Thyroglossal Duct Cyst

Introduction

Thyroglossal duct cysts (TGDCs) are the most common congenital midline cervical anomalies in children and account for approximately 70% of all congenital neck lesions. The differential diagnosis of a midline mass in the neck mass in a child includes TGDC, dermoid, lymph node, lipoma, hemangioma, ranula, and inflammatory lesion. One study that evaluated preoperative computed tomography (CT) and histopathologic findings of excised midline neck lesions found that TGDCs were most common (55% of cases). Other common findings were dermoids in 21%, ranula in 10%, and the remaining were inflammatory lesions.

During embryogenesis, the foramen cecum develops at the floor of the primitive pharynx. The thyroid tissue begins to descend from the foramen cecum anterior to the hyoid bone and laryngeal cartilages to finally reach its normal adult pretracheal position. The proximal portion of the diverticulum that connects the thyroid gland and foramen cecum typically obliterates and atrophies over time. TGDCs are thought to occur due to failure of the thyroglossal duct to obliterate after the thyroid gland completes its descent into the inferior aspect of the neck.

TGDCs tend to present in childhood as a painless midline mass just inferior to the hyoid at the level of the thyrohyoid membrane (65%). Other locations include the suprahyoid location in up to 20% to 25% of the cases and at the level of the hyoid in 15% to 50% of the cases. TGDCs usually occur in equal frequencies in males and females. Because this is a congenital lesion, it would not be surprising for the most common age of presentation to be in childhood. One of the largest reviews of patients with TGDCs revealed that these lesions occur frequently in children with nearly one-third of the cases in children less than 10 years of age. However, nearly one-third of the cases occurred in patients in their third decade or older. Similarly, recent reports suggest a bimodal incidence with the most common average age in children to be 6 years and in adults to be 41 to 45 years. TGDCs are benign cysts that mainly consist of abundant colloid and are lined predominantly with ciliated columnar epithelium. Carcinoma has been shown to occur rarely in these cysts, with an incidence of 1%.

Key Operative Learning Points

• The most common location for TGDC is in the midline, just inferior to the hyoid bone.

• The Sistrunk procedure, which involves removing the midportion or body of the hyoid bone with the cyst and a core of tongue muscle, is the recommended surgery for TGDC.

• The thyroid notch is used as a landmark to mark the midline of the neck.

• The cricoid cartilage in very small children can be high in the neck and mistaken for the hyoid bone.

Preoperative Period

Surgical excision of a midline mass in the neck is useful for diagnostic and therapeutic purposes. Indications for excision of a midline mass in the neck mass include diagnosis, cosmetic appearance, prior infection, and possibility of malignancy. The recommended surgery for TGDC is a Sistrunk procedure that includes removal of the cyst along with the central portion of the hyoid bone, including a core tissue at the base of the tongue. The Sistrunk procedure has been shown to decrease the rate of recurrence to approximately 5%.

Thorough history taking and a physical examination are essential to diagnosis. The majority of the patients present with the history of a rapidly enlarging midline mass in the neck and oftentimes report a history of a preceding upper respiratory illness. When acutely infected, the mass can be painful, erythematous, and warm to touch. Some may present with recurrent infections that have been previously treated and improved on antibiotics. Others may have had incision and drainage procedures due to misdiagnosis. Patients may be completely asymptomatic or can have dysphagia, odynophagia, and a feeling of obstruction if severely enlarged.

On examination, cysts usually measure 1 to 2 cm but can be as large as 10 cm. The mass is characteristically described as moving with swallowing or protrusion of the tongue due to its attachment to the hyoid bone. Cysts are usually nontender unless acutely infected. Some patients may have a draining tract from the site of a prior incision and drainage, recurrence due to incomplete excision, or a ruptured cyst.

History and physical examination are the mainstay for diagnosis and therapeutic planning in terms of TGDC. However, a number of studies have been used to aid in diagnosis when not clear and when there is suspicion for extensive disease beyond the appearance of a cyst. These include radionuclide studies, ultrasonography (US), CT, and magnetic resonance imaging (MRI).

Historically, radionuclide studies were used to identify functional thyroid tissues and to eliminate the possibility of mistaking ectopic thyroid gland for TGDC. Excision of ectopic thyroid gland with no functioning thyroid gland elsewhere will result in hypothyroidism. Radionuclide studies are now less used to avoid the unnecessary radiation with minimal diagnostic advantage offered in comparison to US, CT, or MRI.

US is an invaluable initial test for evaluation of TGDC. It avoids the exposure to ionizing radiation from CT scans and possible need for sedation in MRI studies, especially in young children, and is low cost. In addition, it has been shown to have sensitivity and accuracy comparable to CT or MRI19. An uncomplicated TGDC appears as an anechoic, well-circumscribed, thin-walled cyst. At times, the presence of proteinaceous fluid can give a pseudosolid appearance, while prior infection and hemorrhage may give a heterogeneous appearance.

CT and MRI can be useful to delineate the extent of the lesion when it is extensive and help if there is difficulty ascertaining the diagnosis on US. On CT, TGDCs tend to be smooth, well circumscribed, midline, and closely related to the hyoid bone. They tend to be unilocular but can have septations. In the setting of prior infection, there may be a thickened cyst wall, increased fluid attenuation, and loss of tissue planes. MRI features are usually homogeneous low signal on T1-weighted images and homogeneous high signal on T2-weighted images due to the fluid within the cysts. The duct tract can sometimes be traced on T2-weighted fat saturated images.

If presurgical imaging is attained, suspicion of malignancy should arise if dense or enhancing mural nodules, calcification, or both are seen within the lesion. Calcifications are best seen on CT and are due to psammoma bodies, the histologic hallmark of papillary carcinoma. However, the diagnosis of carcinoma is usually made incidentally on histologic examination of pathology specimens following surgical excision.

Operative Period