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Limitations of FNAC in detecting parotid malignancies: insights from a surgical cohort using the updated Milan System
Andrea Galli1,2, Bright Oworae Howardson3,4, Carlo Scionti2
1Department of Otorhinolaryngology - Head and Neck Surgery, IRCCS San Raffaele Scientific Institute, Via Olgettina 60, 20132, Milan, Italy.
Purpose:
To evaluate the diagnostic accuracy of the second edition Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) in predicting the risk of malignancy (ROM) in parotid tumors, through correlation with final histopathological diagnoses in a large consecutive single-center surgical series.
Methods:
A retrospective study was conducted on 249 consecutive patients who underwent parotid surgery between June 2017 and March 2024 in a tertiary referral center. Preoperative fine-needle aspiration cytology (FNAC) results were classified according to the MSRSGC. Diagnostic performance metrics were calculated, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic concordance. Cytological findings were correlated with definitive histopathology to calculate ROM, risk of high-grade malignancy (ROM-HG), and risk of neoplasia (RON). Multivariate logistic regression was performed to identify preoperative predictors of malignancy.
Results:
FNAC showed high accuracy in diagnosing pleomorphic adenoma and Warthin tumor. Sensitivity for malignancy detection was 68%, In alternative analyses, sensitivity decreased to 56% and increased to 74% when indeterminate categories (MSRSGC III- AUS and IV - SUMP) were considered test-negative or test-positive, respectively.. Within these indeterminate categories, ROM was 18.6%, while ROM-HG was 0%. Among 29 primary malignant tumors, 86.7% of low/intermediate-grade malignancies were classified as benign or indeterminate on FNAC. Multivariate analysis identified male gender and hypomobility as predictors of malignancy.
Conclusions:
Although the updated MSRSGC has improved FNAC-based classification of parotid tumors, diagnostic performance remains limited for low/intermediate-grade malignancies, which are frequently classified as benign or indeterminate. The absence of HG-malignancies within indeterminate categories suggests a limited clinical impact of these diagnostic uncertainty.
