The rare entity of primary T-cell lymphoma of thyroid gland may pose great diagnostic challenges to the clinician. We report a case of malignant T-cell lymphoma of the thyroid gland that developed in a 36-year-old man with a past history of Hashimoto's thyroiditis. The chief complaint was a rapidly growing neck mass and pressure symptoms. This man, diagnosed with Hashimoto's thyroiditis for the previous several years. CT and ultrasonographic examination revealed a diffuse large thyroid gland with cervical lymphadenopathy. It was suspected that thyroid lymphoma involved regional lymph nodes. Fine needle aspiration cytology diagnosed chronic thyroiditis， and ultrasound-guided core needle biopsy was performed. Finally, peripheral T cell lymphoma was diagnosed.
Keywords: T-cell lymphoma; puncture biopsy; thyroiditis; ultrasonography.
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