Lingual thyroid


 * Associate Editor-in-Chief: Awni D. Shahait, M.D.[mailto:awnishahait@yahoo.com], The University of Jordan

Synonyms and keywords: LT

Overview
Lingual Thyroid (LT) is a rare developmental thyroid anomaly in which the thyroid gland is located in the medial line at the base of the tongue.

Incidence
The incidence is 1 in 100,000. This condition represents 90% of all cases of ectopic thyroid.

Sex
Females are affected more frequently.

Age
There is no age predisposition.

Pathophysiology
Although the pathogenesis of lingual thyroid is not fully understood, it has been speculated to be due to failure of migration of thyroid tissue along the path from ventral floor of the pharynx to its normal location and sequestration within the tongue substance leads to the development of lingual thyroid.

Infants and Children
The abnormality may be identified during routine screening.

Adolescents
Adolescents may present with dysphagia or symptoms of oropharyngeal obstruction. As a response to the increased metabolic demands for thyroid hormone during puberty, hypertrophy of the gland may be seen.

Conditions of Metabolic Stress
A similar response is also encountered during other metabolic stress conditions like pregnancy, infections, trauma, menopause.

Physical Examination
LT usually presents itself as a midline, nodular mass at the base of the tongue. The surface of the lesion is usually smooth and vascularity can be seen.

Imaging
A scintigraphic scan is the imaging modality of choice. It detects the ectopic thyroid tissue within the lingual thyroid, and also confirms the presence of a functioning thyroid gland, which is reported to be absent in 70% of LT cases.

Laboratory Findings
It’s reported that up to 70% of patients with lingual thyroid have hypothyroidsm and 10% suffer from cretinism.

Indications for Treatment
Surgical treatment is indicated when there are symptoms such as dysphagia or dyspnea, and/or complications such as ulceration, bleeding or the presence of rapidly growing mass, suggesting malignant transformation.

Iodine 131 Ablation
In patient with obstructive symptom, Iodine 131 ablation of the ectopic thyroid tissue has been proven successful and may be less invasive than syrgery.

Transoral Approach
The transoral approach is the most frequent approach.

Lateral Pharyngotomy
Lateral pharyngotomy is useful only in the treatment of lesions located in the posterior wall or lateral walls of hypopharynx. It provides a wide exposure compared to transoral approach.

Transhyoid Approach
Another approach is transhyoid which is more advantageous than the other two approaches in that it provides wider and a direct exposition through the midline.

Transplantation of Thyroid Tissue
In patient lacking thyroid tissue in the neck, the lingual thyroid can be excised and autotransplanted to the muscles of the neck.