What Are Thyroid Nodules?

Thyroid nodules are discrete, localized lesions within the thyroid gland that differ in texture or composition from surrounding thyroid tissue. They are among the most common endocrine abnormalities encountered in clinical practice, with prevalence estimates ranging from 19% to 68% in adult populations—depending on the detection method used. Most nodules are asymptomatic and discovered incidentally during routine physical examination, neck ultrasonography performed for unrelated reasons, or imaging studies such as CT or MRI.

While the vast majority of thyroid nodules are benign—often representing colloid nodules, follicular adenomas, or areas of focal Hashimoto’s thyroiditis—approximately 4% to 7% are malignant. Papillary thyroid carcinoma is the most common histologic subtype, accounting for roughly 80–85% of all thyroid cancers. Other malignancies include follicular, medullary, and anaplastic carcinomas, as well as lymphoma arising in a background of chronic autoimmune thyroiditis.

Clinical evaluation begins with a thorough history—including assessment of radiation exposure, family history of thyroid cancer or multiple endocrine neoplasia syndromes—and physical examination focusing on nodule size, consistency, mobility, and presence of cervical lymphadenopathy. Serum thyroid-stimulating hormone (TSH) measurement is routinely obtained; suppressed TSH levels may suggest a hyperfunctioning (“hot”) nodule, which carries an exceedingly low risk of malignancy.

High-resolution thyroid ultrasound remains the cornerstone of imaging evaluation. Sonographic features associated with increased malignancy risk include microcalcifications, irregular or spiculated margins, marked hypoechogenicity, taller-than-wide shape, and intranodular vascularity. Ultrasound-guided fine-needle aspiration (FNA) cytology is recommended for nodules meeting size and sonographic risk criteria per established guidelines (e.g., American Thyroid Association or European Thyroid Association).

Management is individualized based on cytologic diagnosis, molecular testing results when indicated, and clinical context. Benign nodules typically require periodic surveillance with repeat ultrasound. Indeterminate cytology may prompt reflex molecular testing or diagnostic lobectomy. Malignant or highly suspicious nodules generally warrant surgical resection, followed by risk-stratified adjuvant therapy—including radioactive iodine ablation and thyroid hormone suppression—as appropriate.