MR findings with dynamic evaluation in Riedel's thyroiditis.

We reported the findings on MRI in a patient with proven Riedel's thyroiditis. The lesion was seen as slightly heterogeneous hypointensity on both T1- and T2-weighted images and had a mild enhancement after administration of gadpentate dimeglumine (Gd-DTPA). Dynamic MR study showed gradual increase in signal intensity of the lesion. These findings were different from those of thyroid neoplasms and were considered to reflect the mixture of inflammatory cells infiltration and fibrosis of Riedel's thyroiditis.