When and how should Ultrasound be used to evaluate a transjugular intrahepatic portosystemic shunt (TIPS)?
Color spectral Doppler US is the initial study of choice for evaluating a TIPS used to treat portal hypertension. The TIPS procedure consists of placing a stent between the higher pressure portal system and the lower pressure hepatic veins. A TIPS is most commonly placed between the right portal vein and the right hepatic vein, with resulting hepatopedal flow in the main and right portal veins, but hepatofugal flow in the left portal vein and the anterior and posterior branches of the right portal vein, as all the portal veins now flow toward the TIPS ( Figure 64-8 ). The most common complication of TIPS is stent stenosis. US is used to routinely monitor TIPS and detect early stent stenosis to allow for stent recanalization before clot matures and the stent fully occludes, which would necessitate a second TIPS. Normal flow in a patent TIPS is turbulent, with mean PSV of 95 to 120 cm/sec but potentially up to 190 cm/sec. Higher and lower PSV in the stent or a significant change in stent PSV (i.e., >40 to 60 cm/sec change) compared to a prior ultrasound examination also suggests a stent stenosis. A late sign of TIPS stenosis is a change in the direction of flow in the portal veins from toward the stent (hepatofugal) to away from the stent (hepatopedal).