Imaging features of benign mass lesions in the nasal cavity and paranasal sinuses according to the 2017 WHO classification.

The World Health Organization (WHO) 2017 classification of head and neck tumors has been just published and has reorganized tumors of the nasal cavity and paranasal sinuses. In this classification, three new entities (seromucinous hamartoma, NUT carcinoma, and biphenotypic sinonasal sarcoma) were included, while the total number of tumors has been reduced by excluding tumors if they did not occur exclusively or predominantly in this region. Among these entities, benign tumors were classified as sinonasal papillomas, respiratory epithelial lesions, salivary gland tumors, benign soft tissue tumors, or other tumors. In contrast, inflammatory diseases often show tumor-like appearances. The imaging features of these benign tumors and tumor-like inflammatory diseases often resemble malignant tumors, and some benign lesions should be given attention in the follow-up period and before surgery to avoid recurrence, malignant transformation, or massive bleeding. Understanding the CT and MR imaging features of various benign mass lesions is clinically important for appropriate therapy. The purpose of this article is to describe the clinical characteristics and imaging features of each of clinically important nasal and paranasal benign mass lesions, as classified according to the WHO 2017 classification of head and neck tumors, along with some inflammatory diseases.