Objective: The aim of this study was to compare the clinical usefulness of MRI and radioiodine (¹³¹I) whole-body scintigraphy for the detection of lymph node metastases in differentiated thyroid carcinoma (DTC).
Materials and methods: After surgery and ¹³¹I therapy, 40 patients with DTC underwent ¹³¹I whole-body scintigraphy and MRI. Each patient was clinically suspected of having or already had evidence of nodal recurrences (confirmed by laboratory studies, cytologic analysis, or whole-body scintigraphy). Planar whole-body scintigraphy was done after administration of 111 MBq of ¹³¹I, and MRI was done using spin-echo T1- and T2-weighted imaging, T1-weighted spin-echo imaging with fat suppression, and STIR sequences.
Results: MRI detected nodal metastases as partly or entirely cystic and as heterogeneously enhanced on contrast-enhanced T1-weighted images. Hyperintense cystic areas appeared on T1- and T2-weighted images and STIR sequences in 57% of cases. Nodal metastases showed extracapsular spread in 24% of patients. MRI results were true-positive in 76%, true-negative in 90%, false-negative in 24%, and false-positive in 11% of cases, whereas ¹³¹I whole-body scintigraphy results were true-positive in 71%, true-negative in 91%, and false-negative in 29% of cases. There were no false-positive results of ¹³¹I whole-body scintigraphy. False-negative whole-body scintigraphy was induced by tumor dedifferentiation. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of MRI were 76.2%, 89.5%, 82.5%, 88.9%, and 77.3%, respectively, and the corresponding values for ¹³¹I whole-body scintigraphy were 71.4%, 100%, 85%, 100%, and 76%, respectively.
Conclusion: Whole-body scintigraphy is more specific than MRI in the detection of nodal metastases in patients with DTC. The principal value of MRI is in non-iodine-avid recurrences and in evaluation of mediastinal foci.