Background: The detection of recurrence or metastasis might be challenging in patients,
who underwent total thyroidectomy and radioactive iodine therapy for Differentiated Thyroid Carcinoma
(DTC), with increased serum Thyroglobulin (Tg) levels and negative 131I whole body scan
Aims: The purpose of this study was to compare the ability of Magnetic Resonance Imaging (MRI)
and 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F FDG
PET-CT) to detect recurrence or cervical and upper mediastinal metastases in postoperative DTC
patients who had negative 131I-WBS despite elevated serum Tg levels.
Study Design: This study has a retrospective study design.
Methods: We evaluated cervical and upper mediastinal MRI and 18F FDG PET-CT of 32 postoperative
patients with DTC (26 patients with papillary thyroid carcinoma and 6 patients with follicular
Results: We evaluated 44 lesions in 32 patients. For all lesions, the Positive Predictive Value,
(PPV) Negative Predictive Value (NPV), sensitivity, specificity, and accuracy of MRI were 81.4%,
76.4%, 84.6%, 72.2%, and 79.5% respectively. The PPV, NPV, sensitivity, specificity, and accuracy
of 18F FDG PET-CT were 100.0%, 85.7%, 88.4%, 100.0%, and 93.1%, respectively.
Conclusion: Although we could not replace 18F FDG PET-CT, MRI might be used as an adjunct to
18F FDG PET-CT for the evaluation of recurrent or cervical and upper mediastinal metastatic thyroid
cancers; however, MRI is inadequate for the detection of metastases in small lymph nodes.