Hirschsprung's disease results from failure of neural crest cell migration to colonize the hindgut. The aganglionic segment always begins at which part of the gut?

• A The internal anal sphincter region and extends proximally for variable lengths ✓
• B The splenic flexure and extends to the rectum
• C The ileocecal junction and extends proximally into the ileum
• D The ascending colon and involves the entire right colon

Explanation

In Hirschsprung's disease (congenital megacolon), craniocaudal migration of neural crest cells is arrested before colonizing the hindgut. The aganglionic segment ALWAYS starts at the internal anal sphincter (the most distal segment, where cells migrating from above fail to reach) and extends proximally. The length is variable: short-segment (rectosigmoid, 75% of cases), long-segment, or total colonic. The aganglionic zone is the narrow, tonically contracted segment; the dilated proximal bowel (with ganglia) is the megacolon. Diagnosis is confirmed by absent ganglion cells on rectal suction biopsy. The splenic flexure and ascending colon are not the starting points.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.