Congenital thyroglossal cyst and fistula, also known as midline cervical cyst and fistula, results from the incomplete degeneration or persistence 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 found along the midline of the anterior neck or slightly to one side. When the cyst is situated 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 Etiology

Thyroglossal cysts are often lined with stratified columnar epithelium, stratified squamous epithelium, or transitional epithelium. The cyst fluid is mucoid and becomes purulent when infected. 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, a 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 that is not adherent to the skin and moves up and down with swallowing. Puncturing the cyst may 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. Injecting methylene blue into the external fistula opening may reveal the dye flowing out from the foramen cecum if the fistula is complete. Injecting methylene blue through the fistula opening not only aids in diagnosis but also helps ensure complete surgical removal of the fistula.

bubble_chart Diagnosis

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

1. It is more common in children and young adults. There is a round mass below the hyoid bone in the anterior neck, with a smooth surface, clear boundaries, cystic sensation, no adhesion to the skin, and movement up and down with swallowing. A cord-like structure can be palpated along the direction of the hyoid bone, and the mass may retract and lift when opening the mouth and extending the tongue.
2. When the cyst becomes secondarily infected, local redness, swelling, and tenderness occur. If it ruptures spontaneously or is incised and drained, it may form a persistent fistula.
3. The mucoid secretion often contains columnar and squamous epithelial cells.

bubble_chart Treatment Measures

Non-surgical therapies such as cauterizing the fistula with corrosive agents are generally ineffective, and surgical complete excision is usually 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 dissected.
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 through the fistula opening or into 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 dissecting reaches the hyoid bone, the blind end of the tract is carefully examined to determine whether 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 of the tongue. At this point, the surgeon’s index finger is inserted into the mouth to push the foramen cecum forward and downward. A protruding point can be seen posteriorly in the surgical field, marking the endpoint of the fistula, which is then excised. 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.

Surgical treatment involves excision of the cyst, fistula, and the middle segment of the hyoid bone, extending to the foramen cecum. Methylene blue injection may be used intraoperatively to facilitate identification. For patients with acute infection, antibiotics should be administered first to control the infection, or incision and drainage should be performed. Surgical excision is recommended three months after the inflammation subsides.