Hilar and mediastinal sarcoid-like reaction after the treatment of malignant tumors: imaging features and natural course on 18 F-FDG-PET/CT

This study aimed to assess the imaging features and natural course of hilar and mediastinal sarcoid-like reaction on F-fluorodeoxyglucose (FDG) PET/CT after the treatment of malignancies. Sixteen patients with the appearance of sarcoid-like reaction seen on F-FDG-PET/CT after treatment were included. Hilar and mediastinal lymph node metastases were pathologically or clinically ruled out. Posttreatment F-FDG-PET/CT imaging features were assessed. The maximum standardized uptake values of sarcoid-like reaction were 3.8-13.6 (mean 6.8). FDG uptake of hilar nodes was symmetrical in 12 (75%) patients and asymmetrical in 4 (25%). The time interval between the initiation of therapy and appearance of sarcoid-like reaction was 9-86 months (median 27.1 months). Among 14 patients who underwent further follow-up using F-FDG-PET/CT, sarcoid-like reaction regressed in 11 (79%) patients and did not regress in 3 (21%) patients. The time interval between the appearance of sarcoid-like reaction and its regression was 3-80 months (median, 8.5 months). After the treatment of malignancies, benign sarcoid-like reaction was rarely observed during follow-up. Although sarcoid-like reaction appeared a long time after the treatment of malignancies, it frequently and spontaneously regressed in a relatively short period of time.