Intrathyroid Thyroglossal Duct Cyst Extending into the Mediastinum: A Case Report and Review of Literature

Thyroglossal duct cyst (TGDC) is the most common congenital cyst in the neck and usually presents in children. It is most commonly located at the infrahyoid level. However, intrathyroid TGDC in the adult is extremely rare and its pathogenesis remains unclear. Curiously, an intrathyroid TGDC was found on the lateral aspect of the inferior pole of the thyroid gland. Given the unique position of this lesion, and its capacity to stimulate other nodules in the thyroid, it should be differentiated from other lateral neck masses, such as: thymic cysts, branchial cleft cysts, cystic hygroma, lipomas, lymphadenopathies, cervical teratomas, and lymphomas. In this case, a separate cystic mass was found in the right inferior pole of the thyroid gland and extended to the mediastinum. We confirmed it as TGDC by pathology and histological examination.