Are Hepatic Arteries End Arteries?

Are hepatic artery branches are "essentially end arteries" as some textbooks and articles assert?

Some sources say that they are... including the venerable Michels, whose delineations of hepatic arterial supply have generally been considered the standard.  Michels even went so far as to say that "each hepatic artery is an end-artery with a selective distribution to a definite area of liver and cannot be sacrificed without resultant necrosis of liver tissue."

The traditional view is that anastomoses between hepatic lobes are observed mainly in the extrahepatic segments (25% of cadaver specimens) and in the liver capsule, as a response to hepatic arterial occlusion (such as with embolization procedures), and that arterial interconnection within the liver parenchyma does not exist.

Others are not so sure, and allow for the possibility of "translobar collateral flow."  Their position is that cadaver specimen casts do not demonstrate the tiny connections that in vivo angiography studies do.

In cadaver studies, from which Michels and other earlier anatomists drew their connections, it seems clear that there does not appear to be any interconnection.  In an elegant experiment (shown below) Mays and Mays used a resin cast to show no mixing of the arterial supply in the cadaveric human liver.

In this experiment, the right hepatic artery of a cadaveric human liver was injected with red resin, and the left hepatic artery was injected with yellow resin.  There was no intermixing between the two colors. The arrow points to the middle hepatic artery territory  (ref 2)

During angiography, however, evidence of translobar anastomoses is common.  In the images below, a

Middle Hepatic Artery

The middle hepatic artery (MHA) is a separate arterial supply of segments 4a and 4b of the liver (aka the "quadrate lobe"). It has been reported to infrequently contribute to segments 1, 2, 3, and the cystic artery as well.

Although the MHA is an intraparenchymal artery, it originally began as a more general hilar artery in the embryo.  In a recent study, the MHA was identified as a separate, discrete artery in 71% of living renal donor transplant evaluations (the remaining 29% supplied segment 4 from a branch of the left hepatic artery).





In an image from the same arterial run as in the previous post ("Right Gastric Artery, 10/9/2012"), a well-opacified middle hepatic artery is present...

Celiac axis angiogram demonstrates a middle hepatic artery in addition to the usual left and right hepatic arteries.

Right Gastric Artery

Localization of the right gastric artery ("pyloric artery")  is critical before a hepatic embolization procedure or placement of a chemoinfusion catheter, where nontarget radioactive spheres or chemotherapeutic molecules have the potential to lodge in the capillaries of the stomach and duodenum, causinge a nasty spot of ulcerative necrosis.

But unlike its large compatriot, the left gastric artery, the right gastric artery is a small twig-like artery that, when it is seen, most frequently arises off the proper hepatic artery (53%) and extends backward across the lesser curvature of the stomach to anastomose with the left gastric... and it can easily be missed if one is not looking for it.

Celiac trunk angiogram in preparation for a hepatic chemoembolization.  This early image in the run shows a small twig-like right gastric artery originating off the proximal proper hepatic artery, near an almost trifurcation of the left and right hepatic arteries and the GDA (first red arrow: origin of the R gastric artery; second red arrow: course of the R gastric artery)

The Double Aorta and Mesenteric Arterial Varations

So why are there so many variations in mesenteric arteries, anyway?  There seems to be much more variability in the configuration of the celiac, superior mesenteric, and inferior mesenteric arteries than with arteries in other parts of the body -- if a mesenteric artery can think of an aberrant origin or connection, you know it's tried it out at some point.

A large part of it is due to the complexity of controlled regression in the dorsal aortae, vitelline arteries, and the ventral anastomotic artery. 

First, a preface:  During development from days 8-23, the aorta are paired dorsal structures in the embryo which communicate through a ventral anastomotic artery.

Days 8-23 of the fetus, the dorsal aortae have two ventral branches which are connected via a ventral anastomotic artery that usually disappears during differentiation (not shown).  (ref 2)

Then around day 30, the dorsal aortae fuse... by day 36 the ventral branches fuse...