Diagnostic accuracy of fine needle aspiration biopsy cytology and ultrasonography in patients with thyroid nodules diagnosed as benign or indeterminate before thyroidectomy.

Fine-needle aspiration biopsy cytology (FNABC) and ultrasonography (US) play an important role in differentiating benign thyroid nodules from malignant nodules. We retrospectively investigated the prevalence of follicular thyroid carcinoma (FTC) in patients with thyroid nodules whose FNABC and US readings were not malignant before thyroidectomy. Between 2007 and 2008, 3333 patients underwent thyroidectomy at our institution, and the 737 of them who had thyroid nodule that had been diagnosed as hyperplastic nodule or follicular tumor by FNABC and US preoperatively were the subjects in this study. Postoperative histopathology showed hyperplastic nodule in 416 patients, follicular adenoma in 200 patients, FTC in 99 patients, and other disease in 22 patients. By FNABC, 34 (6.7%) of the 505 patients with diagnosis as benign and 65 (28%) of the 232 patients with diagnosis as indeterminate, were diagnosed as having FTC. The diagnosis was FTC in 56 (9.6%) of the 582 patients with a preoperative diagnosis of hyperplastic nodule by US and 43 (27.7%) of the 155 patients with a diagnosis of follicular tumor by US. The diagnosis of FTC was made in 21 (4.8%) of 438 patients who were concurrently diagnosed as benign by FNABC and as hyperplastic nodule by US, and in 30 (34.1%) of 88 patients who were diagnosed as indeterminate by FNABC and follicular tumor by US. FNABC has been the mainstay for the preoperative evaluation of thyroid nodule. The results of this study showed that US can also be a useful tool for diagnosing FTC.