A circulatory anastomosis is a connection between two blood vessels, such as between arteries, between veins or between an artery and a vein. Anastomoses between arteries and between veins result in a multitude of arteries and veins, respectively, serving the same volume of tissue. Such anastomoses occur normally in the body in the circulatory system, serving as backup routes for blood to flow if one link is blocked or otherwise compromised, but may also occur pathologically.
Physiologic
Arterio-arterial anastomoses include actual and potential varieties. There are many examples of normal arterio-arterial anastomoses in the body. Clinically important examples include:
Coronary anastomoses are a clinically vital subject: the coronary anastomosis is the blood supply to the heart. The coronary arteries are vulnerable to arteriosclerosis and other effects. Inadequate supply to the heart will lead to chest pains or a heart attack. These can be ameliorated by surgical intervention to create a bypass using the anastomosis technique. Creation of an end-to-end anastomosis is a basic microsurgical skill that is taught to surgical residents and fellows.
Naturally occurring
Coronary anastomoses are anatomically present though functionally obsolete. There was some suggestion that they may be helpful if a problem develops slowly over time but in the case of the pathogenesis of CHD they do not provide a sufficient blood flow to preventinfarction. There are anastomoses between the Circumflex and right coronary arteries and between the anterior and posterior inter-ventricular arteries. In the normal heart these anastomoses are non-functional.
Arterio-venous
Superficial arterio-venous anastomoses open when the body reaches a high temperature, and enable the body to cool itself. As warm arterial blood passes close to the surface it will decrease in temperature. This occurs together with sweating.
Pathologic
anastomoses result from trauma or disease and may involve veins, arteries, or intestines. These are usually referred to as fistulas. In the cases of veins or arteries, traumatic fistulas usually occur between artery and vein. Traumatic intestinal fistulas usually occur between two loops of intestine or intestine and skin. Portacaval anastomosis, by contrast, is a veno-venous anastomosis between a vein of the portal circulation and a vein of the systemic circulation, which allows blood to bypass the liver in patients with portal hypertension, often resulting in hemorrhoids, esophageal varices, or caput medusae. Circulatory anastomoses between monochorionic twins may result in twin-to-twin transfusion syndrome.
