Surgery for Pediatric Anorectal Malformation (Imperforate Anus) 

Updated: Apr 15, 2020
Author: Richard J Wood, MD, MBChB, MRCS(Eng), Dip PEC(SA), FCPaedSurg(SA); Chief Editor: Eugene S Kim, MD, FACS, FAAP 

Overview

Background

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

Throughout the centuries, doctors have seen and attempted to treat infants born with imperforate anus. Given that few patients were described in the early literature, most are assumed to have died without treatment. Paulus Aegineta, in the 7th century CE, recorded the earliest account of successful surgery for imperforate anus. He suggested rupturing an obstructing membrane with a finger or knifepoint and then dilating the tract until healing was complete. This approach was used for many years.

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

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

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

In 1980, the surgical approach to repairing ARMs altered dramatically with the introduction of the posterior sagittal approach by Peña and Devries. This approach allowed pediatric surgeons to obtain a clear view of the anatomy of ARMs and to repair them under direct vision, with better visualization and understanding of the anatomic relations than previous approaches allowed. Georgeson subsequently added laparoscopy so that any abdominal dissection could avoid an incision.

Since the introduction of these two approaches, there has been considerable debate regarding their efficacy. In recent years, there has been a growing consensus that some malformations are best approached transabdominally (via laparoscopy or open surgery, depending on available expertise and equipment) and others posterior-sagittally. 

Anatomy

Several classifications have been used for ARMs in the past. At present, it is widely accepted that the Krickenbeck classification from 2005, which was a modification of the previous Peña classification, should be used to describe ARMs (see Table 1 below). This is a departure from the previous Wingspread classification (1984) insomuch as it relies on the specific anatomy of each defect rather than on broad and unhelpful terms such as high, intermediate, and low which have only a limited bearing on prognosis.

Table 1. Krickenbeck Classification of Anorectal Malformations (Open Table in a new window)

Major Clinical Groups Rare/Regional Variants
Perineal (cutaneous) fistula Pouch colon

Rectourethral fistula

  • Prostatic
  • Bulbar
Rectal atresia/stenosis
Rectovesical fistula Rectovaginal fistula
Vestibular fistula H fistula
Cloaca Others
No fistula  
Anal stenosis  

The goal of this type of classification system is to define the anatomy of malformations reliably. This is especially important for comparing data from different sites, both nationally and internationally. Making meaningful comparisons is greatly facilitated by using clearly defined anatomic definitions. A 2019 publication by Halleran et al sought to further define the anatomy of rectourethral malformations.[1]

Pathophysiology and Etiology

A sound understanding of the anatomy is helpful to prevent damage to important structures during the surgical repair and to preserve the best potential for fecal and urinary continence.

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

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

The surgeon’s primary concerns in correcting these anomalies are to accomplish a successful anatomic reconstruction and to achieve bowel and urinary control. Problems with sexual function and fertility must also be considered.

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

Some patients experience fecal and occasional urinary incontinence despite excellent anatomic repair. Associated problems (eg, poorly developed sacrum, pelvic musculature, and pelvic nerve roots, as well as tethered cord or myelomeningocele) likely contribute to an inability to achieve continence. For patients with true fecal incontinence, an effective bowel management can provide social cleanliness and effective evacuation of stool. This in turn may improve urinary function, reduce urinary tract infections (UTIs), and improve quality of life. (See Bowel Management.)

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

Epidemiology

ARMs occur in approximately one out of every 3000-5000 births and are slightly more common in males,[2, 3]  with a 1% risk that a family will have a second child with an ARM.[4, 5]

A rectourethral fistula is most common in males, and a rectovestibular fistula is most common in females. Having no fistula at all is rare (5% of patients) and is associated with Down syndrome.[6]

In the past, cloaca was considered a rare defect, whereas rectovaginal fistula was commonly reported. In fact, the converse is true: Cloacas are the third most common defect in females, after vestibular and perineal fistulas. A true rectovaginal fistula is rare (< 1% of cases).[7]  Incorrect diagnosis in such a case leads to surgical treatment in which only the rectal component is repaired and the patient is left with a a persistent urogenital sinus.[8]

Prognosis

In evaluating the results of treatment of ARMs, patients should not be grouped into the traditional high, intermediate, and low categories from the 1984 Wingspread classification. This classification is flawed in several ways. For instance, within the high group, different ARMs have different treatments and carry different prognoses (eg, rectoprostatic fistula compared with rectobladderneck fistula). Both of these would be considered high in the Wingspread classification; however, the two malformations are so different that they should not be grouped together.

