The normal thyroid is a solid tissue with a uniform texture and weighing about 20 g. An enlarged thyroid gland is a goiter. If the texture remains homogeneous, it is called a diffuse goiter, or if there are nodules, usually multiple, it is called a nodular goiter. Nodular goiter may or may not be combined with hyperthyroidism. It is classified according to the cause as endemic (prevalent in endemic areas), sporadic and compensatory (after partial thyroidectomy). In general cities or regions, mostly non-endemic, it is basically sporadic.
Morbidity
Except for a portion of sporadic nodular goiters, the majority of nodular goiters are associated with endemic iodine deficiency and are therefore a worldwide disease. The incidence is higher in underdeveloped countries, especially in mountainous, semi-mountainous and hilly areas far from the coast, reaching up to 85% of the inhabitants. Approximately 20% of the world’s population lives in iodine-deficient areas, and in recent years, after iodine prophylaxis, about 10% of the population still suffers from endemic goiter. In non-endemic areas, it is generally disseminated. The prevalence in the total population is 4% for adults in the United States and at least 7% in China. Clinically detected goiters are nodules that can be palpated by hand or are already enlarged, and many are nodules that can only be seen microscopically and are not clinically detectable, so the actual incidence is much higher. The presence of thyroid nodules has been reported in 50% of cases, of which 75% are multiple and 25% are solitary. Age-related endemic goiter is more prevalent from 10 to 18 years of age, whereas sporadic goiter occurs mainly in adults, and the older the age, the higher the incidence. The incidence is much higher in women than in men, ranging from 4 to 13 times higher by gender.
Causes
1. Iodine deficiency in the living environment is a recognized cause of goiter. According to WHO standards, adults need 150 ug of iodine daily, and children between the ages of l and l0 need 70 to 100 ug of iodine daily. women during pregnancy and lactation have an increased need for iodine and are prone to relative deficiency. Long-term iodine deficiency is bound to affect the production of thyroid disorders, resulting in increased secretion of thyrotropic home (TsH) by the pituitary gland, stimulating thyroid hyperplasia and nodule-like changes.
2, thyroxine synthesis disorder is the main cause of sporadic nodular goiter in non-endemic areas.
(1) Consumption of goitrin-causing substances (goitrin): Some substances can interfere with the synthesis or release of thyroxine at a certain point in the process, resulting in an insufficient amount of thyroid wrap production, with the same consequences as iodine deficiency, such as thiocyanates, phenols, and bioflavonoids. These substances or their precursors are often found in certain food crops, such as millet, sorghum, beans and vegetables. In addition, nitrates can all contribute to the development of goiter.
(2) Goiter-causing drugs: Thiourea compounds, lithium salts, certain drugs such as para-aminosalicylic acid and sulfonamide have the potential to cause goiter.
3. Somatic factors May be related to heredity. It is believed that the occurrence of goiter is polygenic and there may be a combination of multiple factors.
4. Post-surgical compensatory factors When the thyroid gland needs to be surgically removed for various reasons, including nodular goiter and major excision, the remaining thyroid gland gradually proliferates and enlarges in order to produce enough thyroxine for the body’s needs, resulting in goiter of the residual thyroid tissue.
5. Other factors Some studies have found that the occurrence of goiter may be related to the autoimmunity of the thyroid gland. In addition, a history of previous radiation exposure to the neck may also induce goiter. In recent years, it has been found that high iodine levels can also lead to goiter.
Pathogenesis and pathology
According to the dynamic balance mechanism of the hypothalamus-pituitary-thyroid axis, a decrease in the level of thyroxine in the body leads to an increase in TsH secretion, while an increase in the level of the thyroid gland leads to a negative feedback and a decrease in TsH production. The thyroid gland, as a target organ, is fully under the regulation of TsH function. There are also irregular cyclic changes in the thyroid gland holding cells (follicular epithelial cells) according to the metabolic demands of the body. When the dynamic balance of the hypothalamus-pituitary-thyroid axis is disturbed, the histological changes in the thyroid gland become even more irregular. If the enhanced TsH stimulation continues or worsens, the thyroid gland evolves into pathological changes with a slow process and diverse histological changes, which can be divided into 5 phases.
(1) Diffuse enlargement of the thyroid gland with increased vascularity, some for the appearance of enlarged small follicles, but with essentially uniform histology.
