[Diagnostic imaging of thyroid tumor]

Recently, thyroid nodules are found frequently when other imaging test was performed, and selection of diagnostic methods and its handling have become a problem clinically. Although it is possible to differentiate the malignant tumor from benign one using B-mode ultrasound, it can be obtained more detailed information in combination of other modalities such as color Doppler and tissue elasticity imaging (elastography). The malignant B-mode findings are irregular shape, indistinct border, hypoechoic and inhomogeneous internal echo, and fine calcification. CT/MRI is useful to evaluate the extention of thyroid cancer to adjacent organs beyond the thyroid capsule. It is also useful to evaluate distant metastases to lung or brain of thyroid cancer. In nuclear medicine, 125I scintigraphy is used to measure thyroid uptake rate, 131I scintigraphy is used to investigate the distant metastasis of thyroid cancer. It is necessary to be careful that some false-positive cases exist in 18FDG-PET.