Abstract
A 70-year-old woman noticed a nodule in the lower anterior aspect of the neck along with horseness of voice. Cervical ultrasonography revealed a homogeneous and hypoechoic tumor of 31 mm in diameter in the lower pole of the left thyroid, in addition to swelling in the perijugular lymph nodes. Cervical computed tomography demonstrated a homogeneous tumor in the lower pole of the left thyroid to the superior mediastinum and small bilateral nodules in the lungs. Although fine-needle aspiration biopsy cytology from the tumor mass is considered to be insufficient specimens, we diagnosed thyroid cancer with lymph nodes metastases based on image diagnosis. Subtotal thyroidectomy, adjacent lymphadenectomy, left recurrent laryngeal nerve resection, and left branchiocephalic vein resection were performed. Immunohistochemistry demonstrated positive staining of tumor cells for CD5 and negative for TTF-1 and thyroglobulin. As a result, we diagnosed as carcinoma showing thymic-like differentiation (CASTLE). Postoperative radiotherapy was subsequently performed, and no recurrence has been noted in a three-year period. Hence, CASTLE should be considered as a differential diagnosis in tumors of the lower pole of the left thyroid to the superior mediastinum.
