ENT Conjoint Final Exam 2005 – Short Notes
Lingual thyroid is caused by a rare developmental disorder due to aberrant embryogenesis during the descent of thyroid gland to the neck.
It is the most frequent ectopic location of thyroid gland.
The incidence of LT is reported as 1:100,000.
It is 7 times higher in females.
Hickmann recorded the first case of lingual thyroid in 1869. Montgomery stressed that for a condition to be branded as lingual thyroid, thyroid follicles should be demonstrated histopathologically in tissues sampled from the lesion
Early in embryogenesis, thyroid gland appears as proliferation of endodermal tissue in the floor of the pharynx between tuberculum impar and hypobranchial eminence (this area is the later foramen caecum).Normally thyroid gland descends along a path from foramen cecum in the tongue, passes the hyoid bone, to the final position in front and lateral to the second, third, and fourth tracheal rings by 7 weeks gestation. During this descent thyroid tissue retains its communication with foramen cecum. This communication is known as thyroglossal duct. Once the thyroid reaches its final destination, the thyroglossal duct degenerates.
Persistence of thyroglossal duct even after birth leads to the formation of thyroglossal cyst. These cysts usually arise from the remnants of thyroglossal duct and can be found anywhere along the migration site of thyroid gland. This descent may arrest anywhere along this path and this condition may remain unnoticed until puberty. 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. 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.
Majority of these patients are asymptomatic.
oropharyngeal obstruction may include dysphagia (mild or severe), dyspnea and dysphonia, fullness in the throat, sleep apnoea.
Stridor is most common in neonates.
About 33% of the patients show hypothyroidism findings.
Bleeding is rarely described.
The clinical presentation of LT could be classified into two groups according to the appearance of the symptoms: infants and young children whose lingual thyroid is detected via routine screening may suffer from failure to thrive and mental retardation, or even severe respiratory distress, resulting in a medical emergency. Other cases may present with onset of slowly progressing dysphagia and symptoms of oropharyngeal obstruction before or during puberty. This occurs as a response to the increased demand for thyroid hormone in these hypermetabolic states. Similar response is also encountered during other metabolic stress conditions like pregnancy, infections, trauma, menopause, etc.
head and neck examination :
midline, nodular pinkish mass in the base of the tongue. On palpation this mass could be felt as solid firm and fixed mass. It would be seen attached to the tongue at the junction of anterior 2/3 and posterior 1/3. approximately foramen cecum is supposed to be present. palpate the neck in the region of thyroid to ascertain whether normal thyroid tissue is present in the neck.
- thyroid function tests (often demonstrate normal gland functions).
- USG neck no thyroid in neck, Xray neck (globular mass at tongue base hyoid region), CT scan neck
- Technetium scanning confirms the presence of ectopic thyroid tissue at the base of tongue.
- FNAC, LT resembles normal thyroid tissue.
1.Suppressive therapy with exogenous thyroid hormone should be tried first in order to decrease the size of the gland.
- surgical removal if emergency. levothyroxine therapy should be initiated after as the lingual thyroid is the only functioning thyroid tissue found in 70% of these patients.