The optimal study execution of rabbit experiments involving hepatic transcatheter arterial manipulations is affected by the operator’s ability to successfully select or superselect the tumor feeding vessel. Because of small size and tortuosity of rabbit hepatic arteries, successful selective vessel catheterization is not always possible, even in the presence of a skilled and experienced operator or when a wide range of microcatheters is available.
The rabbit celiac artery gives rise to the splenic artery, the right gastric artery, and the common hepatic artery (). The common hepatic artery then passes forward and to the right, giving the rise to the gastroduodenal artery and the caudate lobe artery. The proper hepatic artery then forms the main hepatic artery, which bifurcates to the right and left hepatic arteries. The latter bifurcates to the medial and lateral segmental branches. This branching pattern may be seen in approximately 95% of cases (7
). Variations also exist, such as a separate origin of the common hepatic artery off the superior mesenteric artery or a separate origin of the left hepatic artery off the celiac artery. In most cases, the left hepatic artery gives rise to the medial and lateral lobe branches.
Figure 3 Illustration of rabbit hepatic arterial anatomy. (Available in color online at www.jvir.org.)
In most studies, VX2 carcinoma is implanted into the medial lobe of the liver because it is easy to access during laparotomy and is thick enough to tolerate the tumor implantation manipulations (1
). However, many tumors implanted in the left medial lobe have shown angiographically small and tortuous feeding arteries, leading to nonselective and nontargeted intraarterial therapy, with compromised results. This angiographic appearance of the VX2 liver tumor was thought to be an inherent characteristic of the specific tumor vascularity. An initial nonintentional tumor implantation in the left lateral lobe revealed a more convenient angiographic scenario of a hypervascular tumor, with a single and long hypertrophic artery, which smoothly originated off the left hepatic artery. This initial observation led us to further assess whether the site of VX2 tumor implantation affects the way the tumor recruits feeding vessels and the size of these feeding vessels. Interestingly, our initial observations were confirmed, and more importantly, there were statistically significant anatomic differences between the two groups. In the left medial lobar artery group, the tumor feeding artery was small and short, originating at an acute angle off the left hepatic artery. In this group, the tumor feeding artery often showed spasm induced by catheter or guide wire manipulation, leading to longer fluoroscopy times, additional vasodilator administration, eventual thrombosis, and failure of the intervention. In the left lateral lobar artery group, we observed a longer single tumor feeding vessel, which was easier to select without arterial spasm. As a result, the success rate of selective angiography was higher than in cases of left medial lobe tumor implantation. To our knowledge, there is a paucity of literature describing such anatomic differences that may subsequently be exploited for transcatheter arterial interventions. We assume that these differences are related to the rabbit hepatic arterial anatomy (7
). The left medial lobar hepatic artery is often short, whereas the left lateral lobar artery is longer. As implanted tumors receive blood from these arteries, it is expected that tumors implanted in the lateral lobe would recruit vessels from the longer lateral lobar artery and that tumors implanted in the medial lobe would recruit vessels from the shorter medial lobar artery.
Our success rate in the left lateral lobe group was not 100%, despite the favorable arterial anatomy. This may partially attributed to the use of JB1 catheters (Cook) instead of microcatheters, which are more flexible and easier to manipulate.
According to these results, we now choose the left lateral lobe of the liver for VX2 tumor implantation in the rabbit. The anatomic advantages of the left lateral lobar artery, combined with fiber braided microcatheters and guide wires, may facilitate selective angiography and chemoembolization and increase the success rate of targeted intraarterial interventions in rabbits.
In conclusion, for selective hepatic arterial interventions in rabbits, the left lateral lobe of the liver may be more favorable than the left medial lobe as a VX2 tumor implantation site.