As stated above an anatomically based grouping is of more clinical value, and this is provided by the Krickenbeck classification (see Table 1 below).[9]

Table 1. Krickenbeck Classification of Anorectal Malformations (Open Table in a new window)

Major Clinical Groups Rare/Regional Variants
Perineal (cutaneous) fistula Pouch colon

Rectourethral fistula

  • Prostatic
  • Bulbar
Rectal atresia/stenosis
Rectovesical fistula Rectovaginal fistula
Vestibular fistula H fistula
Cloaca Others
No fistula  
Anal stenosis  

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

Approximately 75% of all patients with ARMs have voluntary bowel movements. Approximately 50% have soiling episodes. Such episodes are usually related to constipation; when constipation is treated properly, the soiling usually improves. Approximately 40% of all patients have voluntary bowel movements and no soiling. This is the group which would be described as continent. Most recently definitions of continence based on Rome Criteria (Ref), one or less accidents per week, have been used to describe continence. This change will make it easier to compare results between various malformations.

At least 30% of patients with ARMs have fecal incontinence and need a bowel management regimen with a daily enema to keep clean (see Bowel Management). Apart from the anorectal anomaly itself, the status of the sacrum, spine, and muscular development greatly affects a patient's chances of having fecal continence. Even with a perfect reconstruction, a patient with complex malformation, a poor sacrum or an abnormal spinal cord may not achieve continence.

Potential for continence must be evaluated when the child is older than 3-4 years.

Patients with less complex malformations (eg, rectoperineal fistula or rectal atresia) have excellent outcomes. Girls with rectovestibular fistulas have very good outcomes, except for a tendency to develop constipation.[10] Approximately 60% of boys with rectourethral fistulae and normal sacra have good outcomes. More than 70% of patients with a short common channel cloacal malformation and a normal sacrum can develop continence. Patients with very complex malformations (eg, rectobladderneck fistula in boys and long common channel cloacal malformations in girls) have poor outcomes.

The sacrum is a good predictor of outcome, in that it correlates with the overall development of the pelvis, including the sphincter muscles and pelvic nerves. Patients with a normal sacrum are much more likely to have fecal continence; those with a hypodeveloped sacrum are much more likely to be incontinent. A sacral ratio has been developed to allow more objective assessment of the sacrum (see the image below). Patients with a sacral ratio of less than 0.4 rarely achieve continence. A hypodeveloped sacrum is also a good predictor of associated spinal and urologic abnormalities. Sacral x-rays should not be taken in the first 3 months of life as the coccyx is not yet calcified and may lead an under read of the sacral ratio.

Calculation of sacral ratio. Calculation of sacral ratio.

A method that uses the sacral ratio and other variables to assess the likelihood that a patient with an ARM will have continence is outlined in Table 2 below.

Table 2. Numerical Scoring of Chances of Having Fecal Continence for Patient With Anorectal Malformation (Open Table in a new window)

Type of ARM Score
Perineal fistula 1
Anal stenosis 1
Rectal atresia 1
Rectovestibular fistula 1
Rectobulbar fistula 1
ARM without fistula 1
Cloaca < 3 cm common channel 2
Rectoprostatic fistula 2
Rectovaginal fistula 2
Rectobladderneck fistula 3
Cloaca ≥3 cm common channel 3
Cloacal exstrophy 3
Spine Score
Normal termination of conus (L1-2) 1
Normal filum appearance 1
Abnormally low termination of conus (below L3) 2
Abnormal fatty thickening of filum 2
Myelomeningocele 3
Sacrum Score
Sacral ratio ≥0.7 1
Sacral ratio ≥0.4, ≤0.69 2
Hemisacrum 2
Sacral hemivertebrae 2
Presacral mass 2
Sacral ratio < 4 3

ARM = anorectal malformation.

