Diagnostic Utility of the Sydney System in Lymph Node Cytopathology: A Retrospective Analysis

Fine-needle aspiration biopsy (FNAB) is a widely used technique for the evaluation of lymphadenopathy. The recently proposed Sydney System offers a framework for the categorization, evaluation, and reporting of lymph node cytopathology. This study aimed to assess the diagnostic accuracy and risk of malignancy (ROM) for each diagnostic category of the Sydney system.

A two-year retrospective single-center study analyzed 392 lymph node FNAB cases, and categorized according to the proposed Sydney system. The findings were tabulated and analyzed using Jamovi (Version 2.5) and SPSS version 26.0.

Of the 392 lymph node FNAB cases, 72 (18%) had histopathological follow-up. The mean age of the patients was 44 years, with a range of 1-90 years. A slight male predominance was seen, with male to female ratio of 1.17: 1. The cervical group was the most commonly aspirated node (n=241, 61%). Using the Sydney System, 69 (17.6%) were classified in the non-diagnostic/inadequate category, 211 (54%) were reported as benign (L2), 5 (1.2%) as atypical cells of undetermined significance (L3), 2 (0.5%) as suspicious for malignancy (L4), and 105 (26.7%) as malignant (L5). The sensitivity was 96.8%(95% CI: 82.8% to 99.4%), specificity was 96.6%(95% CI: 83.8% to 99.4%), positive predictive value was 96.8%(95% CI: 83.8% to 99.4%), negative predictive value was 96.6%(95% CI: 82.8% to 99.4%), and diagnostic accuracy was 96.7% (95% CI: 88.7% to 99.1%) for the verified subset(n=60). The risk of malignancy was 46.7% to 91.1% for the inadequate category, 0.6% to 17.2% for the benign category, and 88.6% to 100% for the malignant category. ROM was not calculated for L3 and L4 due to the absence of malignant cases and a very small sample size.

The Sydney System provides precise, standardized lymph node FNAB reporting, enhancing diagnostic accuracy, risk assessment, and informed clinical management.