RESUMO
Primary thyroid leiomyosarcoma (LMS) is an extremely rare tumor. We report a case of a 47-year-old male with a rapidly growing neck mass and disfagia. Preoperative investigations were diagnostic of anaplastic carcinoma. Total thyroidectomy with partial esophagectomy and dissection of right infrahyoid muscles was performed. Through histolological and immunohistochemical evaluations a primary thyroid high-grade LMS was diagnosed. At 2 months of follow-up a local recurrence was detected and consequently the patient was submitted to chemotherapy with partial response. He is still alive 9 months after surgery. Diagnosis of primary thyroid LMS is difficult due to its similarity to other more common thyroid tumors. To date, there is no standard therapy and prognosis is poor.