Abstract
Ectopic parathyroid adenoma can be seen in various locations. Sometimes ultrasound and even fine needle aspiration studies cannot distinguish this lesion from thyroid lesions. A 29-year-old woman with a prominent nodule of left thyroid lobe was referred to surgical department. Thyroid function test were normal. She had no family history of parathyroid disease, other endocrine disease, and any other malignancies and had received no radiation. Ultrasonography revealed a solid and hypoechoic mass, 25x20 mm in size, with a regular shape and contour without calcification in the inferior of left lobe of the thyroid gland. For definite diagnosis, immunohistochemistry study of the lesion with three markers was done. Finally, PTH marker was positive in cytoplasms of cells so parathyroid adenoma was confirmed. Fine needle aspiration of the nodule was suspicious for follicular neoplasm; however, postoperative histopathology and immunohistochemistry revealed a parathyroid adenoma. Ultrasonography may be helpful to identify localized thyroid lesions especially in parathyroid adenoma.