Wednesday, October 10, 2012

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.

Zoom-in of the image from the celiac run above.  The green arrow points to the middle hepatic artery.

From a little later in the same run, showing progressive filling of the hepatic arterial system.

So why would identifying a middle hepatic artery be important?

For one thing, it could be useful for avoiding non-target radioembolization or chemoembolization to segments 4.... or on the flip-side, a hepatic tumor may receive a significant part of its blood flow collaterally from the middle hepatic artery, and selective treatment into the middle hepatic may be of use.

Identification of a middle hepatic artery, on a diagnostic angiogram or CTA, can also be very useful to a surgeon who is planning hepatic resection.  Accidental damage to a middle hepatic artery can lead to a decrease in size of the left hepatic lobe, hepatic arterial thrombosis, or ischemic cholangiopathy in the territory supplied by the artery.

Variations in the origin of the middle hepatic artery.  The type shown in the angiogram above is Type 1 (from Ref 1)

I've been told by someone that "there is no middle hepatic artery," assuming, I mean that what we are calling the middle hepatic artery is just a prominent branch supplying hepatic segment 4, and has no regular pattern.

Others in favor of the term "middle hepatic artery" point out its embryologic origin -- the embryologic liver is supplied by a LHA from the LGA, an MHA from the CHA, and a RHA from the SMA... the persistent vessel to hepatic segment 4 is then considered a residual of this early embryonic vessel. Oddly enough, the embryologic patten has rarely been observed persisting into adulthood (below).

In this example, there is a replaced RHA off of the SMA (not shown), and this angiogram of the celiac axis shows not only a replaced LHA off the LGA, but an MHA arising off the CHA (fetal configuration). The patient was not considered a candidate for a hepatic arterial infusion catheter (ref 2)

1. Wang S, He X, Li Z, et al. "Characterization of the middle hepatic artery and its relevance to living donor liver transplanation." Liver Transpl. (Jun 2010) Vol 16:6, pp 736-41.
2. Kapoor V, Brancatelli G, Federle MP, et al. "Multidetector CT Arteriography with Volumetric Three-Dimensional Rendering to Evaluate Patients with Metastatic Colorectal Disease for Placement of a Floxuridine Infusion Pump" AJR. (Aug 2003) Vol 181:455-463. 
3. "Diagnostic Angiography" Kadir S. (1986)