Thyroglossal cyst is a congenital cyst formed in the neck after incomplete degeneration of the thyroglossal duct during the development of the thyroid gland in early embryonic life. The cyst often has epithelial secretion accumulation within the cyst can be connected to the oral cavity through the blind hole of the tongue, and secondary infection of the cyst can break down to form a thyroglossal fistula. Zhang Mei, Department of Two Gland Surgery, Shandong Qianfo Mountain Hospital
Etiology
The normal thyroglossal fistula is located in front of the hyoid bone, with a diameter of 1~2mm, and is closely connected to the front of the hyoid bone and cannot be separated. It begins in the fourth week of embryonic life, when epithelial cells proliferate in the midline of the primitive pharyngeal wall, which corresponds to the plane of the second and third pairs of gill arches, forming a blind duct that extends caudally, i.e., the thyroid gland proto
Thyroglossal duct cyst
The base of the thyroglossal duct is called the thyroglossal duct. The thyroglossal duct descends along the midline of the neck to the anterior aspect of the future trachea, and the end expands to the sides, forming the left and right lateral lobes of the thyroid gland. Under normal conditions, the thyroglossal duct begins to atrophy and degenerate by the sixth week of embryonic life. After the degeneration of the upper part of the thyroglossal duct disappears, a shallow concavity remains at the beginning of the opening, called the blind foramen. If for some reason the thyroglossal duct does not disappear or degenerates incompletely after the 10th week, the residual tube-like structure may form a cyst in the middle of the anterior cervical region between the root of the tongue and the thyroid gland due to accumulation of epithelial secretions, which is called a thyroglossal cyst. There are 3 forms of fistula: complete fistula, which goes from the blind foramen to the outer skin of the neck; inner blind, which opens in the blind foramen; and outer blind, which opens in the skin of the neck.
Pathogenesis
Cysts of the thyroglossal duct occur in the midline of the neck and can occur anywhere between the blind foramen and the sternal notch, but are most commonly found near the hyoid bone, mostly between the thyroid gland and the hyoid bone. Cysts above the plane of the hyoid bone are mostly located in the midline, and those below the plane of the hyoid bone can be located in the midline or to the side, with the left side being the most common. Thyroglossal cysts often have an intact envelope, with a thin wall, surrounded by fibrous tissue and lined with pseudostratified ciliated columnar epithelium, flattened epithelium, complex squamous epithelium and other epithelial cells with abundant lymphoid tissue, and inflammatory cells in cases of co-infection: there can be thyroid tissue within the cyst wall. The contents of the capsule are mostly mucus-like or jelly-like material, which contains proteins and cholesterol. The disease can also be carcinogenic. Ucherman first described carcinoma of the thyroglossal duct in 1915, and since then more than 150 cases have been reported in the literature, mostly papillary carcinoma, but also follicular carcinoma and squamous carcinoma. However, there is still controversy about its origin. Some believe that it is the result of the spread of occult thyroid cancer, while others believe that it originates from ectopic thyroid tissue within the wall of the thyroglossal duct cyst.
Clinical presentation
Thyroglossal duct cyst
Thyroglossal duct cyst
The majority of patients have an anterior cervical swelling, which can occur anywhere in the midline from the foramen magnum to the sternal notch, but the superior and inferior hyoid bones are the most common, sometimes to one side.
The slow-growing round cyst may be accompanied by local symptoms such as neck distension, swallowing discomfort and foreign body sensation in the pharynx. If the cyst is located near the blind foramen of the tongue, it can elevate the root of the tongue and cause swallowing, speech and respiratory dysfunction. If the cyst is located near the blind foramen of the tongue, it can elevate the tongue root and cause dysphagia, speech and respiratory disorders. If the cyst is infected, it can appear as a painful mass or abscess.
