Ectopic Thyroid Gland Intern 陳君豪 2005/08/22

Ectopic Thyroid The entire thyroid gland can fail to descend to its normal adult site In approximately 1 in 200,000 normal subjects and 1 in 6,000 patients with thyroid disease

Ectopic Thyroid The most frequent midline cervical masses in the pediatric population are thyroglossal duct cysts (TGDCs) Avoid the excision of what may be the only source of functioning thyroid tissue

Embryology During the fourth week of gestation, a ventral diverticulum of the foramen caecum is formed from the first and second pharyngeal pouches

Embryology This diverticulum, with its narrow neck connected to the tongue, descends in the midline of the neck as the thyroglossal tract to the position of the normal thyroid

Embryology The tract usually atrophies and disappears by the tenth week of gestation

Thyroglossal Duct Cysts The most common form of congenital cyst in the neck Cysts of epithelial remnants of the thyroglossal tract

Thyroglossal Duct Cysts

Thyroglossal Duct Cysts Patients with thyroglossal duct cysts often have ectopic thyroid glands 57% had ectopic thyroid tissue among patients with thyroglossal duct cysts

Ectopic Thyroid Prevalence is higher in females than in males, with a female-to-male ratio of 7:1 In approximately 1 in 200,000 normal subjects

Ectopic Thyroid Lingual and sublingual, prelaryngeal, intralaryngeal, intratracheal, submandibular site Aortic wall, intrathymic, retropharyngeal, intracardiac site, in the esophagus and in the abdomen

Ectopic Thyroid Lingual thyroid: descent is completely arrested at the level of the base of tongue

Ectopic Thyroid Sublingual or prelaryngeal position: partial descent Substernal ectopic gland: excessive migration Among ectopic thyroid glands, 90% are lingual and 10 percent occur in other sites

Parapharyngeal ectopic thyroid

Ectopic Thyroid In patients presenting with a lingual thyroid, over 70 percent have no thyroid tissue in the normal location

Symptoms and Signs Clinically, the majority of patients with thyroid ectopia are asymptomatic, so that the true incidence is unknown Obstructive symptoms and hypothyroidism have been observed

Symptoms and Signs The ectopic tissue is typically found incidentally though these masses can be symptomatic dyspnea, dysphagia, dysphonia, hemoptysis or hoarseness.

Diagnosis - US Ultrasound can localize and characterize anteromedial neck masses, the presence contour, and size is highly likely to be a normally functioning gland

Diagnosis - CT CT scans often reveal a homogenous hyperdense mass because of the high iodine content The thyroid gland also enhances because of its vascularity Not typically recommended in the routine evaluation of pediatric anterior neck masses because of radiation exposure

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Diagnosis - MRI Most useful in lingual thyroid cases for situations in which delineation of thyroid tissue from tongue muscle is difficult Lingual thyroid tissue is hyperintense compared with tongue musculature on both Tl and T2 MRI sequences, and it strongly enhances with contrast injection

Diagnosis - MRI MRI offers less radiation exposure than CT However, disadvantages include increased cost, longer imaging time, and necessitates the use of anesthesia in the pediatric population.

Diagnosis - Thyroid Scan Clinical evidence of hypothyroidism or when ultrasound fails to visualize glandular tissue in the normal position Assess if the mass is functioning and to determine if this tissue is the only viable thyroid material

Diagnosis - Thyroid Scan Tc 99m sodium is a radio-active tracer that is actively transported into thyroid cells by an iodide pump. Evaluation of anterior neck masses in children is controversial. Given the comparative rarity of cervical ectopic thyroid, the vast majority of routine preoperative thyroid scans will yield negative results

Management The treatment of ectopic thyroid depends on its location and size and on the presence of symptoms or complications In cases of small and asymptomatic ectopic thyroid, the functioning thyroid should be kept under observation

Management The mainstay of treatment for ectopic thyroid is hormonal therapy Thyroid hormone therapy will also typically suppress the production of thyroid stimulating hormone Clinically symptomatic or cosmetically disturbing cervical glandular enlargement.

Management Progressive hypothyroidism, dysphagia, bleeding, or airway obstruction despite hormonal therapy are indications for surgical excision Such excision of ectopic thyroid commits the patient to lifelong thyroid hormone replacement

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