Imaging of benign salivary gland tumors: an update based on the fifth WHO classification, with a focus on rare histologic types and newly listed entities—part I

The salivary glands give rise to a diverse range of histologic tumor types. The World Health Organization (WHO) Classification of Head and Neck Tumors has been revised from the fourth edition (2017) to the fifth edition; the online version was released in March 2022, followed by the publication of the WHO Blue Book in March 2024. In the current classification of salivary gland tumors (SGTs), 15 benign and 21 malignant epithelial tumor types are categorized. Furthermore, four new benign entities were added: intercalated duct adenoma/hyperplasia, striated duct adenoma, sclerosing polycystic adenoma, and keratocystoma. Imaging features of prevalent benign tumors, such as pleomorphic adenoma, Warthin tumor, basal cell adenoma, salivary gland myoepithelioma, and oncocytoma, are thoroughly documented in the radiologic literature. Conversely, infrequently encountered and newly categorized benign tumors often remain unrecognized by many radiologists. In this Part I of a two-part series, we evaluate infrequently encountered benign SGTs within the current WHO classification, including cystadenoma of the salivary glands, canalicular adenoma, sialadenoma papilliferum, ductal papillomas, sebaceous adenoma, and lymphadenoma. The discussion focuses on diagnostic criteria with an emphasis on radiologic-pathologic correlations.