|Year : 2015 | Volume
| Issue : 3 | Page : 110-115
Thyroid ectopia: A case series and literature review
Madhuri Patil, Vageesh Ayyar, Ganapathi Bantwal, Anantha Raman, Belinda George, Vivek Mathew
Department of Endocrinology, St John's Medical College Hospital, Bangalore, India
|Date of Web Publication||16-Oct-2015|
Dr. Madhuri Patil
Department of Endocrinology, St. John's Medical College Hospital, Bangalore - 560 034, Karnataka
Source of Support: None, Conflict of Interest: None
Thyroid ectopia is a dysgenesis of thyroid gland. A series of seventeen patients with ectopic thyroid tissue and dyshormonogenesis is presented here. Patient data were reviewed retrospectively for this descriptive study. At presentation, age of the patients ranged from 2 months to 50 years (mean age -13.7 yr). Male to female ratio is 1: 7.5. Hypothyroidism is present in 94.1% cases whereas 5.88% (one case) cases have thyrotoxicosis. Though dyshormonogenesis was the main reason for reference of these cases to our department, a variety of other symptoms like dysphagia (5.88%), obstructive sleep apnea (5.88%), swelling in the neck (17.6%), slow growth were also present (5.88%). Other than thyroid replacement therapy for hypothyroidism and radioactive iodine therapy for thyrotoxicosis, surgical removal was advised in two cases of persisting obstructive symptoms.
Keywords: Congenital hypothyroidism, ectopic thyroid, hyperthyroidism, hypothyroidism, thyroid dysgenesis
|How to cite this article:|
Patil M, Ayyar V, Bantwal G, Raman A, George B, Mathew V. Thyroid ectopia: A case series and literature review. Thyroid Res Pract 2015;12:110-5
|How to cite this URL:|
Patil M, Ayyar V, Bantwal G, Raman A, George B, Mathew V. Thyroid ectopia: A case series and literature review. Thyroid Res Pract [serial online] 2015 [cited 2019 Nov 18];12:110-5. Available from: http://www.thetrp.net/text.asp?2015/12/3/110/157917
| Introduction|| |
Ectopic thyroid is thyroid tissue present at locations other than the normal cervical position of thyroid gland (i.e., overlying the second or third cartilaginous rings of the trachea). Existence of ectopic thyroid tissue may occur with or without the presence of eutopic thyroid gland. Earlier days it was thought to be a rare thyroid anomaly but advanced diagnostic techniques have revealed many cases of single, double and even triple thyroid ectopia with or without the presence of eutopic thyroid tissue. ,,,,,,,,, Herein, we are presenting a case series of 17 patients diagnosed to have thyroid ectopia with a review of literature. All our cases were seen in the outpatient department of endocrinology during a period of January 2004 to June 2012. Outpatient Hospital records were accessed to collect the retrospective data.
The Series of 17 Cases of ectopic thyroid gland [Figure 1], [Figure 2], [Figure 3] and [Table 1]
Two of these patients are males and fifteen are females (male: Female ratio = 1: 7.5). Age at presentation ranged from 2 months to 50 years. Three of the patients though diagnosed to have congenital hypothyroidism during infancy; ectopia was diagnosed at later age when they were investigated further at our outpatient department.
Sixteen of these (patient 1 to patient 16) have hypothyroidism, Out of them seven (41.1%) cases are of congenital hypothyroidism detected in infancy or early childhood, whereas nine (52.9%) had pubertal or adult onset hypothyroidism. All of these nine patients had presented with either midline swelling in the anterior aspect of neck, in cases of suprahyoid, sublingual ectopia or with dysphagia, in cases of lingual thyroid. One of the cases (patient 17) presented with thyrotoxicosis. This is the only patient who also has eutopic thyroid tissue present in usual pretracheal area. This eutopic portion of thyroid showed Grave's pattern uptake of pertechnate.
Thyrotropin (TSH) levels in hypothyroid patients ranged from 7.44 μIU/mL to >100 μIU/mL.
Primary investigations included ultrasonography, radionuclide scintigraphy or computed tomography (CT) scan. One case of mediastinal mass was confirmed by fine needle aspiration cytology (FNAC) after the CT scan revealed a mass.
One of these cases had dual ectopia - One at suprahyoid location other at sublingual area. [Table 2] gives location-wise distribution in the ectopia cases.
Patients with hypothyroidism are started on L-thyroxine replacement and are being followed up regularly in our outpatient department. The average dose of L-thyroxine in patients with congenital hypothyroidism was 4.16 μg/kg bodyweight/day. Two patients with lingual thyroid gland were referred for surgical removal due to persisting symptoms of obstructive apnea and dysphagia. Patient with thyrotoxicosis has been advised to undergo radio-iodine therapy for the hyper functioning gland.
| Discussion|| |
Development of thyroid gland
Thyroid is the largest endocrine gland in humans and it is the first endocrine structure to develop during fetal life. Development span of thyroid gland is from about 3 rd week till 9 th week of gestational period. 
