Real-world experience with the Sydney System on 1458 cases of lymph node fine needle aspiration cytology

Introduction: Lymph node (LN) fine needle aspiration cytology (FNAC) is a safe, quick, inexpensive, reliable, and minimally invasive technique for the diagnosis of lymphadenopathies. Recently, an international committee of experts proposed guidelines for the performance, classification, and reporting of LN-FNAC: the Sydney System. We set out to analyse the diagnostic performance of the Sydney System in a retrospective study. Methods: We retrieved 1458 LN-FNACs, reformulated the diagnoses according to the Sydney System, and compared them to the histological control where available (n = 551, 37.8%). Results: The risk of malignancy for each of the five categories was 66.7% for inadequate/insufficient, 9.38% for benign (overall: 0.84%), 28.6% for atypical, 100% for suspicious and 99.8% for malignant. LN-FNAC showed a sensitivity of 97.94%, a specificity of 96.92%, a positive predictive value of 99.58%, and a negative predictive value of 86.30%. Conclusions: These data support the usage of LN-FNAC as an agile first-level technique in the diagnosis of lymphadenopathies. The Sydney System supports and enhances this role of LN-FNAC, and its adoption is encouraged. In negative cases, coupled with ancillary techniques, LN-FNAC can reassure the clinician regarding the benignity of a lymphadenopathy and indicate the need for clinical follow-up, which will catch possible false negatives. In positive cases, LN-FNAC can provide sufficient information, including predictive biomarkers, to initiate management and obviate the need for subsequent, more invasive procedures. Given its speed, minimal invasiveness, and low cost, LN-FNAC can be performed in most cases, even when more invasive techniques are not feasible.