In order to understanding these anomalies it should be first known the development of thyroid gland

Development of thyroid gland

the thyroid gland develops from the thyroglossal duct (median bud of the pharynx) during the fourth embryonic week and passes ventrally from the foramen caecum at the back of the tongue to the pharynx just below the position of the developing hyoid cartilage . this line of descend is called the thyroglossal duct thus formed usually degenerates but it is incomplete regression results in the following 

Congenital abnormalities

which are rarely evident at birth as

thyroglossal cyst

which 1- may occur with patent or closed thyroglossal duct 2- may occur at any age but 40%present in the age group 0-10 years 3- incidence :male = female 4- midline usually but may deviate slightly 5- commonest midline cervical tumour in infants 6- does not usually transilluminate 7- usually situated above or below the hyoid bone 8- moves up on protrusion of tongue  it is lined by squamous or ciliated pseudostratified epithelium and may contain thyroid or lymphoid tissue which may be dysplastic in the wall .

the diagnosis is made on clinical grounds but many surgeons request an ultrasound or radioisotope scan preoperatively to exclude ectopic thyroid tissue

thyroglossal sinus

this is not congenital but results from infection in or inadequate excision of a thyroglossal cyst it is 1- midline orifice with tract leading cranially 2- cresentic fold of skin (concavity faces down) at skin orifice 3- mucopurulent discharge 4- recrrent infection 5- lined by columnar epithlium

Treatment by Sistrunk,s operation this is the operation of choice for thyroglossal cyst and sinus a transverse incision is made over the cyst (transverse elliptical incision around the mouth of a sinus)and the tract followed up between the strap muscles to the hyoid bone . the tract , duct cyst or sinus is then excised with the central portion of the hyoid bone to prevent the recurrence . for suprahyoid cysts or sinuses . the tract should be followed to the base of the tongue

lingual and aberrant thyroid 

A lingual thyroid gland
Represents failure of descend of part or all of the embryonic thyroid gland from the foramen caecum . in most cases it represents the only thyroid tissue present . it may remain symptomless or develop any of the recognized thyroid abnormalities . clinical problem occur most commonly in young women when physiological hypertrophy at time of pregnancy or development of an adenoma occur .

Symptoms and sign

Include 1- dysphagia 2- speech impairment 3- respiratory obstruction 4- haemorrhage 5- smooth vascular dark red projection at the base of the tongue
symptomless glands should be left alone . if treatment is required an iodine or technetium isotope scan should be performed to determine the presence of any other thyroid tissue gland may be reduced in size by antithyroid drugs thyroxine or radioiodine .

Excision is required if malignant change occurs
aberrant thyroid tissue may occur in any site along the thyroglossal tract and this may be the only thyroid tissue present . if a non cystic mass is found during sistrunk operation the procedure should be abandoned and an isotope scan performed to determine the site of all thyroid tissue the term lateral aberrant thyroid gland is a misnomer the thyroid tissue found in these lateral sites being cervical node metastases from 
a papillary thyroid carcinoma

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