Lymphoepithelial cyst of the thyroid mimicking malignancy on sonography.

A 52-year-old man presented with a palpable left neck mass that had been present for several months. A sonogram showed a 2-cm hypoechoic mass with internal coarse macrocalcifications in the left lobe of the thyroid gland. CT revealed a well-demarcated hypodense mass within the left thyroid lobe. A left thyroidectomy was performed at the patient's request because of the possibility of malignancy based on sonographic findings. Pathologically, the mass was composed of pseudostratified ciliated columnar epithelial cells simulating respiratory epithelium surrounded by florid lymphoid hyperplasia with germinal centers, consistent with an intrathyroidal lymphoepithelial cyst.