Functional disorders
Changes in thyroid activity lead to two opposite syndromes.
Hypothyroidism is decreased function. It results from medical interventions (surgical removal, radiation therapy), pituitary pathology (secondary), or hypothalamic pathology (tertiary). In early childhood, hormone deficiency leads to irreversible intellectual impairment — cretinism. In adults, it causes myxedema (mucinous edema), bradycardia, achlorhydria, drowsiness, and cold intolerance.
Hyperthyroidism (thyrotoxicosis) is an excess of hormones. It manifests as accelerated metabolism: weight loss, activation of lipolysis, hyperglycemia, and osteoporosis. Systemic effects include thyrotoxic cardiomyopathy, muscular dystrophy, diarrhea, and liver damage.
Thyroiditis (inflammatory diseases)
Depending on the course, thyroiditis is classified into acute, subacute, and chronic:
- Acute infectious (suppurative) thyroiditis is caused by bacteria (streptococci, staphylococci). It is characterized by pain, high fever, and fluctuation.
- Subacute granulomatous (de Quervain) thyroiditis has a viral etiology. It is accompanied by the formation of macrophage granulomas with giant cells.
- Chronic lymphocytic (Hashimoto's goiter) is an autoimmune disease associated with a CD8+ T-lymphocyte defect. The glandular tissue is infiltrated by lymphocytes with follicle formation, leading to hypothyroidism.
- Chronic fibrous (Riedel's goiter) is characterized by the proliferation of dense fibrous tissue, making the gland "woody" hard and causing compression of the trachea.
Goiter (struma)
Goiter is an enlargement of the thyroid gland due to hypertrophy and hyperplasia.
Diffuse toxic goiter (Graves' disease, Basedow's disease) is an autoimmune pathology characterized by the production of antibodies (IgG) that stimulate thyrocyte receptors independently of TSH. The gland becomes "meat-like", the epithelium forms pseudopapillae, and the colloid becomes liquefied.
Endemic goiter occurs in iodine-deficient regions. Reduced hormone synthesis triggers a compensatory release of TSH by the pituitary gland, which stimulates gland growth.
Morphologically, non-toxic goiter goes through two stages:
- Hyperplastic stage: small follicles lined with columnar epithelium.
- Colloid involution stage: upon reaching an euthyroid state, the follicles become distended with colloid, and the gland becomes dense and gelatinous.
Thyroid tumors
Neoplasms most commonly develop from the follicular epithelium.
Benign tumors are represented by adenomas. The most frequent is the follicular adenoma. When accompanied by thyrotoxicosis without eye symptoms, it is referred to as Plummer's disease (toxic adenoma).
Malignant epithelial tumors (carcinomas):
- Papillary carcinoma (60%). Grows in papillae-like structures. Characterized by hypochromic "empty" nuclei and psammoma bodies. Prognosis is favorable (survival >20 years in 90% of cases).
- Follicular carcinoma (20%). Invades blood vessels and produces hematogenous metastases to bones, lungs, and liver. Prognosis is unfavorable.
- Anaplastic carcinoma (15%). Occurs in elderly individuals. Distinguished by marked cellular polymorphism, infiltrative growth, and treatment resistance.
Briefly: answers to topical questions
What are the histological types of malignant epithelial tumors of the thyroid gland?
There are several major and rare types of malignant epithelial tumors (carcinomas) of the thyroid gland.
- Papillary carcinoma is the most common form, accounting for up to 60% of all cases.
- Follicular carcinoma accounts for up to 20% of cases.
- Medullary carcinoma is a tumor arising from C-cells, accounting for 5–10% of cases.
- Anaplastic carcinoma accounts for approximately 15%.
Rarer histological variants include Hürthle cell carcinoma of the thyroid, high-grade follicular carcinomas, high-grade differentiated thyroid cancer, poorly differentiated thyroid cancer, anaplastic follicular cell carcinoma, mucoepidermoid carcinoma, secretory carcinoma, sclerosing mucoepidermoid carcinoma with eosinophilia, cribriform-morular carcinoma, as well as mixed medullary and follicular carcinomas.
What etiological factors lead to the development of primary hypothyroidism?
Primary hypothyroidism is caused by iatrogenic factors and various diseases of the thyroid gland itself.
- Iatrogenic causes are medical interventions, including gland removal, radiation therapy, and medication use.
- Autoimmune disorders — chronic lymphocytic thyroiditis (Hashimoto's goiter) causes progressive hypothyroidism due to parenchymal destruction.
- Iodine deficiency — endemic goiter eventually progresses from an euthyroid state to hypothyroidism.
- Genetic defects — disorders in hormone synthesis, secretion, and metabolism lead to congenital hypothyroidism.
From which cell types do thyroid carcinomas develop?
Thyroid carcinomas develop from follicular and parafollicular cells.
- Follicular cells serve as the origin for differentiated forms of cancer, as well as aggressive poorly differentiated cancer and anaplastic follicular cell carcinoma.
- Parafollicular cells (C-cells) serve as the origin for medullary carcinoma (C-cell carcinoma), which may occur sporadically or as part of a hereditary multiple endocrine neoplasia syndrome.
What macroscopic and microscopic changes are characteristic of subacute de Quervain's thyroiditis?
Subacute granulomatous de Quervain's thyroiditis is characterized by specific changes at the macroscopic and microscopic levels.
- Macroscopic changes include asymmetrical enlargement and induration of the affected thyroid lobe.
- Early microscopic changes show focal neutrophilic infiltrates accompanied by microabscess formation in the tissue.
- Late microscopic changes feature the formation of macrophage granulomas admixed with multinucleated giant cells, along with the proliferation of fibrous tissue.
Papillary carcinoma: P-ale nuclei, P-sammoma bodies, P-rognosis is good.
Class and exam questions
What is the difference between endemic and sporadic goiter?
Endemic goiter is caused by iodine deficiency in specific geographical regions. Sporadic goiter occurs universally, and its causes are not precisely established (likely genetic defects in iodine metabolism).
What are the classic microscopic features of papillary carcinoma?
It is characterized by hypochromic "empty" nuclei without nucleoli, eosinophilic intranuclear inclusions, grooved nuclei, and psammoma bodies in the center of the papillae.
Which thyroid carcinoma metastasizes via hematogenous spread?
Follicular carcinoma. It is typically characterized by vascular invasion and early hematogenous metastasis to bones, liver, and lungs.
What else to study on this topic
- Pathogenesis of Graves' disease and the role of CD8+ T-lymphocytes
- Specific mutations in cancer (c-fos, ret, c-myc)
- Morphological differential diagnosis of adenoma types
- Complications of the colloid involution stage of goiter
- Features of Hürthle cell carcinoma
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