Lingual Thyroid

Late in the first month of life the anlage of the thyroid gland descends from the posterior dorsal midline of the tongue (actually the floor of the pharyngeal gut) to its final position in the lower neck. The initial site of descent eventually becomes the foramen caecum, located in the midline at the junction of the anterior (oral) tongue and the tongue base. If the embryonic gland does not descent normally, ectopic or residual thyroid tissue (technically either a choristoma or hamartoma) may be found between the foramen caecum and the epiglottis.

Of all ectopic thyroids, 90% are found on the lingual dorsum, where they are called lingual thyroid or ectopic lingual thyroid.  Rarely, parathyroid glands are associated with the ectopic thyroid tissue. Other sites of ectopic thyroid deposition include the cervical lymph nodes, submandibular glands and the trachea. Approximately two-thirds of patients with lingual thyroid lack thyroid tissue in the neck.

The lingual thyroid is four times more common in females than in males. It presents as an asymptomatic nodular mass of the posterior lingual midline, usually less than a centimeter in size but sometimes reaching more than 4 cm. in size (Figure 1).  Larger lesions can interfere with swallowing and breathing, but most patients are unaware of the mass at the time of diagnosis, which is usually in the teenage or young adult years. Up to 70% of patients with lingual thyroid have hypothyroidism and 10% suffer from cretinism.

The lingual thyroid consists of a nonencapsulated collection of embryonic or mature thyroid follicles which may extend between muscle bundles, raising suspicions of malignant invasion. The follicular cells, however, are normal or atrophic in appearance (Figure 2). All diseases capable of affecting the normal thyroid gland can, of course, affect the glandular tissue entrapped in the tongue. Thyroid adenoma, goiter, hyperplasia, inflammation, and carcinoma occur in lingual thyroids and must, therefore, be evaluated in the same fashion as would any biopsied thyroid gland.  Parathyroid tissue may be seen but has not been neoplastic in reported cases.

Surgical excision or radioiodine therapy are effective treatments for lingual thyroid, but no treatment should be attempted until an ¹³¹iodine radioisotope scan has determined that there is adequate thyroid tissue in the neck.  In those patients lacking thyroid tissue in the neck, the lingual thyroid can be excised and autotransplanted to the muscles of the neck. Most cases require no treatment and biopsy should be considered with caution because of the potential for hemorrhage, infection or release of large amounts of hormone into the vascular system (thyroid storm). Occasional patients with parathyroid tissue associated with their lingual thyroid have developed tetany after their inadvertent removal.

Rare examples of thyroid carcinoma arising in the mass have been reported, almost always in males, but an enlarged lingual thyroid is more likely to reflect a normal compensatory response to thyroid hypofunction.  Endocrine evaluation for hypothyroidism should, therefore, be done in such cases. In this light, it is important to know that three of every four patients with infantile hypothyroidism have ectopic thyroid tissue.

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Diaz-Arias AA, et al. Follicular carcinoma with clear cell change arising in lingual thyroid. Oral Surg Oral Med Oral Pathol 1992; 74:206-211.

Williams JD, Sclafani AP, Slupchinskij O, Douge C. Evaluation and management of the lingual thyroid gland. Ann Otol Rhinol Laryngol 1996; 105:312-216.