In the classical description of the arterial anatomy, 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. From this point onward, the arterial branching pattern follows the segmental anatomy of this organ and hence the right hepatic artery further divides into the right anterior and posterior hepatic arteries, while the left hepatic artery divides into branches supplying segment II and segment III. The arterial supply to segment IV may occur from one or more branches arising from the right, left, or proper hepatic artery. However, this classical description of the hepatic arterial anatomy occurs in only 55–65 % of the population. Any hepatic arterial anatomy that differs from what has been so far described is considered to represent an anatomical variation.

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 (Fig. 2). 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.

The first published description of aberrant hepatic arteries is attributed to Haller in 1756. The data necessary for the study of such variations may be obtained from direct observation of large autopsies, surgical series, or from radiological studies, initially by conventional angiography including DSA or more recently from CT or MR angiography.

In 1953, Michels published his classical study of hepatic arterial anatomy, which detailed the results following the dissection of 200 cadavers (Michels 1953).

He defined 10 anatomical variations of the hepatic artery (Table 1). Later on in 1966, Michels proposed an internationally recognized classification of these hepatic abnormalities, which was later, modified by Hiatt in 1994 (Hiatt et al. 1994).

In the conventional anatomy defined as type I according to Michels’ classification (Fig. 3), the main hepatic artery originates from celiac trunk, gives off the gastroduodenal artery and the proper hepatic artery, the proper hepatic artery continues as the right hepatic artery after giving off the left hepatic artery and then the right hepatic artery splits into its anterior and posterior branches. The left hepatic artery splits into branches that feed segments II and III. Segment IV is fed by the branch or branches originating from the right, left, or the proper hepatic artery. The left hepatic artery originating from the left gastric artery (replaced left hepatic artery) is defined as type II (Fig. 4), the right hepatic artery stemming from the superior mesenteric artery (replaced right hepatic artery) as type III (Fig. 5), and coexistence of both situations is defined as type IV. The left lobe is also fed by the accessory left hepatic artery originating from the left gastric artery in type V variation, and the right lobe is also fed by accessory right hepatic artery originating from the superior mesenteric artery in type VI variation. Both the left and right accessory artery exist in type VII; the replaced right hepatic artery and the accessory left hepatic artery or the accessory right hepatic artery and the replaced left hepatic artery coexist in type VIII. The hepatic trunk originates from the superior mesenteric artery in type IX and from the left gastric artery in type X.

The reported prevalence of anomalies not included in Michels’ system varies from 1.8 (Koops et al. 2004) to 16.6 % (Coskun et al. 2005). The knowledge of these aberrant vessels can be useful in radioembolization, in order to recognize liver parenchyma supplied these arteries and if necessary embolize them before treatment.

Additional clinically relevant anatomical variants are summarized in Table 2 (Figs. 6, 7, and 8).