Thyroglossal Duct Cysts and Sinuses
Embryology: The thyroid gland, although situated in the lower portion of the neck around the trachea, originates in the mouth at the back of the tongue and then moves down the neck during development. As the thyroid gland moves down to its normal position, there is a connection to the base of the tongue that should disappear by the time the thyroid reaches its final position. If it does not, there may be a persistent hollow tube that may allow accumulation of mucoid material and the formation of a cyst at the end (Figure 1).
Figure 1: Thyroglossal cyst. A, Diagram of locations: (1) by the tongue (rare), (2) above the hyoid bone (uncommon), (3) below the hyoid bone (common). B, Incision for removing a thyroglossal duct cyst or sinus. C, Removal of the thyroglossal cyst by the hyoid bone, removing a 1-cm segment of bone. The sinus tract is followed up to the base of the tongue. An assistant’s finger inserted over the tongue locates the end of the sinus tract. The sinus tract is tied off and divided at the back of the tongue.
This is known as a thyroglossal duct cyst. Frequently this is noted soon after a cold when there has been swelling of the tonsils and other lymphoid tissue of the throat.
Approximately three-fourths of thyroglossal duct abnormalities present as cysts, whereas 25 percent present as a draining sinus on the skin. A sinus occurs as a result of infection (in the cyst) and rupture onto the skin with persistent drainage. The cysts are generally asymptomatic and are noticed by the family as a soft swelling under the chin over the area of the hyoid bone, a floating bone in the upper neck to which the tongue muscles are partially attached.
Thyroglossal cysts are usually single, smooth, and usually 1-3 cm in size and move when the patient swallows or protrudes the tongue. The other causes for masses in this area of the neck include abnormally located thyroid tissue, lymph nodes, and dermoid cysts. X-rays are not usually needed, as the diagnosis is frequently made by examining the mass. Thyroid scanning is not generally necessary, but is reserved for patients who have either no detectable thyroid tissue in the neck on examination or who following surgery have thyroid tissue noted within the surgical specimen. The tissue in this abnormal location is best removed, and if no other thyroid tissue is identified the patient requires lifelong thyroid hormone replacement therapy.
The treatment of choice for thyroglossal duct cyst is complete removal of the cyst along with the extension to the back of the tongue. This is done in conjunction with removal of the central portion of the hyoid bone and is known as the Sistrunk procedure, named for the man who described it in 1920. Delay in treatment often results in another infection, which necessitates antibiotic therapy and delay of surgery until all the infection and inflammation are resolved.
Removal is carried out generally as an outpatient under general anesthesia.
Approximately 10 percent of the cysts come back and are usually treated by a second removal. Reoccurrences are more common in patients who have had infected or previously drained thyroglossal duct cysts. Cancer has been reported in a small number of patients in whom the cyst was not removed until adulthood. Although rare, multiple recurrences have also been reported, usually requiring wider removal of tissue in the region of the remaining hyoid bone.
Ranulas are soft fluid-filled masses in the floor of the mouth related to blocked openings of the small salivary glands under the tongue. They may be on either side or both sides under the tongue and may be found as large swellings in the mouth or on the undersurface of the chin. Surgical treatment involves unroofing the cyst without complete removal, allowing drainage of the cyst fluid into the mouth.
Article and graphics adapted from O'Neill: Principles of Pediatric Surgery. © 2003, Elsevier.