Histopathologic and clinical outcomes of Milan System categories “non-diagnostic” and “non-neoplastic” of salivary gland fine needle aspirations

Introduction: The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) specifies six categories with estimated risks of malignancy (ROM) and suggested management. The estimated ROM is 25% for Non-Diagnostic (ND) category, and 10% for Non-Neoplastic (NN). This study aimed to investigate histopathologic and clinical outcomes of MSRSGC categories ND and NN at the authors’ institution. Materials and methods: Cytopathology fine needle aspiration reports from 2008-2020 were searched for the word “salivary”, “parotid”, and “submandibular”. Cases fitting Non-Diagnostic (ND) and Non-Neoplastic (NN) categories were identified. Follow-up cyto-/histopathologic and clinical data were extracted. Results: There were 43 ND and 46 NN cases. The average age was 58.3 years. Neoplastic lesions were found in 13 of 43 (30%) ND and 3 of 46 (6.5%) NN. The rate of malignancy in ND category was 14.0% (6/43) and 0% (0/46) in NN category. Four cases in ND (9.3%) and 6 (13.0%) in NN had no neoplasm and instead had an underlying reactive condition (e.g., chronic sialadenitis) or inflammatory lesion (e.g., lymphoepithelial cyst) on histologic follow-up. There was no follow-up pathology in 46.5% NDs (20/43) and 82.6% NNs (38/46); however, no lesions were apparent clinically with a mean follow-up of 3 years and 1.5 years, respectively. Conclusions: MSRSGC categories ND and NN are helpful for reporting salivary gland FNA results. With proper clinical and radiologic correlation, ROM of NN is low; however, ROM of ND remains significant. Repeat FNA after correlation for ND cases seems prudent as neoplasms and malignancies may have gone undetected.