Individual scores for ARM type, spine, and sacrum are added together. Total scores are interpreted as follows:

  • 3 or 4 - Good potential for continence
  • 5 or 6 - Fair potential for continence
  • 7, 8, or 9 - Poor potential for continence
 

A child's outcome may be predicted reasonably accurately. Both patients with good prognoses and those with poor prognoses can be identified. Patients falling between these two categories, however, have proved more difficult to identify, and this issue is being examined in a multicenter study currently under way. Parents can be realistically informed of their child's potential for bowel control, within the first year of life. This avoids a great deal of frustration later in life. Establishing the functional prognosis early is vital to avoid raising false expectations in the parents.

Once the diagnosis of the specific defect is established, the functional prognosis may be predicted. The status of the spine, sacrum, and perineal musculature will affect the counseling given to the parents.

If a given defect is one that carries a good prognosis (eg, rectovestibular fistula, rectoperineal fistula, rectal atresia, rectourethral bulbar fistula, or ARM without fistula), the child may be expected to potty train by age 4-5 years. Such children require supervision and treatment to avoid fecal impaction, constipation, and soiling.

Certain defects indicate a poor prognosis, such as a complex cloaca (common channel >3 cm with a short urethra) or a rectobladderneck fistula. Parents should be informed that the child may require a bowel management program to remain clean. The program should be implemented at age 3-5 years (see Bowel Management).

Patients with rectoprostatic fistulas have an almost equal chance of continence or incontinence. Toilet training should be attempted at age 3-5 years; if this is unsuccessful, a bowel management program can be initiated, depending individual home circumstances. Each year, during vacation, potty training should be attempted; if this is unsuccessful, bowel management should be restarted. As the child grows older and more mature, the likelihood of achieving bowel control improves. Once it is determined that a daily enema is needed, those patients can continue rectal enemas, if well tolerated or these enemas can be given via a Peristeen device or in an antegrade manner via a Malone appendicostomy.[11]

Urinary incontinence occurs in boys with ARMs only when they have an extremely defective or absent sacrum or an abnormal spine or when the basic principles of surgical repair are not followed and important nerves are damaged during the operation. The vast majority of boys have urinary control. This is also true for girls, with the exception of the group with complex cloaca, who not infrequently need clean intermittent catheterization (CIC; see Cloacal Malformations).

Careful, regular observation is necessary in these patients for accurately reassessing their prognosis and for avoiding problems that can dramatically affect their ultimate functional results. In addition, this group also requires close follow-up of their kidneys to help mitigate the development of renal impairment by actively treating common problems such as recurrent urinary tract infections and reflux and by ensuring good bladder emptying.

 

Presentation

History

For neonates born with an anorectal malformation (ARM), accurate early diagnosis and expert treatment are crucial.

During the first 24-48 hours of life in a newborn with an ARM, the following two questions should be answered:

  • Does the newborn have any associated anomalies that need to be addressed immediately?
  • Should the neonate undergo a primary procedure without a protective colostomy with dilations as a temporizing measure, or should he or she undergo a protective colostomy with definitive repair deferred to a later date?

The surgeon must also determine whether female neonates have a distended vagina (hydrocolpos), whether it should be drained, and whether urinary diversion is required. These maneuvers are intended to prevent sepsis and metabolic acidosis and to protect the kidneys with the aim of preventing the development of chronic renal impairment (see Cloacal Malformations).

Physical Examination

Colostomy vs anoplasty

The decision whether to perform an anoplasty during the early newborn period or to perform a colostomy and delay the repair is based on physical examination findings in the newborn, the appearance of the perineum, and changes that occur during the first 24-36 hours of life. The patient's overall condition and the presence of significant comorbidities also must be considered in making these decisions.

