Thyroglossal duct cysts and fistulas are congenital developmental anomalies caused by incomplete degeneration of the thyroglossal duct. If the epithelial cells within the duct do not degenerate during development, thyroglossal cysts can form anywhere along the midline between the blind foramen and the sternocervical notch, and the cysts form fistulas after infection or surgical incision. Most of them appear around 5 years of age, slightly more in males than in females, and about 40% of patients are complicated by infection, which is also found in adults.
Thyroglossal cysts and fistulas – etiology
In the third week of embryonic life, an s-chambered thyroglossal base forms in the median part of the original oral cavity between the 1st and 2nd pairs of pharyngeal depressions. This primordium migrates downward along the median line in front of the larynx to the neck, and its course forms an elongated duct called the thyroglossal duct. The hyoid bone develops from the sides toward the middle and surrounds the duct or resides anteriorly and posteriorly, forming the thyroid gland at its lower end. By the fifth week, the thyroglossal duct degenerates into a parenchymal fibrous strip that remains at the oral end as a blind foramen at the root of the tongue. If the epithelial cells within the duct do not degenerate during development, a thyroglossal cyst may form anywhere along the midline between the blind foramen and the sternocervical notch.
The inner wall of a thyroglossal cyst is lined with compound squamous or columnar epithelial cells, and the wall of the cyst or fistula is composed entirely of connective tissue without lymphoid tissue, and the cyst contains yellowish mucus-like fluid.
Thyroglossal cysts and fistulas – clinical manifestations
In the middle of the neck corresponding to the thyroid cartilage under the hyoid bone, a round mass of 1 to 2 cm in diameter with a smooth surface and clear edges is visible, and the cyst is solid due to filling and tension. It is more fixed and cannot be pushed up and down or left and right, but can be moved slightly up and down with swallowing or tongue extension movement. In small cysts, a cord can be found attached to the hyoid bone. When infection does not occur, it does not adhere to the skin without pressure, pain, and tenderness, and it forms a thyroglossal fistula after self-rupture or incision and drainage. The fistula often discharges clear or cloudy mucus from the fistula, and after a certain period of time, the fistula may temporarily close and crust over, but it soon ruptures and flows again, which can recur and persist over time.
Thyroglossal cysts and fistulas – diagnosis and examination
1. Most commonly seen in children and young adults. It is a round mass under the plane of the anterior hyoid bone of the neck with a smooth, well-defined, cystic appearance and no skin adhesions, which moves up and down with swallowing. It is palpable along the direction of hyoid bone, and the swelling can be felt to retract and lift up when the tongue is opened and stretched.
2, cyst secondary infection, local redness, swelling, tenderness, self-rupture or incision and drainage, can form a fistula that does not heal.
3, mucus secretion, often containing columnar and squamous epithelial cells.
Diagnostic basis
1, in the anterior middle of the neck is equivalent to the thyroid cartilage under the hyoid bone, can be seen in the garden-shaped mass, smooth surface, clear edges, swallowing or tongue extension slightly up and down movement.
2. The mass may be red, swollen, painful and painful due to infection, and the fistula often discharges clear or turbid mucus after self-rupture or incision and drainage, and the fistula may be temporarily sealed and crusted, but repeatedly ulcerated and drained for a long time.
Auxiliary examinations
1. In general, a check box “A” is sufficient;
2. Additional “B” tests can be performed when preparing for surgery to clarify the boundaries of the fistula and surrounding structures.
Thyroglossal cysts and fistulas – differential diagnosis
10-20% of the cysts are located above the hyoid bone and should be distinguished from the subchin lymphadenitis and dermatomal cysts that occur in this area. Cysts located between the sternum and the thyroid should be differentiated from tracheogenic cysts dermatomal cysts, thyroid cysts, softened tuberculous lymph nodes, and ectopic salivary gland cysts. Special attention should be paid to the ectopic thyroid gland, which has been reported in the literature to have hypothyroidism after misincision, as it lacks a normal thyroid gland in 70% of cases. Therefore, thyroid scans and functional examinations should be performed if necessary. Cysts that are slightly off the midline should be differentiated from cysts of gill origin.
1. Differential diagnosis of thyroglossal cysts
(1) Chronic lymphadenitis and lymphatic tuberculosis under the chin: it is manifested as a swelling under the chin, and lymphatic tuberculosis can also form a fistula for a long time if it breaks down. However, the lymph node lesions are more superficial than parenchymal masses often with pressure pain, which can be differentiated by medical history and biopsy.
(2) Ectopic thyroid: ectopic thyroid and thyroglossal cyst are both congenital abnormalities of the thyroid gland, and they are closely related in embryonic development. ectopic thyroid is often located at the root of the tongue or the pharynx of the blind foramen of the tongue, with a tumor-like protrusion, purple-blue surface, soft texture and clear borders, while the ectopic thyroid of the tongue is mainly located in the anterior part of the neck. Since 75% of ectopic thyroids are the only functioning thyroid tissue, incorrect removal will result in lifelong hypothyroidism. Clinical attention should be paid to the differentiation of the two, and radionuclide scanning is the most effective method of identification. When 131I or 99mTc scan is used, nuclear concentration in the ectopic thyroid site or absence of thyroid in the neck is seen.
