Vascular Anatomy and Its Implication in Radioembolization

The anatomy of the mesenteric system and the hepatic arterial bed has a high degree of variation. The celiac trunk trifurcates into the left gastric, splenic, and common hepatic arteries. The common hepatic artery divides into the gastroduodenal artery and proper hepatic artery. This itself bifurcates into a right and left branch to supply each of the lobes of the liver. Quite often the hepatic artery has an incomplete set of branches because one or the other of its usual branches arises from a source other than the proper hepatic artery from the celiac trunk. Such a vessel, if from an outside source, is spoken of as ‘aberrant’ (a variation). Aberrant hepatic arteries are of two types, replacing and accessory. An aberrant hepatic artery refers to a branch that does not arise from its usual source (i.e. proper hepatic artery from the celiac trunk). This type of artery may be a substitute for the usual hepatic artery that is absent, in which case it is referred to as an aberrant ‘replaced’ hepatic artery. In other cases there may be an additional artery to the one normally present, hence the term aberrant ‘accessory’ artery. In 1953, Michels published his classical study of hepatic arterial anatomy, which detailed the results following the dissection of 200 cadavers. He defined 10 anatomical variations of the hepatic artery. Later on in 1966, Michels proposed an internationally recognized classification of these hepatic abnormalities, which was later, modified by Hiatt in 1994. When performing a radioembolization procedure, it is of utmost importance to identify and isolate any vessel which may supply blood to organs other than the liver as this may result in non-target 90Y administration. Many hepatic vessels originating from non-hepatic sources and extrahepatic collateral pathways to the liver may be established in various conditions such as following surgical ligation of the hepatic artery or arterial injury induced by repeated endovascular treatments.