(2) Some follicles in the thyroid gland continue to enlarge, with increased gliosis and the appearance of more columnar epithelium, but some follicular holds show inactivity and no further changes, with uneven follicular size and the beginning of uneven histological changes.
(3) Some follicles continue to increase in size, some fuse with each other, nodules are formed, the nodules themselves are of different sizes and very unevenly distributed, and the thyroid gland shows obvious multiple nodules. The follicular epithelium may appear papillary hyperplasia, and bleeding may occur within the follicles. The tissue around large nodules is compressed and gradually becomes the perineurium of the nodule.
(4) Some nodules continue to enlarge, fuse, and become cystic. Because the nodules are non-functional, the colloid that they fit becomes thin, and hemorrhage may still occur. The surrounding tissues become more compressed, and the tissues outside the peritoneum undergo atrophy and fibrosis. Thyroid nodules vary in size, are unevenly soft and hard, and coexist as cystic and solid.
(5) Cystic degeneration continues to develop, hemorrhage is common, tissue necrosis may occur within the capsule due to ischemia, fibrosis of the extracapsular thyroid tissue is more severe, and calcification may occur. Sometimes the remaining relatively normal thyroid tissue can have neoplastic follicle formation.
In conclusion, the pathology of nodular goiter is characterized by the coexistence of proliferative and atrophic lesions, progressive and degenerative lesions, and cystic and solid lesions.
Nodular goiter generally refers to a normal functioning thyroid gland, but there are a few cases of nodular goiter combined with hyperthyroidism in about 5% of patients, especially in elderly patients with a long history of the disease. This hyperthyroidism is secondary.
Clinical manifestations
Patients often come to the doctor only because they find thickening of the neck when tying the collar button or unintentionally touching a lump in the front of the neck, and many patients are found by the doctor during physical examination. Sometimes internal bleeding occurs due to individual cysts and the patient finds a sudden lump in the neck, which rapidly increases in size and is accompanied by pain. If there is a significant increase in rent or a bulging swelling in the neck, the patient often suffers from an affected appearance, and when the swelling increases to a certain extent, compression symptoms may appear. It often occurs as compression of the trachea, with conscious breath-holding and dyspnea, aggravated when lying down, and even croup. When the thyroid gland enlarges laterally and posteriorly, such as compression of the esophagus, it can cause difficulty in swallowing; compression of the internal jugular vein, resulting in congestion of the same side; compression of the recurrent laryngeal nerve, resulting in hoarseness; involvement of the superior laryngeal nerve causes choking and coughing.
The larger the thyroid gland is, the more prominent the neck enlargement or anterior neck protrusion is, and the larger the individual xu nodes are, the more localized the elevation or asymmetry of the two cases. The normal thyroid gland is not palpable on palpation, but can be palpated when the thyroid gland is enlarged, especially because the thyroid gland is hardened and easier to mold. Nodules less than 125 px in diameter are not easily palpable, while nodules over 25 px are generally palpable, often multiple, large or small, and unevenly distributed. If there is bleeding in the cyst, the cyst is tense to touch and may have pressure pain. If the cyst or the compressed thyroid tissue is fibrotic or even calcified, the texture becomes hard and the entire thyroid gland is unevenly soft and hard. A giant goiter should be noted for the presence of Horner’s sign, which is ipsilateral suit face drooping, pupil narrowing, and absence of facial sweating. Patients with breath-holding without corresponding enlargement of the thyroid gland should pay special attention to the presence of a retrosternal goiter. If there is hoarseness, a vocal cord examination should be performed. After completing the thyroid examination, do not miss to check the lymph nodes on both sides of the neck and pay attention to any enlargement.
3.Imaging examination
(1) Ultrasound: Ultrasound is the preferred test. It can determine the presence of nodules and scan for nodules below 25px, the size of the nodules, whether the nodules are single or multiple, and also clarify whether the nodules are cystic or solid. It is also helpful to know if there is a retrosternal goiter.
(2) CT: CT is helpful to understand the extent of goiter, whether there is compression of the trachea, and whether there is a retrosternal goiter.
(3) Nuclear imaging: It can help to understand the size and shape of the thyroid gland and the presence of nodules. It can also be divided into cold, warm and hot nodules according to the depth of the imaging, which can help to understand the function of nodule uptake and help to judge the nature of nodules.
