Correlation between cytology and histology in patients with atypia of undetermined significance thyroid nodules at a tertiary laboratory in the Western Cape province, South Africa.
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INTRODUCTION: The atypia of undetermined significance (AUS) category of the Bethesda System for Reporting Thyroid Cytopathology remains challenging due to its cytologic heterogeneity and variable risk of malignancy (ROM). This study assessed the frequency of AUS diagnoses, correlated cytologic and histologic outcomes, and compared ROM between AUS with nuclear atypia and with other atypia (AUS-Other) subcategories in a tertiary laboratory. MATERIALS AND METHODS: A retrospective review of all thyroid fine needle aspiration cytology reported between 2016 and 2021 was performed using the National Health Laboratory Service database. AUS cases were subcategorized according to the third edition of the Bethesda System for Reporting Thyroid Cytopathology. ROM was calculated using histopathologic follow-up, excluding noninvasive follicular thyroid lesion with papillary-like nuclear features and other low-risk neoplasms from the malignant category. Clinical and demographic variables were analyzed using descriptive and comparative statistics, with significance set at P < 0.05. RESULTS: Of 1,703 thyroid fine needle aspiration cytology, 137 (8.0%) were categorized as AUS. Histologic follow-up was available for 40 cases (29.2%). The ROM among AUS cases that had surgical resections was 42.5% (17/40). AUS with nuclear atypia demonstrated a higher ROM than AUS-Other (50.0% versus 36.4%), although the difference was not statistically significant (P = 0.39). Malignant outcomes showed subtype-specific patterns: papillary thyroid carcinoma and follicular variant of papillary thyroid carcinoma predominated in AUS-Nuclear, while follicular thyroid carcinoma predominated in AUS-Other. Patient age showed no significant association with histologic outcome. CONCLUSIONS: The two-tier AUS subclassification provides functional stratification for identifying higher risk nodules in our setting. However, larger national multicentre studies integrating clinical and radiological data are needed to validate and refine AUS risk stratification and improve patient outcomes in our resource-limited environment.