CT imaging findings of pulmonary neoplasms after treatment with radiofrequency ablation: results in 32 tumors

OBJECTIVE: The purpose of this study is to describe the CT appearance of thoracic neoplasms after treatment with radiofrequency ablation (RFA). MATERIALS AND METHODS: Thirty-two thoracic neoplasms in 26 patients had pulmonary RFA and imaging follow-up. Fourteen neoplasms were primary lung cancer and 18 were metastases. The mean pretreatment neoplasm size was 3.1 cm (range, 1.0-7.0 cm), and the average number of neoplasms treated per patient was 1.2 (range, 1-3). The mean follow-up was 10.1 months (range, 1-30 months). Imaging findings on CT were evaluated by three radiologists and documented by consensus. RESULTS: The most common finding immediately after treatment was peripheral ground-glass opacity surrounding the treated neoplasm, seen in 27 of 32 tumors (84%). This rapidly resolved in all but one patient by the end of the first month. Cavitation was seen in 10 of 32 tumors (31%) on follow-up CT and was most common in neoplasms in the inner two thirds of the lung and adjacent to a segmental bronchus. Sixty percent of the cavitations decreased in size on follow-up scans. Ten of 32 tumors (31%) that did not develop cavitation developed bubble lucencies on follow-up CT. Pleural thickening was found in 12 of 22 (55%) parenchymal neoplasms, and linear opacifications were seen between the treated lesion and adjacent pleura in 14 of 22 parenchymal tumors (64%). Pleural effusions were seen in four patients (15%). Fourteen of 22 tumors (64%) with follow-up imaging at 1 month enlarged from pretreatment CT scans. At 3 and 6 months after RFA, the majority remained stable in size. CONCLUSION: Peripheral ground-glass opacity, cavitation, bubble lucencies, and pleural changes are common findings on CT after RFA. Many treated neoplasms increase in size from baseline on 1- to 3-month follow-up CT scans and then remain stable thereafter. Enlargement of a treated tumor after 6 months is felt to represent local recurrence. Stability of a treated lesion beyond 6 months does not guarantee continued stability.