Computed tomographic appearance of lung tumors treated with percutaneous cryoablation

Purpose: To describe the computed tomographic (CT) appearance of lung tumors treated with cryoablation to establish a reliable reference profile. Materials and Methods: CT images of 56 patients who underwent follow-up CT for at least 1 year for treatment with cryoablation of 79 tumors from 2003 to 2010 were retrospectively reviewed. Patients had a follow-up CT scan immediately after the procedure; 1 day, 1 week (two-phase dynamic CT), and 1 month later; and then at 3-month intervals. The appearance of ablation zones on CT images was classified into five patterns, and bidimensional diameters and other imaging features were evaluated. Results: Seventy-eight percent of ablation zones (62 of 79) showed transformation similar to the following: a consolidation or nodular pattern was seen within the 1-week follow-up, involution and a "stripe" pattern was shown at 1 month or later, and zones later became indistinct. Eighty percent of cases of local progression (eight of 10) arose from the stripe pattern on follow-up CT 6 months or later, after the ablation zones showed a transformation opposite the aforementioned pattern. Ice balls could not always be visualized exactly because of dense peritumoral hemorrhage. Internal and marginal enhancement of the ablation zone within the 3-month follow-up did not show a direct relationship with local progression. In total, cavitation and peritumoral ground-glass opacity were seen in 35% (n = 28) and 85% (n = 66) of ablation zones, respectively. Conclusions: The reference profile of CT appearance, which is mandatory for follow-up, has been established. No single indicator of complete ablation was proven throughout this study. Careful long-term follow-up with CT is indispensable.