Thyroid metastasis from rectal carcinoma coexisting with Hashimoto's thyroiditis: gray-scale and power Doppler sonographic findings.

We present the gray-scale and power Doppler sonographic findings in a case of rectal carcinoma metastasis to the thyroid that mimicked a primary thyroid neoplasm and coexisted with Hashimoto's thyroiditis in a 67-year-old man. Gray-scale sonography revealed a hypoechoic mass with ill-defined borders in the left lobe of the thyroid; the mass extended through the isthmus to the right lobe. Sonography also showed multiple enlarged cervical lymph nodes. Power Doppler sonography showed increased flow in the nontumorous thyroid gland and decreased flow in the tumor. This contributed to the differentiation between the tumor and the remainder of the thyroid, which was involved with Hashimoto's thyroiditis.