Endocrine Abstracts

Background: To stratify the risk of malignancy, thyroid fine-needle aspiration cytology (FNAC) is an important and cost-effective method to evaluate nodules. The Bethesda System for Reporting Thyroid Cytopathology III, IV and V categories are diagnostic challenges, falling between benign and malignant.

Objective: Determinate the malignancy rates of thyroid nodules classified as Bethesda Categories III-V.

Methods: Retrospective study of patients’ records with thyroid nodules classified as III-V by the Bethesda system, between January 2014-June 2016.

Results: Of a total of 2791 cytologies, 176 (6%) were classified as III-V, with the following distribution: 93 (3%) atypia of undetermined significance (AUS, III); 50 (1,8%) suspicious for follicular neoplasm (SFN, IV) and 33 (1%) suspicious for malignancy (SM, V). Malignancy rates for IV and V FNAC diagnostic groups were 27% (10/37) and 85% (22/26), respectively. Among patients in group III, 27 patients underwent surgery after a single AUS report (final diagnosis of malignancy – 33%), 39 repeated the FNAC and the remaining are under surveillance. The second cytology report was as follows: 24 benign, 9 AUS, 4 SM, 1 SFN and 1 unsatisfactory; surgery was performed in 9 patients (5AUS+1SFN+3SM) and the final diagnosis of malignancy was 44%. The malignancy rate based on histology was not statistically different between patients with one or two cytologies (P=0,693).

Conclusions: Incidences of III-V diagnostic categories in our study resemble the predicted by the Bethesda System. The malignancy rate for the AUS category was higher than expected and similar to the one found in SFN. Repeating the FNAC in the former group offered minimal additional benefit.