The purpose of this study was to investigate the development and evolution of the microwave ablation (MWA) lesion in the normal lung by using a swine model at various time points and to compare post-procedural computed tomography (CT) and gross pathologic findings during the first month post-ablation.

Twenty-seven percutaneous MWA procedures were performed on swine lungs at 100W for either 2min (low dose, 18 ablations) or 10min (high dose, 9 ablations). Animals were sacrificed at either 2 days (n=5) or 28 days (n=5) after ablation. All animals underwent CT imaging immediate post-treatment and prior to sacrifice, with additional imaging at 7 and 14 days for the 28-day cohort. After euthanasia, lungs and trachea were removed en bloc and underwent gross pathology analysis.

In both dose treatment groups, CT measurements of the ablation zone were maximum at Day 7 (low dose: 7.50±3.08 cm³; high dose: 24.87±11.34 cm³) and significantly larger compared to the immediate post-ablation measurements (low dose: 2.54±1.81 cm³; P=0.00011; high dose: 9.14±3.42 cm³; P=0.00374). No significant differences in dimensions were observed between CT and gross pathologic images for both high and low dose ablations in both cohorts.

The treatment zone following MWA in the lung can vary in the sub-acute setting, achieving largest size at 7 days post-treatment. Furthermore, measurements from CT closely matched with gross pathologic ablation size.