Thyroid nodules are common, with as many as two-thirds of adults harboring nodules detectable by ultrasound and about 5% by palpation.
1,2 Ultrasound has proven useful in estimating the likelihood of malignant tumors and selecting nodules for fine-needle aspiration (FNA) biopsy.
3-7 More than 600 000 thyroid FNAs are performed every year in the United States alone, and the number has been increasing annually by 16%.
8,9 Thyroid FNA cytology can accurately classify most nodules as benign and a minority as malignant, but the results remain indeterminate in about 20% (range, 10%-38%) of nodules when cytological features lack specific characteristics needed for a definitive diagnosis.
10 Further, the proportion of indeterminate cytology results appears to be rising.
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