Incidental asymmetric tonsillar FDG uptake in adults is not malignant

1504 Objectives: To evaluate the incidence of incidentally detected tonsillar asymmetry and the prevalence of malignancy in asymmetric tonsillar uptake (ATU) on F-18 FDG PET in adults. Methods: We retrospectively reviewed a total of 2928 cases (58.4±12.3 yrs, M/F=1060/1868) who underwent F-18 FDG PET/CT during a 1-year period with various indications except primary tonsillar cancer and lymphoma evaluation. FDG-PET data were analyzed by visual interpretation. Positive finding was defined as asymmetric tonsillar uptake compared to contralateral side. The incidence of ATU and the prevalence of malignancy in ATU according to the clinical factors such as age, sex, season, study indications (health check, head & neck cancer, metastasis of unknown origin (MUO), and other cancers) and associate PET findings. Final diagnosis was confirmed by histopathology and/or clinical follow-up for at least 6 month. Results: Of 2928 cases, 295 (10.1%) were identified to have ATU. ATU showed seasonal variation in incidence and was most frequently detected in the winter (12.6%), however, there was no significant difference in the incidence of ATU according to other clinical factors. In 295 cases with ATU, 210 were clinically and pathologically confirmed as benign or malignant and 5 (2.4%) of these were confirmed as malignant tonsillar lesions (4 primary cancer of MUO, 1 metachronous cancer of hypopharyngeal cancer). ATU with abnormal uptake of cervical L/N (4/19), MUO (4/7) were frequently associated with malignant tonsillar lesion (p Conclusions: Incidental tonsillar asymmetry on FDG PET was commonly observed with seasonal variation but showed low malignant prevalence. Therefore, most of the incidental asymmetric tonsillar FDG uptake lesions is not clinically significant except in cases with MUO.