Histopathological diagnoses of "accessory" thyroid nodules diagnosed as benign by fine-needle aspiration cytology and ultrasonography

Abstract

Background: Patients who have thyroidectomies for thyroid nodules that are suspected of being malignant, called here "main nodules," occasionally have second nodules, called here "accessory nodules" that are evaluated by ultrasonography (US) and fine-needle aspiration cytology (FNAC). Most accessory nodules are diagnosed as benign based on preoperative US and FNAC. To evaluate the accuracy of US and FNAC for a group of nodules which were likely to be mostly benign we evaluated procedures to diagnose accessory nodules.

Patients and methods: In a total of 643 patients who underwent thyroidectomy for their main nodules, 866 accessory nodules were evaluated by US and/or FNAC preoperatively. All were evaluated by histopathological examination postoperatively. Of the 866 accessory nodules, 501 were evaluated by US only and 365 were evaluated by US and FNAC.

Results: While the 363 accessory nodules were diagnosed as malignant by histopathology, 235 nodules were malignant by US and histopathology and 115 nodules were malignant by FNAC and histopathology. Among the accessory nodules that were diagnosed as benign by histopathology, 7.2% were malignant by US, and 4.4% were malignant by FNAC. Among the accessory nodules that were diagnosed as benign by FNAC, 15.0% were malignant by histopathology. This was a significantly higher percentage than the value of 6.2% for the accessory nodules diagnosed as benign by US but malignant by histopathology. Accessory nodules with a benign cytology on FNAC that were malignant were significantly smaller than those with a benign cytology and histopathology. Among the 126 accessory nodules that were read as benign by both US and FNAC, only one (0.8%) was diagnosed as papillary thyroid carcinoma by histopathology.

Conclusion: These data suggest that diagnostic accuracy of benign nodules based on both US and cytological evaluation was supported by the evidence of high-level histopathological compatibility in accessory nodules. FNAC and US have a low but not negligible false-negative diagnostic rate. When FNAC is combined with US the false-negative rate is probably very low.