Root Cause Analysis and Risk of Malignancy of Non-Diagnostic Category per the Milan System for Reporting Salivary Gland Cytopathology.

Introduction: We aim to perform a root cause analysis (RCA) of the non-diagnostic (ND) category of the Milan System for Reporting Salivary Gland Cytopathology.

Methods: The salivary gland fine needle aspiration (FNA) samples with ND diagnosis and corresponding surgical resections from 2013 to 2023, in the age group of 18 years and above, were included in the cohort for RCA. The cytology and surgical resection slides of cases from this RCA cohort were reviewed. The demographic parameters, clinical features, radiologic characteristics, usage of rapid on-site evaluation (ROSE), corresponding surgical diagnosis, and repeat FNA were noted.

Results: A total of 2292 FNAs were performed between 2013 and 2023, of which 354 cases were ND. RCA was performed on 57 (16%) ND FNA cases that had corresponding surgical resection. The causes were grouped as man, method, machine, and material related. The primary cause predominantly was man-related sampling errors in 36 (63%) cases. There were no interpretative errors by the pathologist. The second most common primary cause was material related, found in 21 (37%) cases, due to cystic, fibrotic, vascular, and small lesions. The most common secondary cause was method related, in which 41 (72%) cases had no image guidance. There were no machine-related causes. The risk of malignancy in the RCA cohort was 17%.

Conclusion: Majority causes of ND cytology were method-related due to lack of image guidance and ROSE. This proves that the FNA procedure under radiologic guidance with ROSE is an effective way to circumvent ND cytology of salivary gland FNAs.