False-negative fine-needle aspiration of thyroid nodules cannot be attributed to sampling error alone

BackgroundThe goal of this study was to determine whether sampling error was the major cause for false-negative fine needle aspiration (FNA) results for thyroid nodules.MethodsPatients who underwent preoperative FNA between 1994 and 2008 were identified, and the results were compared with surgical pathology findings. Other related variables including nodule number and size were also recorded.ResultsExcluding the microcarcinomas, the false-negative rate was 4% (19/479). Sampling errors occurred in only 4 (21%) cases in which the malignant nodule was not actually biopsied. Of the other 15 cases, 8 (53%) were solitary nodules, 8 (53%) were ≥4 cm in size, and 5 (33%) had underlying thyroiditis. Because of the missed diagnosis, 9 patients (47%) had lobectomy only as the initial surgery, which then required a completion thyroidectomy.ConclusionsSampling error is a minor cause for false-negative FNAs, suggesting that there are some inherent limitations to cytological evaluation of the thyroid.