Surgery for Pediatric Anorectal Malformation (Imperforate Anus) Workup

Updated: Jun 17, 2022
  • 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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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.

Crossfire 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.