ectopic thyroid is a developmental defect of thyroid gland that leads to presence of thyroid tissue at sites other than its normal cervical location .
it is frequently found along the course of the thyroglossal duct but can also be found at remote distant sites .
it is very rare to have two ectopic foci of thyroid tissue , and only a very few cases of dual ectopia have been reported in the world literature . in 70% of cases of ectopic thyroid ,
it is extremely rare to have dual ectopic thyroid with a normally located pretracheal thyroid gland .
a seventeen - year - old female presented with history of a swelling at the base of the tongue first noticed about eight months ago . the swelling gradually increased in size causing dysphagia .
there was no history of pain , ulceration , or bleeding from the swelling or any symptoms of airway obstruction .
local examination revealed a pink 2.5  2.5 centimeter swelling covered with intact mucosa and visible vessels over it at the base of the tongue ( figures 1 and 2 ) .
thyroid function test suggested primary hypothyroidism with tsh 31.6  miu / l ( 0.44.0 ) , t4 50.5  nmol / l ( 57.9161 ) , and t3 1.82  nmol / l ( 1.252.74 ) .
ultrasonography of the neck showed normally located thyroid gland but both lobes were hypoplastic ( figure 3 ) .
fnac from the swelling was done which showed thyroid follicular cells in loosely cohesive sheets , microfollicular as well as macrofollicular arrangements ( figure 4(a ) , 4(b ) , 4(c ) , and 4(d ) , 400x , mgg ) .
a thyroid scan with technetium-99 m showed two foci of intense uptake , one at the base of the tongue and another in the submental region consistent with dual ectopic thyroid ( figures 5 and 6 ) .
she has since been put on 100 microgram of levothyroxine daily and is on regular followup .
ectopic thyroid was first described by hickman in 1869 in a newborn who was suffocated 16 hours after birth because of a lingual thyroid causing upper airway obstruction .
lingual thyroid is the most common ectopic thyroid accounting for 90% of all cases with a prevalence between 1  :  100000 and 1  :  300000 and a clinical incidence between 1  :  4000 and 1  :  10000 .
other sites of ectopic thyroid are suprahyoid and infrahyoid , lateral aberrant thyroid , substernal goiters , struma ovarii , and struma cordis .
ectopic thyroid has also been found in larynx , trachea , oesophagus , pericardium , diaphragm , and branchial cysts .
rare cases of ectopic thyroid are described in parathyroid , cervical lymph nodes , submandibular gland , duodenal mesentery , adrenals , and carotid bifurcation .
ectopic thyroid occurs more commonly in females and are usually seen during adolescence and pregnancy when the demand for thyroid hormone increases .
upto 70% of patients with lingual thyroid have hypothyroidism , and 10% suffer from cretinism .
the thyroid gland is not found in its usual location in 70% of patients with ectopic thyroid .
presence of two ectopic foci of thyroid tissue simultaneously is rare , and very few such cases of dual thyroid ectopia have been reported in the world literature . in an extensive review of the literature , sood et al
. found that the mean age of these patients was 15 years , more common in females with an f  :  m ratio of 1.25  :  1 .
the symptoms varied from asymptomatic to anterior neck swelling with or without altered thyroid status . in almost all of these patients , one site of ectopy was at lingual or sublingual region .
familial dual ectopic thyroids with perihyoid ectopic thyroid and lingual thyroid have also been described .
lingual thyroid can cause foreign body sensation in tongue , dysphagia , dysphonia , or sensation of choking .
large blood vessels present on the surface of lingual thyroid predispose it for ulceration . all diseases capable of affecting the normal thyroid can affect the ectopic thyroid like adenoma , hyperplasia , inflammation , and malignancy .
the rate of malignant transformation in ectopic thyroid is no greater than in normally placed thyroid .
carcinoma of the lingual thyroid is a rare clinical entity with an estimated incidence of 1% .
carcinoma of lingual thyroid presents in the same manner as a symptomatic patient with a lingual thyroid .
therefore , for exact pathological diagnosis a biopsy should always be taken . in our case
lingual thyroid usually has a poorly defined capsule that leads to intermingling of glandular tissue with muscle elements raising the suspicion of malignancy .
the most important diagnostic modality for ectopic thyroid is a thyroid scan with technetium-99 m , but ultrasonography , ct scan , and mri may help in defining the extension and location of the ectopic thyroid gland .
asymptomatic and euthyroid patients do not require any treatment , but they should be followed up and looked after for any complications .
patients with raised tsh with swelling should be put on replacement therapy with thyroid hormone which can produce a slow reduction of the mass . when medical treatment fails or there are obstructive symptoms or haemorrhage or suspicion of malignancy , then surgery should be considered .
as malignant transformation has been described , some authors consider complete excision of ectopic thyroid as an appropriate treatment in all cases .
 dual ectopic thyroid is a rare presentation of thyroid ectopia . 
 only a few cases have been reported in the world literature . 
 dual ectopic thyroid in the presence of a normally located thyroid is even rarer . 
 we report a case of dual ectopic thyroid in the lingual and submandibular areas in a seventeen - year - old female with hypoplastic thyroid gland in its normal location . 
 the patient presented with a midline swelling at the base of tongue with dysphagia . 
 thyroid function test revealed primary hypothyroidism . 
 ultrasonography of the neck showed hypoplastic thyroid in its normal location . a thyroid scan with technetium-99  m pertechnate showed two intensely hyperfunctioning foci of ectopic thyroid tissue at a higher level in the midline consistent with dual ectopic thyroid , one at the base of tongue and the other in submental region . 
 no uptake was seen in the normal bed . 