Define Hirschsprung Disease. Describe its clinical features, investigations, management and complications.

Definition

• Hirschsprung disease (congenital aganglionic megacolon) is a developmental disorder characterised by the absence of ganglion cells in the myenteric and submucosal plexuses of the distal bowel, causing a functional obstruction.
• The aganglionic segment is tonically contracted; the normal bowel proximal to it dilates.

Pathology

• Failure of the normal cranio-caudal migration of neural crest cells → aganglionosis, always starting at the anus and extending proximally for a variable distance.
• Most commonly involves the recto-sigmoid region (short-segment disease); associated with Down syndrome.

Clinical Features

• Delayed passage of meconium (> 48 hours) in a term newborn — the classic clue.
• Abdominal distension, bilious vomiting and reluctance to feed; chronic constipation in older infants.
• Hirschsprung enterocolitis — fever, explosive diarrhoea and distension — a dangerous complication.

Investigations

• Contrast (barium) enema — shows a transition zone between the narrow aganglionic and dilated proximal bowel.
• Anorectal manometry — absent recto-anal inhibitory reflex.
• Rectal biopsy — the gold standard (absence of ganglion cells; hypertrophied nerve trunks).

Management

• Initial decompression/washouts and treatment of enterocolitis.
• Definitive surgery — a 'pull-through' procedure that removes the aganglionic segment and anastomoses normal bowel to the anus.

Associations & Variants

• Strong association with Down syndrome; also with other congenital anomalies.
• Short-segment (recto-sigmoid, commonest) vs long-segment vs total colonic aganglionosis.

Key Complication — Enterocolitis

Hirschsprung-associated enterocolitis (fever, explosive foul diarrhoea, distension, sepsis) is the most dangerous complication and can be life-threatening — it needs urgent decompression, fluids and antibiotics.

Differential Diagnosis

• Other causes of neonatal intestinal obstruction — meconium ileus (cystic fibrosis), meconium plug, anorectal malformation, intestinal atresia.
• Functional constipation in older children (normal ganglia, later onset, soiling common) — distinguished by history and rectal biopsy.

Rectal biopsy showing absent ganglion cells is diagnostic.