Abdomen Anatomy · Vascular

Inferior Mesenteric Artery Branches

The IMA arises from the anterior aorta at L3, supplying the hindgut — from the distal transverse colon to the upper rectum — via three named branches.

✦ The Mnemonic

"Left Sigmoid Supply — IMA's Three"

Left colic · Sigmoid arteries · Superior rectal — the IMA's three branches

LC Left Colic Artery Ascends to supply descending colon and splenic flexure; anastomoses with MCA via Drummond's arcade

SA Sigmoid Arteries (2–4) Multiple branches to sigmoid colon; variable number

SR Superior Rectal Artery Terminal branch; descends into pelvis; anastomoses with middle rectal

📚 Clinical Breakdown

The IMA is ligated during left hemicolectomy. Preserving Drummond's marginal artery is essential — it protects the splenic flexure. The splenic flexure is a 'watershed' area vulnerable when both SMA and IMA are compromised.

Sudeck's critical point: the left colic–sigmoid junction where the marginal artery may be tenuous — colon here is at risk of ischaemia after IMA ligation.

The rectum receives blood at three levels: superior rectal (IMA), middle rectal (internal iliac), inferior rectal (internal pudendal → internal iliac). Preserving the middle rectal artery is important in anterior resection.

IMA territory Distal transverse colon → upper rectum

Watershed zone Splenic flexure

Terminal branch Superior rectal artery

Three rectal vessels Superior / Middle / Inferior rectal

⭐ Clinical Pearl

Post-aortic surgery sigmoid ischaemia: IMA ligated during AAA repair. If Drummond's arcade is inadequate, sigmoid ischaemia occurs days 2–3 post-op. Colonoscopy within 48 hours is performed in high-risk patients. Ischaemic colitis presents with bloody diarrhoea.

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