Rectal portosystemic anastomosis (superior rectal to middle and inferior rectal)
Termination
The superior rectal vein (to the inferior mesenteric, splenic and portal veins) communicates in the rectal submucosal plexus with the middle rectal veins (to the internal iliac vein) and the inferior rectal veins (to the internal pudendal and internal iliac veins, then the IVC). In portal hypertension, portal blood escapes backwards down the inferior mesenteric and superior rectal veins into the systemic pelvic veins.
Traced from the start
- Inferior mesenteric veinShort gastric and left gastro-omental veins
- Jejunal, ileal, ileocolic, right colic and middle colic veinsRight gastro-omental and pancreaticoduodenal veins
- Oesophageal veins (lower third)
- Splenic veinSuperior mesenteric veinLeft gastric (coronary) vein
- Hepatic portal vein
- Rectal portosystemic anastomosis (superior rectal to middle and inferior rectal)
Detail
- Portal limb
- Superior rectal vein via the inferior mesenteric vein
- Systemic limb
- Middle rectal (internal iliac) and inferior rectal (internal pudendal) veins
- Produces
- Anorectal varices
When it goes wrong
Portal hypertension distending the rectal venous plexus
Rectal varices: dilated submucosal veins beginning more than 4 cm above the anal verge that cause painless rectal bleeding; these are distinct from haemorrhoids, which are prolapsed anal cushions and are not more common in portal hypertension
Low rectal or anal carcinoma invading veins below the anastomosis
Haematogenous spread through the middle and inferior rectal veins into the systemic circulation, so lung metastases can appear without liver involvement, unlike colon cancer spreading via the portal vein
Practise this structure
1 question in the bank tagged Hindgut.