Inferior Mesenteric Artery

• Supplies as far as the upper third of the Anal Canal, i.e. to the level of the Pectinate Line
• Arises from front of Aorta:
  • Behind the inferior border of the 3rd part of the Duodenum
  • Opposite L3 vertebra
  • At the level of the umbilicus
  • 3-4cm above the Aortic Bifurcation
• Smaller than the Superior Mesenteric Artery
• Runs obliquely down to the pelvic brim, immediately beneath the peritoneal floor of the left infracolic compartment
• Gives off the:
  • Left Colic Artery
  • Sigmoid Arteries
• Crosses the Pelvic Brim at the bifurcation of the Left Common Iliac Vessels over the Sacroiliac Joint
  • Then converges towards the Ureter with the Inferior Mesenteric Vein lying in between them at the apex of the attachment of the Sigmoid Mesocolon
• Branches cross to the left in front of the Ureter
• Continues as the Superior Rectal Artery beyond the Pelvic Brim within the roof of the Sigmoid Mesocolon

1. Left Colic Artery

• Passes upwards and to the left behind the peritoneum
• Divides into an ascending and a descending branch after a short course
• Ascending branch:
  • Continues laterally and upwards
  • Crosses the Left Psoas, Gonadal Vessels, Ureter, Genitofemoral Nerve, and Quadratus Lumborum
  • Crossed anteriorly by the Inferior Mesenteric Vein
• Descending branch:
  • Passes laterally and downwards
• Branches of these two arteries anastomose with each other as well as the left branch of the Middle Colic Artery and with the highest Sigmoid Artery

2. Sigmoid Arteries

• 2-4 branches
• Pass between layers of the Sigmoid Mesocolon
• Last sigmoid branch anastomoses with the 1st branch of the Superior Rectal Artery

Venous Drainage

Superior Rectal Vein

• Runs up in the root of the Sigmoid Mesocolon
• To the left of the Superior Rectal Artery to the Pelvic Brim
• Renamed the Inferior Mesenteric Vein above the Pelvic Brim

Inferior Mesenteric Vein

• Receives tributaries identical with the branches of the Inferior Mesenteric Artery
• Runs vertically upwards to the left of the Inferior Mesenteric Artery
• Lies beneath the peritoneal floor of the left infracolic compartment
• Lies on the Left Psoas, in front of the Gonadal vessels, Ureter, and Genitofemoral Nerve
• Lies to the left of the Duodenojejunal Flexure at the upper limit of the left infracolic compartment just below the attachment of the Transverse Mesocolon
• Curves to the right and often raises a ridge of peritoneum – the Paraduodenal recess
• Passes behind the lower border of the Body of the Pancreas
  • In front of the Left Renal Vein
• Joins the Splenic Vein
• Variation: Curves to the right more sharply and…
  • Passes behind the Pancreas
  • Below and Parallel with the Splenic Vein
  • In front of the Superior Mesenteric Artery
  • Open directly into the Superior Mesenteric Vein