Thyroid disease is a very common disease in surgical clinics, and the incidence of thyroid tumor is also increasing year by year, which is a great concern and problem for the people, this article introduces some knowledge about thyroid disease, hoping that those who read this article can have a general understanding of thyroid disease. I. What is the thyroid gland? What are its important functions? The thyroid gland is a very important endocrine gland in the human body. It is located on both sides of the trachea under the thyroid cartilage in the neck, generally weighing 20-30 grams (equivalent to half a tael), and is divided into two lateral lobes connected by an isthmus in the middle. The thyroid gland has two blood supply systems and is the organ with the most abundant blood flow in the body. The recurrent laryngeal nerve and the superior laryngeal nerve are closely related to the thyroid gland, and if these two nerves are damaged during surgery, hoarseness can result. Generally speaking, there are also a variable number of parathyroid glands on the back of the thyroid gland. The weight of the parathyroid glands is usually 35-40 mg/pc (equivalent to 12,000 cents per pound of pork, with each parathyroid gland taking up one part). Since the number and location of parathyroid glands vary from person to person, thyroid surgery (especially when all the thyroid glands are removed bilaterally) can easily lead to removal of the parathyroid glands and thus cause the corresponding symptoms. The thyroid gland is composed of thyroid follicles and parafollicular cells. The thyroid follicular cells mainly secrete thyroxine and the parafollicular cells (C cells for short) mainly secrete calcitonin. The main physiological effects of thyroxine are: 1. Thermogenesis Thyroxine increases oxygen consumption and thermogenesis, which plays an important role in maintaining normal body temperature. Patients will feel hot when the thyroid gland is hyperactive and cold when the thyroid gland is hypothyroid. 2, promote metabolic effect Thyroxine can promote the body’s sugar, protein and fat metabolism. 3, the effect on the neuropsychiatric system Thyroxine has a very important role in the development of nerve cells during the embryonic period, children with congenital hypothyroidism have severely impaired intellectual development and are demented; thyroid hormone also plays a great role in maintaining the normal function of the adult nervous system and has sympathetic activity, so when the thyroid gland is hyperactive, the patient will have symptoms such as agitation, insomnia, panic and mania. In contrast, hypothyroidism may cause symptoms such as unresponsiveness, apathy, drowsiness, and slowed heartbeat. Effects on growth and development Thyroid hormones affect the growth of the epiphysis, and children with congenital hypothyroidism may develop short stature and mental retardation, commonly known as “cretinism”. In addition to these physiological effects, thyroid hormones have important effects on vitamin metabolism, calcium and phosphorus metabolism, gastrointestinal activity, heart and gonads. Clinical knowledge of the function of the thyroid gland is mainly based on the detection of thyroid hormone levels in the blood. What are the common diseases of the thyroid gland? How should they be treated? Generally speaking, thyroid disorders can be divided into three categories: functional, inflammatory and neoplastic diseases. (A) Functional diseases include hyperthyroidism and hypothyroidism. 1. Hyperthyroidism can be divided into three types: primary hyperthyroidism (Graves’ disease), secondary hyperthyroidism (Plummer’s disease) and hyperfunctional adenoma. Their clinical manifestations include panic attacks, impatience, increased appetite but weight loss, poor sleep at night, fear of heat, easy sweating, protruding eyes in some patients, decreased menstrual flow in female patients, and decreased libido in male patients. Physical examination may reveal an enlarged thyroid gland, trembling when the hands are raised, rapid heartbeat, and excessive skin sweating. Blood tests for thyroid function indicate elevated TT3, TT4, FT3 and FT4 (some patients show elevated T3 or T4 only) and decreased sTSH. The treatment of hyperthyroidism varies. Primary hyperthyroidism can be controlled by medication, radioactive iodine and surgery, while secondary hyperthyroidism should be treated by surgery. 2. Hypothyroidism, destruction of thyroid follicles for various reasons, too little thyroid tissue remaining after surgery, and impaired thyroxine synthesis for various reasons can all lead to hypothyroidism. Mild hypothyroidism can be clinically asymptomatic, with only elevated sTSH on thyroid function tests, and some patients may have an enlarged thyroid gland; severe hypothyroidism can be clinically indifferent, chilly, and non-sunken edema of the lower extremities. The treatment for hypothyroidism is thyroid hormone supplementation. (B) Inflammatory diseases Thyroiditis can be divided into 3 types: acute, subacute and chronic 1. Acute thyroiditis is rare clinically, often due to oral or neck infection. It is characterized by painful swelling of the thyroid gland, increased body temperature, and elevated white blood cells. Early antibiotic treatment may be given, and if an abscess forms it should be drained with an incision. It is often secondary to influenza, tonsillitis or mumps, and is therefore presumed to be related to viral infection. The virus destroys the thyroid follicles, releasing a large