1544 AJR:190, June 2008 the site of local tumor progression exactly correlated with insufficient ablative margin, contiguous large vessels, and subcapsular lo- cation, that is, concordance between local tumor progression at the susceptible sites with the risk factors. The second purpose of our study was to assess the morphologic pat- tern and exact site of local tumor progression with relation to the risk factors. Materials and Methods Patient Population From January 2001 to March 2007, we treated a total of 1,756 patients with 2,431 HCCs and 414 metastases using radiofrequency ablation in our institution. All the patients met the criteria for treatment with radiofrequency ablation adopted by our hospital: a single nodular tumor ≤ 5 cm in maximum diameter, multinodular (up to three in number) tumor ≤ 3 cm in maximum diameter each, the absence of extrahepatic metastases, prothrombin time ratio > 50% and platelet count > 70,000 cells/ mm 3 , and Child-Pugh class A or B liver cirrhosis (in patients with HCC). For this retrospective study, we included 86 patients treated by radiofrequency ablation using an internally cooled electrode who showed local tumor progression during the follow-up. Sixty-two patients had 65 hepatocellular carcinomas and 15 patients had 17 hepatic metastases. For HCC, local tumor progression was defined as any enhancing lesion inside or abutting the radiofrequency abla- tion zone at the arterial phase with washout lesion at the delayed phase of the CT examination during follow-up. For metastases, enlargement or growth abutting the ablation zone would be labeled as local tumor progression. Tumor that was not Local Tumor Progression After Radiofrequency Ablation of Liver Tumors: Analysis of Morphologic Pattern and Site of Recurrence Shiu Kong Kei 1,2 Hyunchul Rhim 1 Dongil Choi 1 Won Jae Lee 1 Hyo K. Lim 1 Young-sun Kim 1 Kei SK, Rhim H, Choi D, Lee WJ, Lim HK, Kim Y 1 Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50, Ilwon-Dong, Kangnam-Ku, Seoul 135-710, South Korea. Address correspondence to H. Rhim (forest@smc.samsung.co.kr). 2 Present address: Department of Diagnostic Radiology, Tuen Mun Hospital, Tuen Mun, New Territories, Hong Kong. Abdominal฀Imaging฀•฀Clinical฀Observations AJR 2008; 190:1544–1551 0361–803X/08/1906–1544 © American Roentgen Ray Society V arious ablative therapies have been developed and practiced as nonsurgical treatments for pri- mary and secondary malignant hepatic tumors [1]. Radiofrequency ablation has been well established and widely prac- ticed because it has been shown to provide more consistent local tumor control than other ablative techniques in several studies [2–4]. In some centers of Asia and Europe, radiofre- quency ablation has been performed as a first- line treatment option for small hepatocellular carcinoma (HCC) with promising results, even in patients suitable for surgery [5–7]. With the increasing number of long-term survivors after radiofrequency ablation, it is predictable that the number of cases of local tumor progression will also increase accord- ingly. The reported rate of local tumor pro- gression after various ablative techniques ranges from 2% to 60% [2, 5, 8–10]. Recog- nition of the morphologic pattern of local tumor progression would be helpful for early detection. The first purpose of our study was to observe the most common morphologic pattern of local tumor progression. Various types of risk factors for local tumor progression have been proposed in different studies, with controversial results [11–18]. Several independent risk factors for local tu- mor progression proposed in the previous investigations related to the geometry of the ablation zone and liver anatomy including lack of peritumoral ablative margin, heat sink effect of contiguous vessels, and subcapsular location. However, to our best knowledge, there has been no study to assess how much Keywords: hepatic tumor, hepatocellular carcinoma, local tumor progression, metastases, radiofrequency ablation DOI:10.2214/AJR.07.2798 Received June 29, 2007; accepted after revision December 14, 2007. OBJECTIVE. The purpose of our study was to assess the morphologic pattern and exact site of local tumor progression with relation to various risk factors after radiofrequency abla- tion of liver tumors. CONCLUSION. Local tumor progression after radiofrequency ablation shows mostly the peripheral nodular type. The site of local tumor progression shows a higher concordance rate with insufficient ablative margin than contiguous vessel and subcapsular location. Kei et al. Radiofrequency Ablation of Liver Tumors Abdominal Imaging Clinical Observations Downloaded from www.ajronline.org by 52.73.204.196 on 05/16/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved