Details
53 year old female with a 3 cm left inferior maxillary sinus mass. Incidental finding on head CT.
Inverted papillomas (IP) are the most common type of sinonasal papilloma and have a 2% risk of malignant transformation. They are usually found on the lateral wall of the nasal cavity and affect males more commonly than females in the 5th-6th decades of life.
Grossly, IPs tend to be large, bulky, polypoid lesions with a cerebriform appearance. Histologically, IPs show proliferation of sinonasal epithelium (non-keratinizing, stratified transitional/squamoid) in an endophytic pattern, projecting into the underlying stroma with an intact basement membrane. The squamous epithelium is usually markedly thickened and contain intraepithelial neutrophils, goblet cells and mucous cysts. Clear cell changes within the epithelium can be seen. The stroma may be edematous, myxoid, or fibrous with acute and/or chronic inflammatory changes.