amount of colloidal material into the follicles and causing a foreign body reaction in the thyroid gland. The disease often presents with painful enlargement of the thyroid gland on one or both sides and symptoms of hyperthyroidism, such as panic, fever and sweating. The disease is a self-limiting disease, so if the symptoms are not obvious, no drug treatment is required. If the pain is severe, symptomatic treatment or treatment with adrenocorticotropic hormone is possible, and antibiotic treatment is not effective. Chronic lymphocytic thyroiditis, also known as Hashimoto’s disease, is now considered to be an autoimmune disease, with elevated thyroglobulin antibodies (TGAB) and thyroid microsomal antibodies (TMAB) found in the serum. Pathologically, the main manifestations are follicular destruction and massive perifollicular lymphocytic infiltration. In the early stage, mild hyperthyroidism may be present, and in the late stage, hypothyroidism may be present. The thyroid gland is symmetrically enlarged and has a firm texture. The disease progresses slowly and does not require treatment in the early stages. In case of hypothyroidism, thyroxine supplementation should be used for replacement therapy. （Benign thyroid tumors are mainly thyroid adenomas, with follicular adenomas being the most common. They are mostly solitary, slow-growing and vary in size, but can increase rapidly with pain due to bleeding inside the adenoma, otherwise there is no special discomfort. It can be detected by ultrasound and CT. Surgery is the main treatment. (2) Malignant thyroid tumor 1) Differentiated thyroid cancer includes papillary carcinoma and follicular carcinoma, which accounts for about 85% of clinical thyroid cancer. In the early stage, there is no special clinical discomfort, but it can also be a painless lump with hard texture, and in the advanced stage, it can invade adjacent tissues and organs. Papillary carcinoma is mainly local infiltration and lymph node metastasis in the neck, while follicular carcinoma is more often hematogenous. Some patients with thyroid cancer have enlarged lymph nodes in the neck as the first symptom. Ultrasound and CT examination are the main diagnostic methods in clinical practice. With the increase of clinical application of high frequency ultrasound, the detection rate of early thyroid cancer has increased. Treatment is mainly surgical and the prognosis is good. (2) Medullary thyroid carcinoma originates from parafollicular cells (C cells) of the thyroid gland and is a neuroendocrine tumor. It accounts for about 10% of clinical thyroid cancer and is one of the multiple endocrine tumors. It can be disseminated, but some of them are hereditary in families. The clinical manifestations are similar to those of differentiated thyroid cancer. The prognosis is moderate with surgery as the main treatment. (3) Undifferentiated thyroid cancer is mostly seen in the elderly, accounting for about 5% of clinical thyroid cancer. (4) Other malignant tumors of thyroid gland include thyroid lymphoma and thyroid squamous carcinoma, which are rare in clinical practice and will not be described here. The parathyroid glands secrete parathyroid hormone, which regulates the metabolism of calcium and phosphorus in the body. The number of parathyroid glands varies, with about 80% of the population having four glands, mostly attached to the back of the thyroid gland. The most common clinical parathyroid disorder is primary hyperparathyroidism, mostly due to parathyroid adenomas. The main clinical manifestations are skeletal pain, osteoporosis, pathological fractures and bone deformities; recurrent kidney or ureteral stones; nausea and vomiting due to hypercalcemia, recurrent pancreatitis, and long-standing peptic ulcers. Because of the low incidence and slow progression of the disease, it is easily misdiagnosed clinically. Elevated serum parathyroid hormone and elevated blood calcium are the basis for diagnosis. Surgical removal of the diseased parathyroid adenoma is the main treatment method. Accurate preoperative localization is the key to successful surgery, and the commonly used localization methods are ultrasound, CT, MRI, radioisotope imaging, etc. Common complications after thyroid surgery 1, bleeding Mostly due to incomplete intraoperative hemostasis or dislodgement of the ligature, which can lead to asphyxia due to compression of the trachea and is a serious complication that can endanger life. 2.Choking and coughing or muffled voice Injury to the internal branch of the superior laryngeal nerve during surgery can cause choking and coughing, and injury to the external branch of the superior laryngeal nerve can cause muffled voice. 3, hoarseness is mostly caused by injury to the recurrent laryngeal nerve. Temporary nerve injury due to surgical pulling of the recurrent laryngeal nerve or edema and compression of the tissue next to the recurrent laryngeal nerve can lead to complete recovery of the voice after surgery; permanent nerve injury due to surgical cutting of the recurrent laryngeal nerve can be recovered to some extent after surgery by compensating for the vocal cords on the healthy side. Bilateral laryngeal nerve injury can cause asphyxia due to vocal fold closure. 4. Hypoparathyroidism is mostly caused by inadequate blood supply to the parathyroid glands due to intraoperative removal of the parathyroid glands or ligation of blood vessels. In hypoparathyroidism, blood calcium is reduced and generalized skin numbness and twitching of the extremities may occur.