Imaging findings after radiofrequency ablation of adrenal tumors

The purpose of this study was to describe the imaging findings after radiofrequency ablation of adrenal tumors.

We retrospectively reviewed the imaging findings of all patients with adrenal tumors treated with radiofrequency ablation in our department from January 2001 through August 2009. The studies were reviewed in consensus by two attending abdominal imaging radiologists and an abdominal imaging fellow. Imaging findings before, immediately after, and at short- and long-term follow-up after ablation were recorded.

Fourteen patients (seven men, seven women; mean age, 56 ± 8.4 years) underwent radiofrequency ablation of adrenal tumors. One case of small pneumothorax and one case of small hemothorax were the only minor complications (complication rate, 14%). The expected side effects of radiofrequency ablation were found in 35% of patients: in two patients adjacent liver parenchyma was ablated, in two patients the diaphragmatic crus was injured, and in two patients local hematoma occurred (in one patient, both adjacent liver and diaphragmatic crus were ablated). Immediate soft-tissue findings after radiofrequency ablation included air bubbles in 12 patients (86%) and fat stranding around the adrenal gland in 13 patients (93%). A fat rim sign was found in 60% of patients at long-term follow-up. The attenuation of the tumor immediately after the procedure increased an average of 7 HU (median, 5 HU; range, -2 to 18 HU) and tended to decrease in long-term follow-up. At long-term follow-up, most (75%) of the tumors had decreased in size and attenuation.

Air bubbles and fat stranding are frequently seen immediately after radiofrequency ablation of adrenal tumors. A fat rim sign is a common finding at long-term follow-up. Attenuation of the ablated zone increases immediately after the procedure and decreases in long-term follow-up. The volume of the ablated zone has a variable size response, suggesting the need for baseline imaging.