An anastomosis is a connection of normally separate parts or spaces so they intercommunicate. An anastomosis may be naturally occurring or artificially constructed. An anastomosis may, for example, connect two blood vessel such as an artery and a vein or it may connect adjacent segments of the intestine. Anastomosis can develop as an embryological abnormality; it can develop as part of a disease process, and it can be surgically constructed. When a vein and an artery have between them an anastomosis, it is considered an abnormal anatomical feature and is called an A-V shunt.