eMedicine Specialties > Pediatrics: Surgery > General Surgery

Imperforate Anus: Surgical Perspective

Author: Marc A Levitt, MD, Assistant Professor of Surgery and Pediatrics, University of Cincinnati; Associate Director, Colorectal Center for Children, Department of Pediatric Surgery, Cincinnati Children's Hospital Medical Center
Coauthor(s): Alberto Pena, MD, Consulting Surgeon, Colorectal Center for Children, Department of Pediatric Surgery, Cincinnati Children's Hospital Medical Center
Contributor Information and Disclosures

Updated: Aug 10, 2007

Introduction

Anorectal malformations comprise a wide spectrum of diseases that affect boys and girls and can involve malformations of the distal anus and rectum, as well as the urinary and genital tracts.

Malformations range from minor, easily treated defects that carry an excellent functional prognosis, to complex defects that are difficult to treat, are often associated with other anomalies, and carry a poor functional prognosis.

History of the Procedure

Throughout the centuries, doctors have seen and attempted to treat babies born with imperforate anus. Because few patients have been described in the early literature, most are assumed to have died without treatment. Paulus Aegineta recorded the earliest account of successful surgery for imperforate anus. He suggested rupturing an obstructing membrane with the 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 and emphasized preservation of the puborectalis muscle. This surgery and its modifications were the standard approach until 1980.

In 1980, the surgical approach to repairing anorectal malformations altered dramatically with the introduction of the posterior sagittal approach. This approach allowed pediatric surgeons to clearly view the anatomy of anorectal malformations and to repair them under direct vision, with better visualization and understanding of the anatomy than previous approaches allowed. Surgeons were able to understand the complex anatomic arrangement of the rectum-genitourinary tract junction.

Frequency

Anorectal malformations occur in approximately 1 per 5000 live births.

Etiology

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

Pathophysiology

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 demonstrate the spectrum of anorectal anomalies.

Improved imaging techniques and a more thorough knowledge of the anatomy and physiology 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 concern in correcting these anomalies is bowel control. Although uncommon, problems with urinary control and sexual function 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 such as a poorly developed sacrum, nerve supply, and spinal cord likely contribute to an inability to achieve continence. For patients with fecal incontinence, an effective bowel management program has been devised to improve quality of life (see Bowel Management).

Presentation

Diagnosis and early treatment

For neonates born with an anorectal anomaly, early treatment is crucial.

During the first 24-48 hours of life in a newborn with an anorectal malformation, the following 2 questions should be answered:

• Does the newborn have any associated life-threatening anomalies that need to be addressed immediately?
• Should the neonate undergo a primary procedure without a protective colostomy, or should he or she undergo a protective colostomy with definitive repair at a later date?

The surgeon must also determine whether female neonates have a dilated vagina, if it should be drained, and whether urinary diversion is required. These maneuvers are intended to prevent sepsis and metabolic acidosis (see Cloacal Malformations).

The decision to perform an anoplasty during the newborn period or to delay the repair and perform a colostomy is based on physical examination findings in the newborn, the appearance of the perineum, and changes that occur during the first 24 hours of life.

Operating earlier and in a single stage is potentially beneficial to the patient, but this should be decided carefully, based on 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 compared with anoplasty based on sex are as follows:

• Newborn boys
  • Anoplasty - Rectoperineal fistula
  • Colostomy - Rectobulbar urethral fistula, rectoprostatic urethral fistula, rectovesical fistula, imperforate anus without fistula, rectal atresia
• Newborn girls
  • Anoplasty - Rectoperineal fistula
  • Colostomy - Rectovestibular fistula, imperforate anus without fistula, persistent cloaca, rectal atresia, rectovaginal fistula

Decision-making in newborn boys with anorectal anomalies

In 80-90% of newborn boys, clinical evaluation and urinalysis provide 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 to 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 distension 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 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 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 high malformation; therefore, a colostomy should be performed.

Perineal signs found in patients with low malformations 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 can 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 situation is necessary in only approximately 10% of patients. Obtain cross-table lateral radiographs with the newborn prone, with the pelvis elevated, and with a radiopaque marker placed on the perineum (see Image 3). 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 for 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.

