Hirschsprung's Disease
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Hirschsprung's Disease (HD) is a congenital disorder characterised by the absence of enteric ganglion cells in the distal bowel. It creates a functional intestinal obstruction because the affected bowel cannot relax.
Key Pathophysiological Concepts
- Aganglionosis: Absence of Myenteric (Auerbach) and Submucosal (Meissner) plexuses.
- Obstruction: The aganglionic segment remains in a state of tonic contraction.
- Megacolon: The proximal, normally innervated bowel dilates due to downstream blockage.
Clinical Scenario: The Constipated Neonate
A 2-day-old term infant is reviewed on the postnatal ward. He has not yet passed meconium. He is feeding poorly and has just vomited dark green fluid. His abdomen is distended.
Key Teaching Points
- **Bilious vomiting** in a neonate is a sign of intestinal obstruction until proven otherwise.
- Delayed meconium (>48h) is the cardinal sign of Hirschsprung's (seen in >90% of cases).
- Differential diagnosis includes Meconium Ileus (Cystic Fibrosis), Intestinal Atresia, or Malrotation.
- Immediate action: Stop feeds, NGT (suction), IV fluids, and refer to Paediatric Surgery.
- Incidence: Approx 1 in 5,000 live births.
- Sex: Male predominance (4:1 in short-segment disease).
- Genetics:
- Trisomy 21 (Down Syndrome): Occurs in 10% of Hirschsprung's patients.
- RET proto-oncogene: Mutation found in 50% of familial cases.
- Other associations: Waardenburg syndrome, MEN 2.
Neural Crest Migration
- During embryology (weeks 5–12), neuroblasts migrate craniocaudally (from mouth to anus) to form the enteric nervous system.
- In HD, migration arrests before reaching the anus.
- Always involves the anus and extends proximally for a variable distance.
Classification by Extent
- Short-segment (80%): Rectum and sigmoid colon only.
- Long-segment (15%): Extends to splenic flexure or transverse colon.
- Total Colonic Aganglionosis (5%): Entire colon involved.
Neonates (Most Common)
Older Infants / Children (Chronic Presentation)
- General: Dysmorphic features (Down syndrome)? Hydration status?
- Abdomen: Gross distension, visible bowel loops (peristalsis). Tympanic on percussion.
- Perineum: Check for patency (exclude anal atresia).
- PR Exam: Tight anal tone. Rectum feels empty. Withdrawal may cause "squirt sign" (blast of stool).
Radiology
- Abdominal X-ray (AXR): Dilated bowel loops with absence of gas in rectum.
- Contrast Enema:
- Using water-soluble contrast.
- Signs: Recto-sigmoid ratio < 1 (rectum narrower than sigmoid).
- Transition Zone: Cone-shaped area between narrow distal (aganglionic) and dilated proximal (ganglionic) bowel.
- Note: In neonates or total colonic disease, transition zone may not have developed yet.
Pathology (Gold Standard)
- Rectal Suction Biopsy: Bedside procedure. Uses a suction device to capture submucosa (not just mucosa).
- Histology:
- Absence of ganglion cells in submucosal plexus.
- Hypertrophied extrinsic nerve trunks.
- Positive Acetylcholinesterase (AChE) staining (increased).
Manometry (Anorectal)
- Shows absence of the Recto-Anal Inhibitory Reflex (RAIR).
- (Normally, distension of rectum causes internal sphincter relaxation. In HD, sphincter does not relax).
A. Initial Resuscitation (Decompression)
- Stop oral feeds.
- NG Tube free drainage (green bile).
- IV Fluids.
- Rectal Washouts: Often successful in relieving obstruction temporarily. A large bore tube is passed above the aganglionic segment to wash out stool/gas.
B. Surgical Repair (Resection & Pull-Through)
The goal is to remove the aganglionic bowel and bring ganglionic bowel down to the anus.
- Stoma: Occasionally needed usually if severe enterocolitis or gross dilation (levelling colostomy). Most centres now aim for primary pull-through without stoma.
- Procedures:
- Swenson: Complete resection of aganglionic segment.
- Duhamel: Leaves rectal stump but bypasses it (side-to-side anastomosis). Lower risk to pelvic nerves.
- Soave (Endorectal): Mucosa of rectum stripped; normal colon pulled through the muscular cuff.
- Trans-anal Pull-Through: Minimally invasive, performed entirely through anus. No scars.
C. Hirschsprung's Associated Enterocolitis (HAEC) Management
- Life-threatening sepsis.
- Broad spectrum IV antibiotics (Metronidazole + Gentamicin/Cephalosporin).
- Urgent rectal washouts.
- Fluid resuscitation.
Disease-Related
- HAEC (Enterocolitis):
- Can occur pre-op or post-op.
- Stasis leads to bacterial overgrowth (Clostridium/Staph) -> mucosal ischaemia -> translocation -> sepsis.
- Mortality up to 30% if untreated.
- Presenting with "Explosive foul smelling diarrhoea", fever, and shock.
Post-Operative
- Constipation: Due to persistent aganglionosis (residual segment) or sphincter achalasia.
- Incontinence: Damage to sphincter or sensation.
- Enterocolitis: Risk remains even after surgery.
- Survival: Excellent (>90%) with modern surgery.
- Bowel Function: Most achieve faecal continence by puberty, though some have long-term soiling or constipation issues.
- Total Colonic Disease: More challenging. May require long-term TPN or extensive surgery; complications are higher.
- BAPS (British Association of Paediatric Surgeons): Management standards.
- APSA Guidelines: Recommendation for rectal biopsy diagnosis and HAEC management.
What is Hirschsprung's Disease? The bowel pushes poo along using waves of muscle squeezing (peristalsis). This relies on nerves in the bowel wall. In Hirschsprung's, these nerves are missing from the bottom part of the bowel (rectum) because they didn't grow all the way down before birth.
What happens? The part of the bowel without nerves clamps shut and cannot relax. Poo backs up behind it, causing the tummy to swell.
How do we know?
- Newborns: Don't pass the first black sticky poo (meconium) within 2 days. They vomit green fluid (bile).
- Older kids: Severe constipation that laxatives don't fix.
- Test: A tiny biopsy (tissue sample) is taken from the bottom to look for nerves.
How is it fixed? Surgery is needed. The surgeon removes the part of the bowel that doesn't work and joins the healthy bowel above it directly to the anus ("Pull-through"). This allows the child to poo normally.
What are the risks? The biggest risk is a serious bowel infection called Enterocolitis. If your child suddenly gets a swollen tummy, fever, and smelly diarrhoea, you must go to A&E immediately.
- Ambartsumyan L, Smith C. Hirschsprung disease and anorectal malformations: mediated by old and new genes. J Pediatr Gastroenterol Nutr. 2018.
- Langer JC. Hirschsprung disease. Curr Opin Pediatr. 2013;25(3):368-374.
- Gosain A, et al. Guidelines for the diagnosis and management of Hirschsprung-associated enterocolitis. Pediatr Surg Int. 2017;33(5):517-521.