13.1 Introduction

TGDCis the most common congenital malformation of the neck. ¹ It is usually diagnosed in children, but it may occur at any age. ² TGDCs form as a result of failure of the thyroglossal duct to obliterate during the embryonic period.

Thyroid development is usually completed by the end of the eighth week of gestation, and the thyroglossal duct involutes between the 8th and 10th week of gestation. If viable epithelium persists somewhere along the path of the thyroglossal duct, TGDC may form. Hence, TGDC can appear anywhere from the foramen cecum to the level of the thyroid gland. ^{3 , 4} Most commonly the tract is located anterior to the hyoid bone, ⁵ but it may be located posterior to the hyoid bone in up to 30% of the patients. ⁶

TGDC usually presents as an asymptomatic, painless, mobile neck mass that move superiorly upon swallowing. ^{7 , 8} TGDCs most commonly appear in the midline. Less than 1% are located off the midline. ^{3 , 4}

Shah and colleagues ⁹ classified the location of TGDC into four subdivisions:

1. 
   

   Intralingual.

   
   
2. 
   

   Suprahyoid/submental.

   
   
3. 
   

   Thyrohyoid.

   
   
4. 
   

   Suprasternal.

It is usually located just above or below the hyoid bone, but up to one-third of the cases may present in the lower cervical regions or in the submental space.

The differential diagnosis includes: Dermoid cysts, branchial cleft cysts, lymphadenopathy, lymphatic malformations, lipomas, hemangiomas, ectopic thyroid gland, and sebaceous cysts. TGDC carcinoma is very rare in children, and is reported to occur in less than 1% of TGDCs in adults. ^{10 , 11}

Although usually asymptomatic, TGDC may present with acute suppurative infection—swelling, erythema of the skin, pain, and spontaneous drainage of pus. Surgery is deferred in these cases, and a course of antibiotics should be administered first. Surgery should be performed 6 weeks after resolution of the infection. The lingual subtype may cause upper airway obstruction, dysphagia, odynophagia, and even stridor.

The radiologic criteria for differentiating TGDC from other midline cervical masses is based on the presence of cystic or ductular structures. ¹² Recently, Choy et al ¹³ reported of additional features that can differentiate TGDC from dermoid cysts. TGDC were significantly more likely than dermoid cysts to have an irregular shape, ill-defined margins, attachment to the hyoid bone, an intramuscular location, multilocularity, heterogeneous internal echogenicity, and longitudinal extension into the tongue base. ¹³

Because of the high risk for recurrent infections and the possibility (although rare, approaching 1%) of malignancy, the treatment of TGDC is surgical excision.

Traditionally, excision of a TGDC included simple excision of the cyst and the duct. In 1893, Schlange ¹⁴ reported of excision of the cyst, the duct, and the middle portion of the hyoid bone, based on his knowledge in embryology. In 1920, Sistrunk ¹⁵ reported of a new technique, which included also resection of a cuff of lingual musculature. This procedure, named after him as “the Sistrunk procedure,” is still recognized as the most effective surgical treatment of TGDC, due to its low rate of recurrence. ² Several authors reported of variants of the Sistrunk procedure, basically suggesting wider dissections, removal of more tongue base tissue or central neck dissection. ¹⁶

Although uncommon, when the TGDC is located low in the neck, a stepladder approach with at least two separate horizontal incisions is required in order to be able to complete the dissection all the way to the hyoid bone and the deep lingual musculature. ¹⁷