Some authors have performed definitive repair in the newborn period. Advantages to this approach include avoiding colostomy and repairing the malformation earlier; however, because the surgeon does not know the precise anorectal defect, the urinary tract is at considerable risk. To definitively determine the patient's anorectal defect, perform distal colostography, which 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 bowel function.

The rare exception occurs when the cross-table lateral radiograph obtained at 16-24 hours reveals that the rectum is located just below the coccyx. In this case, the rectum may be reached from the posterior sagittal approach.

Obtain urinalysis and place gauze over the penis to reveal the presence of fecal matter in the urine, which is considered evidence of a rectourinary fistula.

Abdominal ultrasonography must be performed to evaluate for the presence of an obstructive uropathy. At the same time, spinal ultrasonography may be performed to evaluate for spinal anomalies, including the presence of a tethered cord.

Methods to reveal the location of the distal rectum before 16 hours of life are flawed because of the contracted state of the funnel-like sphincter mechanism. Typically, the funnel-shaped muscle structure is contracted unless overcome with a distending force. Tests such as MRI, ultrasonography, CT scanning, or injection of contrast through the perineum falsely locate the distal rectum as high in the pelvis.

Distal colostography (typically obtained 1 mo after colostomy opening) 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 4-8 weeks later.

Decision-making in newborn girls with anorectal anomalies

The decision to perform colostomy in newborns girls is less complicated in newborn girls. In 90% of patients, a meticulous perineal inspection demonstrates the anorectal defect. Waiting 16-24 hours for enough abdominal distension to demonstrate the presence of a rectoperineal fistula or rectovestibular fistula also applies to newborn girls.

The most common anomaly in newborn girls is a rectovestibular fistula. Perineal inspection reveals a typical urethra, typical vagina, and another orifice, which is the rectal fistula in the vestibule.

In newborns with clinical evidence of a rectovestibular fistula, a diverting colostomy is the safest option for surgeons without extensive experience in anorectal anomalies. Colostomy prior to the main repair avoids the complications of infection and dehiscence. Definitive repair of this anomaly in the newborn period should be reserved for surgeons who have significant experience repairing these defects. Once this anomaly is repaired, patients have an excellent prognosis; therefore, complications that may affect continence must be avoided.

Patients with rectovestibular fistulas in whom primary repair failed in the newborn period are the most common referrals for re-operations to tertiary centers that care for anorectal anomalies. 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.

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

Similar to boys, the rectum location is not clinically evident in less 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.

The presence of a single perineal orifice in a patient is clinical evidence of persistent cloaca (see Image 4). Patients with these anomalies also have small genitalia. See Cloacal Malformations for details regarding treatment of persistent cloaca. In patients with persistent cloaca, abdominal examination may reveal a mass that likely represents a distended vagina (hydrocolpos), which is present in 50% of patients with persistent cloaca. Abdominal ultrasonography is helpful to reveal the presence of an obstructive uropathy and hydrocolpos.

During the perineal inspection, newborn girls are commonly given an incorrect diagnosis of imperforate anus with rectovaginal fistula; however, all 3 structures (ie, urinary tract, vagina, rectum) actually meet in a common channel, and the baby has persistent cloaca. This misconception carries important therapeutic implications.

Making the correct determination is vital, because 90% of newborns with persistent cloaca have an associated urologic problem and 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 persistent cloaca commonly means that an obstructive uropathy is overlooked. The patient may then receive only a colostomy, resulting in subsequent sepsis, acidosis, and, occasionally, death.

The other implication of missing the diagnosis of persistent 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
• Neurogenic bladder
• Renal dysplasia
• Megaureter
• Hydronephrosis
• Ectopic ureter

Indications

See Colostomy versus anoplasty.

Relevant Anatomy

See Pathophysiology.

Contraindications

No absolute contraindications to surgery exist.  The presence of associated malformations, such as prematurity and congenital cardiac disease, often postpones definitive colorectal reconstruction.

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