Operating earlier and in a single stage is potentially beneficial to the patient, but this should be decided carefully, on the basis of the specific circumstances of the newborn and the experience of the surgeon. A more conservative approach is warranted in neonates with low birth weight and associated cardiac or respiratory conditions.

The indications for colostomy versus anoplasty for newborn boys are as follows:

  • Primary anoplasty - Rectoperineal fistula
  • Colostomy - Rectobulbar urethral fistula, rectoprostatic urethral fistula, rectobladderneck fistula, imperforate anus without fistula, rectal atresia

The indications for colostomy versus anoplasty for newborn girls are as follows:

  • Primary anoplasty - Rectoperineal fistula, rectovestibular fistula
  • Colostomy - Imperforate anus without fistula, cloacal malformation, rectal atresia, rectovaginal fistula

In all situations where one may opt for an anoplasty, temporizing with dilations is acceptable if the child’s condition warrants it. Alternatively, the two procedures may be combined—that is, the anoplasty is performed, but the repair is protected with a stoma.

Decision-making in newborn boys with anorectal anomalies

In 80-90% of newborn boys, clinical inspection provides enough information for the surgeon to decide whether a colostomy is required.

After birth, an intravenous line is placed for fluids and antibiotics. A nasogastric tube is inserted to keep the stomach decompressed and thereby avoid the risk of vomiting and aspiration.

Meconium is not usually observed at the perineum in a newborn with rectoperineal fistula until at least 16-24 hours of life. Abdominal distention does not develop during the first few hours of life but is required to force meconium through a rectoperineal fistula, as well as through a urinary fistula. This is because the most distal part of the rectum in these children is surrounded by a funnel-like voluntary muscle structure (levator) that keeps part of the rectum collapsed and empty.

The intra-abdominal pressure must be high enough to overcome the tone of the muscles that surround the rectum to force meconium through the fistula. Therefore, the decision to perform a colostomy or an anoplasty must be delayed for 16-24 hours while the surgeon evaluates for clinical evidence of the passage of meconium either on the perineum or in the urine, thereby confirming the diagnosis of the newborn’s anorectal anomaly.

Clinical inspection of the buttocks is important. A flat bottom or flat perineum, as evidenced by the lack of a midline gluteal fold and the absence of an anal dimple, indicates that the patient has poor muscles in the perineum. These findings are associated with a complex ARM; therefore, a colostomy should be performed.

Perineal signs found in patients with malformations amenable to primary repair include the presence of meconium at the perineum, a bucket-handle malformation (ie, a prominent skin tag located at the anal dimple, below which an instrument can be passed), and an anal membrane (through which meconium is visible).

Newborn boys with rectoperineal fistula do not require a colostomy. They are candidates to undergo a posterior sagittal anoplasty.

Newborn boys with evidence of a rectourinary tract communication should undergo fecal diversion with a colostomy.

If none of the clinical signs to reveal the location of the anorectal anomaly are evident by 24 hours, obtaining radiographs can help. This step is necessary in only approximately 10% of patients. Obtain a cross-fire radiograph with the newborn prone and the pelvis elevated and with a radiopaque marker placed on the perineum (see the image below).

Cross-fire radiograph in which air column in dista Cross-fire radiograph in which air column in distal rectum can be observed close to perineal skin.

Rarely, radiography reveals the column of air in the distal rectum to be within 1 cm of the perineum; in these instances, treatment is similar to that of a rectoperineal fistula, and a newborn perineal operation may be performed. If the air column is more than 1 cm from the perineum, a colostomy is indicated.

A definitive repair in the newborn period avoids a colostomy; however, because the surgeon does not know the precise anorectal defect, the urinary tract is at considerable risk. For a definitive determination of the patient's anorectal defect, distal colostography is necessary, and this 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 and may find and damage other unexpected structures (eg, posterior urethra, seminal vesicles, vas deferens, ectopic ureters) during the search for the rectum. Finally, without fecal diversion, the risk of dehiscence and infection exists. These complications may compromise the chance of achieving fecal and urinary continence.

