Could 18F-FDG-PET/CT avoid unnecessary thyroidectomies in patients with cytological diagnosis of follicular neoplasm?

PURPOSE: Preoperative diagnosis of thyroid nodules with "follicular neoplasm" (FN) based on fine-needle aspiration cytology (FNAC) forces thyroidectomy to exclude malignancy. This study explores if (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG-PET/CT) provides information enough to prevent unnecessary thyroidectomies in this clinical setting.

METHODS: This is a prospective study involving 46 consecutive patients scheduled for thyroidectomy due to follicular neoplasm diagnosis in FNAC (36 follicular, 10 Hürthle cell neoplasms, Bethesda classification) since January 2009 until April 2012. All patients underwent preoperative (18)F-FDG-PET/CT. Abnormal (18)F-FDG thyroid uptake was assessed visually and by measuring the maximum standard uptake value (SUV max). Results were compared with definitive pathology reports.

RESULTS: Thirteen out of 46 patients (28.3 %) were finally diagnosed with thyroid cancer. Focal uptake correlated with a greater risk of malignancy (p = 0.009). (18)F-FDG-PET/CT focal uptake showed sensitivity, specificity, positive and negative predictive values and overall accuracy of 92.3, 48.5, 41.4, 94.1 and 60.9 %, respectively. The optimal threshold SUV max to discriminate malignancy was 4.2 with an area under receiver-operating characteristic curve of 0.76 (95 % confidence interval, 0.60-0.90). Use of (18)F-FDG-PET/CT could reduce by 13-25 % the number of thyroidectomies performed for definitive benign nodules. However, it has demonstrated worse predictive ability in the subgroup of patients with diffuse uptake, oncocytic pattern in FNAC and lesions smaller than 2.

CONCLUSIONS: (18)F-FDG-PET/CT can play a role in the management of thyroid nodules larger than 2 cm cytologically reported as follicular neoplasm without oncocytic differentiation, allowing the avoidance of a significant number of thyroidectomies for definitive benign lesions.