Application of the Milan System for Reporting Salivary Gland Cytopathology: A Single Institutional Experience of 354 Cases with Cytologic-Histologic Correlation

Background: Evaluation of salivary gland lesions is routinely done preoperatively by fine-needle aspiration cytology (FNAC). The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC), with diagnostic categories I-VI, has been recommended to standardize the reporting of salivary gland lesions by FNAC. We aimed to reclassify archival salivary gland FNAC samples using MSRSGC, correlate the samples with surgical resections, and calculate the risk of malignancy (ROM) for each category. Methods: A total of 354 salivary gland FNAC samples (2013-2018) were reviewed. All FNAC results were retrospectively classified according to the MSRSGC. All cases had surgical follow-up. Histology was used to calculate the ROM, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy. Results: The 354 aspirates were classified as: nondiagnostic (ND) 17.0% (60), non-neoplastic (NN) 1.4% (5), atypia of undetermined significance (AUS) 11.0% (39), benign neoplasm (BN) 49.4% (175), salivary gland neoplasms of unknown malignant potential (SUMP) 10.7% (38), suspicious for malignancy (SM) 3.4% (12), and malignant (M) 7.1% (25). The ROM was as follows: ND 22%, NN 20%, AUS 15%, BN 2%, SUMP 53%, SM 75%, and M 96%. The diagnostic accuracy for separating benign versus malignant neoplasms was 96%. Cytologic-histologic correlation yielded a false-negative rate of 2.7%, false-positive rate of 10.5%, PPV of 89%, NPV of 97%, sensitivity of 87%, and specificity of 98%. Conclusion: MSRSGC helps standardize cytology reports, provides useful information for appropriate clinical management, and ensures the best care of patients with salivary gland lesions.