Retrospective evaluation of focal hypermetabolic thyroid nodules incidentally identified by 18 F-FDG PET/CT in a large population

Objective To investigate the prevalence of focal hypermetabolic thyroid nodules incidentally detected by 18 F-FDG PET/CT in a relatively large population and explore its value in differentiating malignancy from benign thyroid nodules.Methods During August 2007 to March 2010,8463 patients with no history of thyroid cancer or thyroidectomy underwent 18F-FDG PET/CT.Among them,145 patients were found to have abnormal hypermetabolic thyroid nodules.Sixty-eight patients were conformed with histopathological or clinical follow-up,including 37 with malignancy and 31 with benign nodules ( male 21,female 47,average age (53.66 ± 10.85)y).The SUVmax,nodule size,single or multiple nodules,with or without calcification and patient's age were chosen as the parameters for predicting malignancy in hypermetabolic thyroid nodules.Univariate analysis was performed using t test,x2 test and Fisher exact test.Binary logistic regression was performed for multi-variate analysis.The AUCs of SUVmax and logistic regression analysis were compared.Results The incidence of focal hypermetabolic thyroid nodules was 1.71％ ( 145/8463 ),with malignancy rate 54.41％ ( 37/68 ).The SUVmax of benign and malignant nodules were 5.13 ±4.02 and 7.61 ± 4.78,respectively ( t =2.235,P =0.029 ).Logistic regression indicated that SUVmax,with or without calcification,single or multiple nodules,nodule size and patient's age were all the predictors for malignancy in hypermetabolic thyroid nodules.The AUC of logistic regressive model( AUCL ) and SUVmax (AUCs )were 0.878 ±0.043 (95％ CI:0.793-0.962,P＜0.05) and 0.694 ±0.067 (95％ CI:0.562-0.825,P＜0.05),respectively (P ＜ 0.05).Conclusions Focal hypermetabolic thyroid nodules incidentally identified by 18F-FDG PET/CT come with high rate of thyroid malignancy.Differential diagnosis could be improved significantly using SUVmax and logistic regressive model aided by other parameters from 18F-FDG PET/CT as well as patient's age. Key words: Thyroid nodule; Tomography, emission-computed; Tomography, X-ray computed; Diagnosis, differential; Deoxyglucose