Pediatric Imperforate Anus Surgery Workup

Updated: Dec 01, 2015
  • Author: Marc A Levitt, MD; Chief Editor: Eugene S Kim, MD, FACS, FAAP  more...
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Workup

Imaging Studies in Newborn Period

The radiologic evaluation of a newborn with imperforate anus includes abdominal ultrasonography to evaluate for urologic anomalies. In patients with persistent cloaca, a distended vagina (hydrocolpos) may be identified.

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).

Calculation of the sacral ratio. Calculation of the sacral ratio.

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

Cross-table lateral 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 in 16-24 hours.

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Imaging Studies After Newborn Period

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

Hydrostatic pressure under fluoroscopic control is required. A Foley catheter is placed in the mucous fistula, and the 3-cm3 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 height.

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, rectum height, perineum, fistula location, bladder, vesicoureteral reflux (if present), and urethra. When colostography is performed correctly, voiding cystography and cystoscopy are not necessary.

Colostography is vital in determining the anatomy to plan definitive repair. 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 (except for those with persistent cloaca), distal colostography is not necessary because the fistula is clinically evident.

If the spine was not evaluated with ultrasonography in the newborn period, magnetic resonance imaging is necessary after age 3 months to exclude the presence of tethered cord and other spinal anomalies.

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