Pediatric Imperforate Anus (Anorectal Malformation) Clinical Presentation

Updated: Aug 08, 2016
  • Author: Nelson G Rosen, MD, FACS, FAAP; Chief Editor: Carmen Cuffari, MD  more...
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Presentation

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

During a thorough physical examination, attention should be focused on the abdomen, genitals, rectum, and lower spine. [3]

The umbilicus should be examined for the absence of an umbilical artery (2-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).

Fourchette fistula. This malformation is somewhere Fourchette fistula. This malformation is somewhere halfway between perineal fistula and vestibular fistula. The fistula has a wet vestibular mucosal lining on its anterior half, but the posterior half is dry perineal skin.

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

Cloaca. This is the classic appearance of a girl w Cloaca. This is the classic appearance of a girl with a cloacal malformation with a single perineal orifice. The genitals appear quite short, which is a finding consistent with cloaca.

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.

Distal colostogram, posteroanterior view. The init Distal colostogram, posteroanterior view. The initial phase of augmented-pressure distal colostography aims to determine where the colostomy was placed in the colon and how much colon is available for pull-through, without taking down the colostomy.
Distal colostogram, lateral view. This image shows Distal colostogram, lateral view. This image shows the second phase of distal colostography, in which the patient is placed in the lateral position. A radio-opaque marker is clearly visible in the lower right side of the image, marking the muscle complex on the skin. This image shows that the rectal pouch joins the urinary tract at the level of the bulbar urethra, a relatively common malformation in boys.

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 GI malformations have been described in association with imperforate anus. As many as 10% of patients have tracheoesophageal abnormalities. [4] 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. [5]

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. [6] 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. 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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Causes

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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