Histopathological Correlation and Determination of Malignancy Risk in Reporting Parotid Gland Masses According to the Milan System.

OBJECTIVE

The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) provides a standardized framework for interpreting salivary gland fine-needle aspiration cytology (FNAC) samples and estimating the associated risk of malignancy (ROM). This study aimed to retrospectively reclassify parotid gland fine-needle aspiration (FNA) samples from our institution according to the MSRSGC, evaluate the correlation between preoperative cytological and postoperative histopathological findings, and determine the ROM for each diagnostic category.

MATERIALS AND

METHODS

A total of 277 parotid gland FNAC cases with subsequent surgical excision between 2010 and 2024 were included. Cytological smears were independently reviewed and reclassified according to MSRSGC by two blinded pathologists. Cytology-histology concordance was assessed, and diagnostic performance metrics, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy, were calculated. ROM for each Milan category was derived from the final histopathology.

RESULTS

Of the 612 patients who underwent FNAC, 277 (45.3%) had available histopathological follow-up. The mean age was 49.6 ± 15.67 years, with a male-to-female ratio of 1.2:1. Benign neoplasm (Category IVa) was the most frequent cytological diagnosis (71.1%). Histopathology revealed 235 benign and 42 malignant lesions. FNAC demonstrated a sensitivity of 85.2%, specificity of 99%, PPV of 92%, NPV of 98%, and an overall diagnostic accuracy of 97.4%. ROM values were 16% for nondiagnostic, 20% for nonneoplastic, 11% for atypia of undetermined significance (AUS), 1.5% for benign neoplasm, 47% for salivary gland neoplasm of uncertain malignant potential (SUMP), 100% for suspicious for malignancy (SFM), and 90% for malignant cases. False-negative results were primarily associated with lymphoma, acinic cell carcinoma, and secretory carcinoma. The combined ROM for indeterminate categories (AUS, SUMP, and SFM) was 46%.

CONCLUSION

FNAC is a highly accurate and minimally invasive diagnostic method for parotid gland lesions. The Milan System offers valuable guidance for risk stratification and clinical management, although indeterminate categories continue to pose diagnostic difficulties. Multidisciplinary assessment and larger multicenter studies are needed to improve diagnostic precision.