Diffusion-weighted MRI is not superior to FDG-PET/CT for the detection of neck recurrence in well-differentiated thyroid carcinoma.

ABSTRACT

BACKGROUND: Management of patients with well-differentiated thyroid carcinoma (WDTC) and positive thyroglobulin (Tg)/negative iodine-131 whole body scintigraphy (WBS) remains challenging. Here, we investigate the specific role of diffusion-weighted magnetic resonance imaging of the neck (DW-MRI) as compared to rhTSH stimulated FDG-PET/CT in such patients. METHODS: Patients with WDTC, positive Tg/negative WBS were prospectively enrolled in the study. FDG-PET/CT and neck DW-MRI were performed on the same day after rhTSH stimulation. Neck-US was performed 24 hours after FDG-PET/CT and MRI to guide fine-needle aspiration (FNA). Patients with positive FNA underwent surgery. Patient with negative workup underwent new explorations at 6 and 18 months. RESULTS: A total of 86 FDG-PET/CT and 83 DW-MRI tests were performed in 40 patients (23 females; 17 males; 52±16 years). For detection of neck recurrences, sensitivity was equivalent for FDG-PET/CT and to DW-MRI at baseline (46% vs. 43%), at 6 months (30% vs. 20%) and at 18 months (11 vs. 10%). The comparison with a non-weighted Kappa test shows significant concordance between FDG-PET/CT and DW-MRI (K=0.741±0.062; P<0.0001). A relationship was observed between Tg and results of FDG-PET/CT, but not for DW-MRI. FDG-PET/CT permitted to detect iodine-refractory distant metastasis in 4 patients. CONCLUSIONS: In Tg-positive/WBS-negative DTC patients, low tumour burden, neck DW-MRI does not provide additional information compared to rhTSH-stimulated FDG-PET/CT. FDG-PET/CT has the best sensitivity, is acceptable for patients, allows whole body exploration and distant metastasis detections, and is correlated with Tg levels.