FCPS Paediatrics TOACS · Interactive Station

✅ Candidate's answer:
• Diagnosis: Hirschsprung disease (congenital aganglionic megacolon).
• Key neonatal features:
1️⃣ Failure to pass meconium within 48 hours of birth – this infant is now 5 days old with only a small pellet on day 2 (classic).
2️⃣ Progressive abdominal distension (days 2-5).
3️⃣ Bilious vomiting (suggests distal obstruction).
4️⃣ Explosive passage of gas and stool after rectal examination (pathognomonic sign).
5️⃣ Tight anal sphincter on digital examination.
6️⃣ Enterocolitis (fever, diarrhea, shock, abdominal distension) – a life-threatening complication.

✅ Candidate's answer:
• Pathophysiology: Failure of migration of neural crest cells (enteric ganglion cells) to the distal bowel during weeks 5-12 of gestation → absence of both Meissner (submucosal) and Auerbach (myenteric) plexuses in the affected segment.
• Consequently, the aganglionic segment remains tonically contracted (spastic) → functional obstruction, proximal bowel dilates (megacolon).
• Most common (75-80%): Short-segment disease – aganglionosis confined to rectosigmoid colon.
• Long-segment disease (10-15%): extends proximal to sigmoid.
• Total colonic aganglionosis (5-10%): entire colon involved.
• Genetic basis: RET proto-oncogene mutations (>50% familial cases), also EDNRB, EDN3, SOX10.

✅ Candidate's answer:
• HAEC: life-threatening inflammation of the bowel proximal to the aganglionic segment, often with mucosal ulceration, bacterial translocation, and sepsis.
• Presentation: explosive, foul-smelling watery diarrhea (may be mistaken for gastroenteritis), abdominal distension, fever, lethargy, hypotension, shock, septicemia.
• Treatment (medical emergency):
- Rectal irrigation with normal saline (decompression).
- Intravenous antibiotics (cover gram-negatives and anaerobes: metronidazole + gentamicin/cefotaxime).
- IV fluids, correction of electrolytes, and vasopressors if shock.
- Nasogastric decompression.
- Avoid barium enema during acute episode.
- Definitive surgery (pull-through) after stabilization.
• Recurrent enterocolitis may occur even after pull-through.

✅ Candidate's answer:
• 1. Abdominal X-ray (to rule out perforation, shows dilated bowel loops, no distal air).
• 2. Contrast enema (barium or water-soluble): Demonstrates a transition zone – narrow, irregular aganglionic distal segment with dilated proximal colon. Retained barium after 24 hours (delayed evacuation) supports diagnosis. Do not perform in acute enterocolitis (risk of perforation).
• 3. Rectal suction biopsy (gold standard): Performed at 2-3 cm above dentate line. Shows absence of ganglion cells and hypertrophic nerve trunks (acetylcholinesterase staining – positive thick nerve fibers in lamina propria and muscularis mucosae).
• 4. Anorectal manometry: Absence of rectoanal inhibitory reflex (RAIR) – reflex relaxation of internal anal sphincter with rectal distension is absent. Less reliable in neonates.
• 5. Full-thickness rectal biopsy (if suction biopsy inconclusive, or for definitive pathology prior to surgery).

✅ Candidate's answer:
• Transition zone: A cone-shaped or funnel-shaped area where the narrow, spastic distal (aganglionic) segment meets the dilated proximal (ganglionic) colon.
• In short-segment disease, the transition zone is usually in the rectosigmoid.
• In long-segment disease, the transition zone is more proximal (splenic flexure, transverse colon).
• Other findings: Irregular contractions of aganglionic segment (sawtooth appearance), delayed evacuation of contrast (>24 hours).
• Important: In neonates, the transition zone may not be well-developed initially because the proximal bowel has not yet dilated significantly. Repeat enema after a few weeks may be helpful.
• Total colonic aganglionosis: Microcolon, no clear transition zone, shortened colon.

