Accuracy of parotid gland FNA cytology and reliability of the Milan System for Reporting Salivary Gland Cytopathology in clinical practice.

Background: Differentiating between malignant and benign salivary gland tumors with fine-needle aspiration cytology (FNAC) can be challenging. This study was aimed at testing the validity of the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) and at assessing possible differences in the sensitivity and specificity of parotid gland FNAC between dedicated head and neck (H&N) centers, subdivided into head and neck oncology centers (HNOCs) and head and neck oncology affiliated centers (HNOACs), and general hospitals (GHs).

Methods: The Dutch Pathology Registry (PALGA) database was searched for patients who had undergone a salivary gland resection between January 1, 2006, and January 1, 2017, and had a preoperative FNAC result. The FNAC reports were retrospectively assigned to MSRSGC categories. The risk of malignancy (ROM) was calculated for each category. The sensitivity and specificity for diagnosing malignancy were calculated and compared among HNOCs, HNOACs, and GHs.

Results: In all, 12,898 FNAC aspirates were evaluated. The ROMs for each category were as follows: 12.5% in MSRSGC I, 10.3% in MSRSGC II, 29% in MSRSGC III, 2.3% in MSRSGC IVa, 28.6% in MSRSGC IVb, 83% in MSRSGC V, and 99.3% in MSRSGC VI. The sensitivity of FNAC was highest in HNOCs (88.1%), HNOACs scored lower (79.7%), and GHs had a sensitivity of 75.0%.

Conclusions: The MSRSGC is a valid tool for reporting parotid gland FNAC; therefore, these results strongly advocate its use. On the basis of the higher sensitivity of FNAC in dedicated H&N centers, the authors recommend that GHs use the presented management strategies to help to minimize the chances of a preoperative misdiagnosis.