We report a case of lymphoepithelial cysts (LECs) of the thyroid gland that was treated by surgery at our institution. LECs are cystic lesions recognized in the head and neck region, that have been assumed to originate from embryonic remnants. Microscopically, the cysts are usually lined by squamous or squamoid epithelium, occasionally accompanied by ciliated columnar epithelium and mucous cells. The cyst wall contains abundant lymphoid tissue with germinal centers. LECs predominantly occur along the lateral neck, especially along the inside of the sternocleidomastoid muscle, when they are called lateral cervical cysts. LECs of the thyroid gland have been very rarely reported, but since they have the same histological features as lateral cervical cysts, some reports suggest that they also arise as a result of embryonic malformations. However, it still remains controversial as to whether LECs are derived from embryonic remnants or as a result of acquired inflammatory changes of pre-existing tissues. We considered that in our case, the epithelial component of the cysts developed as a result of squamous metaplastic change of thyroid follicular cells rather than from embryonic remnants.