(3) Parathyroid gland: it is not connected to the hyoid bone, the mass does not move up and down with swallowing, and it can be differentiated from thyroglossal cyst by ultrasound such as a substantial mass.
(4) Dermatomal cyst: it often appears as a swelling under the chin and can also be located in the superior sternal recess. Generally, the cyst has a thicker envelope, no fluctuating sensation, and a kneading sensation often adheres to the skin, and sebaceous material can be distinguished by puncture and aspiration without swallowing and tongue extension activities.
(5) Thyroid adenoma: This disease is mostly manifested as a painless mass in the anterior neck area with soft texture and clear borders, which can be identified by radionuclide scan with swallowing activities but not with tongue extension activities.
(6) Parotid cleft cyst: Mostly located in the carotid triangle, the mass is mostly deviated from the midline and is not related to the hyoid bone. The punctured material contains skin attachments and cholesterol crystals, which need to be identified by pathological examination. Intraoperatively, a fistula is seen crossing into the pharynx via the internal and external carotid arteries.
(7) Other cervical masses: such as thyroid cone lobe, cystic hydatid, lipoma, sebaceous cyst, sublingual cyst, laryngeal pneumatocyst, parathyroid cyst and teratoma, etc., can be differentiated according to the location and nature of the mass.
2. Differential diagnosis of thyroglossal fistula
(1) cervical tuberculous fistula: most of the fistula is caused by the spread of mediastinal tuberculous lymphadenitis, and the fistula is mostly located in the suprasternal fossa, with a history of the mass breaking down and discharging cheese-like material. The lungs can be differentiated by the presence of tuberculosis foci on X-ray and strong positive PPD.
(2) Gill fistula: This disease is located at the anterior border of the sternocleidomastoid muscle and sometimes the fistula is born with a clear, watery fluid. The fistula cord extends to the carotid artery and is not connected to the hyoid bone. If necessary, radiographs are taken through the fistula with contrast. The direction of the fistula can be understood for identification.
(3) Gill-derived median cervical fissure: The skin of the hyoid bone to the underside of the thyroid cartilage is found to be split after birth, 3-5 cm long and 2-5 cm wide, covered with a red moist lining, with a blind distal canal of several millimeters and a lentil-sized fibroid or fibrocartilage proximal to it, sometimes with upward fibrocartilage cords fixed to the chin nodes on each side.
Thyroglossal cysts and fistulas – treatment
There is no consensus on the necessity of removing small cysts, but given the complexity of surgery and the increased recurrence rate after infection, early surgery is preferable after diagnosis. The surgeon must be familiar with the characteristics of the following structures: (1) the fistula is closely attached to and penetrates the hyoid bone; (2) the fistula behind the hyoid bone is very small and fragile; and (3) the fistula has a s-compartment-like protrusion or lateral branches. The main point of surgery is to remove a part of the hyoid bone and all of the cyst and fistula to avoid postoperative recurrence, and the recurrence rate is about 4-5% due to incomplete excision. In cases with infection, an incision and drainage is made and antibiotics are given, and then surgery is performed to cure the infection after it has subsided.
Treatment principles
1. In principle, the disease should be treated mainly by surgery, and the surgery can be postponed for young and weak people as appropriate.
2, the complication of infection, first with antibacterial control of infection, high tension first incision and drainage.
If there is a fistula, surgery should be performed after the inflammation is controlled.
Thyroglossal cysts and fistulas – prevention and prognosis
(1) Make use of intraoperative US blue tracing and try to cut out small branches or fistulas. When performing US blue tracing, large cysts or fistulas can generally have good results as long as they are handled carefully to prevent US blue from contaminating the operative field. For small cysts or small fistulas, preoperative ultrasound localization analysis can be combined with no injection of US blue. Then do not pull off the fistula or small branch when separating, and after separating along the branch or fistula to the hyoid bone, resect the middle section of the hyoid bone about 1.5 cm. electrocoagulate the broken end of the hyoid bone, and then circumferential suture.
(2) The extent of hyoid bone resection should be adequate. From the embryonic development of thyroglossal cyst, the fistula of cyst and fistula do not all penetrate from the central part of the hyoid bone. They can be removed from different parts of the middle part of the hyoid body or through the surrounding tissues without penetrating the hyoid bone. Horisawa et al. found that at the level of the hyoid bone, the most distal branch of the thyroglossal canal was 0.24-0.96 cm from the midline, so it is necessary to remove at least 1.0 cm of the hyoid bone and the attached tissue. Generally, about 1.5cm of the hyoid bone is removed.
(3) For cases of recurrent infection or recurrence, it is firstly to control the infection well and to operate after the inflammation has subsided for 2 months. Secondly, all scar tissue, fistula and cystic wall should be removed as much as possible during surgery, such as those that cannot be removed can be cauterized by electrocoagulation.