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]

SAQ 2 — Hirschsprung-associated enterocolitis (10 marks)

A 3-week-old infant with biopsy-confirmed short-segment Hirschsprung disease is awaiting surgery and has been managed with daily rectal washouts. His mother brings him to the emergency department with a 12-hour history of fever, worsening abdominal distension, lethargy and explosive foul-smelling diarrhoea. On arrival he is tachycardic, peripherally shut down, and his capillary refill is 4 seconds. [2]

State the diagnosis and why it is dangerous (3 marks), outline the immediate resuscitation and medical management (4 marks), and describe the principles of definitive surgical management and how this presentation might change the surgical plan (3 marks). [2]

Diagnosis and danger (3 marks): This is Hirschsprung-associated enterocolitis (HAEC), the leading cause of death in Hirschsprung disease. It occurs in 20 to 40 per cent of patients preoperatively and is driven by stasis and bacterial overgrowth behind the obstructed aganglionic segment, with mucosal barrier failure and bacterial translocation. The danger is rapid progression to septic shock, toxic megacolon, perforation and death if not treated aggressively. The child is already showing signs of shock with a 4-second capillary refill. [2] [3]

Resuscitation and medical management (4 marks): Give immediate isotonic intravenous fluid boluses (10 to 20 mL per kg of normal saline) for shock, repeating as needed to restore perfusion. Start broad-spectrum antibiotics: metronidazole for anaerobic cover plus an aminoglycoside such as gentamicin for Gram-negative cover. Place a nasogastric tube on free drainage for decompression and perform frequent rectal washouts with warm normal saline to decompress the obstructed bowel. Monitor urine output, capillary refill, lactate and abdominal girth. Involve paediatric intensive care if shock persists or if perforation is suspected. [2] [3]

Surgical management and change of plan (3 marks): The definitive principle is to resect the aganglionic bowel and bring ganglionic bowel to the anal canal via a pull-through procedure (Swenson, Soave or Duhamel), with levelling biopsies to confirm ganglion cells at the anastomosis. This presentation of enterocolitis before surgery may shift the plan from a primary neonatal pull-through to a staged approach. The child may need a temporary diverting stoma to allow the inflamed bowel to settle before definitive pull-through is attempted weeks later. The priority in the acute setting is resuscitation and decompression, not definitive surgery. [9] [1] [2]