Splenic flexure (watershed)
Organ supplied · Midgut Hindgut
The highest and most acute colonic bend, where the last SMA branch (left branch of the middle colic) meets the first IMA branch (ascending left colic) — Griffiths' point. The marginal artery is thinnest or absent here in up to ~18% of people, making this the commonest site of ischaemic colitis.
Traced from the start
Detail
- Boundary
- Midgut → hindgut; SMA → IMA
- Anastomosis
- Griffiths' point on the marginal artery, ± arc of Riolan
- Marginal artery deficient
- ~5–18% at the flexure
- Second watershed
- Rectosigmoid junction (Sudeck's point)
When it goes wrong
Systemic hypotension, cardiac failure, dialysis, vasopressors, cocaine or aortic surgery in an elderly arteriopath
Ischaemic colitis: sudden cramping left-sided pain, urgency and bloody diarrhoea within 24 h with only mild tenderness; CT thumbprinting; segmental oedema on colonoscopy sparing the rectum; most resolve, some stricture or perforate
Colonic anastomosis fashioned at the flexure on an interrupted arcade
Ischaemic breakdown and leak — surgeons check the marginal artery pulsatile bleed before joining bowel
Practise this structure
1 question in the bank tagged Mesenteric Arterial Supply.