Histology and aspiration cytology of benign thyroid diseases.

The thyroid is an endocrine gland involved in the homeostatic regulation of the organism by means of its products, the hormones thyroxine (T4) and triiodothyronine (T3). Its basic morphologic unit is the follicle, composed of thyrocytes producing the inactive hormonal form thyroglobulin which is stored in the center of the follicle. The diseases affecting the thyroid are classified into benign and malignant. Benign diseases include goiter, either diffuse (Graves' disease when hyperfunctioning) or nodular (nodular hyperplastic goiter), thyroiditis (including Hashimoto's autoimmune form) and benign neoplasms (adenomas). All benign thyroid diseases can be investigated preoperatively with a fine-needle aspiration biopsy. This technique is simple and safe and allows an accurate cytological diagnosis of these benign lesions.