Congenital thyroglossal cyst and fistula, also known as midline cervical cyst and fistula, results from the incomplete degeneration or disappearance of the thyroglossal duct during thyroid development. It can occur anywhere from the foramen cecum to the suprasternal notch. The internal opening of a thyroglossal fistula is located at the foramen cecum, while the external opening is on or slightly off the midline of the anterior neck. When the cyst is below the hyoid bone, the fistula connecting the cyst to the foramen cecum may pass anterior to, through, or posterior to the hyoid bone, with the posterior route being the most common.

bubble_chart Pathological Changes

Thyroglossal duct cysts are often lined with stratified columnar epithelium, stratified squamous epithelium, or transitional epithelium. The cyst fluid is mucoid and becomes purulent after infection. Thyroid tissue can be observed beneath the epithelium.

bubble_chart Clinical Manifestations

1. Thyroglossal cyst Smaller cysts located above the hyoid bone may be asymptomatic. When the cyst enlarges, symptoms such as a swollen sensation in the tongue, foreign body sensation in the throat, and unclear speech may occur. Examination reveals a round protrusion at the base of the tongue. Cysts located below the hyoid bone and anterior to the thyrohyoid membrane are more common. Patients often have no obvious symptoms, and examination shows a semicircular protrusion under the skin of the anterior neck, with a smooth, tough, and elastic surface, not adherent to the skin, and movable with swallowing. Puncture of the cyst can yield translucent or turbid fluid of varying consistency.

2. Thyroglossal fistula The external fistula opening is usually located along the midline of the anterior neck between the chin and the thyroid cartilage or slightly to one side. The fistula opening may discharge secretions, and if secondary infection occurs, pus may be discharged. Injection of methylene blue into the external fistula opening may reveal methylene blue discharge at the foramen cecum if it is a complete fistula. Injecting methylene blue through the fistula opening not only aids in diagnosis but also helps ensure complete surgical removal of the fistula.

Fistula or cyst X-ray iodized oil contrast imaging helps to clarify the diagnosis, but it should be differentiated from branchial cleft cysts, dermoid cysts, and ectopic thyroid glands.

bubble_chart Treatment Measures

Non-surgical therapy, such as cauterizing the fistula with corrosive agents, is generally ineffective, and complete surgical excision is recommended. The surgical procedure is as follows:

1. The patient is placed in a supine position with a pillow under the shoulders and the head tilted backward.

2. Incision: A transverse incision is made along the skin lines at the most prominent part of the cyst. If a fistula is present, a transverse fusiform incision is made around the fistula opening, and the upper and lower skin flaps are separated.

3. Exposure of the cyst and dissection of the fistula: The sternohyoid muscle is separated longitudinally to expose the cyst membrane. To determine the course and depth of the fistula, methylene blue is injected into the fistula opening or the cyst. The cyst or the skin opening of the fistula is grasped with tissue forceps and dissected toward the hyoid bone. Care must be taken during the procedure to avoid injury to the superior laryngeal nerve and blood vessels.

4. Resection of the middle portion of the hyoid bone: When dissection reaches the hyoid body, the blind end of the tract is carefully examined to determine if it terminates there. If it does, the fistula and cyst are excised together. If the tract ascends around the hyoid bone, the hyoid bone is transected 0.7–1 cm on either side of the midline, and a 1.5–2 cm segment of the hyoid bone is removed. The hyoglossus muscle is incised along the midline, and the fistula is dissected deep into the tongue toward the base. At this point, the surgeon’s index finger is inserted into the mouth to push the foramen cecum forward and downward. A protruding point, marking the endpoint of the fistula, becomes visible in the posterior surgical field. The fistula is then excised, and the defect at the foramen cecum is sutured with catgut.

5. The incision is closed layer by layer, and a rubber drainage strip is placed.

Postoperatively, oral hygiene should be maintained, and antibiotics or sulfonamides should be administered to control infection.