Background: Suspected recurrence of thyroid carcinoma is a diagnostic challenge when findings of both a radio\niodine whole body scan and ultrasound are negative. PET/CT and MRI have shown to be feasible for detection of\nrecurrent disease. However, the added value of a consensus reading by the radiologist and the nuclear medicine\nphysician, which has been deemed to be helpful in clinical routines, has not been investigated. This study aimed to\ninvestigate the impact of combined FDG-PET/ldCT and MRI on detection of locally recurrent TC and nodal\nmetastases in high-risk patients with special focus on the value of the multidisciplinary consensus reading.\nMaterials and methods: Forty-six patients with suspected locally recurrent thyroid cancer or nodal metastases\nafter thyroidectomy and radio-iodine therapy were retrospectively selected for analysis. Inclusion criteria comprised\nelevated thyroglobulin blood levels, a negative ultrasound, negative iodine whole body scan, as well as combined\nFDG-PET/ldCT and MRI examinations.\nNeck compartments in FDG-PET/ldCT and MRI examinations were independently analyzed by two blinded\nobservers for local recurrence and nodal metastases of thyroid cancer. Consecutively, the scans were read in\nconsensus. To explore a possible synergistic effect, FDG-PET/ldCT and MRI results were combined. Histopathology\nor long-term follow-up served as a gold standard.\nFor method comparison, sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy\nwere calculated.\nResults: FDG-PET/ldCT was substantially more sensitive and more specific than MRI in detection of both local\nrecurrence and nodal metastases. Inter-observer agreement was substantial both for local recurrence (�º = 0.71) and\nnodal metastasis (�º = 0.63) detection in FDG-PET/ldCT. For MRI, inter-observer agreement was substantial for local\nrecurrence (�º = 0.69) and moderate for nodal metastasis (�º = 0.55) detection. In contrast, FDG-PET/ldCT and MRI\nshowed only slight agreement (�º = 0.21). However, both imaging modalities identified different true positive results.\nThus, the combination created a synergistic effect. The multidisciplinary consensus reading further increased\nsensitivity, specificity, and diagnostic accuracy.Conclusions: FDG-PET/ldCT and MRI are complementary imaging modalities and should be combined to improve\ndetection of local recurrence and nodal metastases of thyroid cancer in high-risk patients. The multidisciplinary\nconsensus reading is a key element in the diagnostic approach.
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