MRI features of histological subtypes of thyroid cancer in comparison with CT findings: differentiation between anaplastic, poorly differentiated, and papillary thyroid carcinoma

Purpose: This study aimed to evaluate the MRI features of the main histological subtypes of thyroid cancer and enable differentiation between anaplastic thyroid carcinoma (ATC), poorly differentiated thyroid carcinoma (PDTC), and papillary thyroid carcinoma (PTC). Materials and methods: This study included 79 patients with histopathologically proven thyroid cancer (14 ATCs, 8 PDTCs, and 57 PTCs) who underwent neck MRI. MRI images were retrospectively reviewed and compared between the three pathologies. Results: The maximum diameter was larger in ATCs and PDTCs than in PTCs (65.2 mm and 38.4 mm vs. 26.0 mm, p < 0.01). The signal intensity ratio of the solid components on T2-weighted images (T2WIs) was higher in ATCs than in PTCs (1.13 vs. 0.89, p < 0.05). The predominant signal intensity of the solid components on T2WI exhibited hyperintensity relative to the spinal cord in ATCs more frequently than in PTCs (71% vs. 30%, p < 0.01), whereas hypointensity was more frequent in PTCs than in ATCs and PDTCs (60% vs. 0% and 13%, p < 0.01). Intratumoral ring-shaped hypointensity on T2WI was more frequent in ATCs than in PDTCs and PTCs (64% vs. 13% and 18%, p < 0.01). An ill-defined margin was more frequent in ATCs and PDTCs than in PTCs (93% and 63% vs. 25%, p < 0.01). Extrathyroidal extension, tracheal invasion, esophageal invasion, vascular invasion, and venous thrombosis were more frequently observed in ATCs than in PTCs (p < 0.05). Conclusions: MRI could characterize the differences between ATCs, PDTCs, and PTCs.