Variability of Size and Shape of Necrosis Induced by Radiofrequency Ablation in Human Livers: A Volumetric Evaluation

Abstract

Background: Definite size and shape of radiofrequency-induced ablations (RFAs) cannot be evaluated intraoperatively. Instead, surgeons choose a radiofrequency device that is supposed to cause a necrosis of a determined size greater than the malignant lesion. The aim of this study was to measure the variability of the induced necroses postoperatively and to define a reproducible ablation volume in human liver. Methods: In 24 patients, 34 RFA procedures were performed with single applications of the device. The deployment was 3 cm (n = 16), 4 cm (n = 5), or 5 cm (n = 13). The induced necroses were analyzed by volumetric reconstructions of computed tomography (CT) scans. Measured volumes were compared with the expected volumes. Furthermore, the shape of the necrosis was classified according to an index of the diameters. Results: The measured volumes of postoperative necroses were 14 ± 8 cm³ (deployment, 3 cm), 24 ± 12 cm³ (4 cm), and 45 ± 42 cm³ (5 cm). The diameter of a sphere fitted into the necroses reached 2.9 ± .5 cm (3 cm), 3.5 ± .7 cm (4 cm), and 4.1 ± 1.1 cm (5 cm), at P < .02, significantly smaller than the deployment. The classification of shapes yielded a spherical shape (n = 14), a teardrop shape (n = 13), or an irregular shape (n = 7). The energy consumption was 2.1 ± 1.5 kJ/cm³ (3 cm), 2.6 ± .5 kJ/cm³ (4 cm), or 3.5 ± 2.0 kJ/cm³ (5 cm). Conclusions: The diameter of RFA-induced liver necrosis is significantly smaller than expected from needle deployment, especially with full-needle deployment. The shape of the lesion differs in more than half of the cases from the anticipated spherical pattern. The upper limit for reproducible necrosis induction is a tumor diameter of 3.4 cm.