Dual ectopic thyroid located at the tongue base and left parapharyngeal space with transient congenital hypothyroidism.

Ectopic thyroid is a rare developmental anomaly. In ectopic thyroid, thyroid tissue develops outside its normal position (anterior to the trachea), and it can occur within or outside the migratory pathway of the thyroid gland primordium. Ectopic thyroid tissue located in two sites is referred to as dual ectopic thyroid. This report describes a case of transient congenital hypothyroidism (CH) who had dual ectopic thyroid glands: one located at the base of the tongue (within the migratory pathway) and the other in the left parapharyngeal space (outside the migratory pathway). A 24-year-old woman, diagnosed with CH in the neonatal period, had been treated with levothyroxine. Since levothyroxine was discontinued at the age of 7 years, her thyroid function has remained normal. At 24 years of age, she was reevaluated because of throat discomfort. Although her thyroid function remained normal, ultrasonography revealed two ectopic thyroid masses. 99mTc thyroid scintigraphy confirmed thyroid tissue in both locations. Genetic analysis did not reveal any suspicious genetic changes related to CH. Currently, she is under observation without treatment. This rare case of dual ectopic thyroid with transient CH underscores the importance of anatomical evaluation and long-term follow-up in patients with neonatal thyroid disorders.