Obtaining a urinalysis and placing gauze over the penis can reveal the presence of fecal matter in the urine, which is considered evidence of a rectourinary fistula.

Abdominal ultrasonography (US) must be performed to evaluate for the presence of hydronephrosis, which could potentially represent an obstructive uropathy. Significant vesicoureteral reflux may also be the cause. At the same time, spinal US may be performed to evaluate for spinal anomalies, including the presence of a tethered cord, and the presacral space should be inspected to rule out a presacral mass.

Methods to reveal the location of the distal rectum before 16 hours of life are flawed because of the contracted state of the rectum within the funnel-like sphincter mechanism. Typically, the funnel-shaped muscle structure is contracted unless overcome with a distending force. Tests such as magnetic resonance imaging (MRI), US, computed tomography (CT), or injection of contrast through the perineum may conclude that the distal rectum is falsely high in the pelvis.

Distal colostography (obtained before the definitive repair) must have adequate pressure to demonstrate a fistula from the rectum to the urinary tract. If pressure is inadequate, this method also falsely locates the distal rectum as high in the pelvis.

Once the patient recovers from colostomy and demonstrates good growth and development, the definitive operation can be planned for 4-12 weeks later.

Decision-making in newborn girls with anorectal anomalies

In a female, the following questions should be asked:

  • How many orifices are present?
  • If three are present, is the anal orifice correctly located within the muscle complex (defined by an area of hyperpigmentation and muscle contraction with electrical stimulation at examination under anesthesia [EUA]), and is the anal opening of adequate size (Hegar size 12 at birth is normal)?
  • Is there an adequate perineal body?

Whereas it is vital not to miss an ARM, many babies are incorrectly diagnosed with an “anteriorly misplaced anus” that is in fact normal, with the anal opening properly centered in the sphincters. These patients require no surgery. In females, one must decide if one is dealing with a perineal fistula, a vestibular fistula, a cloaca, a no-fistula defect, or some rare or complex malformation; in males, the observation records whether there is a perineal fistula, no fistula, or (most commonly) a rectourethral fistula. Decisions regarding surgical management in the newborn period are led by this initial assessment.

Newborns (male or female) with a perineal fistula and females with a vestibular fistula, provided that they have no severe comorbidities, can be managed with a posterior sagittal anorectoplasty (PSARP) without the need for a colostomy. If there is a single perineal orifice (see the image below), the diagnosis of a cloaca should be made, and treatment consists of a divided proximal sigmoid colostomy.

Perineum of newborn with cloaca. Note single perin Perineum of newborn with cloaca. Note single perineal orifice.

In view of the high incidence of associated urologic malformations, an evaluation that includes abdominal and pelvic US to look for hydronephrosis and hydrocolpos is mandatory. If hydrocolpos is present, it can be adequately drained at the same time as the colostomy formation, either via clean intermittant catheterization (CIC) perineally or via a vaginostomy; in almost all cases, this helps resolve the hydronephosis.

Occasionally, the fistulas are large enough to decompress the gastrointestinal tract. They may be dilated to facilitate fecal drainage until the baby is older and a definitive repair is performed. Definitive repair involves a posterior sagittal approach. The most delicate part of this operation is the separation of the rectum and vagina, which share a common wall.

Like boys, newborn girls may also have a rectoperineal fistula, which necessitates an anoplasty procedure in the newborn period.

As in boys, the rectum location is not clinically evident in fewer than 5% of newborn girls after 24 hours. They may have imperforate anus with no fistula. Cross-table lateral radiography should be performed, which helps determine the need for a colostomy.

During the perineal inspection, newborn girls are commonly given an incorrect diagnosis of imperforate anus with rectovaginal fistula; however, all three structures (ie, urinary tract, vagina, and rectum) actually meet in a common channel, and the baby has a cloaca. The key part of the examination is the location of the urethra and rectal fistula in relation to the hymen. If the urethra lies inside the hymen, the diagnosis is cloaca. If the urethra is outside the hymen then cloaca is excluded.