On physical examination, a mass can be palpated near the midline of the neck, soft in texture, 1-5 cm in diameter, round or oval, smooth surface, clear border, soft texture, no adhesion to the surface skin and surrounding tissues, elastic or fluctuating feeling. For cysts located below the hyoid bone, tough cords can be palpated between the hyoid body and the cyst and the hyoid body adhesions can move up and down with tongue extension movement.
Complications.
The cyst may become infected secondary to communication with the oral cavity through the blind foramen of the tongue. Repeated infections may rupture on their own, or after incision and drainage of a misdiagnosed abscess, a thyroglossal fistula may develop. Primary fistulas may also be seen after birth. If left untreated for a long time, thyroglossal fistulas can also become cancerous.
Examination
Thyroglossal cysts
Ultrasound examination The ultrasound image of thyroglossal duct cysts is mostly a round or oval liquid dark area with clear borders, mostly a single cyst, with a few thin-walled separations. The border may be blurred in long-standing cases or with infection, and a variable number of floating light spots may be seen in the liquid dark area. In the case of fistula formation, a shallow to deep central faint cord-like structure can be detected connected with the mass or the hyoid bone.
2. CT examination can understand the nature of the swelling. Most of the thyroglossal cysts are cystic occupations anywhere between the blind foramen of the tongue and the incision of the sternocervical vein in the anterior part of the neck, with an intact envelope, thin cyst wall and low density of the cystic contents. In some patients (about 30%), the characteristic density shadow of thyroid tissue can be seen in the wall.
Radionuclide imaging is also helpful in the diagnosis of this disease. 131I or 99mTc scans can assess the size of the mass, understand the presence of active thyroid tissue, and help to differentiate it from a thyroid swelling.
4. Neck X-ray and barium esophagogram are helpful for diagnosis
5. iodine oil imaging can clarify the fistula pathway of thyroglossal cysts.
Diagnosis
Thyroglossal cyst
The initial diagnosis of thyroglossal cyst can be made based on the site of the swelling in front of the neck and the movement of tongue extension, and the transparent and slightly cloudy yellow thin or mucous fluid can be drawn out by puncture. Imaging examination can help to further clarify the diagnosis, among which ultrasound examination is more significant.
Differential diagnosis.
1. Differential diagnosis of thyroglossal cyst
Thyroglossal duct cyst
(1) Chronic lymphadenitis and lymphatic tuberculosis under the chin: manifested as a swelling under the chin, lymphatic tuberculosis can also form a fistula if it breaks down for a long time. However, lymph node lesions are more superficial than parenchymal swellings often have pressure pain, which can be differentiated by history and biopsy.
(2) Ectopic thyroid: ectopic thyroid and thyroglossal cyst are both congenital abnormalities of the thyroid gland, both 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, the patient often has slurred speech, and in severe cases, swallowing and breathing difficulties. Since 75% of ectopic thyroid glands are the only functional thyroid tissue, incorrect removal will result in lifelong hypothyroidism with serious consequences. 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 area or absence of thyroid in the neck can be 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 distinguished from thyroglossal cyst by ultrasound as a substantial mass.
(4) Dermatomal cyst: it often appears as a subchin swelling and can also be located in the superior sternal recess. Generally, the cyst has a thicker envelope, no fluctuating sensation, 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 border, which can be distinguished by radionuclide scan with swallowing activity but not with tongue extension activity.
(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, fistulae are 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: Mostly, the fistula is caused by the spread of mediastinal tuberculous lymphadenitis and the fistula is located in the suprasternal fossa, and there is a history of the mass breaking down and discharging cheese-like material. The lungs can be differentiated by the presence of tuberculous 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 flow. The fistula cords extend to the carotid artery and are not connected to the hyoid bone. If necessary, radiographs are taken through the fistula with contrast. The direction of fistula travel can be understood for identification.
(3) Gill-derived median cervical fissure: the disease is found postnatally with a split in the skin from the hyoid bone to the underside of the thyroid cartilage, 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 palpable upward fibrous cords fixed to the chin nodes on each side, so it is easily distinguished from a thyroglossal fistula.
