IMPORTANCE: Incidental thyroid nodules are defined as nodules originally detected in a patient with no thyroid-related clinical symptoms, examination findings, or suspected thyroid disease. Medical imaging for diseases in the neck, chest, and spine is a common source of incidental thyroid nodules. They are easily detected but poorly characterized. The next step is to decide whether the incidental thyroid nodule should be further evaluated with ultrasonography. OBSERVATIONS: Indiscriminate workup of incidental thyroid nodules with ultrasonography is not cost-effective and is potentially harmful. Although the concern for malignant neoplasms drives workup, the risk for poor outcomes without evaluation is minimal. The rate of malignant tumors in patients with 1 or more thyroid nodules larger than 5 mm is only 1.6%, and most small thyroid cancers are indolent. Substantial evidence suggests that a reservoir of thyroid cancers does not progress, and workup after detection with imaging leads to epidemiologic overdiagnosis. Finally, a significant proportion of patients with benign nodules have cytologic results that are not definitive and require lobectomy. Evidence-based recommendations for incidental thyroid nodules detected at computed tomography, magnetic resonance imaging, nuclear medicine studies, and extrathyroidal ultrasonography include selection criteria for nodule workup based on suspicious imaging findings, patient age, and nodule size. In the absence of clinical risk factors or suspicious imaging findings, workup with dedicated thyroid ultrasonography is only recommended for nodules at least 1.5 cm in patients 35 years or older and for nodules at least 1.0 cm in patients younger than 35 years. CONCLUSIONS AND RELEVANCE: Only a few select incidental thyroid nodules require further evaluation with ultrasonography based on recommendations that aim to diagnose clinically significant thyroid cancers while reducing unnecessary workup and provide guidance for clinical practice.
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