Purpose: To compare the accuracy of FDG PET/CT and ultrasonography (US) for detection of recurrence or metastasis after surgical treatment in patients with differentiated thyroid carcinoma.

Materials and methods: One hundred and twenty-eight patients with differentiated thyroid carcinoma, who had previously undergone neck operation, were evaluated with FDG PET/CT and US. The two studies were performed within 3 months of each other. Diagnosis of recurrence or metastasis was based on histological results. The results of FDG PET/CT and US were analyzed and sensitivity and specificity values were calculated statistically.

Results: Recurrence or metastasis occurred in 40 out of 128 patients. Thirty-one patients were detected in both FDG PET/CT and US. Eight patients were detected only in US. One patient who had high SUV on FDG PET/CT was not detected by US due to its location which was just posterior to thyroid cartilage. The sensitivity, specificity, accuracy, positive, and negative predictive values of FDG PET/CT were 80%, 82%, 82%, 68%, and 90%, respectively. Whereas, those of US were 97%, 85%, 89%, 75%, and 99%. US-guided percutaneous needle aspiration was performed in 57 recurrent or metastatic lesions of 37 patients. Twenty-eight lesions of 57 recurrences or metastasis occurred in level VI.

Conclusion: In our study, US of neck proved to be more accurate than FDG PET/CT. To detect recurrent or metastatic disease after surgical treatment in patients with differentiated thyroid carcinoma, US of neck is a better screening modality.