Surgery for Pediatric Anorectal Malformation (Imperforate Anus) Clinical Presentation

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  more...
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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).

Next:

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
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