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Anorectal malformations (imperforate anus and cloaca)
In an anorectal malformation the first decision is whether it can be repaired at once through the perineum (a perineal fistula) or needs a colostomy first — and the decision is made after re-examining the perineum at 24 hours, because meconium needs time to appear.
Why it matters in the exam
The exam asks about the common type by sex, the work-up for associated anomalies, the site of the stoma and the prognosis for bowel control. In boys the common type is a recto-urethral fistula (meconium in the urine), and in girls a fistula to the vaginal vestibule (vestibular). A perineal fistula — a small opening in front of the expected anal site, meconium on the perineum or a "bucket handle" in the skin — is repaired without a stoma. A girl with a single perineal opening has a cloaca: urine, vagina and bowel drain into a common channel, and hydrocolpos and hydronephrosis must be sought at once.
About half of children with an anorectal malformation have another anomaly. The work-up includes an echocardiogram, renal and urinary tract ultrasound, spinal ultrasound (tethered cord), sacrum and spine X-rays, and passing a gastric tube to exclude oesophageal atresia (VACTERL). The sacrum is the key predictor of later continence: the sacral ratio is measured on X-ray and calculated as the distance from the line through the posterior-inferior iliac spines to the tip of the sacrum, divided by the distance between the iliac crest line and that line; a ratio below 0.4 predicts poor bowel control.
The standard repair is PSARP (a posterior midline approach bringing the rectum down into the centre of the sphincter). When a stoma is needed, a divided colostomy is made in the descending colon, so the distal segment stays long enough to pull down and allows a contrast study to define the fistula. After PSARP a dilatation programme starts, and the stoma is closed once the opening reaches the target size. Later, true incontinence must be told apart from "pseudo-incontinence" due to constipation with overflow: for constipation — laxatives; for hypermotility — daily enemas, a constipating diet and loperamide.
Key points
- Wait 24 hours before deciding on a stoma.
- Perineal fistula — primary repair without a stoma.
- Boys: recto-urethral fistula; girls: vestibular fistula; single opening — cloaca.
- Look for VACTERL, tethered cord and a sacral anomaly.
- A sacral ratio below 0.4 predicts poor continence.
Summary table
| Type | Finding | What is done | Continence prognosis |
|---|---|---|---|
| Perineal fistula (both sexes) | Small opening in front of the anal site, meconium on the perineum | Primary repair without a stoma | Very good |
| Recto-urethral fistula (boys) | Meconium in the urine | Colostomy then PSARP | Intermediate; worse with a bladder-neck fistula |
| Vestibular fistula (girls) | Opening in the vaginal vestibule | PSARP (sometimes without a stoma) | Good |
| Cloaca (girls) | Single perineal opening | Colostomy, drainage of hydrocolpos, complex reconstruction | Depends on the length of the common channel |
| No fistula | No meconium after 24 hours | Prone X-ray; colostomy if the bowel is far from the skin | Intermediate; common in Down syndrome |
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Sources
- Holcomb and Ashcraft's Pediatric Surgery, 7th edition (2019) — Anorectal Atresia and Cloacal Malformations
- Krickenbeck international classification of anorectal malformations, 2005 — Diagnostic groups and outcome assessment
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.