(4) Others: In recent years, positron emission tomography (PET) has been reported to be quite accurate in detecting malignant nodules, but the number of cases is small and more experience has to be accumulated.
Diagnosis and differential diagnosis
The thyroid gland is located on the surface of the body, making it easy to examine. Goiter and nodules are easily detected. The diagnosis of nodular goiter is generally not difficult. It should be noted that small nodules often cannot be molded, but there may be a feeling of uneven texture of the thyroid gland, at which point an ultrasound examination is needed to help determine the presence of nodules and their size and number. If necessary, further nuclear tests should be done. In addition, when making the diagnosis, attention should be paid to the combination of hyperthyroidism. In the case of a large thyroid gland, attention should be paid to the presence or absence of pressure on the recurrent laryngeal nerve and sympathetic nerve, trachea and veins. When a retrosternal goiter is suspected, a cT examination is often required in addition to ultrasound. If a posterior sternal mass is found, it should be differentiated from a mediastinal mass, which is located entirely in the mediastinum, whereas a posterior sternal goiter is usually partly attached to the lower part of the neck above the cytomeles, but if the entire enlarged thyroid gland sinks and falls into the mediastinum, it is not easy to differentiate, and nuclear imaging is useful for diagnosis. Sometimes it is also necessary to distinguish it from an aneurysm of the aortic arch, which is not difficult to identify because it has a distinct pulsation.
Treatment
Nodular goiter is a benign disease with a long and slow progression. Unless there are symptoms of pressure, the patient only feels discomfort in the front of the neck. Endemic goiters located in endemic areas, because they are actually a compensatory lesion, can be given sufficient doses of iodine to keep the disease from progressing or to have some degree of reduction. Adolescent goiter is caused by a surge in demand for thyroxine during growth and development, and is also a compensatory simple goiter. Strictly speaking, it is a different disease concept from nodular goiter, which can return to normal on its own after puberty without treatment or surgery, and has a high recurrence rate if the enlarged thyroid gland is mistakenly removed, resulting in more loss of thyroid function. In adults with sporadic nodular goiter, if the enlargement is not obvious, the nodules are not very large and evenly distributed and do not affect the appearance heavily, alternative therapy can be used to give thyroid preparations. The dosage of medication should be adjusted during the course of treatment according to whether the enlarged thyroid gland has shrunk or not and whether the patient has symptoms of hyperthyroidism. The use of substitution therapy is contraindicated in cases of nodular goiter with hyperfunction, and should be used with caution in patients with heart disease. Further investigations, including FNAB, should be performed, especially if there is a suspicion of cancer. For compensatory nodular hyperplasia after thyroid surgery, reoperation is not recommended in principle unless it significantly affects the appearance or produces pressure pox, and if the diagnosis is malignant or cancer recurrence. However, sometimes the use of surgical treatment is necessary.
Indications for surgery.
(1) The thyroid gland is large, has affected the appearance, and the patient insists on surgery.
(2) Symptoms of compression of adjacent organs.
(3) Post-thoracic goiter.
(4) Huge goiter that not only hinders the appearance
(5) Those who cannot exclude malignancy by various examinations.
(6)FNAB confirmed to be malignant
(7) Those who have been previously treated surgically for a diagnosed thyroid adenoma or goiter and then have a recurrence, but special attention should be paid to exclude simple irregular enlargement of the remaining thyroid gland.
(8) Secondary hyperthyroidism.
Surgery: It is not necessary to follow the scope of removal required by standardized major thyroidectomy. The amount of removal can be decided according to the number and distribution of nodules. If the nodules are individually large and the remaining nodules are few in number and more concentrated, partial thyroidectomy is feasible. If, after partial thyroidectomy, there are still a few scattered nodules in the remaining thyroid gland, they can be removed one by one, preserving as much normal thyroid tissue as possible. If there are few nodules on one side, the thyroid gland on that side can be removed with fewer nodules, but it is important to remove the nodules. If one side is cancerous or suspicious, a lobectomy is possible on that side and a partial excision on the opposite side. A retrosternal goiter can usually be done through a cervical incision, but requires endotracheal anesthesia. In huge goiters with a long history of disease, especially when organ compression symptoms are present, the possibility of tracheal tenderness should be monitored, and tracheal extubation can be delayed and tracheotomy performed if necessary.