Fine-needle aspiration of follicular patterned lesions of the thyroid: diagnosis, management, and follow-up according to thyroid Bethesda system.

Objective: The goal of this study was to report an experience with thyroid fine-needle aspiration (FNA) cases that can be placed into National Cancer Institute-designated thyroid FNA diagnostic categories for follicular patterned lesions divided into three diagnostic categories: follicular lesion of undetermined significance/atypia of undetermined significance (AUS/FLUS), suspicious for follicular neoplasm (SFON), and suspicious for malignancy.

Study Design: The study cohort included 4,284 cases for the period between January 2007 and July 2011 and all available follow-up data was obtained. All cases classified as 'atypical' and 'rule out follicular neoplasm' were included in the AUS/FLUS category (n = 3,903), whereas cases classified as 'suspicious for' or 'consistent with follicular or Hürthle cell neoplasm' (n = 381) were included in the SFON diagnostic category and compared with histopathologic follow-up.

Results: During this period, 14,628 thyroid FNAs were reported in 12,238 patients. Repeat FNA (RFNA) was performed in 1,366/3,903 (35%) patients classified as AUS/FLUS. Histologic outcome data was available in 1,756/3,903 (45%) cases diagnosed as AUS/FLUS and 243/381 (64%) cases diagnosed as SFON. The rate of malignancy in AUS/FLUS cases with and without RFNA was 29 and 14% respectively, and it was 26% in SFON cases.

Conclusion: The current data shows that the malignancy rates differ between categories and AUS/FLUS cases are best managed by RFNA for selection of cases that can benefit from surgical excision.