✅ Candidate's answer:
• Findings:
- Absence of ganglion cells in submucosal (Meissner) and myenteric (Auerbach) plexuses.
- Presence of hypertrophic, non-myelinated nerve trunks in the lamina propria and muscularis mucosae.
• Staining: Acetylcholinesterase (AChE) histochemistry is the gold standard – shows strongly positive thick nerve fibers in the lamina propria and muscularis mucosae (normally absent or fine).
• Calretinin immunostaining: Absence of calretinin-positive ganglion cells and nerve fibers (rapid, reliable alternative).
• H&E staining: can identify ganglion cells but experienced pathologist required.
• Biopsy must be adequate (at least 3-5 mm of submucosa, 2-3 cm above dentate line).

✅ Candidate's answer:
• Meconium plug syndrome – contrast enema reveals meconium plugs, but ganglion cells present.
• Meconium ileus (cystic fibrosis) – distal small bowel obstruction, ground-glass appearance on X-ray, no transition zone.
• Small left colon syndrome – infants of diabetic mothers, transition at splenic flexure; usually resolves spontaneously.
• Intestinal atresia / stenosis – X-ray shows complete obstruction, no contrast passage.
• Necrotizing enterocolitis (NEC) – pneumatosis, clinical sepsis, usually later onset (but can occur in first week).
• Hypothyroidism – constipation, but not explosive stool after rectal exam.
• Functional constipation (rare in first 48h, but possible by day 5).
• Rectal biopsy differentiates.

✅ Candidate's answer:
• Down syndrome (Trisomy 21): Most common association – 2-10% of Down syndrome patients have Hirschsprung.
• Waardenburg syndrome (pigmentary anomalies, deafness) – due to EDNRB, EDN3, SOX10 mutations.
• MEN2A (multiple endocrine neoplasia type 2A): RET mutation – Hirschsprung + medullary thyroid carcinoma + pheochromocytoma.
• MEN2B: Hirschsprung + mucosal neuromas, marfanoid habitus.
• Bardet-Biedl syndrome (obesity, polydactyly, retinitis pigmentosa).
• Congenital central hypoventilation syndrome (CCHS, Ondine’s curse) – associated with RET, PHOX2B mutations.
• Goldberg-Shprintzen syndrome (microcephaly, intellectual disability).
• Mowat-Wilson syndrome.

✅ Candidate's answer:
• Definitive treatment: Surgical resection of the aganglionic bowel and pull-through of normally ganglionic colon to the anus.
• Timing: Traditionally after 4-6 weeks of age (weight >4 kg). Now primary pull-through in the neonatal period (1-3 months) is increasingly performed if the infant is stable and no enterocolitis. Previously, a two-stage approach: initial leveling colostomy (in sick or very young infants) followed by pull-through at 6-12 months.
• Common pull-through procedures:
1️⃣ Swenson procedure: Resection of aganglionic segment + end-to-end anastomosis (preserves anal sphincter).
2️⃣ Soave procedure: Endorectal pull-through – aganglionic mucosa/submucosa resected, ganglionic bowel pulled through muscular cuff.
3️⃣ Duhamel procedure: Retrorectal pull-through with side-to-side anastomosis.
• Transanal pull-through (TEPT) is now preferred for short-segment disease (no abdominal incision).
• Laparoscopic-assisted pull-through for long-segment or total colonic.
• Post-operative complications: anastomotic leak, stricture, persistent constipation (residual aganglionosis), enterocolitis, soiling (incontinence).

✅ Candidate's answer:
• TCA: Entire colon (and sometimes terminal ileum) is aganglionic; accounts for 5-10% of Hirschsprung.
• Presentation: Delayed meconium passage, severe abdominal distension, vomiting, and early enterocolitis.
• Diagnosis: Contrast enema shows a microcolon or “question mark” colon (short, straight, no transition zone). Rectal suction biopsy confirms absence of ganglion cells. Intraoperative biopsies of colon and ileum are required to determine level of aganglionosis.
• Management:
- Initial diversion (ileostomy) at the level of ganglionic bowel (usually terminal ileum).
- Pull-through procedure: Ileal (or right colon) pull-through with creation of a reservoir (cecal patch, J-pouch) to reduce diarrhea and malabsorption.
- Lifelong risk of: bacterial overgrowth, chronic diarrhea, failure to thrive, need for parenteral nutrition in some cases.

