Acute portal venous injury after microwave ablation in an in vivo porcine model: a rare possible complication

Purpose: To evaluate the damage caused by microwave ablation to vessels inside and outside the ablation zone in an in vivo swine model. Materials and Methods: Four pigs underwent microwave liver ablation with a 2.45-GHz generator and a 14-gauge water-cooled antenna with a miniature choke. Each animal underwent four 15-minute microwave ablations (two at 40 W, two at 60 W). Mean minimum and maximum diameters of ablation areas were calculated on gross pathologic and histologic examination. At minimum, a whole-mount section and two to four specimens were obtained from each ablation and stained with hematoxylin and eosin. Specimens were analyzed to verify the presence of damaged vessels in and outside the ablation area. Results: Mean ablation diameters at gross pathologic examination, including the hemorrhagic halo, were 3.1 cm ± 0.5 at 40 W and 3.6 cm ± 1.1 at 60 W. All ablation zones presented a characteristic pattern consisting of three concentric zones: (i) a central area consisting of coagulative necrosis (mean maximum diameter, 8.5 mm ± 2.6), (ii) a larger area characterized by irreversibly damaged hepatocytes (mean maximum thickness, 11.7 mm ± 3.4), and (iii) a hemorrhagic halo. Twenty-one veins outside the ablation zone were evaluated (mean diameter, 5.6 mm), three of which (14%) showed diffuse endothelial damage. All three represented a continuation of a portal vein within the ablation area. Conclusions: In a small percentage of microwave ablation cases, endothelial damage can extend from a portal vessel included in the ablation zone to a segment of the vessel situated outside the ablation zone. Further investigation of the clinical significance of this finding is needed.