Figure 1. A midline mass is noted at the base of the tongue.
The term lingual thyroid refers to thyroid tissue located at the base of the tongue. The abnormal placement is the result of complete absence of descent of the thyroid anlage during the early stages of development.
Thyroid tissue develops early in embryogenesis. On roughly day 16 of fetal life, the medial thyroid anlage develops from an outpocket of epithelial cells extending from the floor of the primitive pharynx between the first and second branchial arches. The thyroid precursor cells then rapidly divide, obliterating the lumen of the diverticulum and expanding laterally to form the bilobed gland. The medial anlage is then pulled into place as the developing heart descends, maintaining its connection to the pharynx through the thyroglossal duct.1
Beginning at the foramen cecum of the tongue, the medial anlage passes through the musculature of the tongue, passes the hyoid bone, and by 7 weeks' gestation settles anterior and lateral to the second, third, and fourth tracheal rings.2 Once the thyroid reaches its final destination the thyroglossal duct fragments and degenerates.
Any functioning thyroid tissue found outside of the normal thyroid location is termed ectopic thyroid tissue. Although it is usually found along the normal path of development, ectopic tissue has also been noted in the mediastinum, heart, esophagus, and diaphragm.3- 6 Lingual thyroid is the result of failure of descent of the thyroid anlage from the foramen cecum of the tongue. The reasons for the failure of descent are unknown.
According to data collected from neonatal screening programs, primary congenital hypothyroidism occurs in approximately 1 in 4254 live births.7 Approximately 23% of these infants have ectopic thyroid tissue located predominately at the base of the tongue.7 The true incidence of lingual thyroid is unknown since many patients are asymptomatic until later in life, and some cases never come to medical attention.
Lingual thyroid glands are commonly discovered during evaluation for congenital hypothyroidism initiated by abnormal results from routine newborn thyroid screening tests. These infants are generally asymptomatic although if the thyroid is large, neonates may present with airway obstruction and stridor.
If the gland is functioning normally, children with lingual thyroid may remain asymptomatic until later in life. The disorder often presents during times of growth and increased metabolic activity such as puberty, pregnancy, and menopause.8 The lingual thyroid gland is generally smaller than the normally situated gland, and although thyrotropin may stimulate gland enlargement to increase the production of thyroid hormone, the hypertrophy is limited.9 Hypothyroidism occurs in 33% of patients.10 Obstructive symptoms include dysphagia, dysphonia, dyspnea, and a sensation of a foreign body in the throat.8,10,11
Replacement thyroid hormone is used to treat hypothyroidism and to shrink the size of the gland by decreasing endogenous thyrotropin effects. Surgical excision is necessary only when the mass causes life-threatening obstruction or excessive discomfort.2 The risk of hemorrhage is extremely high with surgical intervention owing to the vascular nature of the gland. Additionally, levothyroxine therapy should be initiated after surgical excision as the lingual thyroid is the only functioning thyroid tissue found in 70% of these patients.8
Accepted for publication February 22, 2000.
Reprints: Bernard L. Silverman, MD, Department of Endocrinology, Children's Memorial Hospital, 2300 Children's Plaza, Chicago, IL 60614-3394.
Picture of the Month. Arch Pediatr Adolesc Med. 2000;154(8):843-844. doi: