pubic symphysis diastasis and may have a spinal malformation, most commonly myelocystocele.

Thankfully, this complex malformation is rare but it has devastating implications on quality of life.

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Approach Considerations

Proper consultation and surgical management are important. Transferring these patients to a facility that provides pediatric surgical care aids in proper classification, diagnosis, and management. Optimal resources for the care of these children includes a pediatric surgeon with experience in anorectal malformations, a pediatric urologist, a pediatric anesthesiologist, a critical care specialist, and a neonatologist.

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Medical Care

Newborns with imperforate anus should not be fed and should receive intravenous hydration. Life-threatening comorbidities take precedence and must be treated first.

If a urinary fistula is suspected, broad-spectrum antibiotics can be administered, although anaerobic coverage is unnecessary within the first 48 hours of life. Any cardiac murmurs identified upon physical examination should be evaluated using echocardiography prior to surgical intervention. The remainder of treatment includes diagnostics and surgical evaluation and management.

Postoperative management

After initial colostomy, the child is able to eat and grow, and any other associated malformations may be addressed. Most patients are discharged once their ostomy has started to function and they tolerate a regular diet.

Following definitive repair, inpatient course is dictated by the presence or absence of a colostomy.

• If a child has been diverted with a colostomy prior to definitive repair and the repair is effectively completed using a posterior sagittal incision without laparotomy, the postoperative course is usually brief. The child may eat after the anesthesia wears off and requires a short hospitalization with perioperative antibiotic administration.
• Complicated repairs that require laparotomy also require more lengthy postoperative courses. These children usually require several days before intestinal function returns and a diet may be resumed.
• Repairs made without a colostomy may be treated with a "medical colostomy," meaning the child is not fed (ie, strict nothing-by-mouth [NPO] status) and a central line is placed for total parenteral nutrition. After an arbitrary period (commonly 5, 7, or 10 d, determined at the discretion of the surgeon in consideration of a host of factors), a diet is resumed and the total parenteral nutrition is stopped. The central line is removed, and the child may then be discharged.

Following ostomy closure, the child usually remains in the hospital for 2-3 days until intestinal function returns. Diet is then resumed, and the child may be discharged.

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Surgical Care

The decision-making process aims to determine which children should undergo primary repair in the neonatal period and which children require colostomy and definitive repair in a staged fashion. Children with anorectal malformations may undergo one or several of the following surgical procedures based on the child's presentation, physical examination findings, and imaging study findings.

Neonatal colostomy

A colostomy is performed in children who are not amenable to primary pull-through either because of malformation complexity (any urinary fistula in boys, vestibular fistula and cloaca in girls, no fistula in either sex >1 cm from perineal skin) or associated comorbidity.

The colostomy is usually fashioned through a left lower quadrant incision. The colon is divided at the point where the descending colon meets the sigmoid colon, and both ends are brought to the abdominal wall. By fashioning the colostomy at this location, the entire sigmoid colon is kept in place; thus, when the pull-through is eventually performed, a large portion of the colon is available for the surgeon to bring down to the perineal skin.

The mucous fistula (the downstream segment) should be very small, flush with the skin, and far enough from the proximal end to be outside the colostomy appliance (or under the flange) to avoid continued urinary soiling with feces.

During this operation, the distal segment of the colon must be exhaustively irrigated to clean out the impacted meconium, which is always significant. This prevents postdiversion urinary sepsis and allows for effective distal colostography.

Primary neonatal pull-through without colostomy

Many pediatric surgeons opt for primary pull-through in children with perineal fistulas (or no fistulas) and close (< 1 cm) rectal pouches on 24-hour lateral pelvic radiography. Some pediatric surgeons who specialize in colorectal problems often offer the same procedure for girls with vestibular fistulas.

Cystoscopy is usually performed to rule out associated malformation. This is performed immediately prior to the pull-through operation. A Foley catheter is inserted following the cystoscopy.

The preferred surgical approach is the posterior sagittal approach developed by Peña et al.

• The child is placed in the prone position with generous padding under the face and chest and a large bolster under the hips to elevate the area of interest.
• A muscle stimulator is used to show the precise position of the rectal muscle complex to enable exact division at the midline. The midline for this operation is defined by the line that precisely divides the muscle complex in half.
• Dissection proceeds until the rectal pouch is identified. The pouch is then mobilized until adequate length is obtained and the rectum is fully separated from its attachment to the genitourinary tract. Even if the structures do not communicate, they remain intimately associated until fully mobilized. This step ensures that the surgeon does not miss a fistula that was missed on urinalysis findings.
• Once the rectum has been mobilized, the muscle stimulator is used to mark the anterior and posterior limits of the muscle complex. The perineal body is then reconstructed, and the rectum is tacked down in the middle of the muscle complex. The posterior wound is closed and anoplasty is performed.

