Monday, November 26, 2012

Hepatic Artery Complications Following Liver Transplant

After a liver transplant, the anastomosed hepatic artery, portal vein, and hepatic veins/IVC can all be a source of problems.  Of the three systems, the hepatic artery connection(s) tends to be the most common offender, particularly with stenosis and thrombosis at the anastomosis site. The incidence of hepatic anastomosis complications has been reported at somewhere between 4-25%.

Problems are usually detected on routine Doppler ultrasound of the hepatic vasculature.

The hepatic artery normally demonstrates a low-resistance waveform with continuous forward flow during diastole. The resistive index is somewhere between 0.5 - 0.7. With stenosis, there is a focal area of increased flow with post-stenotic aliasing, and, as with stenoses elsewhere, there can be a downstream tardus parvus waveform.

Normal hepatic low-resistance arterial flow (from Ref 3)

In this post-transplant hepatic artery stenosis a focal area of increased flow and downstream turbulence corresponded to a stenosis seen on angiogram (top two images).  A tardus-parvus waveform is present in the downstream arteries (bottom). Images from Ref. 3

If Doppler ultrasound detects a problem, the area can be further investigated with angiography.  In the two examples below, the high-grade stenosis turned out to be asymptomatic and not to be flow-limiting, so therapy was deferred... however stenosis can lead to graft dysfunction, bilary leak (transplant bile ducts receive all their blood supply from the transplant hepatic artery), or frank hepatic necrosis.

High-grade stenosis at the hepatic arterial anastomosis.

A high grade stenosis in a patient who had received a pediatric liver transplant. (steep LAO projection). There was no pressure gradient across the stenosis and therapy was deferred.

Risk factors for hepatic arterial thrombosis include a pediatric liver transplant, a transplant involving multiple anastomoses (donor liver with variant arterial anatomy), or an anastomosis directly to the aorta via a donor iliac artery conduit (the so-called "aortohepatic conduit.")  The aortohepatic conduit is usually employed when there is a problem with the native hepatic artery.

An example of an aortohepatic conduit.  A stenosis at the distal anastomosis site is evident. (from Ref. 1)

The therapy for stenosis is balloon angioplasty, with stents used in recurrent cases.  Oversizing of the balloon is carefully considered due to the relatively fragile anastomosis site vs. native artery. Systemic anticoagulation is also used, similarly to renal percutaneous angioplasty.

In addition to stenosis, thrombosis and pseudoaneurysms are also arterial complications of transplant that should also be watched for.

Thrombosis occurs in 8% of transplants and accounts for 60% of all posttransplant vascular complications. It has a 20-60% mortality and usually occurs with 15 days of transplant... but, fortunately, ultrasound is 92% accurate in picking it up... and its ultrasound characteristics make sense: post-stenotic tardus-parvus, delayed time to systolic peak, and decreasing resistive index.  It should be remembered, however, that these findings can often lead to a false-positive study, so if they occur, another more specific study should be pursued.  Catheter-directed thrombosis has been attempted, but such an approach has to be considered against the risk of anticoagulating a recently transplanted liver.

Hepatic artery pseudoaneurysms tend to be mycotic, and surgical correction is usually required.

1. Andrews JC. "Vascular Complications Following Liver Transplantation" Seminars in Interventional Radiology. Vol 24:4 (2004).
2. "Introduction to Vascular Ultrasonography" Zweibel and Pellerito, ed. 5th ed (2005)
3. Crossin JD, Muradali D, Wilson SR. "US of Liver Transplants: Normal and Abnormal" RadioGraphics 2003; 23:1093–1114