Making the correct determination is vital, because 90% of newborns with cloaca have an associated urologic problem and as many as 50% have hydrocolpos. The urinary tract and distended vagina both may require treatment in the newborn period to avoid serious complications.

Missing the diagnosis of a cloaca commonly means that an obstructive uropathy may be overlooked. The patient may then receive only a colostomy, which results in subsequent sepsis, acidosis, and, in 30-50% of patients with a cloaca, renal failure necessitating transplantation.

The other implication of missing the diagnosis of a cloaca involves repairing only the rectal component of the anomaly, leaving the patient with a persistent urogenital sinus.

Types of urinary tract malformations are as follows:

  • Renal agenesis
  • Vesicoureteral reflux
  • Renal dysplasia
  • Megaureter
  • Hydronephrosis
  • Ectopic ureter
 

Workup

Imaging Studies

In newborn period

Diagnostic imaging of a newborn with imperforate anus includes abdominal ultrasonography (US) to evaluate for urologic anomalies, which should be performed after 72 hours of life (see the image below). An early sonogram may miss abnormalities as a result of physiologic oliguria at birth.[12] In patients with a cloacal malformation, a distended vagina (hydrocolpos) may be identified.

Ultrasonography demonstrating hydronephrosis in ne Ultrasonography demonstrating hydronephrosis in newborn with imperforate anus.

Plain radiography of the spine may reveal spinal anomalies, such as spina bifida and spinal hemivertebrae.

Plain radiography of the sacrum in the anterior-posterior and lateral projections may demonstrate sacral anomalies, such as a hemisacrum and sacral hemivertebrae. In addition, the degree of sacral hypodevelopment may be assessed, and a sacral ratio can be calculated by measuring the distances between key bony structures (see the image below). The sacral assessment should not be done until after the ossification of the coccyx has taken place (>3 months of age).

Calculation of sacral ratio. Calculation of sacral ratio.

Spinal US in the newborn period and up to age 3 months (the point at which the sacrum ossifies) may be performed to find evidence of a tethered spinal cord and other spinal anomalies and to rule out a presacral mass.

Cross-fire radiography may help demonstrate the air column in the distal rectum in the small percentage of patients in whom clinical evidence does not delineate the likely anorectal anomaly within 16-24 hours.

After newborn period

High-pressure distal colostography is performed on an outpatient basis, after the colostomy has been created. (See the image below.) Hydrosoluble contrast material is injected into the distal stoma to demonstrate the precise location of the distal rectum and its likely urinary communication.

Distal colostography in patient with imperforate a Distal colostography in patient with imperforate anus and rectourethral fistula, in this case at prostatic level.

Hydrostatic pressure under fluoroscopic control is required. A Foley catheter is placed in the mucous fistula, and the 3-mL balloon is inflated and pulled back to occlude the stoma during contrast injection. The hydrostatic pressure must be high enough (manual syringe injection) to overcome the muscle tone of the striated muscle mechanism that surrounds the rectum and keeps it collapsed. This is the best way to demonstrate a rectourinary communication and determine the rectum's true location in the pelvis and perineum.

The contrast material usually fills the proximal urethra and bladder through the fistula. The injection is continued until the child voids, and pictures are taken during micturition to reveal, in a single picture, the sacrum, the location of the rectum, the perineum, the fistula location, the bladder, vesicoureteral reflux (if present), and the urethra.

Colostography is vital in determining the anatomy so that a definitive repair can be planned.[13]  In 10% of patients, the fistula is at the level of the bladder neck; in these instances, during the main repair, the surgeon knows that the rectum can be found only through the abdomen, and a combined posterior sagittal and abdominal or laparoscopic approach is used.

The anorectal defect of imperforate anus without fistula may also be demonstrated with this radiologic evaluation. Occurring in approximately 5% of patients, imperforate anus without fistula has a good functional prognosis and is common in individuals with Down syndrome.

In most newborn girls with anorectal malformations (ARMs), except for those with a cloaca and rectovaginal fistula (very rare), distal colostography is not necessary, because the fistula is clinically evident.

