Risk stratification of fine-needle aspiration cytology of parotid neoplasms based on the Milan system-Experience from a tertiary center in Asia.

Abstract

The recently described Milan system provides a unified way of categorizing salivary gland fine-needle aspiration (FNA) cytology. We aim to use this system to stratify risk of malignancy in parotid FNAs. In this retrospective case series, 376 FNAs were preoperatively performed for 573 parotidectomies over 14 years. Risk of malignancy on FNA is as follows: nondiagnostic 14.5%, non-neoplastic 26.7%, atypia of undetermined significance 29.3%, benign neoplasm 2.7%, neoplasm of uncertain malignant potential 19.1%, suspicious for malignancy 87.5%, and malignant 100%. The specific diagnoses of pleomorphic adenoma and Warthin tumor on FNA have high positive predictive value of 97.5% and 96.6%, respectively. Multivariate regression associates smaller size of lesion with a nondiagnostic or indeterminate result. Seniority of operator is associated with a lower likelihood of a nondiagnostic result. This large Asian series validates the Milan system as a valuable tool in stratifying malignancy risk of parotid FNAs.