Low-grade oncocytoid neoplasm in the Milan system: Tips for the diagnosis of Warthin tumor and other differential diagnostic considerations

The current review article deals with the evaluation of the oncocytic/oncocytoid lesions in the salivary gland. The authors will focus on the diagnosis of Warthin tumor (WT) as a launching point to detail important morphologic findings that should prompt designation of an aspirate as oncocytic salivary gland neoplasm of uncertain malignant potential or other Milan categories. Oncocytic cells are defined as cells with a moderate to abundant amount of eosinophilic finely granular cytoplasm, round-to-oval nuclei, and large-distinct nucleoli. In contrast, the term oncocytoid is also frequently used in this discussion and indicates tumor cells with similarly abundant and sometimes granular cytoplasm but lacking all the definitive features of a true oncocyte. Several helpful tips are provided in hopes of improving an accurate diagnosis of WT on an aspirate sample. Using these types allows for consideration of important differential diagnoses, including both benign and malignant entities, when faced with an oncocytic salivary gland neoplasm. The morphological criteria as well as the possible application of ancillary techniques are also discussed.