Thyroid gland is formed of one median anlage and two lateral anlages. Thyroid follicular cells arise as a thickening of endoderm that occurs in the floor of primitive pharynx (the median anlagen). This median anlagen is situated adjacent to the newly differentiating myocardium, between first and second branchial arches. It continues to grow ventrally as a diverticulum. Follicular cells in the median anlagen proliferate fast at its distal end, and then later laterally, to give it a bilobular shape. This diverticular anlagen remains attached to the floor of the pharynx by a tubular stalk called thyroglossal duct. The thyroglossal duct rapidly elongates due to the caudal migration of the diverticulum. Eventually thyroglossal duct fragments and disappears. When thyroid reaches its final position, it connects bilaterally to the two lateral anlagen-ultimobranchial bodies. These ultimobranchial bodies originate from the endoderm of fourth phayngeal pouch and ectoderm of the fifth pouch. They contain parafollicular or the C-cells. 
Postulated etiologies of thyroid ectopia
Morphogenetic errors during the development period result in the most developmental thyroid abnormalities. Migration defects like incomplete migration or displacement of cells derived from the medial anlagen result in ectopic presence of thyroid tissue. Migration defects are believed to be the most common etiology of thyroid ectopia. Juxtapositioning of thyroid with heart during development can result in abnormal thyroid migration, when there is abnormal morphogenesis of the heart or if abnormal interactions exist between the thyroid primordium and the heart. 
Thyroglossal duct, if not degenerated fully, can result into thyroglossal cyst, sinus or fistula containing thyroid tissue. 
Mutations in thyroid related transcription factors are thought to be a rare cause of ectopia.
Role of new genes (genes involved in embryonic development) is highly suspected.  Nineteen genes [a few to name - Paired box gene eight (PAX8), TTF-2, NKX2.1 and NXK2.5] were found to be exclusively associated with thyroid ectopy.  [Table 3] shows description of some common transcription factors involved in thyroid gland genesis and migration.
Epidemiology of thyroid ectopia
Seven percent of adults possess ectopic thyroid tissue.  Female to male ratio is approximately 2:1. Female child is more likely to be affected by biochemical severity of thyroid functions than the male child. ,
Ingbar mentions that thyroid dysgenesis accounts for 80% to 90% cases of permanent primary congenital hypothyroidism. Out of these nearly 60% cases are due to thyroid ectopia,  25% cases of CH were reported to have ectopic thyroid in a retrospective study of CH patients diagnosed with radionuclide scintigraphy.  In a study involving Greek population, 36% of CH cases were reported to have thyroid ectopia.  In iodine sufficient regions, 85% of CH is due to thyroid dysgenesis, out of them two-third (around 36%) cases are due to ectopia. Incidence of CH varies from 1 in 800 to 1 in 10,000 newborns depending on the region and population.  In India 1 in 2500 newborns are detected to have CH. 
About 144 cases of lingual thyroid are reported by montgomary. Buckman reported 244 cases of ectopia.  One in 100,000 live births are reported to have a lingual thyroid;  and about 10% of autopsies had lingual thyroid remnants.  About 1.6% lingual thyroid infants miss out from diagnosis by TSH screening of newborns.  Webb R (1953) reported that 15 out of 41 cases of thyroglossal cysts had thyroid tissue in them.  Thoren (1947) reported that 6% to 7% of endotracheal tumors are intralaryngeal or intratracheal thyroid tissues. 
Common locations of ectopic thyroid
Location of ectopic thyroid tissue can be anywhere from the base of the tongue till diaphragm. Ectopic thyroid in cervical locations is found along the migration path of developing thyroid. Intrathoracic locations of thyroid tissue are trachea, esophagus, and heart. In the neck, median locations are more common than the lateral locations.
Presence of functional thyroid tissue in regions far from neck and thoracic regions (e.g. dermoid cycts, ovarian tumors) are not due to developmental errors of the thyroid tissue migration, but they represent developmental anomaly of the fetus as a whole.
Lingual thyroid is the most common (up to 80%) form of ectopia.  About 70% of the lingual thyroid cases are associated with absence of normal cervical thyroid gland. Most of the lingual thyroid cases are associated with concomitant hypothyroidism.
Suprahyoid and infrahyoid thyroid glands are seen in a midline position above or below the hyoid bone. Hypothyroidism is commonly present because of the absence of a normal thyroid gland in most instances. They are commonly manifested during infancy and childhood, but often they can be mistaken for a thyroglossal duct cyst because of the same anatomic position.
