Abstract
Aim 18F-FDG PET/CT by combining both metabolic and anatomical informations has proven to be an effective modality for detecting many types of cancer. Some differentiated forms of cancer like differentiated thyroid carcinoma (DTC) are less FDG avid and thus less easily detectable. Nevertheless 18F-FDG PET/CT has been proved useful in DTC especially in case of suspected recurrent disease with negative whole-body radioiodine scintigraphy ( 131I WBS) and elevated thyroglobulin (Tg) or thyroglobulin autoantibodies (AbTg) levels. Impact on clinical management after 18F-FDG PET/CT examinations has been analyzed in patients with suspected recurrent DTC in this retrospective study. Methodology Fifty-five 18F-FDG PET/CT were performed in 45 patients with suspected recurrent or residual disease either because of elevated Tg/AbTg levels ( n = 45) or uncertain conventional imaging ( n = 10) including 131I WBS, cervical echography and CT scan if necessary. 18F-FDG PET/CT results were compared with histopatology and/or clinical follow-up with evaluation of impact on clinical management. Results Twenty-nine exams were positive (53 %). There were 20 true-positive (TP) (14 locoregional relapses and six with distant metastases) and nine false-positive (FP) (all cervical). SUV max median values of hypermetabolic foci were significantly higher in TP (5.1) than in FP (2.8). Overall, 20 (36 %) 18F-FDG PET/CT directly affected clinical management resulting in 13 (65 %) new surgical operations. Sensitivity, specificity, predictive positive value, predictive negative value and accuracy of 18F-FDG PET/CT were estimated for the whole group (respectively 83 %, 71 %, 69 %, 85 % and 76 %) and for two subgroups depending on Tg level (less or more than 1.2 ng/mL). Discussion and conclusion 18F-FDG PET/CT is a powerful and useful tool in patients with suspected DTC recurrence or residual disease and should be systematically performed when basal Tg level is above 1.2 ng/mL. Thanks to given anatomical informations it can guide surgical re-operation.
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