Ischemic Colitis

Ischemic colitis is the most common form of gastrointestinal ischemia, occurring when blood flow to the colon is transiently reduced to a level insufficient to maintain cellular metabolic function, resulting in mucosal injury that ranges from reversible mucosal ischemia to transmural necrosis and gangrene. The colon receives its blood supply from branches of the superior mesenteric artery (SMA), which supplies the right colon and proximal two-thirds of the transverse colon, and the inferior mesenteric artery (IMA), which supplies the distal transverse colon, descending colon, sigmoid colon, and upper rectum. The watershed areas -- regions located at the junction of two arterial territories where collateral flow is weakest -- are the most vulnerable to ischemic injury. The two most clinically significant watershed areas are the splenic flexure (Griffiths point, at the junction of the SMA and IMA territories) and the rectosigmoid junction (Sudeck point, at the junction of the IMA and hypogastric artery territories). The rectum is typically spared because it has dual blood supply from the IMA and the internal iliac (hypogastric) arteries. The pathophysiology involves a reduction in mesenteric...