Presentation of the ectopic thyroid gland differs depending on the location of the gland and age at which it presents. Congenital hypothyroidism is the most common presentation of ectopic thyroid diagnosed during infancy. During pubertal age or adulthood, it can present with thyroid hormone abnormalities and as midline mass in the neck in case of supra- or infra-hyoid location. Apart from remaining asymptomatic, cases of lingual thyroid can present as obstructive dyspnea, dysphagia, dysphonia or also as bleeding in the throat. Intratracheal or intralaryngeal thyroid can present with respiratory obstruction, stridor, and hymoptysis, whereas intraesophageal thyroid mass can present with dysphagia. Ectopic thyroid at aortic, pericardiac and cardiac locations generally present with no symptoms. But some cases presenting with right ventricular outflow obstruction due to large tumor and symptoms of chest pain and palpitations due to compression of right atrium and irritation of the pericardium are also reported. 
Significance of ectopy
Diffuse or nodular hyperplasia and anatomical positioning of the ectopic thyroid gland in neck and thorax can be accompanied by space occupying or pressure symptoms. Euthyroidism is rare in cases of ectopic thyroid tissues. Hypothyroidism is more common. This can be due to the total functional gland size is small as it does not exist in normal bilobular form. About 36% cases of congenital hypothyroidism are associated with thyroid gland ectopia. Hyperthyroidism is very rare and was thought to be only from dermoid cysts or ovarian teratoma, but ectopic thyroid tissue in neck with thyrotoxicosis has been reported. ,,
Cases of malignancies in ectopic thyroid glands, either primarily harbored, or as metastasis of carcinoma arising in concurrent eutopic thyroid, are reported. ,,,, Also cases of primary carcinoma in ectopic thyroid mass with normal tissue in concurrent eutopic thyroid gland are reported. Although all kinds of malignant forms are reported, papillary thyroid carcinoma is the most common form and medullary thyroid carcinoma is the rarest form of malignancy in ectopic thyroid tissue.  One in 100 cases of lingual thyroid is said to have a malignancy.  Two cases of Sarcoma are reported by Buckman.  Life threatening bleeding has been reported. ,
Diagnosis of ectopia
Thyroid ectopia should be ruled out in all cases of congenital hypothyroidism. Ultrasonography (USG) can be used as a primary tool to detect ectopia or it can also serve as a confirmatory tool for findings of radionuclide scan. Radionuclide scintigraphy (using Tc-99m pertechnate or radioIodine-I 131 or I-123) is sensitive and specific to differentiate thyroid tissue from other masses  and it is proven to be safe with no evidence of risk for thyroid cancer.  Plain CT and magnetic resonance imaging (MRI) can also be used to study the extent of the tissue into the surroundings and relationship with important surrounding structures if surgical excision is planned. Color Doppler USG (CDU) has been reported to be more sensitive  in one of the studies comparing sensitivity of gray scale ultrasound or MRI. CDU helps assessment of thyroid volume, characterizes tissue vascularization and identifies nodules if any. FNAC or excisional biopsy is essential to confirm morphology of the thyroid tissue in suspected cases of primary or secondary malignancy. FNAC of lateral swellings in the neck are highly recommended due to their potential to be malignant.
Differential Diagnosis of midline and lateral swelling in the neck
Knight et al. have reported that 52% of 146 children with an anterior neck swelling had a thyroglossal cysts.  Thyroglossal cysts are seen at birth in about 25% of cases, mostly in early childhood, while the rest become apparent only after the age of 30 years. Usually they appear in the midline or just off the midline, between the isthmus of the thyroid and the hyoid bone. Not enough thyroid tissue in a thyroglossal cyst helps differentiation of a cyst from an ectopic thyroid during radionuclide scintigraphy.
The lateral swelling can be lymph nodes with metastasis, thyroglossal cysts or aberrant thyroid tissue. Cervical lymph node malignancy presents as well with differentiated malignant tumors. It needs more rigorous approach for diagnosis. Clinical management is totally different than that of benign ectopia.
Management of ectopic thyroid
Preference to options of management of ectopic thyroid tissue is not uniform everywhere. But, in general, ruling out degenerative changes and/or malignancy, the benign goiters to be treated depending on the patient's health status.  Thyroid hormonal supplement is essential for hypothyroidism. Suppression therapy by L-thyroxine or by Iodine-131 therapy is tried by a few researchers. , If the tissue causes dysphagia, dysphonia or cosmetic deformities and if it is not invading nerves and important blood vessels, surgical removal of the gland is recommended. Intrathoracic gland should be removed, as there is a risk of downward growth and compressive symptoms.  When ectopic thyroid is the only functional tissue, autotransplant of midline cervical ectopic thyroid has been reported to have good functional and cosmetic results. ,, But autotransplant of laterally occurring ectopic thyroid tissue should not be tried because of its high incidence of malignancy [Table 4].
|Table 4: Summary of location and suggested management of Thyroid ectopia |
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| Conclusion|| |
Once thought to be a rare phenomenon, presence and so detection of the thyroid ectopia is certainly noticed with increasing frequency. Evaluation of the ectopic thyroid tissue to rule out dyshormonogenesis, bleeding tendency, mass effects or potential malignant complications is recommended. Options of medical and/or surgical interventions have to be considered on individual case basis.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]