322 chapter 4 mutation were respectively obtained the contralateral PET incidentaloma. On histopathology, all four contralateral nodules were benign. In 15 (65%) patients, diagnostic and/or therapeutic consequences were considered unbeneficial yet minor (Table 11). Diagnostic confidence in [18F]FDG-PET/CT was high: only one of six patients who underwent surgery (three during and three after study follow-up) despite advised surveillance (Figure 1), was not fully reassured by the negative [18F]FDG-PET/CT result. The main reason for surgery in all six patients, however, was not the fear or suspicion of cancer, but increasing compressive symptoms causing discomfort. Noncompliance to the surveillance advice did not change the one-year therapeutic yield in the [18F]FDG-PET/CT-driven group, as patient crossover between surgical and non-surgical management occurred in both directions (Figure 1). Based on theoretical full compliance to the given treatment advice, a maximum 41% reduction in futile diagnostic surgeries for benign nodules (i.e., 26 [18F]FDG-negative nodules of 63 benign nodules) was estimated following full implementation of [18F]FDG-PET/CT (p=0.86). Subgroup analysis of the 101 non-Hürthle cell nodules (60 AUS/FLUS and 41 FN/SFN) and 31 Hürthle cell (HCN/SHCN) nodules was performed. The malignant/borderline rate was 17% (10/60) in Bethesda III as compared to 33% (24/72) in Bethesda IV nodules (p=0.03), of which 37% (15/41) in FN/SFN and 29% (9/31) in HCN/SHCN nodules (p=0.50). In non-Hürthle cell nodules, the fractions of unbeneficial management and prevented surgeries for benign nodules after one year were 37% (95% CI, 25%-49%) and 48% (95% CI, 33%-63%) in the [18F]FDG-PET/CT-driven group, as compared to 85% (95% CI, 68%-95%) (p<0.001) and 0% (95% CI, 0%-18%) (p<0.001) in the diagnostic surgery group (Table 12). Sensitivity, specificity, NPV, PPV, and benign call rate in non-Hürthle cell nodules were 92.0% (95% CI, 74.0%-99.0%), 50.0% (95% CI, 38.3%-61.7%), 95.0% (95% CI, 83.1%-99.4%), 37.7% (95% CI, 25.6%-51.0%), and 39.6% (95% CI, 30.0%-49.8%), respectively (Table 7). Therapeutic yield and diagnostic accuracy were similar in AUS/FLUS and FN/SFN nodules. In Hürthle cell nodules, [18F]FDG-PET/CT showed a benign call rate of only 3.2% (1/31). Consequently, [18F]FDG-PET/CT-driven management was not contributory to improve the diagnostic workup: the fractions of unbeneficial management and prevented surgeries for benign Hürthle cell nodules were low and similar in both FNAC=fine needle aspiration cytology. *: in one patient, TT was performed because Bethesda VI cytology was obtained from a third nodule during ultrasound and FNAC evaluation of the PET incidentaloma. On histology, this was a mere 3 mm PTC. The [18F]FDG-avid incidentaloma was benign. Therefore, this surgery is considered futile. **: two malignancies were located ipsilateral to the investigated thyroid nodule. ***: unbeneficial major consequences are defined as substantial therapeutic consequences, i.e., extension of diagnostic surgery to TT for a nodule with final benign histopathology. ****: Unbeneficial minor consequences include minor therapeutic consequences (i.e., nodulectomy in addition to hemithyroidectomy) and overdiagnosis for benign disease that without the [18F]FDG-PET/CT had likely never been detected nor evaluated.
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