A thyroglossal duct cyst is a congenital cyst formed in the neck as a result of incomplete degeneration and non-disappearance of the thyroglossal duct during the development of the thyroid gland in early embryonic life. The occurrence of thyroglossal duct cysts is not significantly related to gender, and can occur in both men and women, and can occur at any age, but is more common in adolescents under 30 years of age. Cysts can occur anywhere between the anterior median lingual foramen and the sternal notch, most commonly above and below the body of the hyoid bone, and sometimes to one side. The thyroglossal duct cyst is a congenital, developmental cyst that arises from the remnant epithelium of the thyroglossal duct, which is left in the deep cervical tissue due to incomplete degeneration of the thyroglossal duct during the formation of the thyroid gland during the embryonic period, and is formed by the accumulation of secretions from the overlying epithelium in the lumen of the duct. In the fourth week of embryonic development, the endoderm between the first pair of pharyngeal sacs, ventral to the pharyngeal cavity, plunges downward to form a diverticulum-like structure, the base of the thyroid gland, which later extends into the underlying mesenchyme to form a normal thyroid gland in front of the median cervical trachea; by the sixth week, the thyroglossal duct degenerates on its own, leaving only a shallow concavity at its starting point, the blind lingual foramen. If the thyroglossal duct degenerates incompletely during this process, the remaining epithelium may form a thyroglossal duct cyst within the trip from the root of the anterior median cervical trachea to the thyroid gland, and the cyst may communicate with the blind foramen of the tongue through the undegenerated thyroglossal duct. Examination 1.B ultrasound examination Ultrasound shows that the cyst has an intact envelope, clear boundary and regular morphology. The cyst wall is thin, and the cyst is mostly a liquid dark area with good sound transmission, and a few have linear separation echogenicity. In case of combined infection, the cyst wall may be thickened and not smooth, and a weak dot echogenicity can be seen in the liquid dark area. In some cases, papillary nodular echogenicity is seen in the wall of the capsule, which may be the echogenicity of thyroid tissue. Color Doppler ultrasonography shows a cystic echogenic dark area, in which no blood flow signal is seen, but blood flow and spectrum can be detected in the periphery, and this can be used to distinguish enlarged lymph nodes and ectopic thyroid gland. 2.CT examination can understand the nature of the mass, its size and the adjacent relationship with the surrounding tissues. Typical diagnostic criteria: typical site: the lesion is located between the blind foramen of the tongue and the thyroid gland, mostly above and below the hyoid bone, and is closely related to the hyoid bone; typical CT signs: round or oblate liquid density image, the cyst wall is mostly smooth and intact, when combined with infection, the cyst wall can be seen rough, when forming fistula, the shape is mostly irregular; enhanced scan: the lesion is mostly non-enhanced, when combined with infection, the cyst wall can be significantly enhanced; indirect signs: adjacent Indirect signs: adjacent tissue structures may be displaced by pressure; wall nodules: they appear as small mound-like protrusions from the cyst wall into the lumen, with a wider base, and may be enhanced during enhancement. Radionuclide imaging is also useful in the diagnosis of this disease, to assess the size of the cyst or fistula, to understand the presence of active thyroid tissue, and to differentiate it from a thyroid mass. 4. Iodine oil imaging can clarify the course of the thyroglossal fistula, but is less commonly used in clinical practice. Diagnosis The initial diagnosis of thyroglossal cyst can be made based on the location of the cystic swelling in front of the neck, the movement of the tongue, and the extraction of clear, slightly cloudy, yellow, thin or mucous fluid by puncture. Differential diagnosis 1. Chronic lymphadenitis and lymphatic tuberculosis under the chin manifests as a swelling under the chin, and lymphatic tuberculosis can also form a fistula if it breaks down for a long time. However, lymph node lesions under the chin are more superficial, often parenchymal swelling and pressure pain, which can be differentiated based on medical history and biopsy results. 2. Ectopic thyroid gland Ectopic thyroid gland and thyroglossal duct cyst are both congenital abnormalities of the thyroid gland, which are closely related to each other in embryonic development. The ectopic thyroid gland 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. Since 75% of ectopic thyroids are the only functioning thyroid tissue, incorrect removal of them will result in serious lifelong hypothyroidism. Radionuclide scans are the most effective method of differentiation, and the diagnosis can be made by the presence of nuclear concentrations in the ectopic thyroid gland or by the absence of thyroid tissue in the neck. The parathyroid gland is not connected to the hyoid bone, the mass does not move up and down with swallowing, and the ultrasound shows a substantial mass, which can be distinguished from a thyroglossal cyst. 4.Dermatomal cyst often appears as a swelling under the chin, and may also be located in the superior sternal recess. Generally, the cyst has a thicker envelope, no sense of fluctuation, often adheres to the skin, and does not move with swallowing and tongue extension. 5, thyroid adenoma This disease is mostly manifested as a painless mass in the anterior cervical region and thyroid tissue, soft, with clear borders, which can move with swallowing, but not with tongue extension, and can be identified with the help of radionuclide scan. 6, parotid cleft cyst Mostly located in the lateral neck or carotid triangle, the mass is mostly deviated from the midline, not related to the hyoid bone. The punctured material may contain skin attachment and cholesterol crystals, which need to be identified by pathological section. Other neck masses such as thyroid cone lobe, cystic hydatid, lipoma, sebaceous cyst, sublingual cyst, laryngeal air-containing cyst, parathyroid cyst and teratoma can be identified according to the location and nature of the mass. Surgery is the main method to cure a thyroglossal cyst or fistula. Because of the close relationship between the cyst and fistula and the hyoid body, the middle part of the hyoid body connected to it should be removed during surgery to prevent recurrence. A transverse incision should be made along the skin line of the neck on the surface of the cyst at a length that fully exposes the surgical field, or in the case of a fistula, a shuttle incision including the skin of the fistula; if the cyst is in a low position, another transverse incision should be made when the cyst is stripped to the plane of the hyoid body. The cyst or fistula should be exposed by cutting the skin, subcutaneous tissue, broad cervical muscle, and anterior cervical strap muscle in layers according to the incision design, and then separated along its perimeter, taking care not to damage the nail-shaped hyoid membrane, and when the lower edge of the hyoid body is reached, the hyoid membrane and attached muscles are cut on both sides of the part connected with the hyoid body, and the cyst or fistula is removed together with the severed part of the hyoid body by cutting both sides of the hyoid body with bone scissors. The cyst or fistula was removed together with the severed part of the hyoid body. The wound cavity was rinsed, the bleeding was completely stopped, the fistula muscle at the root of the tongue was sutured to eliminate the dead cavity, and the muscle and periosteum attached to the superficial side of the severed end of the hyoid body were sutured. In case of cystic carcinoma with cervical lymph node metastasis, cervical lymph node dissection is performed. If the postoperative pathological type is papillary carcinoma or follicular carcinoma, thyroxine suppression therapy can be used. In case of squamous cell carcinoma, postoperative radiation therapy is feasible.