Histopathological Review of Diagnostic Categories of the Milan System for Reporting Salivary Gland Cytopathology – An Institutional Experience of 6 Years

INTRODUCTION: Salivary gland malignancies account for 2 to 4% of head and neck cancers. Fine needle aspiration cytology (FNAC) is used in preoperative diagnosis of salivary gland lesions. Although FNAC is a highly reliable technique for preoperative diagnosis, there were no consensus on salivary gland cytopathology reporting. Recently, an international group has recommended a classification system for salivary gland FNAC reporting titled “Milan System for Reporting Salivary Gland Cytopathology” (MSRSGC). In this study, we aimed to evaluate the usability of the Milan System, its ability to determine the risk of malignancy for each category, with comparisons of inital cytologic and final histopathological diagnosis. MATERIALS AND METHODS: We performed a retrospective analysis of salivary gland lesion FNAC in our department from 2013 to 2019. A total of 578 FNACs were performed in 514 patients. Of these, 85 cases had surgical follow-up (parotid gland, n = 73, submandibular gland, n = 12). The cytological samples were categorized according to the MSRSGC into six categories by two pathologists. The risk of malignancy (ROM) and diagnostic accuracy values were calculated for each diagnostic categories. RESULTS: A total of 85 aspirates of the patients with follow-up, the MSRSGC diagnostic categories were as follows: non-diagnostic in 7 aspirates (8.2%), non-neoplastic in 3 (3.5%), atypia of undetermined significance (AUS) in 9 (10.5%), benign neoplasm in 43 (50.5%), salivary gland neoplasm of undetermined malignant potential in 7 (8.2%), suspicious for malignancy in 10 (11.7%), and malignant in 6 (7%). The ROM for each category was 28, 5%, 0%, 33%, 0%, 28.5%, 90%, and 100%, respectively. CONCLUSION: FNAC plays a critical role in the evaluation of patients with salivary gland lesions. The MSRSGC helps in the standardization of the process of diagnosis and clinical management of salivary gland lesions, especially of AUS and SUMP categories that are indeterminate categories in nature.