Anomalies of development . Aplasia is extremely rare at an early age. Hypoplasia often occurs in the fetus in endemic areas and is caused by a lack of iodine in the mother’s body.
An anomaly of development is also manifested by the preservation of the thyroid-lingual duct. In most cases, the persistent duct ends blindly, leading to the formation of a median cyst of the neck. In the cyst wall, residues of the thyroid parenchyma can be found. The cyst is lined with epithelium, which is a continuation of the epithelium of the pharynx. Cyst epithelium can serve as a source of tumor development.
Additional (aberrating) thyroid glands are divided according to localization into the median (at the base of the tongue, above and below the hyoid bone, between the isthmus of the gland and the jugular notch) and lateral (along the jugular vein). Their occurrence is associated with a delay in the development of the gland in embryogenesis or with the additional formation of lateral primordia – derivatives of the pharyngeal pockets. With increased development of the additional thyroid gland, the parenchyma of the main lobes of the gland is reduced in size.
Dystopia is caused by a vicious laying of the organ, and therefore the location of the gland changes. There are mediastinal, intraglottal, intraopharyngeal, retroesophageal and other localizations of the thyroid gland. Sometimes additional thyroid glands are found in the heart bag, myocardium.
Circulatory disorders . Arterial hyperemia of the thyroid gland is observed with diphtheria, scarlet fever, influenza, thyrotoxic goiter, stress. It is accompanied by a persistent expansion of capillaries, sinusoids with prestasis in them.
Venous hyperemia is noted with hypertension of the small circle, tumors of the thyroid gland or organs adjacent to it, nodal stroma.
Thyroid hemorrhages are observed with thyrotoxic goiter, asphyxia of newborns, acute infectious diseases, tumors. Blood flows into the cavity of the follicles or stroma. After extensive hemorrhages, cysts and sclerosis fields form.
Thrombosis and embolism of the vessels of the thyroid gland are rare and are observed mainly in the tumor nodes, sometimes after a stumectomy. Vascular thrombosis leads to the development of ischemic necrosis of the thyroid gland tissue.
Atrophy of the thyroid gland is noted with debilitating diseases, pathology of other endocrine glands (pituitary, adrenal glands), prolonged use of radioactive iodine, thiourea preparations. The size and weight of the thyroid gland is reduced. Histologically, there is a decrease in the size of follicles, flattening of the follicular epithelium, replacement fibrosis, hyalinosis or stromal lipomatosis, weakening of the PAS reaction of the basement membranes of the follicles and colloid. Sharp atrophy of the thyroid gland is observed with the so-called multiple sclerosis of the endocrine glands and thyrosuprarenal syndrome.
Dystrophic processes . Stromal hyalinosis is noted in the outcome of age-related atrophy of the thyroid gland, as well as in Reidel goiter (see Goiter) and tumors.
Amyloidosis can be isolated or a manifestation of a general process. Histologically, amyloid masses are detected in the interfollicular stroma, the walls of blood vessels, and the basement membranes of the follicles. Amyloidosis of the thyroid gland can lead to atrophy.
Obesity of the follicular epithelium is accompanied by the appearance of small drops of fat in the cytoplasm and is observed with cretinism, prolonged venous stasis, senile atrophy. Stromal lipomatosis occurs with age-related atrophy of the gland and a general violation of fat metabolism.
Pigmentation is observed with atrophy of the gland (deposition of lipofuscin), with hemorrhages, hemochromatosis (deposition of hemosiderin) and jaundice of the newborn (deposition of bilirubin).
Hypertrophy of the thyroid gland occurs during puberty, during pregnancy, excessive production of thyroid-stimulating hormone of the pituitary gland, insufficient iodine content in food, and partial resection of the gland. In this case, the thyroid gland increases in size; histologically, neoplasm of the follicles arising from the interfollicular and intrafollicular islets of the thyroid parenchyma, mitotically active areas of the follicles is noted. Epithelial cells become higher, their mitotic activity intensifies, the number of prismatic epithelial cells increases. Elements of physiological regeneration are revealed: an increase in individual cells, elongation of follicles and the formation of foci of follicular epithelium at their poles due to the proliferation of the latter. Hypertrophy of the thyroid gland can be focal or diffuse. Focal hyperplastic growths can reach various sizes. Unlike true tumor growths, the follicular epithelium with hyperplastic growths is capable of differentiation. Hypertrophy of the thyroid gland may be accompanied by an increase in its functional activity. This is evidenced by enhanced intrafollicular proliferation, vacuolization of the parietal wall of the colloid with a change in its glow in a luminescent microscope, increased synthesis of nucleoproteins, the activity of iodide peroxidase and mucoproteolytic enzymes, and an increase in the amount of ascorbic acid.
Thyroid inflammation . Acute thyroiditis (see), more often purulent, is noted often at transition from adjacent organs (larynx, trachea, esophagus) or hematogenous transmission of infection. Histologically, polynuclear leukocytes are found in the lumen of the follicles or stroma. Subacute thyroiditis includes granulomatous, giant cell de Kerwen thyroiditis. Chronic – fibrous goiter Riedel. However, the inflammatory nature of Riedel’s goiter is doubtful.
Of the specific inflammations of the thyroid gland, miliary tuberculosis (with general miliary tuberculosis), large solitary tuberculomas, rarely tuberculous caverns are found. Infection occurs hematogenously or lymphogenously. There are frequent cases of transition of the process from neighboring organs, lymph nodes. Syphilitic damage to the thyroid gland is noted with congenital and acquired syphilis. Either miliary gumma (rarely with congenital syphilis), often combined with a specific vascular lesion, or interstitial thyroiditis is observed. The latter is characterized by the growth of specific granulation tissue, followed by fibrosis and gland atrophy.
A parasitic lesion of the thyroid gland (Chagas disease) is associated with invasion of trypanosomes. The basis of the disease is the destruction of organ cells as a result of the development of parasites in them. Echinococcus is rare in the thyroid gland, usually in the form of a single or multi-chamber cyst. For the most part, the disease is diagnosed as cystic goiter and the error is established only for surgery. Thyroid actinomycosis is extremely rare, accompanied by the formation of fistulas; purulent inflammation with tissue necrosis is histologically observed.
General adaptation syndrome and thyroid gland . Clinical and morphological changes in the thyroid gland in response to stress (surgical intervention, temperature effects, physical strain, acute infections, etc.) are non-specific. They are characteristic of the general adaptation syndrome (see). Histologically, focal parenchyma hyperplasia is observed with an increase in secretory activity: an increase in the height of the cubic epithelium, the appearance of a prismatic, uneven size of the follicles, intrafollicular proliferation, desquamation of the epithelium, vacuolization and pale staining of the colloid in the follicles, colloid edema of the stroma.