Fine needle aspiration cytology for parotid neoplasms: risk of malignancy through inconclusive results and lower grade tumors

Purpose: Fine needle aspiration cytology (FNAC) is a commonly performed procedure for parotid masses, although its accuracy in detecting malignancies widely varies through different series. We evaluated our single-center cohort of parotidectomies to highlight possible limitations of preoperative FNAC. Methods: Seven hundred and eighteen consecutive patients submitted to parotid surgery at San Raffaele Scientific Institute (Milan) were retrospectively evaluated (2002–2018). Five hundred and fifty four FNAC were analyzed. FNAC accuracy was assessed with and without inclusion of “inconclusive” results. The peculiar role of lower grade primary parotid cancers was investigated. Results: FNAC reports were “diagnostic” in 502 cases (90.4%) and “inconclusive” in 52 (9.6%). Histopathology revealed 488 benign lesions (88.1%) and 66 malignancies (11.9%). FNAC sensitivity, specificity, PPV, NPV and accuracy in detecting malignancies were 59%, 99%, 89%, 95%, and 95%, respectively. Sensitivity fell to 48%, when “inconclusive” FNAC was computed. Within 66 parotid cancers, FNAC could discriminate malignancy in 32 cases (48.5%), provide proper grading in 21 (31.8%), and precise histopathological diagnosis in 15 (22.7%). Malignancy was more likely in patients with “inconclusive” FNAC than in those with “diagnostic” cytologies (23.1% vs 10.8%, p = 0.003). Low-intermediate-grade primary parotid cancers were associated to a higher rate of FNAC failure in comparison with high-grade ones (86.4% vs 19.0%; p < 0.001). Conclusion: FNAC is an important tool for preoperative assessment of parotid masses, though its sensitivity in detecting malignancy remains poor. “Inconclusive” FNAC results could further jeopardize FNAC accuracy and should elicit resorting to additional tests, especially when a lower grade parotid cancer is suspected.