Application of the Sydney System in the Classification of 1,000 Lymph Node Fine Needle Aspirations and Assessment of Risk of Malignancy.

Introduction: The evaluation of lymph nodes (LNs) through fine needle aspiration (FNA) is widely used as the first-line approach in the assessment of unexplained lymphadenopathy due to its minimal invasiveness, speed, and cost-effectiveness and the availability of provide material for various auxiliary techniques. The Sydney Lymph Node Cytology Reporting and Classification System was introduced in 2020. The aim of our study was to classify LN-FNAs according to the Sydney System and to evaluate the concordance with histological diagnoses and the rates of malignancy in the available cases.

Methods: Between 2019 and 2023, FNAs were retrospectively reviewed. A total of 1,000 cases were categorized according to the Sydney System as ND (inadequate/insufficient), benign, AUS/ALUS (atypical lymphoid cells of uncertain significance), suspicious, and malignant. The risk of malignancy was calculated for histopathological follow-up available cases.

Results: Cases were categorized into 5 groups: 58 cases (5.8%) as "ND," 560 cases (56%) as "benign," 24 cases (2.4%) as "AUS/ALUS," 32 cases (3.2%) as "suspicious," and 326 cases (32.6%) as "malignant." In the malignant group, 315 cases were metastatic malignancies and 11 were lymphoid malignancies. Histopathological follow-up was possible in 294 cases (29.4%). Among these, 159 were diagnosed as malignant. Of the malignant cases, 33 were diagnosed as lymphoma and 126 as metastatic malignancies. Based on the available data, the concordance rate between cytological and histological diagnoses was 81.0%. The sensitivity, specificity, positive predictive value, and negative predictive value were calculated as 91.11%, 69.49%, 77.36%, and 87.23%, respectively. The risk of malignancy was 52.9% for the nondiagnostic, 12.7% for the benign, 33.3% for the atypical, 80.0% for the suspicious, and 77.3% for the malignant categories.

Conclusion: The Sydney System is easily applied to LN-FNAs and shows a high cytology-histology diagnosis concordance rate and sensitivity. By simplifying reporting and strengthening communication between cytopathologists and clinicians, it enhances the clinical management of malignancy risk.