A thyroglossal duct cyst (TGDC) is a common, benign, fluid-filled congenital neck mass affecting both children and adults. It forms in the midline of the neck, typically near the hyoid bone. The cyst represents a remnant of a temporary structure that forms during early fetal development. Although usually painless, a TGDC often leads to noticeable symptoms and requires medical attention to prevent complications like infection.
Understanding the Embryological Origin
The TGDC originates during the embryonic development of the thyroid gland. The thyroid first appears as a primordium at the base of the tongue and descends into the lower neck along a temporary channel known as the thyroglossal duct.
This epithelial-lined cord normally atrophies and disappears completely between the eighth and tenth weeks of gestation. If any portion of this duct fails to close, it leaves behind a hollow tract of epithelial tissue. Secretions from the epithelial cells lining this remnant duct accumulate over time. This collection of fluid leads to the formation of a thyroglossal duct cyst. The cyst can occur anywhere along the duct’s path, but it is most commonly found below the hyoid bone.
Recognizing the Symptoms
A TGDC typically presents as a soft, smooth, painless, and mobile lump located in the center of the neck. It is often noticed in childhood but may persist until adulthood. A defining characteristic is the upward movement of the lump when the patient swallows or protrudes their tongue. This motion occurs because the cyst is physically connected to the base of the tongue through the remnant duct.
The cyst may become more noticeable after an upper respiratory tract infection. When infected, the cyst becomes inflamed, presenting with tenderness, swelling, and redness of the overlying skin. Uncommonly, an infected cyst may spontaneously rupture, creating a draining fistula.
Diagnostic Steps
Diagnosis involves a physical examination by a healthcare provider. The physician confirms the midline location of the mass and checks for the characteristic upward movement when the patient swallows or protrudes their tongue. This finding helps distinguish the TGDC from other possible neck masses.
Imaging studies are then used to confirm the cystic nature of the mass and gather information for treatment planning. Ultrasound is the preferred first-line imaging method because it is non-invasive, widely available, and radiation-free. Ultrasound confirms the lesion is a fluid-filled cyst and details its precise location and size. Crucially, imaging must verify the presence of a healthy, normally-located thyroid gland in the lower neck. This is vital because in rare cases, the tissue within the cyst may be the patient’s only functioning thyroid tissue.
Other imaging, such as a CT scan or MRI, may be ordered if the diagnosis is unclear or if the case is complicated. A fine needle aspiration (FNA) may be performed to rule out other cystic lesions or the extremely rare occurrence of malignancy, which is found in less than one percent of cases.
Necessary Treatment
Surgical removal is the definitive treatment for TGDC, given the high risk of recurrent infection and potential for a draining fistula. The procedure of choice is the Sistrunk procedure, which is designed to prevent recurrence. Simple excision of the cyst alone is inadequate, as this leaves the duct remnant behind and results in a recurrence rate exceeding fifty percent.
The Sistrunk procedure involves the complete removal of the cyst, the entire duct tract, and the central portion of the hyoid bone. Removing this section of the hyoid bone is essential because the duct often passes through or is closely associated with it, ensuring the entire duct is fully excised.
When performed correctly, the recurrence rate is low, generally between three and ten percent. Active infections are typically treated with antibiotics before the definitive surgery.