Hirschsprung disease (congenital aganglionic megacolon) results from failure of neural crest cell migration. Which part of the bowel is always affected, and which neural crest population fails to complete migration?

• A Cecum and ascending colon always affected; sacral neural crest failure
• B Entire colon always affected; trunk neural crest failure
• C Rectosigmoid always affected; sacral neural crest cells fail to migrate cranially
• D Rectosigmoid always affected; vagal neural crest cells (from somite levels 1–7) fail to migrate caudally through the bowel wall ✓

Explanation

Hirschsprung disease results from failure of vagal neural crest cells (originating from somite levels 1–7, posterior to the otic vesicle) to complete their craniocaudal migration through the bowel wall to form Auerbach's (myenteric) and Meissner's (submucosal) plexuses. The rectosigmoid region is invariably affected because it is the furthest point from the origin of neural crest migration. The aganglionic segment is in a state of tonic spasm (no inhibitory enteric neurons), causing obstruction. Sacral neural crest contributes supplementary innervation to the distal hindgut but is not the primary source of the enteric nervous system.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.