Proceedings of the 2026 North American Society of Head and Neck Pathology Companion Meeting, San Antonio, TX, March 22, 2026: It’s a Trap!: Diagnostic Pitfalls in Sinonasal Pathology

Sinonasal pathology presents unique diagnostic challenges due to the anatomic complexity of the region, the wide histologic spectrum of lesions, and the frequent limitation of small biopsy specimens.

This review examines key diagnostic pitfalls in select sinonasal lesions using a pattern-based approach, emphasizing morphologic overlap, common sources of misclassification, and the roles of immunohistochemistry and molecular testing.

We review polypoid, glandular, and papillomatous lesions, including the distinction between respiratory epithelial adenomatoid hamartoma/seromucinous hamartoma and low-grade non-intestinal-type adenocarcinoma, DEK::AFF2 sinonasal carcinoma mimicking inverted papilloma, carcinoma arising in inverted papilloma, and HPV-related non-keratinizing squamous cell carcinoma with papillary growth. The differential diagnosis of small round blue cell tumors is discussed, with emphasis on distinguishing features among olfactory neuroblastoma, sinonasal undifferentiated carcinoma, olfactory carcinoma, NUT carcinoma, SMARCB1-deficient sinonasal carcinoma, and adamantinoma-like Ewing sarcoma. Mixed epithelial–mesenchymal tumors are addressed, focusing on the diagnostic challenges of teratocarcinosarcoma. Basaloid and cribriform tumors with myoepithelial differentiation are examined, highlighting the morphologic overlap among HPV-related multiphenotypic sinonasal carcinoma, adenoid cystic carcinoma, and basaloid squamous cell carcinoma. Finally, mesenchymal spindle cell lesions are addressed, including glomangiopericytoma, solitary fibrous tumor, and biphenotypic sinonasal sarcoma.

Recognition of recurrent diagnostic pitfalls, combined with a systematic pattern-based approach and judicious use of ancillary studies, is essential for accurate classification. Integration of morphologic, immunophenotypic, and molecular findings helps avoid misdiagnosis and ensures appropriate patient management.