The role of F-18 FDG PET/CTın the preoperative evaluation of thyroid nodules with ınconclusive fine needle aspiration biopsy results

Aim: The aim of this study was to determine the role of F-18 FDG-PET/CT in the preoperative evaluation of thyroid nodules with inconclusive fine needle aspiration biopsy results.Material and methods: Fourty six patients with thyroid nodules who had inconclusive FNA results for malignancy (possible follicular neoplasia and hurtle cell neoplasia) and who were evaluated at General Surgery and Endocrinology Clinics of Cukurova University Medical Faculty and referred to Nuclear Medicine Deparment for whole body F-18 FDG PET/CT scan before lobectomy or total thyroidectomy between years 2009-2011 were prospectivaly studied. The F-18 FDG uptake patterns and SUVmax of the thyroid nodules were compared with postoperative histopahologic results.Results: Of the total 46 patients, 40 (87.0%) were female and 6 (13.0%) were male. Pathologic evaluation of 46 patients revealed 29 (63%) benign and 17 (37%) malignant nodules. On the ultrasonographic evaluation of the thyroid nodules of 46 patients, 19 (41,3%) had solitary and 27 (58.7 %) had 2 or more thyroid nodules. Nine (47.4 %) of the 19 solitary nodules were malign, 10 (52.6 %) were benign. According to nodule characteristics, 33 (71.7%) patients had solid, 13 (28.3%) had mixed (containing solid and cystic components) nodules. The echo ultrasonographic patterns of the thyroid nodules in 21 (45.7 %) patients were isoechoic, in 23 (50.0 %) were hypoechoic and in 2 (4.3%) were hyperechoic.The mean SUVmax was 5.6±3.5 in malignant cases, 3.8±4.2 in the benign cases and 4.5±4.0 in all cases. No significant difference was obtained in SUVmax values of the malignant and benign nodules (p=0,160). In evaluation with F-18 FDG PET/CT, the patients were categorized in 4 groups according to F-18 FDG uptake patterns as focal, diffuse, irregular and normal basal uptake. Of the 17 patients who had malignant histopathologic diagnosis, 15 (88,2%) had focal uptake, 1 (5.9%) had irregular uptake and 1 (5.9 %) had normal basal uptake. The patients who had benign cytology , 17 (58.6 %) had irregular uptake, 8 (27.6%) had basal uptake, 2 (6.9 %) had diffuse uptake and 2 (6.9%) had focal uptake patterns in thyroid glands. Focal F -18 FDG uptake was the most statistically significant observed pattern in malignant cases (p=0,001).Conclusıon: On ultrasonographic evaluatıon, the number, the echogenicity and the diameter of the thyroid nodules had no statistically significant impact on the benign-malignant determination. On PET-CT evaluatıon, no distinctive SUVmax cut-off values was observed in benign and malignant nodules. We found F-18 FDG uptake pattern as the most differential feature of malignant and benign nodules. In malignant cases focal uptake pattern was seen markedly. This study shows that F-18 FDG PET/CT has an important role in the management of patients who had FNA findings inconclusive for malignancy.Key words: F-18 FDG PET/CT, FDG uptake patern, SUVmax, FNA, thyroid nodule.