Posterior sagittal pull-through with colostomy

This approach is used in boys with rectourinary fistula (bulbar, prostatic, or bladder-neck fistula), in girls with cloaca or vestibular fistula, and in patients of either sex who do not have a fistula when the rectal pouch is further than 1 cm on 24-hour lateral prone abdominal radiography.

The approach is also used in children who may have malformations that were amenable to primary neonatal pull-through but were unable to undergo such a procedure because of extreme prematurity or other comorbidity.

Colostomy is performed after 24 hours (or immediately if one of the above diagnoses is made based on either physical examination findings or meconium in the urine). Several weeks following colostomy, distal colostography is performed, and the specifics of the malformation are clarified.

Cystoscopy is usually performed to clarify anatomy and to rule out associated malformation. This is performed immediately prior to the pull-through operation. A Foley catheter is inserted following the cystoscopy, except in girls with cloaca.

The reconstructive procedure varies based on the malformation, but the essential concepts include identifying and separating the rectum from other structures, dividing and ligating any fistulas, and fully reconstructing the pelvic anatomy with placement of the rectum within the confines of the muscle complex. Procedures for specific malformations are as follows:

• Vestibular fistulas are directly visible but have the longest common wall between the rectum and vagina and require significant delicate mobilization to avoid holes in either structure.
• The posterior sagittal approach is used in boys with bulbar or prostatic urethral fistulas. The rectum is isolated and opened, and the fistula is identified through progressive distal opening. Once the fistula is identified, the rectum proximal to it may be mobilized, and the fistula is then ligated. Reconstruction then proceeds with primary pull-through, as described above.
• Abdominal (open or laparoscopic) and posterior sagittal approaches are best in boys with bladder-neck fistulas because the fistula is best identified in the abdomen.
• Cloaca procedures are complex. A short – common-channel cloaca can be repaired using total urogenital mobilization. The posterior sagittal wound is opened into the cloaca, which is then further proximally opened until the urethral orifice is identified and catheterized. The rectum is then sought. In girls with 2 hemivaginas (50%), the rectum opens in the vaginal septum, although significant asymmetry may be present. After identification, the rectum is separated from the urogenital tract and completely mobilized. The urogenital tract is then mobilized as a solitary structure until the urethral orifice reaches the perineum. This is then reconstructed, and the muscle is marked to enable creation of an adequate vaginal opening and perineal body without impinging on rectal space.
• A long – common-channel cloaca repair often necessitates formal separation of the bladder and vagina, which requires laparotomy and ureteral catheterization. Vaginal replacement is sometimes necessary if the vaginal length is insufficient for reconstruction.

Colostomy closure

Once the wound has completely healed and postoperative dilations have achieved their goal (ie, the neoanus is at the desired size), the colostomy may be closed in traditional surgical fashion.

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Consultations

The following consultations may be indicated:

• Pediatric surgeon: Early consultation with a pediatric surgeon experienced with these anomalies is essential. Ill-conceived procedures during the newborn period may have lifelong consequences for the patient.
• Neurosurgeon: Consultation with a neurosurgeon is warranted if a tethered spinal cord is present (25% of all cases).
• Urologist: The need for consultation with a urologist depends on the malformation and the individual pediatric surgeon.

• References

Diet and Activity

Diet

After the obstruction is relieved using colostomy, primary pull-through, or dilation, children do not require special diet. The most common complication of imperforate anus repair is constipation or anal incontinence; therefore, diet can be a crucial part of management. Many patients may require laxatives, enemas, or other medications or irrigations in addition to dietary manipulations.^[14]  Children should avoid constipating foods, such as those included in the bananas, rice, applesauce, and toast (BRAT) diet. High-fiber and laxative foods (whole-grain foods and breads, dairy, fruits, vegetables, greasy foods, spicy foods) should be encouraged. Unfortunately, dietary manipulation is often of limited effectiveness because of the fussy nature of most children regarding diets. Fiber supplements and laxatives can be critically important in avoiding constipation, which can significantly affect prognosis.

Activity

Children with anorectal malformations are often otherwise healthy. Activity limitations are usually related only to the period around their surgical procedures.

