What is the Thyroid Gland?
The
thyroid gland is a butterfly-shaped organ located in the neck, responsible for producing hormones that regulate metabolism, growth, and development. Histologically, it is composed of follicles lined by epithelial cells that produce thyroxine (T4) and triiodothyronine (T3), and parafollicular cells that secrete calcitonin.
Normal Histological Structure
Under the microscope, a healthy thyroid gland displays numerous
thyroid follicles filled with colloid, a protein-rich substance storing thyroid hormones. The follicular cells, which can be cuboidal or columnar, surround the colloid. Parafollicular cells, or
C cells, are found in the interfollicular spaces and are responsible for producing calcitonin.
Hypothyroidism
Histologically,
hypothyroidism is often characterized by an increased number of small follicles with scanty colloid and hypertrophy of the follicular cells. A common cause of hypothyroidism is
Hashimoto's thyroiditis, an autoimmune disorder where lymphocytic infiltration and formation of lymphoid follicles are observed.
Hyperthyroidism
In contrast,
hyperthyroidism (e.g., in Graves' disease) typically shows enlarged follicles with infoldings of the epithelium and reduced colloid content due to increased hormone production. The follicular cells often appear tall and columnar, reflecting their hyperactivity.
Thyroiditis
Thyroiditis refers to inflammation of the thyroid gland and can be acute, subacute, or chronic. Acute thyroiditis, often bacterial, shows neutrophilic infiltration. Subacute thyroiditis, also known as de Quervain's thyroiditis, is usually granulomatous with multinucleated giant cells. Chronic lymphocytic thyroiditis includes Hashimoto's thyroiditis, characterized by extensive lymphocytic infiltration and formation of germinal centers.
Thyroid Cancer
Thyroid cancer histology varies depending on the type.
Papillary carcinoma features papillary structures with fibrovascular cores and nuclear changes such as grooves and pseudoinclusions.
Follicular carcinoma demonstrates follicular patterns with capsular and vascular invasion.
Medullary carcinoma, arising from parafollicular cells, shows sheets of cells producing calcitonin and amyloid deposits.
Anaplastic carcinoma is highly malignant, displaying undifferentiated cells with pleomorphic nuclei.
Diagnostic Techniques
Accurate diagnosis of thyroid disorders often involves histological examination through methods such as fine-needle aspiration (FNA), biopsy, and immunohistochemistry. FNA is a minimally invasive procedure for obtaining cell samples, while a biopsy provides a larger tissue section for a more detailed analysis. Immunohistochemical staining helps to identify specific cell types and markers, aiding in the diagnosis of various thyroid conditions.
Conclusion
Understanding the histological features of thyroid disorders is crucial for accurate diagnosis and treatment. Histology provides a window into the cellular and structural changes occurring in the thyroid gland, thus playing an essential role in managing thyroid-related diseases.
