Key Takeaways
- Clinical Bottom Line
- Defining the Colonic Watershed
- The Primary Vascular Territories
- Griffith's Point (The Splenic Flexure)
Clinical Bottom Line
| Anatomical Landmark | Vascular Territory Junction | Clinical Consequence of Ischemia |
|---|---|---|
| Griffith’s Point (Splenic Flexure) | Superior Mesenteric Artery (SMA) / Inferior Mesenteric Artery (IMA) | Ischemic colitis of the splenic flexure and descending colon. |
| Sudeck’s Point (Rectosigmoid Junction) | Inferior Mesenteric Artery (IMA) / Superior Rectal Artery (Systemic Iliac) | Ischemic injury to the sigmoid colon; high risk area for colorectal anastomotic leaks. |
| Marginal Artery of Drummond | Continuous collateral vessel connecting SMA and IMA along mesenteric border. | Primary collateral pathway mitigating ischemia during hypoperfusion. |
| Arc of Riolan | Central collateral connecting Middle Colic (SMA) to Left Colic (IMA). | Secondary collateral pathway; often hypertrophied in chronic occlusive disease. |
Defining the Colonic Watershed
The vascular supply of the gastrointestinal tract is a marvel of evolutionary redundancy, yet it contains distinct functional weaknesses known as watershed areas. In vascular anatomy, a watershed area is defined as the absolute distal margin of blood supply where two major arterial territories overlap. Because these zones represent the furthest points of perfusion from the primary cardiac pump, they are uniquely vulnerable to ischemia during episodes of systemic hypotension, shock, or vascular ligation.
The Primary Vascular Territories
To understand the watershed areas, one must first isolate the primary arterial trunks supplying the hindgut and midgut:
- Superior Mesenteric Artery (SMA): Supplies the small intestine, cecum, ascending colon, and the proximal two-thirds of the transverse colon (via the middle colic artery).
- Inferior Mesenteric Artery (IMA): Supplies the distal one-third of the transverse colon, descending colon, sigmoid colon (via sigmoid branches), and proximal rectum (via the superior rectal artery).
- Internal Iliac Artery: Supplies the mid and distal rectum via the middle and inferior rectal arteries.
Griffith’s Point (The Splenic Flexure)
Griffith’s Point is located at the splenic flexure, the sharp bend between the transverse and descending colon. This represents the critical border zone between the SMA (midgut) and IMA (hindgut) circulations.
Specifically, it marks the anastomotic junction between the left branch of the middle colic artery (SMA) and the ascending branch of the left colic artery (IMA). If a patient experiences a sudden drop in cardiac output (e.g., cardiogenic shock or massive hemorrhage), this distal junction is the first area to suffer hypoperfusion, making the splenic flexure the most common site for non-occlusive ischemic colitis.
Sudeck’s Point (The Rectosigmoid Junction)
Sudeck’s Point is located at the rectosigmoid junction. It represents the watershed zone between the lowest sigmoidal arterial branch (from the IMA) and the superior rectal artery (the terminal continuation of the IMA before it meets the systemic internal iliac system).
While the splenic flexure is vulnerable due to distance from the aorta, Sudeck’s point is vulnerable due to a frequent lack of robust collateral circulation in the mucosal and submucosal layers at this specific junction. Sudeck’s point is of paramount importance to colorectal surgeons; if the IMA is ligated high during a rectal cancer resection or an abdominal aortic aneurysm (AAA) repair, the surgeon must verify that retrograde blood flow from the marginal artery is sufficient to perfuse the descending colon, otherwise, the anastomosis will suffer ischemic necrosis and leak.
Collateral Pathways: The Marginal Artery of Drummond
Fortunately, the colon possesses an internal safety net known as the Marginal Artery of Drummond. This is a continuous arterial arcade running along the inner mesenteric border of the colon, connecting the terminal branches of the SMA and IMA.
In a healthy individual, the marginal artery allows blood to bypass a slow blockage. For example, if the IMA slowly occludes due to atherosclerosis over several years, the marginal artery will dilate, allowing the SMA to assume the entirely of the blood supply to the descending colon, completely preventing ischemia. However, in roughly 5% of the population, the marginal artery is incomplete or entirely absent at Griffith’s point—rendering these individuals exceedingly vulnerable to ischemic colitis.
Anatomical review compiled by the Gastroscholar Research Team. Last updated: April 16, 2026. This article is intended for physicians and surgical trainees.