• References

Complications

Pitfalls abound in the diagnosis and treatment of children with anorectal malformations. A logical approach and an experienced eye are essential for starting the child down the right path from the outset. Complications, while sometimes unavoidable, can have devastating ramifications with respect to a child's chances for urinary and fecal continence.

The following are a few of the most common issues encountered at pediatric colorectal centers.

Primary repair without colostomy

Although certain malformations can be primarily repaired by an experienced pediatric surgeon in the neonatal period without the protection of colostomy, more complex malformations should be treated with colostomy at the initial operation. Primary neonatal operations do not afford the surgeon the benefit of distal colostography to help clarify anatomy. This has resulted in devastating injuries that could have been avoided with a staged approach (colostomy, followed by definitive operation, followed by colostomy closure) with appropriate diagnostic studies.

Colostomy type and position

The ideal colostomy position in children with an anorectal malformation is at the junction of the descending and sigmoid colon. The colostomy should be completely divided, with the ends spaced far enough apart to ensure that the mucous fistula is not located within the ostomy appliance. This prevents continued soiling of the urinary tract by feces, which can result in urinary infection. Loop colostomies are never completely diverting and put a child at risk for urinary sepsis. Transverse colostomies seem to be associated with a significant degree of mucous accumulation in the long defunctionalized segment, resulting in chronic distension and dysmotility similar to that seen in children with atresias. Desire to perform laparoscopic pull-through should not be a primary factor in the decision to perform colostomy.^[15]

Intestinal perforation

This complication can arise during any phase of management.

In children diagnosed with imperforate anus at birth, 24 hours is allowed to pass prior to surgical treatment if perineal fistula (or other visible malformation, eg, vestibular fistula or cloaca) is not evident and urinalysis findings do not show meconium. This allows the distal colon to distend a bit, and meconium occasionally leaks out on the perineum from a tiny perineal fistula. This waiting period is advocated by the most experienced surgeons and should not increase the risk of perforation prior to repair or colostomy. Although exceedingly rare, some children have perforated during this period.

Perforation has also occurred during anal dilations. Dilations should always be performed first by the surgical staff. Dilation (performed instead of anoplasty) should be performed only by the surgical staff in extremely low birthweight premature babies. Parents may be taught how to dilate larger babies but must be closely supervised.

Perforation is minimized by appropriately positioning the colostomy while avoiding a transverse colostomy.

Operative complications

Correction of malformations, even those that some surgeons may describe as minor, requires significant experience, a keen eye, and a sensitive hand. Devastating complications (eg, complete dehiscence, postoperative fistula, missed fistula, urologic injury, ischemia) can render a child who may have been continent after a successful operation completely incontinent. Thus, these children should be directed to a subspecialist with a special interest in this area at the earliest possible opportunity.

Stenosis

This is a narrowing of the new anus. A tight ring of scar tissue forms instead of a soft and stretchable anus. This is a devastating complication and usually requires complete surgical repair. A regular schedule of slow progressive dilation of the neoanus prevents stenosis. Weekly dilations increase risk of stenosis. If the dilations are spaced too far apart, the anus can narrow between the dilations. Large dilations provoke tears. Tears heal with scar tissue, which causes stenosis.

Undrained hydrocolpos

Many baby girls born with cloaca have a very large mucous-filled vagina. This may appear as a giant cystic structure on prenatal ultrasonography. Ultrasonography should be performed at birth to look for such a cystic mass. If present, it must be drained either from below (through the cloaca) or at the time of colostomy using a vaginostomy tube. If it is left undrained, complications ensue.

Hydrocolpos can large enough to obstruct the ureters. Some children with undrained hydrocolpos have undergone vesicostomy and ureterostomy, when simple drainage of the hydrocolpos would have sufficed.

Hydrocolpos can also become infected. If the vagina perforates, it usually scars and becomes unusable, often necessitating vaginal replacement

Constipation

Many children who have undergone anorectal malformation repair develop constipation. This must be prevented by strong parental counseling and diligence to ensure the child clears the rectum daily. Constipation on its own is not a complication. The complication is not preventing the constipation through close follow-up and parental counseling.

Once constipation develops, the distal colon can become dilated, which exacerbates the constipation because the dilated bowel has poor motility. The end result is termed encopresis. Fecal impaction forms, and liquid stool leaks around it constantly, leaving the child incontinent. This can be treated but is best prevented.

