Expansion
Herniates at week 6, rotates 270 degrees anticlockwise, returns by week 10
Expansion
- Week 6 - the rapidly growing midgut herniates into the umbilical cord, because the abdomen is too small and the liver is disproportionately large
- While herniated, it rotates 90 degrees anticlockwise around the superior mesenteric artery
- Week 10 - it returns to the abdomen, rotating a further 180 degrees anticlockwise
- Total rotation: 270 degrees anticlockwise
The caecum returns last and descends to the right iliac fossa, which is why the ascending colon ends up on the right and the duodenojejunal flexure on the left.
Failure produces malrotation: the caecum sits high in the right upper quadrant, fibrous Ladd’s bands cross and obstruct the duodenum, and the mesenteric root is narrow, allowing midgut volvulus. A neonate with bilious vomiting must be assumed to have malrotation until proven otherwise.