Hirschsprung’s Disease

SUMMARY

Hirschsprung's disease (congenital aganglionic megacolon) is a developmental disorder defined by the absence of ganglion cells in the Auerbach (myenteric) and Meissner (submucosal) plexuses of the distal colon, arising from failed craniocaudal migration of neural crest cells.

The aganglionic segment remains tonically contracted, producing a functional obstruction with proximal colonic dilation. Neonates classically present with bilious vomiting, abdominal distension, and failure to pass meconium within the first 48 hours; older children present with chronic constipation and failure to thrive. Diagnosis is confirmed by rectal suction biopsy (gold standard) showing absent ganglion cells, and definitive treatment is surgical resection of the aganglionic segment.

Pathophysiology & Etiology

Hirschsprung's disease is a congenital aganglionic megacolon defined by the absence of enteric ganglion cells in both the Auerbach (myenteric) and Meissner (submucosal) plexuses of the distal colon. It results from failed craniocaudal (caudal) migration of neural crest cells along the developing gut, leaving the most distal bowel without intramural ganglia.

Because the aganglionic segment cannot relax, it remains in a state of persistent tonic contraction, creating a functional obstruction. Stool accumulates behind this narrowed segment, producing progressive proximal dilation (megacolon). The rectosigmoid is the most commonly affected level.

Epidemiology: the disease is roughly five times more common in male infants, and up to 80% of cases have a positive family history.

Associations (high-yield): the disorder is classically linked with Down syndrome, Chagas' disease (in which amastigotes destroy ganglion cells), and loss-of-function mutations in RET. See the Down syndrome comorbidities by body system for the other GI, cardiac, and haematologic anomalies that cluster with trisomy 21.

Clinical Presentation

Presentation depends on the patient's age and on the length of the aganglionic segment.

Neonates typically show:

• Failure to pass meconium within the first 48 hours of life
• Bilious vomiting
• Abdominal distension with signs of large bowel obstruction
• ± Enterocolitis (fever, explosive diarrhoea, sepsis)

Children / adolescents (usually short-segment disease) present later with chronic constipation and failure to thrive.

Physical examination: a distended abdomen, an extremely tight anal sphincter, and an empty rectal vault (no stool on digital exam). Withdrawal of the examining finger triggers forceful expulsion of stool and gas — the classic “squirt sign.”

Diagnosis

Work-up proceeds from supportive imaging toward the confirmatory biopsy:

• Biopsy (gold standard): rectal suction biopsy demonstrating absence or paucity of ganglion cells in the submucosa confirms the diagnosis.
• Imaging — contrast enema (adjunct): reveals the rectosigmoid transition zone — a narrowed distal aganglionic segment with abrupt proximal dilation.
• Imaging — abdominal radiograph: distended bowel loops with absence of air in the rectum, consistent with large bowel obstruction.
• Special test — anorectal manometry (adjunct): failure of the internal anal sphincter to relax.

The transition zone is the hallmark radiographic clue on the contrast study.

Differential Diagnosis

Delayed meconium passage and neonatal large bowel obstruction have a broad differential, including:

• Imperforate anus
• Functional constipation
• Intussusception
• Duodenal atresia
• Meconium ileus
• Necrotising enterocolitis

The most important distinction is between Hirschsprung's disease and meconium ileus, separated by their associated disorder, level of obstruction, meconium consistency, and the squirt sign.

Template: Medical Comparison

Management & Complications

Complications:

• Enterocolitis — an increased risk in Hirschsprung's disease and the most serious, potentially life-threatening complication.
• Colonic perforation / rupture.

Management: definitive treatment is surgical resection of the aganglionic segment of colon, restoring continuity by bringing normally innervated (ganglionic) bowel down to the anus.

Key Points for Exams

نقاط مهمة للامتحانات — the highest-yield facts:

• Hirschsprung = congenital aganglionosis (absent Auerbach + Meissner plexuses) from failed neural crest cell migration.
• Classic neonate: bilious vomiting, abdominal distension, failure to pass meconium >48 h.
• Physical exam: tight anal sphincter, empty rectal vault, positive squirt sign.
• Rectosigmoid = most common level; rectal suction biopsy (submucosa) = gold standard.
• Associations: Down syndrome, RET (loss-of-function), Chagas disease.
• Male predominance (~5:1); ~80% positive family history.
• Most feared complication: enterocolitis; definitive treatment is surgical resection of the aganglionic segment.