Assessment of risk of malignancy by application of the proposed Sydney system for classification and reporting lymph node cytopathology

BACKGROUND Fine-needle aspiration cytology (FNAC) is one of the most commonly used techniques for evaluating lymphadenopathy. Recently, the Sydney system was proposed for assessing the performance, classification, and reporting of lymph node (LN) cytopathology. The present study was conducted to assess the risk of malignancy associated with each of the diagnostic categories of the proposed Sydney system. METHODS This was a 2-year retrospective study of LN-FNAs; cytologic diagnoses were categorized by the proposed Sydney system. Cytological diagnoses were correlated with the corresponding histopathological diagnoses to assess diagnostic accuracy and risk of malignancy for each diagnostic category. RESULTS Of 23,335 FNAs during the study period, 6983 (30%) were performed on LNs. Of these, 289 (4.1%) cases were reported as nondiagnostic/inadequate (L1); 3397 (48.6%) were reported as benign (L2); 33(0.5%) as atypical cells of undetermined significance (L3), 96 (1.4%) as suspicious for malignancy (L4) and 3168 (45.4%) as malignant (L5). Subsequent histopathology was available for 618 (8.8%) cases. On cytohistopathologic correlation, 552 (89.3%) were concordant and 66 (10.7%) discordant. The overall sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of LN-FNA were 79.9%, 98.7%, 98.4%, 83.1%, and 89.3%, respectively. The risk of malignancy was 27.5% for the nondiagnostic category, 11.5% for the benign, 66.7% for the atypical, 88% for the suspicious, and 99.6% for the malignant categories. CONCLUSIONS FNAC has high diagnostic accuracy for the diagnosis of various LN pathologies. Application of the proposed Sydney system can help in achieving uniformity and reproducibility in cytologic diagnoses and also help in risk-stratification on cytology.