Epithelial Cyst of Thyroid.

A benign thyroid cyst lined by thyroid follicular epithelial cells lacking immunoreactivity to thyroglobulin is reported. The patient had a 3 yr history of a large cyst in the lateral anterior neck, with no symptoms of hyperthyroidism or hyperparathyroidism. Water-clear fluid was repeatedly aspirated; analysis indicated the absence of parathyroid hormone (PTH0), T3, and T4. Hemithyroidectomy revealed a simple epithelial cyst. Such cysts are rare, comprising approx 1% of thyroid nodules. A differential diagnosis of cystic neck lesions is presented and the possible pathogenesis of this cyst is discussed.