Reversed halo sign after radiofrequency ablation of a lung nodule.

We report a case of the "reversed halo sign" 6 weeks after radiofrequency ablation (RFA) of a lung neoplasm in an 80-year-old man. The "reversed halo sign," first described on computed tomography in cryptogenic organizing pneumonia, has later been described as being associated with a wide range of pulmonary pathologies, including paracoccidiodomycosis, tuberculosis, lymphomatoid granulomatosis, Wegener granulomatosis, invasive pulmonary fungal infections, and sarcoidosis. Although a number of computed tomography findings have been reported after RFA of both primary lung tumors and pulmonary metastases, this case demonstrates that the reversed halo sign may also occur after RFA.