MR imaging of primary leiomyosarcoma of the thyroid gland.

Primary leiomyosarcoma of the thyroid gland is extremely rare and radiological information on this tumor is scant. We presented radiological findings on primary thyroid leiomyosarcoma in a 66-year-old woman in which anaplastic carcinoma was suspected based on clinical and cytological features and discussed the radiological clues to distinguish between the two diseases. Ultrasonography showed an ill-defined hypoechoic mass without halo in the left lobe and the isthmus of the thyroid gland. Computed tomography depicted a low-density mass with calcification and necrosis, which invaded the thyroid cartilage. No lymphadenopathy was seen. The tumor was demonstrated as an isointense mass on T1-weighted MR images and a mass of intermediate signal on T2-weighted images. The tumor showed a fair enhancement on gadolinium-enhanced T1-weighted images. Although the radiological picture was nonspecific, primary thyroid leiomyosarcoma appeared less invasive and far less frequent in developing nodal metastasis than anaplastic carcinoma in light of the literature.