A newborn is brought to the neonatal ward for routine examination. The clinical finding shown at **B** (smooth perineum with absent anal dimple) prompts immediate investigation. The infant has not passed meconium in the first 24 hours and shows abdominal distension. An invertogram is performed at 18 hours of life. Which of the following is the MOST important immediate next step in management if the gas-perineum distance is found to be > 1 cm?

Explanation

## Why "Create a dividing colostomy and defer definitive repair to 3–6 months" is right The finding of **B** (smooth perineum with absent anal dimple) indicates anorectal malformation (imperforate anus). An invertogram gas-perineum distance > 1 cm classifies this as a **HIGH lesion** (above the levator ani muscle). According to Nelson 21e and the Krickenbeck classification, HIGH anorectal malformations require a **staged surgical approach**: initial dividing colostomy in the newborn period to decompress the bowel and allow fecal diversion, followed by definitive posterior sagittal anorectoplasty (PSARP/Peña procedure) at 3–6 months of age when the infant is larger and tissues are more mature. This staged approach reduces morbidity and improves outcomes. ## Why each distractor is wrong - **Perform primary perineal anoplasty under general anesthesia**: Primary perineal anoplasty is reserved for LOW lesions (< 1 cm gas-perineum distance on invertogram). HIGH lesions cannot be safely repaired primarily from the perineal approach and require the staged colostomy-then-PSARP strategy. - **Perform immediate posterior sagittal anorectoplasty (PSARP)**: PSARP is the definitive repair for HIGH lesions but is NOT performed in the immediate newborn period. It is deferred to 3–6 months after initial colostomy to allow the infant to stabilize, grow, and to permit better visualization and tissue handling. - **Observe for spontaneous anal opening and repeat imaging at 48 hours**: Imperforate anus does not resolve spontaneously. Delaying intervention risks bowel perforation, sepsis, and metabolic derangement from prolonged abdominal distension. Immediate colostomy is mandatory to decompress the bowel. **High-Yield:** Gas-perineum distance > 1 cm on invertogram = HIGH lesion = colostomy first, PSARP later (3–6 months). Distance < 1 cm = LOW lesion = primary perineal anoplasty in newborn period. [cite: Nelson Textbook of Pediatrics, 21e, Chapter 358 — Anorectal Malformations; Krickenbeck classification and surgical management]