181. Diseases of the thyroid gland (goiter, thyrotoxicosis, thyroiditis, tumors): macro- and microscopic signs, complications, clinical significance.

Thyroid diseases — goiter, thyroiditis and tumors — are accompanied by hyperthyroidism (thyrotoxicosis) or hypothyroidism (myxedema).

Goiter (struma) is a pathological enlargement of the thyroid gland.

A colloidal goiter consists of follicles of varying sizes filled with colloid. In some cases, the follicles are large, cyst—like, the epithelium in them is flattened (macrofollicular colloidal goiter), in others — small (microfollicular colloidal goiter), in others - small follicles (macro- and microfollicular colloidal goiter) are found along with large ones. In a colloidal goiter, epithelial growth in the form of papillae is possible — a proliferating colloidal goiter. Over time, circulatory disorders occur in the goiter tissue, foci of necrosis and calcification form, connective tissue grows, sometimes with the formation of bone. Colloidal goiter is usually nodular, dense at the incision.

Parenchymal goiter is characterized by the proliferation of follicle epithelium, which grows in the form of solid structures with the formation of small follicle-like formations without colloid or with a very small amount of it. It is often diffuse, has the appearance of a homogeneous gray-pink fabric. Combinations of colloidal and parenchymal goiter are possible.

Thyroiditis is a group of diseases, of which Hashimoto's thyroiditis, or Hashimoto's disease, is a true autoimmune disease. Autoimmunization is associated with the appearance of autoantibodies to microsomal antigen and thyrocyte surface antigens, as well as thyroglobulin. The autoimmune process determined by histocompatibility antigens DR leads to diffuse infiltration of the gland tissue by lymphocytes and plasma cells (see Fig. 6-7), the formation of lymphoid follicles in it. The parenchyma of the gland, as a result of the action of mainly immune effector cells, dies, is replaced by connective tissue. In far-reaching cases, the morphological picture resembles Riedel's thyroiditis (goiter).

Riedel's thyroiditis (Riedel's goiter) is the primary overgrowth of coarse—fibrous connective tissue in the gland, which leads to atrophy of the follicular epithelium, fibrous goiter. The gland becomes very dense — "iron", "stone" goiter. Fibrous tissue from the thyroid gland spreads to the surrounding tissues, mimicking a malignant tumor.

Tumors: Each thyroid cell (A, B, and C) can become a source of benign (adenoma) or malignant (cancer) tumors.

Follicular adenoma develops from A- and B-cells, approaches the thyroid gland in structure, consists of small (microfollicular) and larger (macrofollicular) follicles. A solid adenoma originates from calcitonin-secreting C cells. The tumor cells are large, with a light oxyphilic cytoplasm, and grow among the follicles filled with colloid.

Thyroid cancer often develops from an adenoma.

Follicular

Papillary

Medullary

Undifferentiated

Complications: Due to thyrotoxicosis, a thyrotoxic heart develops — an increase in the volume of the myocardium (especially the left ventricle) due to serous edema of the stroma and intracellular edema of muscle fibers, lymphoid infiltration of the interstitial tissue is also observed. As a result, diffuse interstitial sclerosis develops. Serous edema is observed in the liver with a rare outcome in fibrosis — thyrotoxic liver fibrosis. In the intermediate and medulla oblongata, dystrophy of nerve cells and perivascular cellular infiltrates are detected. It is not uncommon to find an enlargement of the thymus gland, hyperplasia of lymphoid tissue and atrophy of the adrenal cortex.