MRI versus ¹³¹I whole-body scintigraphy for the detection of lymph node recurrences in differentiated thyroid carcinoma

Abstract

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 falsenegative 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. © American Roentgen Ray Society.