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Abstract

Objective: According to Bethesda System for Reporting Thyroid Cytopathology, the category, atypia of undetermined significance (AUS), is estimated to have a low malignancy risk of around 5%-15%. Variable surgical malignancy rates of AUS have been reported in diverse populations. The present study evaluated the malignancy rate at our institution and associated demographic data to identify high-risk nodules.
Methods: In this retrospective study, thyroid nodules with initial fine-needle aspirations (FNAs) reported as AUS from April 2010 to May 2013 were analyzed. Demographic data, clinical managements, and histopathologic results were evaluated.
Results: A total of 7382 aspirations performed during the study period were analyzed; 5.7% were reported as atypia, 70.3% as benign, 1.5% as follicular neoplasm, 2.7% as suspicious for malignancy or malignant, and 19.8% as nondiagnostic. A total of 388 patients with one nodule reported as AUS were enrolled for analysis; 86 (22.2%) underwent surgical biopsy directly, 127 (32.7%) received follow-up FNAs, and 175 (45.1%) received clinical observation. The malignancy rate in the 86 patients who underwent surgical biopsy directly after first AUS was 17.4%. Out of the 127 patients who received follow-up FNAs, 105 were reclassified into the different-rank risk categories (benign, neoplasm or malignancy, and nondiagnostic) and 22 remained in AUS. Among the 33 patients out of 127 who received thyroid surgery after follow-up FNAs, the malignancy rates in the 8 patients with repeated AUS results and 11 patients with benign results in the second FNA were 50% and 9.1%, respectively. No significant difference in sex, age, nodular size, numbers, and preoperative thyroid-stimulating hormone level between the benign and malignant groups in the thyroid AUS cases was observed.
Conclusion: Repeated AUS may be associated with a higher malignancy rate in final histopathology, and other supplementary techniques are required to enhance preoperative diagnostic accuracy.

Keywords: Follicular neoplasm; Fine needle aspirations (FNA); Cytopathology