Background: The introduction of highly sensitive imaging techniques has made it possible to detect many non-palpable nodules, or "incidentalomas," in the thyroid. Discovery of these lesions raises concerns about their malignancy, but the optimal strategy for managing these lesions has not been clearly established.
Purpose: To review evidence about incidentalomas, including prevalence and risk for malignancy, and to provide recommendations for their evaluation and treatment.
Data sources: Literature searches for relevant articles published in the past 15 years in major English-language medical journals, review of selected articles published before this period, and reviews of bibliographies in text-books.
Study selection: Three studies on autopsy findings, 11 studies on ultrasonographic findings, and other reports on nonpalpable thyroid nodules were included.
Data extraction: Data on the prevalence of nodules on autopsy and in ultrasonographic series, palpation compared with ultrasonography, the risk for malignancy in nodules found in irradiated glands, the natural history of thyroid nodules, and the prevalence of occult cancer were collated and reviewed.
Data synthesis: Prevalence of thyroid incidentalomas estimated from autopsy studies ranges from 30% to 60%. Studies comparing clinical palpation with thyroid imaging show a prevalence of 13% to 50%. Prospective studies of randomly selected patients have reported a prevalence of 19% to 67%. The risk for malignancy in asymptomatic nodules found in nonirradiated glands is 0.45% to 13% (mean +/- SD, 3.9% +/- 4.1%).
Conclusions: High-resolution ultrasonography is sensitive and capable of detecting many small, nonpalpable thyroid nodules. Most of these lesions are benign. For most patients with nonpalpable nodules that are incidentally detected by thyroid imaging, simple follow-up neck palpation is sufficient.