A localized swelling in the thyroid gland. Thyroid nodules affect a small segment of the population, usually without symptoms. In rare instances, a thyroid nodule is an indication of thyroid cancer. The nodules are more common in women but are more likely to be cancerous in men. Older people tend to develop nodules more often than younger people, and the nodules are more likely to be cancerous.
A visible or palpable mass in the thyroid gland, benign about 90% to 95% of the time. A history of radiation to the head or neck increases the likelihood that the lesion will be malignant, as does the appearance of the nodule in the first decades of life. Fine-needle aspiration biopsy is the first and often the definitive diagnostic test.