This disease develops as the result of absolute or relative deficiency of iodine intake. Goiter is defined as endemic in areas where more than 10% of the population is affected and sporadic when the incidence is less than that. Endemic goiter occurs in areas of iodine deficiency. Increased requirement for thyroid hormones, individual dietary insufficiency of iodine, ingestion of goitrogens, and subclinical levels of dyshormonogenesis may be important in the pathogenesis of the sporadic form. The pathological features are a combination of hyper-plastic and involutional change and nodule formation. The initial change is related to stimulation of secretion of thyroid hormones by pituitary thyroid-stimulating hormone (TSH) in response to an increased demand for thyrox-ine. This results in thyroid hyperplasia, with the development of increased numbers of small follicles with little storage of colloid. The follicular cells are columnar and may show pleomor-phism and mitotic activity. When the thyroid hormone levels reach normal, the gland undergoes a process of involution. The follicular cells become flattened and there is accumulation of colloid within the follicles. Eventually, after periods of stimulation and involution the thyroid comprises a mixture of hyperplastic and involutional change with areas of degeneration, hemorrhage, and fibrosis. Some nodules may appear larger - dominant nodules. These may be nodules with extensive colloid accumulation and degeneration that are easily recognized on FNA, or hyperplastic nodules that histologically resemble follicular neoplasms. Some may be encapsulated. The question is whether to define them as adenomas or as nodules. In the context of overall nodularity, many pathologists would use the term "adenomatoid nodule." However, molecular analysis has shown that up to 70% of dominant nodules in nodular goiter are monoclonal, suggesting that they are neoplastic, while the remainder show a polyclonal pattern . The specific classification is not important, as long as after appropriate examination there are no features to indicate malignancy. Any nodules within a goiter that have a thick capsule should be processed as for a follicular neoplasm.
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