Incontinence

Many children who have malformations associated with poor prognosis develop fecal or urinary incontinence, even after a flawless operation without complication. While "the plumbing" may seem to be a relatively simple matter of rearranging some tubes, continence is a complex state that requires a delicate balance of nerves, anorectal and colonic motility, and sphincter muscles. Parents should be given realistic expectations and should be made aware of all options, including bowel management or continent diversion and intermittent catheterization, should incontinence occur.

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Long-Term Monitoring

Children with an anorectal malformation require close follow-up for life. Continuity of care is essential in the growing years and into adulthood, as the children deal with issues relating to continence and constipation.

Following the initial colostomy, further investigations in preparation for definitive operation, such as distal colostography or repeat renal ultrasonography, are performed in an outpatient setting.

Following definitive operation in either the neonatal period or after colostomy, follow-up is necessary 2 weeks after surgery. Parents are often instructed as to how to obtain a set of Hegar dilators, which they are to bring to the first postoperative visit. At that visit, the surgeon measures the size of the anus and instructs the parents how to perform the daily dilations. These dilations continue until the anus has reached its goal size. At this time, the colostomy may be closed if one was performed.

Patients with cloacal anomalies need specialized follow-up care after puberty to assess sexual function and to correct genitourinary problems.

• Some girls who have undergone surgical correction for cloaca have incompletely canalized fallopian tubes and can develop painful cystic collections of menstrual blood following menarche. This condition sometimes requires surgical intervention. A pediatric gynecologist can be extremely helpful for these girls and can suppress menstrual blood production through exogenous hormone administration until a clear treatment strategy is established.
• Only within the past 20-30 years have significant numbers of girls with cloaca undergone definitive repair. A few have become pregnant. While this is miraculous, the delivery process should include close involvement of the pediatric surgeon who performed the original repair, if possible. If this is not possible, a surgeon experienced in cloaca repair should be consulted. Caesarean delivery is the only safe way to avoid damage to tissues that originally required complex reconstruction.

Some children present with prolapse during the toilet-training years. Eliminating constipation as a cause helps identify children who need surgical trimming of prolapsed mucosa.

Visits for constipation are frequent, and it is best treated with a regular preventative regimen that includes diet, fiber, and laxatives for as long as they are needed. Dietary water does not influence stool quality in a healthy child.

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Medication Summary

Many children with anorectal malformations require medications for various reasons. Beyond perioperative medications, maintenance medications often include urinary antibiotic prophylaxis or treatment and/or laxatives.

Urinary prophylaxis is used to mitigate the risk of urinary infection and urosepsis in children with risk factors for urinary infection such as urinary fistula, vesicoureteral reflux, or continent diversion. Common agents include oral amoxicillin, oral trimethoprim/sulfamethoxazole, and gentamicin bladder irrigations. Comprehensive information on all these medications and others is available in the eMedicine pediatric topic Urinary Tract Infection.

Common laxatives include senna products, milk of magnesia, and propylene glycol solutions (eg, MiraLax, GlycoLax).

Routine pain medications for surgical procedures are warranted. Acetaminophen (15 mg/kg every 4 h) or morphine sulfate (0.05-0.1 mg/kg intravenously every 2-4 h) usually suffices.

The usual perioperative antibiotics include ampicillin (50 mg/kg every 6 h), gentamicin (2 mg/kg every 8-12 h), and clindamycin (10 mg/kg every 8 h).

Many laxatives have been used to control constipation in these patients. Senna comes in various forms and can be highly effective, although dosage must be individualized. The clinician must be personally engaged and must establish an effective dose response for each patient on a case-by-case basis.

Balanced electrolyte solutions have been used for years as a bowel preparation for surgical procedures. These solutions have only recently been made available in powdered form for mixing at home and for use as a laxative (under the name MiraLax or GlycoLax). These nonstimulant laxatives are very palatable to children because they dissolve in any beverage with minimal impact on taste.

In children who require urinary prophylaxis, standard medications include amoxicillin (first-line medication in newborns), nitrofurantoin, and trimethoprim/sulfamethoxazole (not used in babies aged < 2 mo). To ascertain a prophylaxis dose for one of these antibiotics, calculate a treatment dose based on the normal administration interval (2, 3, or 4 times per day) and then administer that same dose once per day. For example, if the amoxicillin treatment dose is 20-50 mg/kg/d divided every 8 hours and a patient weighs 10 kg, the normal dose may be 30 mg/kg/d (which falls within the recommended range). Because the patient weighs 10 kg, the dose is 100 mg every 8 hours. The prophylaxis dose would then be a once-daily dose of 100 mg.

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