ACUTE INTESTINAL ISCHEMIA

Mesenteric artery thrombosis has the highest mortality rate of all causes of mesenteric ischemia. First described in the late 15th century, little progress was made in its treatment before the 20th century.

In 1901, a patient with a long history of postprandial pain was found to have an atherosclerotic plaque with overlying thrombus of the superior mesenteric artery (SMA). The physician concluded that if a patient could develop pain of the lower extremities secondary to atherosclerosis, it would stand to reason that a patient could present with postprandial pain due to narrowing of the mesenteric vessels. An example of complete occlusion is illustrated in the image below. The pathophysiologic mechanism by which ischemia produces pain remains poorly understood.

The arterial circulation to the gut has extensive collaterals and arcades providing multiple sources of blood inflow. This explains why vascular occlusion is well tolerated as evidenced by the relative lack of clinical intestinal ischemia despite the high prevalence of atherosclerotic disease of the aorta and visceral arteries. Certain collateral patterns are recognized, depending on which artery is blocked. When either the celiac or superior mesenteric artery (SMA) is compromised, the main collateral circulation is by the gastroduodenal and pancreaticoduodenal arteries. The main collateral channels between the SMA and inferior mesenteric artery (IMA) occur in the region of the splenic flexure between the middle and left colic arteries. In the presence of either SMA or IMA occlusion, the marginal artery of Drummond and the arch of Riolan (an ascending branch of the left colic artery anastomosing with branches of the SMA) enlarge significantly. In the presence of an IMA occlusion, another important collateral circulation is between the internal iliac artery and the left colic artery via the superior hemorrhoidal arteries.

The SMA is the critically important vessel in maintaining visceral perfusion, as demonstrated by increased blood flow after eating. This is not seen in the celiac artery. In chronic ischemia, all patients have SMA stenosis or occlusion, in addition to celiac artery and/or IMA involvement.

Date: 2014-12-29; view: 970