Thyroglossal Duct Cyst

Etiology

A thyroglossal duct cyst is an embryologic remnant that forms due to the failure of closure of the thyroglossal duct extending from the foramen cecum in the tongue to the thyroid’s location in the neck. The thyroid begins to develop in the third week of gestation as a median outgrowth from the primitive pharynx. The thyroid primordium originates at the foramen cecum at the junction of the anterior two-thirds and posterior one-third of the tongue. From there, the thyroid descends to the neck, passing anterior and in close relation to the developing hyoid bone. It reaches its final position in the inferior pre-tracheal neck by the seventh week of gestation. 

The thyroglossal duct is the narrow tubular structure left from the thyroid’s descent and connects the thyroid gland to the foramen cecum. The distal part of the duct differentiates into the pyramidal lobe of the thyroid gland in about 50% of people. The thyroglossal duct normally involutes by the tenth week of gestation. If any portion of the duct persists, secretion from the epithelial lining can result in inflammation and thyroglossal duct cyst formation.[2][3]

Epidemiology

Thyroglossal duct cysts are present in about 7% of the population worldwide. They have an equal preponderance between male and female individuals. Although they are known to be the most common pediatric mass, they also present in adults with varying frequency. These types of cysts are closely associated with the hyoid bone. They are about 20% to 25% present at the level of suprahyoid, 15% to 20% present at the level of hyoid, and 25% to 65 % present at the infrahyoid level.[4][5]

Histopathology

Thyroglossal duct cysts are cystic structures lined by respiratory epithelium, squamous epithelium, or a combination of both. Due to a high frequency of infection, inflammatory infiltrates can be present. These can appear as granulation tissue or giant cells. In about 70% of cases, microscopic foci of ectopic thyroid gland tissue can be found, usually within the cyst wall.

History and Physical

Thyroglossal duct cysts typically present as mobile midline neck masses near the hyoid bone. They often are asymptomatic. However, they can present as an abscess or intermittently draining sinus. The mass will elevate with tongue protrusion or swallowing. The mass is closely associated with the hyoid bone and most commonly found at or below the level of the hyoid.

Evaluation

Imaging should be performed to both diagnose the thyroglossal duct cyst and evaluate for the presence of healthy thyroid tissue. If normal thyroid tissue in the inferior neck is absent, the patient and/or parents should receive counseling on the possibility of lifelong thyroid replacement therapy after surgery.

Ultrasound is the ideal initial imaging choice. Ultrasound is readily available, inexpensive, and noninvasive. It does not require ionizing radiation or sedation, which is important in treating children. CT scans and MRI can be used to evaluate thyroglossal duct cysts and the presence of normal thyroid tissue, but ultrasound alone in usually sufficient.

Some surgeons advocate for routine thyroid function testing preoperatively. This may be helpful if ectopic thyroid tissue is expected, but the literature does not support routine lab work for uncomplicated thyroglossal duct cysts.[6][3][7]

Treatment / Management

The treatment for thyroglossal duct cysts is surgical removal to prevent recurrent infections due to the small risk of malignancy. Simple excision of thyroglossal duct cysts is associated with high recurrence rates (45% to 55%). The Sistrunk operation is considered the standard of surgical management and has dramatically reduced recurrence rates. This procedure requires a more extensive surgical resection including the central third of the hyoid bone and a core of base of tongue tissue.[8][9]

The Sistrunk procedure should not be performed in the setting of acute infection. The patient should receive systemic antibiotics and removal should be planned after the infection has resolved. If preoperative evaluation reveals no other functional thyroid tissue, removal can still be performed with the acknowledgment that hormone replacement therapy may be necessary postoperatively.

Differential Diagnosis

The differential diagnosis of thyroglossal duct cysts includes midline neck masses and cystic neck masses, as well as cystic metastatic lymph nodes, dermoid or epidermoid cysts, and second branchial cleft cysts. Cystic metastatic lymph nodes usually originate from either papillary thyroid carcinomas or squamous cell carcinomas of the upper aerodigestive tract. Dermoid or epidermoid cysts can also be midline cystic neck masses. The close relationship of thyroglossal duct cysts with the hyoid bone is a key feature for differentiation. However, the final differentiation is often not made until pathologic diagnosis. Second branchial cleft cysts are also anterior neck cystic masses. However, branchial cleft cysts are lateral and not associated with the hyoid bone.

Surgical Oncology

Less than 1% of thyroglossal duct cysts develop into a carcinoma. Papillary carcinoma is the most common malignancy found (92.1%) followed by squamous cell carcinoma (4.3%). Thyroglossal duct cyst carcinoma typically presents with an asymptomatic midline neck mass. 73.3% of these types of carcinomas were diagnosed as an incidental finding on final pathologic analysis. Patients diagnosed with thyroglossal duct cyst carcinoma tend to be adults and have an older average age than the typical thyroglossal duct cyst patient. Treatment of thyroglossal duct cyst papillary carcinoma involves a Sistrunk procedure followed by evaluation of lateral neck lymph nodes and thyroid. Total thyroidectomy, lateral neck dissection and/or radioactive iodine may be indicated depending on the extent of disease. Overall prognosis is excellent, with a survival rate of 99.4% and a recurrence rate of 4.3%.

Prognosis

Following the Sistrunk procedure, the prognosis is usually excellent. About 10% of thyroglossal duct cysts recur after Sistrunk. There is a much higher recurrence rate with simple excision without excising the middle third of the hyoid bone. 1% of thyroglossal duct cysts are malignant, which is usually diagnosed after surgical removal.

Complications

The most common complication of the Sistrunk procedure is a recurrence of the thyroglossal duct cyst, which occurs in about 10% of cases. Contributing factors to recurrence include incomplete excision, intraoperative rupture, surgical proficiency and experience, and presence of infection. However, recurrence can still occur after technically proficient procedures.

A laryngotracheal injury is a rare and potentially devastating complication of the Sistrunk procedure, resulting in issues with the airway, swallowing, and/or voice. It can be caused by erroneous resection of the thyroid cartilage instead of the hyoid bone. Appropriate identification of the hyoid bone, thyroid cartilage, and the thyrohyoid membrane is essential to prevent this during surgery.

A hypoglossal injury is also rare but has been reported after the Sistrunk procedure, resulting in paralysis of half of the tongue. The hypoglossal nerve travels lateral to the hyoglossus muscle and medial to the stylohyoid muscle and lingual nerve near the lateral portion of the hyoid bone. It is important to keep the hyoid resection medial to the lesser cornu of the hyoid to avoid hypoglossal injury.