Hirschsprung disease — formative SAQs

SAQ 1 — The neonate with delayed meconium (10 marks)

A full-term male neonate, born by spontaneous vaginal delivery at 39 weeks after an uncomplicated pregnancy, has not passed meconium at 52 hours of life. He is breast-feeding poorly. His abdomen is distended but soft. Observations are stable. The midwife is concerned about the delayed meconium. ^[1]

Outline your approach to this neonate, covering the significance of the presenting complaint, the key differential diagnoses, the investigations you would arrange and their interpretation, and the initial management while awaiting definitive diagnosis. (10 marks) ^[1]

Significance (2 marks): Failure to pass meconium within 48 hours in a term neonate is abnormal, with 99 per cent of healthy term infants passing meconium within this window. The combination of delayed meconium with abdominal distension and poor feeding is the classical presentation of a low intestinal obstruction, and Hirschsprung disease must be excluded. ^{[1] [6]}

Differential diagnosis (3 marks): The differential for delayed meconium with distension includes the causes of low neonatal intestinal obstruction: Hirschsprung disease (aganglionosis producing functional obstruction, the diagnosis to exclude), meconium plug syndrome (transient obstruction from thick meconium, often in infants of diabetic mothers), ileal atresia (mechanical obstruction, often with bilious vomiting), meconium ileus (associated with cystic fibrosis), anorectal malformation (excluded on perineal inspection), and sepsis with paralytic ileus (a diagnosis of exclusion after surgical causes are ruled out). ^[1]

Investigations (3 marks): Suction rectal biopsy is the gold-standard test, sampling mucosa and submucosa 1 to 3 cm above the dentate line. Histology shows absent submucosal ganglion cells with hypertrophied nerve trunks. Calretinin immunohistochemistry, which is absent in aganglionic bowel, is the preferred modern stain. Sensitivity approaches 100 per cent with adequate samples. A contrast enema may show a narrowed distal segment with a transition zone to a dilated proximal colon, but the transition zone is only approximately 70 per cent accurate and a normal enema does not exclude Hirschsprung disease. A plain abdominal radiograph may show distended loops with absent rectal gas. Check for associated anomalies including trisomy 21 in roughly 10 per cent of cases. ^{[5] [6] [10] [12]}

Initial management (2 marks): Keep nil by mouth, establish intravenous access, give maintenance fluids, and pass a nasogastric tube for decompression. Start regular rectal washouts with warm normal saline to decompress the bowel and reduce the risk of enterocolitis. Involve the paediatric surgical team. A contrast enema may be performed for planning once the child is stable, but the biopsy is definitive. ^[1]