What Are Thyroid Nodules?
Thyroid nodules are discrete lesions within the thyroid gland that are radiologically distinct from the surrounding thyroid parenchyma and represent the most common finding in the thyroid gland. 1
Clinical Significance and Prevalence
Thyroid nodules are detected in up to 65% of the general population, with prevalence increasing with age—approximately 50% of people have at least one thyroid nodule by age 60 years. 2, 3
The majority of thyroid nodules are benign—only 7-15% harbor malignancy, making the primary clinical challenge distinguishing the small subset of clinically significant cancers from the vast majority of benign lesions. 2, 4, 3
Most thyroid nodules are clinically insignificant and can be safely managed with surveillance, as the majority of small thyroid cancers are indolent. 1
Pathologic Spectrum
Thyroid nodules encompass a wide range of pathologic entities:
Benign lesions include hyperplastic nodules, adenomatous nodules, colloid nodules, and true follicular adenomas. 5
Malignant lesions include differentiated thyroid carcinomas (papillary carcinoma representing 84% and follicular carcinoma 11% of thyroid malignancies), medullary thyroid carcinoma, anaplastic carcinoma, and rare entities such as lymphoma, sarcoma, and metastases. 1
Clinical Presentation
Thyroid nodules can present in several ways:
Palpable structural change detected on physical examination. 1
Incidental discovery on imaging performed for unrelated indications (termed "thyroid incidentaloma"), with prevalence up to 70% on neck ultrasound, CT, or MRI. 3
Functional abnormality with thyroid hormone excess (hyperthyroidism) in approximately 5% of cases. 2
Compressive symptoms including dyspnea, dysphagia, or dysphonia in approximately 5% of cases. 2
Natural History of Benign Nodules
Most solid benign thyroid nodules grow over time—the estimated proportion of nodules with volume increase of 15% or greater after 5 years is 89%. 6
An increase in nodule volume alone is not a reliable predictor of malignancy, as growth occurs in the vast majority of benign nodules. 6
Nodules with greater cystic content are less likely to grow compared to solid nodules. 6
Key Clinical Objectives
The main goals when evaluating thyroid nodules are:
Identification of the small subgroup (≈10%) that harbor clinically significant cancer. 2
Detection of nodules causing compressive symptoms (≈5%). 2
Recognition of nodules progressing to functional disease (≈5%). 2
Avoidance of overdiagnosis and overtreatment, as an estimated 77% of thyroid cancer cases in the United States represent "overdiagnosis" of indolent cancers that would never cause clinical harm. 1