Putting morphology to the test: An established classification scheme reliably stratifies salivary gland cytology by risk of malignancy with substantial interobserver agreement.

ABSTRACT

BACKGROUND: The Milan System for Reporting Salivary Gland Cytopathology describes several salivary gland fine-needle aspiration cytology (SGFNAC) morphologies developed by Griffith et al. Basaloid neoplasms are pleomorphic (PB) or monomorphic with fibrillary (MBFib), hyaline (MBHy), or other (MBOther) matrix. Oncocytoid neoplasms can be pleomorphic (PO), demonstrate granular and/or vacuolated cytoplasm (OGV), or be monomorphic with mucinous (MOMuc), cystic (MOCyst), or other (MOOther) background. In the current study, the authors explore interobserver agreement (IOA) and risk of malignancy (ROM) for these subcategories. METHODS: The study included 169 SGFNAC cases with surgical follow-up. Four reviewers categorized these cases using the criteria of Griffith et al. with consensus determined by majority. For all morphologic categories, IOA (using the Fleiss kappa) and ROM were calculated. RESULTS: ROMs for basaloid categories were PB 100% (1 of 1 case); MBHy 71.4% (5 of 7 cases); MBFib 50.0% (3 of 6 cases); and MBOther 47.4% (9 of 19 cases). ROMs for oncocytoid neoplasms were OGV 100% (10 of 10 cases); MOMuc 92.3% (12 of 13 cases); PO 88.9% (8 of 9 cases); MOOther 33.3% (5 of 15 cases); and MOCyst 0 (0 of 1 case). The system demonstrated substantial agreement overall (κ = 0.69). For basaloid neoplasms, the IOA results were MBHy κ = 0.59; MBFib κ = 0.41; MBOther κ = 0.41; and PB κ = 0.11. For oncocytoid neoplasms, the IOA results were MOMuc κ = 0.88; OGV κ = 0.67; PO κ = 0.63; MOOther κ = 0.57; and MOCyst κ = 0.18. CONCLUSIONS: The SGFNAC scheme proposed by Griffith et al. and incorporated into the Milan System for Reporting Salivary Gland Cytopathology demonstrated substantial agreement overall, with particularly high agreement for the MOMuc, OGV, PO, and MBHy categories. The PB and MOCyst categories demonstrated slight agreement and may be improved by revised criteria. The PB, PO, MOMuc, and OGV categories demonstrated high ROM, and the latter 2 categories might best be classified as suspicious for malignancy.