Ultrasound-Guided Percutaneous Radiofrequency Ablation of Liver Tumors: How We Do It Safely and Completely

Abstract

Ultrasound-guided percutaneous radiofrequency (RF) ablation has become one of the most promising local cancer therapies for both resectable and nonresectable hepatic tumors. Although RF ablation is a safe and effective technique for the treatment of liver tumors, the outcome of treatment can be closely related to the location and shape of the tumors. There may be difficulties with RF ablation of tumors that are adjacent to large vessels or extrahepatic heat-vulnerable organs and tumors in the caudate lobe, possibly resulting in major complications or treatment failure. Thus, a number of strategies have been developed to overcome these challenges, which include artificial ascites, needle track ablation, fusion imaging guidance, parallel targeting, bypass targeting, etc. Operators need to use the right strategy in the right situation to avoid the possibility of complications and incomplete thermal tissue destruction; with the right strategy, RF ablation can be performed successfully, even for hepatic tumors in high-risk locations. This article offers technical strategies that can be used to effectively perform RF ablation as well as to minimize possible complications related to the procedure with representative cases and schematic illustrations.

Keywords: Ablative margin; Complications; Hepatocellular carcinoma; Liver tumors; Radiofrequency ablation.

Fig. 1. Schematic illustration shows four different routes for artificial ascites (AA) infusion.

Perihepatic, sub-hepatic, sub-xiphoid (sub-phrenic), and gastrohepatic (lesser sac) routes can be selectively used for AA infusion based on location of hepatic tumors (T).

Fig. 2. RF ablation using AA via sub-hepatic route in 44-year-old man.

A. Longitudinal US image shows hypoechoic HCC (arrows) in segment 6 near ascending colon (arrowhead). B. Longitudinal US image demonstrates inserted angiosheath (arrowhead) and AA (asterisk) in sub-hepatic space. C. Longitudinal US image during RF ablation depicts transient hyperechoic ablation zone (asterisk), needle electrode (arrow), and angiosheath (arrowhead). D. Immediate follow-up contrast-enhanced CT image reveals low-attenuated RF ablation zone (asterisk) that sufficiently covers index tumor as well as intact adjacent colon (arrowhead). AA = artificial ascites, HCC = hepatocellular carcinoma, RF = radiofrequency, US = ultrasound

Fig. 3. RF ablation using AA method via gastrohepatic (lesser sac) route in 63-year-old woman.

A. Sagittal US image depicts hypoechoic HCC (arrows) in segment 3 near stomach (S). B. Photograph shows inserted angiosheath (arrowhead) through gastrohepatic route and needle electrode into target tumor. C. Sagittal US image during procedure demonstrates transient hyperechoic cloud (asterisk) and AA (arrow) in lesser sac between liver and stomach (S). D. Immediate follow-up contrast-enhanced CT image reveals low-attenuated RF ablation zone (asterisk) that sufficiently covers index tumor as well as intact adjacent gastric wall (arrow). AA = artificial ascites, HCC = hepatocellular carcinoma, RF = radiofrequency, US = ultrasound

Fig. 4. Schematic illustrations show mechanism of leverage (lifting) method.

A. Schematic illustration depicts insufficient hydrodissection between target tumor (T) and adjacent colon (C) after artificial ascites infusion. B. Schematic illustration demonstrates caudal tilting of distal end (handle) of needle electrode by which gap between index tumor (T) and abutting colon (C) is widened.

Fig. 5. RF ablation using leverage (lifting) method in 73-year-old man.

A. Longitudinal US image depicts index tumor with mixed echogenecity (arrows) in segment 6. There is still narrow gap (arrowhead) between tumor and colon (C) even after AA (asterisk) infusion. B. Longitudinal US image during procedure shows that gap (arrowhead) between RF ablation zone (asterisk) and colon (C) is not wide enough to prevent possible thermal damage to colon. Arrow indicates electrode. C. Photograph demonstrates caudal tilting of distal end of electrode by hand (arrow) (leverage method). D. Longitudinal US image during RF ablation shows wider gap (arrowhead) between RF ablation zone (asterisk) and colon (C) that is generated by leverage method. Note less steep slope of electrode (arrow) compared with that shown in B. E. Immediate follow-up contrast-enhanced CT image shows low-attenuated RF ablation zone (asterisk) that sufficiently covers tumor and intact adjacent colon (arrowhead) that is surrounded by infused AA. AA = artificial ascites, RF = radiofrequency, US = ultrasound

Fig. 6. RF ablation under fusion imaging guidance in 67-year-old man with 2.1 cm HCC.

A. Gadoxetic acid-enhanced axial arterial-phase T1-weighted image shows enhancing mass (arrow) in segment 7 of liver. B. Index tumor is not clearly seen on conventional gray-scale US image. HCC = hepatocellular carcinoma, RF = radiofrequency, US = ultrasound C. RF ablation was performed using fusion imaging technique (volume navigation, GE Healthcare). Fused image (left) and its corresponding MR image (right) during procedure show index tumor (T) and transient hyperechoic microbubbles (asterisk). D. Immediate follow-up contrast-enhanced CT image depicts low-attenuated RF ablation zone (asterisk), which sufficiently covers index tumor (arrowhead). HCC = hepatocellular carcinoma, RF = radiofrequency

Fig. 7. RF ablation using parallel targeting along large vessel in 50-year-old man.

A. Gadoxetic acid-enhanced axial hepatobiliary-phase T1-weighted image shows metastasis (arrow) from rectal cancer in segment 7 abutting right hepatic vein (arrowhead). B. Intercostal US image depicts hypoechoic metastasis (arrowhead) abutting right hepatic vein (arrow), which can potentially cause heat-sink effect during RF ablation. C. Intercostal US image during procedure demonstrates needle (arrow) in parallel to right hepatic vein (arrowhead) in order to enlarge contact surface between ablation zone and vessel. D. Immediate follow-up contrast-enhanced CT image shows elongated low-attenuated RF ablation zone (asterisk) along right hepatic vein (arrowhead), which sufficiently covers index tumor, as well as intact right hepatic vein. RF = radiofrequency, US = ultrasound

Fig. 8. RF ablation using bypass targeting technique in 66-year-old man.

A. Pre-RF ablation contrast-enhanced CT image shows HCC (curved arrow) in segment 1 near main portal vein and inferior vena cava (IVC) and right portal vein (arrowhead) on expected approach path (dotted arrow) of electrode. B. Intercostal US image demonstrates hypoechoic HCC (curved arrow) between main portal vein and IVC in segment 1. Note that right portal vein (arrowhead) blocks approach path for needle insertion into index tumor. C. Contrast-enhanced CT image obtained from 5 mm below level of A depicts safe approach path (dotted arrow) without traversing right portal vein. D. Serial schematic illustrations show process of placing electrode while bypassing large vessel in front of target tumor using structural flexibility of liver. HCC = hepatocellular carcinoma, RF = radiofrequency, US = ultrasound E. Intercostal US image during procedure shows that electrode (arrowhead) is safely placed within index tumor (arrow) using bypass targeting without puncturing right portal vein. F. Immediate follow-up contrast-enhanced CT image reveals low-attenuated RF ablation zone (asterisk) and intact right portal vein (arrowhead) with no signs of penetration by electrode. RF = radiofrequency, US = ultrasound