Thyroid cysts have a high clinical incidence, accounting for about 5% to 20% of thyroid nodules. In fact, thyroid cyst is not a single disease, but a clinical manifestation derived from a variety of thyroid diseases. Tian Xuejun, deputy director of general surgery at Tsinghua University Yuquan Hospital, tells us what a thyroid cyst is. A. Etiology The origin of thyroid cysts is complex, and most of them are degenerated thyroid nodules and adenomas. The swelling growth of thyroid nodules and adenomas compresses the surrounding veins. This causes local blood circulation disorders, tissue ischemia, degeneration and necrosis, stasis and edema in the interstitium, and fluid accumulation, resulting in cysts. Compression of peripheral arteries causes ischemic necrosis of tissues, and then necrotic cysts are formed. If perivascular tissue degeneration and necrosis occurs, the blood vessel loses tissue support and ruptures, resulting in a hemorrhagic cyst. In some thyroid adenomas, the follicular cavities are large and may fuse with each other to form a gelatinous cyst. A few cysts originate from the remnants of the lingual ducts of the thyroid gland or the posterior body of the gills. Very few are formed by hemorrhagic necrosis of thyroid carcinoma. Pathology According to the nature of cyst contents, it can be divided into colloid cyst, plasma cyst, necrotic cyst, hemorrhagic cyst and mixed cyst. (1) Gelatinous cysts are formed by the fusion of thyroid follicles with each other, and the cyst fluid is viscous, yellowish, and uniodinated thyroglobulin. The cysts are more compartmentalized and multihoused, and the cyst wall is tied to flattened follicular epithelial cells. (2) Plasmacytoid cysts, mostly degenerating from thyroid nodules or adenomas, have thin, colorless fluid and a fibrous connective tissue wall. A few originate from the remnants of the lingual ducts of the thyroid gland or the posterior body of the gills, and the cyst wall is composed of phosphoepithelial cells. (iii) Hemorrhagic cysts, where the cyst fluid is stale blood and coffee-colored. (iv) Necrotizing and mixed cysts, in which the cystic fluid consists mostly of necrotic tissue and stale blood, is more viscous, and the cystic wall is composed of fibrous connective tissue. Thyroid cysts can be subdivided into partial and complete cysts, called thick-walled cysts and thin-walled cysts, respectively. Thick-walled cysts are due to cystic degeneration of the nodular portion, leaving a partially substantial mass around or on one side of the cyst. Thin-walled cysts are cystic changes in all nodules with thin walls. Third, clinical manifestations Patients do not have any discomfort and find the neck mass by chance, most of them are single, occasionally multiple, and the diameter is mostly between 2~125px. The surface of the mass is smooth, the boundary is clear, there is no tenderness, and it can move up and down with swallowing. When the intracapsular pressure is not high, the texture is soft and cystic to touch, and when the internal pressure is high, the texture is firm. It is difficult to make a diagnosis only by palpation, but ultrasonic examination can accurately determine whether the mass is a cystic or substantial nodule and distinguish between thin-walled and thick-walled cysts, and radionuclide imaging is “cold nodules”, and thyroid function tests are normal. Treatment Thyroid cysts are mostly benign. Thyroid cancer with cysts is rare, about 1% to 2%, and cancerous cysts can usually be detected by cytological examination of cyst fluid. In the past, thyroid cysts were mostly treated by surgery to remove the cyst. Due to the surgical operation left tumor scars, affect the aesthetics, and have certain complications. At present, most advocate puncture and fluid aspiration and injection sclerotherapy. Commonly used sclerosing agents are tetracycline, streptomycin, hydrocortisone and 2% to 3% tincture of iodine. These sclerosing agents can cause aseptic necrosis of the cyst wall, prevent cystic fluid production, and cause adhesion of the cyst wall, fibrosis, cystic cavity occlusion, and achieve the purpose of treating the cyst. This treatment is most effective for thin-walled cysts, with an efficiency of 94%. Thick-walled cysts have poor efficacy. For thick-walled cysts with no obvious demarcation between the substantial mass and the surrounding tissues, and whose cyst contents are bloody and accumulate rapidly after repeated aspiration, the possibility of cancer should be alerted, and surgery is the best treatment. Intraoperative pathological biopsy for malignant tumor is treated as thyroid cancer. After irritating treatment of thyroid cyst puncture and aspiration, oral thyroid hormone preparation is given to reduce cyst recurrence and promote the absorption of residual hard nodes.