AN52.1-8 | Histology & Embryology (Abdomen & Pelvis) — Part 3

CLINICAL PEARL

Hirschsprung's disease — remembering the embryological basis: Neural crest cells migrate craniocaudally along the bowel wall from weeks 5–12. The LAST segment to be colonised is the distal rectum/sigmoid. In Hirschsprung's, migration stops prematurely → the distal segment (beyond the migration arrest) is aganglionic. The aganglionic bowel remains tonically contracted (no Auerbach's/Meissner's plexus → no peristaltic relaxation) → functional obstruction. The dilated proximal bowel (which IS ganglionic and functions normally but cannot empty) is what the surgeon sees — not the aganglionic segment — hence the pull-through operation (resect the aganglionic segment, anastomose ganglionic bowel to the anus). Rectal suction biopsy confirms aganglionosis.