Treatment
Because thyroglossal cysts are often combined with infections and can easily become fistulas, and thyroglossal fistulas can persist for years. Therefore, once this disease is diagnosed, surgery is often recommended as soon as possible.
1. Sistrunk surgery
(1) timing of surgery: cervical thyroglossal cysts without infection, surgery is safer than 1 year old, such as the trend of infection, should be operated as soon as possible; tongue root cysts, although the incidence of only 1% to 2% of the disease, because of the impact on the respiratory tract or swallowing difficulties, surgery is not limited by age, should be performed as soon as possible Sistrunk surgery; neck infection to wait for 2-3 months after the inflammation subsides Sistrunk surgery.
(2) Scope of surgery: The scope of resection includes the cyst, fistula, the middle of the hyoid bone and some tissues around the blind foramen of the tongue.
(3) Operation points: except for children with general anesthesia, adults can choose local anesthesia when peeling off the cyst should pay attention to the bottom and the upper posterior pole, do not leave the tube, should be performed with part of the muscle of the whole excision to the hyoid bone, the cyst and hyoid bone adhesions can be clearly revealed, with bone scissors on both sides of the cyst attached to cut off the hyoid bone, cut off the hyoid bone about 1 cm. this is the key to the success of the operation. After cutting the hyoid bone, dissect to the blind foramen of the tongue with some surrounding tissues for columnar excision. Do not pull violently during surgery to avoid fracture of the cystic wall or the fistula and its branches resulting in partial remnants. At the beginning of the operation for thyroglossal fistula, 1% methylene blue can be injected into the fistula to assist in its identification. If the fistula is long, a “stepped” parallel incision is used as appropriate. If you have a fistula or secondary infection, apply antibiotics as appropriate after surgery.
(4) Postoperative recurrence rate: After proper Sistrunk surgery, the recurrence rate is about 3% to 5%, and most recurrences occur within 1 year after surgery. Re-operation is significantly more difficult. Therefore the success rate of the first surgery must be improved as much as possible.
Common causes of recurrence: cysts or fistulas secondary to infection, when performing Sistrunk surgery, because the anatomy is not clear, not completely removed thyroglossal duct, especially the residual tubular tissue block above the middle part of the hyoid bone is prone to recurrence, so the recurrence rate is relatively high about 7% for those who operate after infection; residual lateral branch gland respiratory epithelial cells fine cysts on both sides of the front of the hyoid bone or its lateral branches communicating with the salivary glands in the tongue. The thyroglossal duct cyst or fistula is not completely removed from the midline of the neck, and there may also be coexisting cystic tissue of the gill slit; the thyroglossal duct adheres to the thyroid gland, or even penetrates into the thyroid gland so that the thyroglossal duct tissue is not completely removed.
2. Cervical lymph node dissection In case of malignant tumors, the Sistrunk procedure can be used to achieve cure because the cancer foci are generally small. In case of cervical lymph node metastasis, cervical lymph node dissection is required.
If the pathological type is papillary carcinoma or follicular carcinoma, thyroxine suppression therapy should be used after surgery.
4.Radiation therapy In case of squamous cell carcinoma, radiation therapy should be applied after surgery.
Prognosis
Postoperative recurrence of thyroglossal cyst may occur after surgical resection. The literature reports that the postoperative recurrence rate of Sistrunk’s surgery is 3%-5%, but there are reports that the recurrence rate is as high as 26.9%. The recurrence rate of postoperative recurrence can be up to 33%.
2. The possibility of carcinoma was first described by Ucherman in 1915. Since then, more than 150 cases have been reported in the literature, mostly papillary carcinoma, but also follicular carcinoma and squamous carcinoma. However, there is still controversy about its origin, with some suggesting that it is the result of the spread of occult thyroid cancer, while others believe that it originates from ectopic thyroid tissue within the wall of the thyroglossal duct cyst.