This pilot study demonstrates the feasibility and safety of ICE for the evaluation of parenchymal alterations in patients with liver cirrhosis and suspected or proven hepatocellular carcinoma.
This technique is a novelty in the field of hepatology, but not in angiology and cardiology, where this tool is frequently used to guide non-surgical interventional procedures and to assess vascular disease [12, 13]. High-resolution portal vein imaging has been the objective of a number of studies for evaluating possible invasion of the venous wall by pancreatic or ampullary cancers [14, 15]. In other studies the liver has been investigated using intravascular ultrasound from the vena cava to guide the placement of direct intrahepatic porto-caval shunts in patients with portal hypertension [16, 17]. However, studies aimed at examining liver parenchymal structure and lesions, as well as portal vein branches and hepatic veins are lacking. In this respect the present study is the first report on the use of this technique.
Beside the assessment of the feasibility and the safety, we also examined the imaging quality performance of ICE. By inserting the ICE catheter into the right and middle hepatic veins it was possible to visualize not only liver parenchyma, focal lesions and vascular features, but also extra hepatic structures such as the gallbladder and the peritoneal cavity to assess the presence of ascites. Due to the specific left hepatic vein anatomy and the size of the ICE catheter, we were not able to place the catheter into the left hepatic vein in order to obtain accurate images from this vessel. The failure to access the left hepatic vein represents an important limitation in cirrhotic patients, because a complete evaluation of the liver is essential for treatment planning. The use of ICE did however not present any other technical drawbacks.
At the end of the procedure patients were asked about the comfort and tolerability of ICE. The procedures were well tolerated, as demonstrated by the absence of pain and the hemodynamic stability throughout the procedure. It must be stressed however that we performed ICE as a complementary investigation following the measurement of HVPG. Hence, the invasiveness of ICE itself was possibly under estimated by the patients. The duration of ICE also represented a negative aspect, because it prolonged the patient's stay in the examination room. Finally, an additional radiation dose was used to guide and to verify the ultrasound catheter position. This supplementary irradiation might be avoidable in further studies by using conventional external ultrasound of the liver to follow the ICE device progression in the hepatic veins.
The performance of ICE in detecting nodules and visualizing blood vessels was tested qualitatively by comparing its findings with those obtained by using other imaging techniques such as CT or MRI in the same patients. Although the number of patients was small and the study was not designed to assess this endpoint, ICE findings were similar to those observed on images obtained by CT or MRI in the right hepatic lobe.
Future studies of ICE should assess the qualitative performance of this technique as a complement to external ultrasound, CT scan and magnetic resonance imaging for the evaluation of satellite small lesions and vascular invasion and/or thrombosis. Nevertheless, these results need first to be replicated in a larger number of patients before being translated into clinical strategies.
An additional point to be considered is the cost of this device, which is approximately 2500 Euros at this time. ICE catheters are for single use and their use must be accurately evaluated and be limited to clinical studies only. Besides diagnostic procedures, this technique might also be evaluated for interventional purposes, for example to assess the placement of transjugular intrahepatic porto-systemic shunts.