Anatomy and Clinical Relevance of the Superior Mesenteric Artery
Course and Anatomical Relationships
- The SMA descends anterior to the uncinate process of the pancreas and third part of the duodenum 3
Territory of Supply
- The ileocolic artery supplies the terminal ileum, cecum, appendix, and ascending colon 1, 4
- When the ileocolic artery is involved in thrombosis, necrosis of the proximal colon results 4
Clinical Relevance in Acute Mesenteric Ischemia
Embolic Occlusion Pattern
- Emboli typically lodge 3-10 cm distal to the SMA origin, classically sparing the proximal jejunum and colon 1, 5, 6
- This occurs at points of normal anatomic arterial narrowing 1, 5
- The distal lodging pattern explains why proximal jejunum is often spared in embolic events 1, 5
- More than 20% of SMA emboli are associated with concurrent emboli to other arterial beds (spleen, kidney) 1, 5
Thrombotic Occlusion Pattern
- Thrombotic occlusion typically occurs at the ostial or proximal SMA origin, often in patients with pre-existing atherosclerotic disease 1, 3, 7
- Thrombosis usually develops at the origin of visceral arteries where atherosclerotic plaques accumulate 1, 7
- Symptomatic SMA thrombosis most often accompanies celiac trunk occlusion due to the need for collateral flow 1, 7
Critical Anatomical Considerations
- Due to extensive collaterals in mesenteric circulation, isolated celiac trunk or inferior mesenteric artery occlusion infrequently leads to intestinal infarction 3, 8
- The small intestine can compensate for 75% reduction in mesenteric blood flow for up to 12 hours 5
- In non-occlusive mesenteric ischemia (NOMI), SMA vasoconstriction affects both small bowel and proximal colon via the ileocolic artery 1, 9