If the spine was not evaluated with US in the newborn period, magnetic resonance imaging (MRI) is necessary after age 6-12 months to exclude the presence of tethered cord and other spinal anomalies.

 

Treatment

Approach Considerations

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.

Medical Therapy

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.

Calculation of sacral ratio. Calculation of sacral ratio.

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.

Colostomy

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 infections
  • 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 urinary tract infection (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
Recommended colostomy with divided stomas, with pr Recommended colostomy with divided stomas, with proximal stoma in descending colon.

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 distal 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

Definitive Repair

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 to also require an abdominal approach.

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).

Electrical stimulator used to show sphincteric con Electrical stimulator used to show sphincteric contractions.
Electrical stimulator probe used to show sphincter Electrical stimulator probe used to show sphincteric contractions. Used with electrical stimulator shown in Image 25.

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.)

Posterior sagittal incision showing parasagittal f Posterior sagittal incision showing parasagittal fibers.

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.)

Operative view of posterior sagittal anoplasty in Operative view of posterior sagittal anoplasty in newborn with rectoperineal fistula.
Posterior sagittal repair of rectovestibular fistu Posterior sagittal repair of rectovestibular fistula.

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

Closure of posterior sagittal incision. Closure of posterior sagittal incision.

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. It is only in rectourethral (bladderneck) fistulas or high prostatic fistulas that it is 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.

Postoperative Care

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 postoperatively. 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

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, he or she risks 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.

Long-Term Monitoring

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.

 

Questions & Answers

Overview

What are anorectal malformations (ARMs)?

How are anorectal malformations (ARMs) classified?

What is the role of anatomic repair in the treatment of anorectal malformations (ARMs)?

What factors contribute to incontinence despite anatomic repair of anorectal malformations (ARMs)?

What causes anorectal malformations (ARMs)?

What is the prevalence of anorectal malformations (ARMs)?

What is the Krickenbeck classification of anorectal malformations (ARMs)?

What is the prognosis of anorectal malformations (ARMs)?

How is the likelihood of fecal continence determined in patients with anorectal malformations (ARMs)?

How does the prognosis vary among anorectal malformations (ARMs)?

Presentation

What are the initial treatment decisions in the first 48 hours after birth of a child with anorectal malformations (ARMs)?

What are the treatment options for newborns with anorectal malformations (ARMs)?

What are the treatment options for male newborns with anorectal malformations (ARMs)?

What are the treatment options for female newborns with anorectal malformations (ARMs)?

Workup

What is the role of imaging in the diagnosis of anorectal malformations (ARMs)?

What is the role of high-pressure distal colostography in the management of anorectal malformations (ARMs)?

What is the role of MRI in the management of anorectal malformations (ARMs)?

Treatment

When is surgery contraindicated for the treatment of anorectal malformations (ARMs)?

How common are genitourinary defects in anorectal malformations (ARMs) and how are they evaluated?

How prevalent is a tethered spinal cord in anorectal malformations (ARMs)?

How does a tethered spinal cord affect the prognosis of anorectal malformations (ARMs)?

How is a tethered spinal cord diagnosed in anorectal malformations (ARMs)?

How prevalent are sacral and spinal defects in anorectal malformations (ARMs)?

How do sacral and spinal defects affect the prognosis in anorectal malformations (ARMs)?

What is the role of colostomy in the treatment of anorectal malformations (ARMs)?

What is the role of posterior sagittal anorectoplasty (PSARP) in the treatment of anorectal malformations (ARMs)?

How is posterior sagittal anorectoplasty (PSARP) performed for the treatment of anorectal malformations (ARMs)?

What is the role of laparoscopic-assisted anorectoplasty in the treatment of anorectal malformations (ARMs)?

How is imperforate anus without fistula repaired?

How is rectal atresia and rectal stenosis repaired?

What is included in the postoperative care following the surgical repair of anorectal malformations (ARMs)?

How is constipation treated following the surgical repair of anorectal malformations (ARMs)?

What are the possible complications of the surgical repair of anorectal malformations (ARMs)?

What is included in the long-term monitoring following the surgical repair of anorectal malformations (ARMs)?