✅ Candidate's answer:
• Enterocolitis (post-pull-through) – can occur in 20-30% even after successful surgery; may require rectal irrigations, antibiotics.
• Persistent obstructive symptoms – residual aganglionosis (if inadequate resection), achalasia of the internal anal sphincter, or anastomotic stricture.
• Constipation and soiling (fecal incontinence) – common, especially in long-segment disease; requires bowel management program.
• Urinary dysfunction (due to pelvic nerve injury during surgery).
• Growth failure, malnutrition (especially total colonic aganglionosis).
• Psychological issues (social stigma, toilet training difficulties).
• Risk of medullary thyroid carcinoma in MEN2A associated cases – requires prophylactic thyroidectomy in childhood.

✅ Candidate's answer:
• Anorectal manometry measures pressures in the anal canal and rectal response to distension.
• Normal response: Rectal distension → reflex relaxation of internal anal sphincter (rectoanal inhibitory reflex, RAIR).
• In Hirschsprung disease: Absence of RAIR due to lack of inhibitory neurons (nitrergic) in the aganglionic segment.
• Utility: High sensitivity and specificity, especially in older infants and children. In neonates, the reflex may be immature, and false positives can occur, so it is not the preferred first-line test in newborns.
• Advantages: Noninvasive, no radiation, can be done as outpatient.

✅ Candidate's answer:
• Gastrointestinal decompression: Nasogastric tube for gastric drainage.
• Rectal irrigations (normal saline) – 2-4 times daily to decompress colon and prevent enterocolitis.
• Intravenous fluids to correct dehydration and electrolyte imbalance.
• Nothing by mouth (NPO) if significant obstruction; total parenteral nutrition (TPN) if prolonged.
• Broad spectrum antibiotics if signs of enterocolitis (metronidazole + gentamicin/cefotaxime).
• Careful monitoring for perforation (abdominal X-ray).
• Definitive surgery (pull-through) after diagnosis and stabilization, ideally before discharge from NICU. In unstable or very small infants, a leveling colostomy may be performed first, with pull-through later.

✅ Candidate's structured answer:
• “Your baby has a condition called Hirschsprung disease, where the nerves in the last part of the intestine are missing, so the bowel cannot push stool out normally. This explains why he hasn’t passed stool properly even at 5 days of age.”
• “The good news is that this is treatable with a surgery called a pull-through. The surgeon will remove the part without nerves and connect the healthy bowel to the anus.”
• “If not treated, the baby can get very sick from obstruction or a serious infection called enterocolitis. But with prompt diagnosis and surgery, most children do extremely well.”
• “After surgery, most children pass stool normally. Some may have constipation or occasional soiling, but these can be managed with diet, laxatives, or bowel training.”
• “The surgery is usually done within the first few months of life. Until then, we will keep the bowel clean with enemas and IV fluids.”
• “We will also test for other conditions sometimes associated, like Down syndrome, but many babies have no other problems.”
• “You are doing the right thing by bringing him now. The prognosis is very good with treatment.”

✅ Candidate's answer:
• Recurrence risk:
- If a child has short-segment Hirschsprung and no family history: risk to siblings <4%.
- If a child has long-segment or total colonic aganglionosis: risk to siblings up to 10-15%.
- If a parent has Hirschsprung disease: risk to offspring 5-10% (higher if parent is female, risk up to 15-20%).
• Prenatal diagnosis: Not routinely possible. Ultrasound may show dilated bowel loops and polyhydramnios in severe long-segment cases, but sensitivity is low. Genetic testing (RET mutation) in familial cases can guide fetal risk assessment but is not diagnostic.
• For at-risk pregnancies, postnatal observation for delayed passage of meconium (beyond 48 hours) and early contrast enema is recommended.