Lingual thyroid

Synonyms and keywords: LT

Overview

Lingual Thyroid (LT) is a rare developmental thyroid anomaly with reported incidence of 1 in 100000, affecting females more frequently. There is no age predisposition and can be seen in every age. Usually it’s located in the med line and in the base of the tongue. It represents 90% of all cases of ectopic thyroid.

Embriology

Although the pathogenesis of lingual thyroid is not fully understood, it suggested 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 LT.

Diagnosis

Symptoms

The clinical presentation of LT could be classified into two groups according to the appearance of the symptoms which its severity depends on size of lingual thyroid tissue. The first group consists of infants and children who had the abnormality found during routine screening. Patients with dysphagia and oropharyngeal obstructive symptoms during or before the puberty constitute the second group that our patient belonged to this group. As a response to the increased demand for thyroid hormone during puberty, hypertrophy of the gland is seen. A similar response is also encountered during other metabolic stress conditions like pregnancy, infections, trauma, menopause etc. It’s reported that up to 70% of patients with lingual thyroid have hypothyroidsm and 10% suffer from cretinism.

Physical Examination

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

Imaging

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

Treatment

The standard treatment of lingual thyroid varies. Surgical treatment is preferred when there are symptoms like dysphagia or dyspnoea, and also complications such as ulceration, bleeding or rapidly growing mass, suggesting malignant transformation. In patient with obstructive symptom, Iodine131 ablation of ectopic thyroid tissue has been proven successful and may be advantageous than syrgery. In patient lacking thyroid tissue in the neck, the lingual thyroid can be excised and autotransplanted to the muscles of the neck. Various surgical approaches have been recommended. Transoral approach has been reported to be the most frequently used one. Another approach is lateral pharyngotomy which 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. 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.