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"D. Cotugno" Hospital Naples 80131, Italy
We read with interest the article written by Dr. Choi and colleagues [1]. They reported that liver abscess developed in 14 tumors of 13 patients after 13 of 751 (1.7%) radiofrequency ablation procedures. They concluded that treatment with an internally cooled electrode system is one of the significant risk factors for liver abscess formation. The abscess rate they observed seems rather high compared with previous experiences [2, 3]. Livraghi et al. [2], in their multicenter study in which a percutaneous internally cooled radiofrequency ablation technique was used, identified six patients (0.3%) with intrahepatic abscesses. Similarly, in our series [3] of liver tumors treated with percutaneous saline-enhanced radiofrequency ablation, only one (0.3%) of 336 patients developed liver abscess after percutaneous treatment. He had a nodule of hepatocellular carcinoma in segment VI.
As we [3] and others [4] have reported, the complication of liver abscess may occur after radiofrequency ablation of tumors near the intestine, probably because of contamination of the area of radiofrequency-induced necrosis by pathogens from the digestive tract. In their study, Choi et al. [1] neither mention the location on the liver of the treated hepatocellular carcinoma nor analyze this risk factor. It would be interesting to know whether the high rate of abscesses they reported was related to tumors that were located in the portion of the liver near the intestine. In the series of de Baère et al. [4] including 582 liver tumors treated using either cooled-tip needles or expandable array needles, liver abscess (n = 7) was the most common complication, just as it was in the study of Choi et al. Nevertheless, in the series of de Baère et al., 124 (35.4%) of 350 procedures were intraoperative.
In our experience, radiofrequency ablation using the perfused needle electrode is a safe and reliable treatment for liver malignancies with fewer major complications than radiofrequency ablation using an internally cooled or expandable needle electrode.
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Samsung Medical Center Sungkyunkwan University School of Medicine Seoul 135-710, South Korea
We thank Drs. Giorgio and Ferraioli for their letter concerning our recent article in the AJR [1] and would like to clarify some of their remarks. The abscess rate in our study—1.7% (13 of 751 radiofrequency ablation procedures)—was higher than those (0.3% and 0.66%) reported by two multi-center study groups [2, 3], respectively. However, it was similar to that of a more recent study conducted at two French institutions [4]. Those researchers reported that seven liver abscesses (2.0%) were discovered after 350 radiofrequency ablation procedures of 582 hepatic tumors in 312 patients. All abscesses were found after 226 percutaneous radiofrequency procedures using either an internally cooled electrode or an expandable electrode system. We think that the differences among the abscess rates reported by researchers at many different institutions might result from differences in the aggressiveness with which researchers perform radiofrequency ablation for treatment of difficult cases.
We would like to add some information regarding the location of the index (original) tumors in our patient series [1]. We observed the 14 index tumors developing abscesses throughout the right hepatic lobe: three tumors in segment V, three in segment VI, four in segment VII, and four in segment VIII. Of 14 ablation zones developing abscesses, only two abutted the colon.
We agree with Giorgio and Ferraioli that some of the liver abscesses could have occurred after radiofrequency ablation of tumors near the colon as a result of direct contamination of the ablation zone by bacteria from the gut. However, we believe that most abscesses in our study were associated with retrograde enteric bacterial contamination of the bile ducts. Radiofrequency ablation could have connected the biliary tract and ablation zone by severe thermal injury to the bile ducts and the ablation zones could have then been contaminated by enteric bacteria. In our study, all cultured organisms except Staphylococcus aureus were noted to be from an enteric source.
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