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Thyroid Gland Pathology

Glandula thyroidea

For medical students2 min readUpdated 2026-10-10

Thyroid pathology encompasses a wide spectrum of disorders, ranging from functional abnormalities and inflammatory conditions to hyperplastic processes (goiter) and neoplasms. These conditions cause profound systemic metabolic disturbances, affecting the nervous, cardiovascular, and other organ systems.

Graves' diseaseThe second most common endocrine disorder, responsible for 80% of thyrotoxicosis cases
Hyperthyroidism triadSevere hyperthyroidism manifests as goiter, exophthalmos, and tachycardia
Papillary carcinomaThe most common malignant tumor of the gland (up to 60% of cases)

Functional Disorders

Alterations in thyroid activity lead to two opposing clinical syndromes.

Hypothyroidism — decreased function. It results from medical interventions (surgery, radiation therapy), pituitary disorders (secondary), or hypothalamic disorders (tertiary). In early life, hormone deficiency leads to irreversible intellectual disability known as cretinism. In adults, it causes myxedema (mucopolysaccharide-rich edema), bradycardia, achlorhydria, lethargy, and cold intolerance.

Hyperthyroidism (Thyrotoxicosis) — excess hormone. It manifests as accelerated metabolism: weight loss, enhanced lipolysis, hyperglycemia, and osteoporosis. Systemic effects include thyrotoxic cardiomyopathy, myopathy, diarrhea, and hepatic dysfunction.

Thyroiditis (Inflammatory Diseases)

Based on their clinical course, thyroiditis is classified into acute, subacute, and chronic forms:

Goiter (Struma)

Goiter is the enlargement of the thyroid gland due to hypertrophy and hyperplasia.

Diffuse toxic goiter (Graves' disease) is an autoimmune pathology characterized by the production of antibodies (IgG) that stimulate thyroid follicular cell receptors independently of TSH. The gland becomes "meat-like," the epithelium forms pseudopapillae, and the colloid becomes thin and pale.

Endemic goiter occurs in regions with dietary iodine deficiency. Reduced hormone synthesis triggers a compensatory TSH release by the pituitary, which stimulates thyroid growth.

Morphologically, non-toxic goiter progresses through two stages:

  1. Hyperplastic stage: small follicles lined by columnar epithelium.
  2. Colloid involution stage: upon reaching a euthyroid state, follicles become distended with colloid, and the gland becomes firm and gelatinous.

Thyroid Tumors

Neoplasms most commonly arise from the follicular epithelium.

Benign tumors are represented by adenomas, the most frequent being the follicular adenoma. When accompanied by thyrotoxicosis without ophthalmopathy, it is referred to as Plummer disease (toxic adenoma).

Malignant epithelial tumors (carcinomas):

Mnemonic

P-apillary carcinoma: P-orphan Annie eyes, P-sammoma bodies, P-rognosis is good.

Frequently asked 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 — the most common form, accounting for up to 60% of all cases.
  • Follicular carcinoma — accounts for up to 20% of cases.
  • Medullary carcinoma — a tumor derived from C-cells, accounting for 5–10% of cases.
  • Anaplastic carcinoma — accounts for approximately 15% of cases.

Rare histological variants include oncocytic carcinoma of the thyroid, high-grade follicular carcinomas, high-grade differentiated thyroid carcinoma, poorly differentiated thyroid carcinoma, anaplastic follicular cell carcinoma, mucoepidermoid carcinoma, secretory carcinoma, sclerosing mucoepidermoid carcinoma with eosinophilia, cribriform-morular carcinoma, and mixed medullary and follicular carcinomas.

What etiologic factors lead to primary hypothyroidism?

Primary hypothyroidism is caused by iatrogenic factors and various primary diseases of the thyroid gland.

  • Iatrogenic causes — medical procedures including thyroidectomy, radiation therapy, and certain medications.
  • Autoimmune disorders — chronic lymphocytic thyroiditis (Hashimoto thyroiditis) causes progressive hypothyroidism due to parenchymal destruction.
  • Iodine deficiency — endemic goiter eventually transitions from a euthyroid state to hypothyroidism.
  • Genetic defects — inherited disorders of hormone synthesis, secretion, and metabolism lead to congenital hypothyroidism.
From which cell types do thyroid carcinomas arise?

Thyroid carcinomas arise from follicular and parafollicular cells.

  • Follicular cells — serve as the origin for differentiated thyroid cancers, as well as aggressive poorly differentiated carcinomas and anaplastic follicular cell carcinomas.
  • Parafollicular cells (C-cells) — give rise to medullary carcinoma (C-cell carcinoma), which may occur sporadically or as part of a multiple endocrine neoplasia (MEN) syndrome.
What macroscopic and microscopic changes characterize subacute de Quervain thyroiditis?

Subacute granulomatous (de Quervain) thyroiditis is characterized by specific macroscopic and microscopic alterations.

  • Macroscopic changes — asymmetric enlargement and firmness of the affected thyroid lobe.
  • Early microscopic changes — focal neutrophilic infiltrates accompanied by microabscess formation.
  • Late microscopic changes — formation of macrophage granulomas mixed with multinucleated giant cells, along with fibrous tissue proliferation.
What is the difference between endemic and sporadic goiter?

Endemic goiter results from iodine deficiency in specific geographical regions. Sporadic goiter occurs worldwide, with exact causes often unclear (likely involving genetic defects in iodine metabolism).

What are the classic microscopic features of papillary carcinoma?

Specific features include hypochromic "orphan Annie eye" nuclei lacking nucleoli, eosinophilic intranuclear inclusions, nuclear grooves, and psammoma bodies located in the cores of papillae.

Which thyroid carcinoma metastasizes hematogenously?

Follicular carcinoma. It is characterized by vascular invasion and early hematogenous spread to bones, the liver, and lungs.

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