<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A papilloma derived from the Schneiderian membrane in which the epithelium invaginates into and proliferates in the underlying stroma. It is two to five times more common in males. It characteristically arises from the lateral nasal wall and often extends secondarily into the sinuses. Isolated cases of inverted papillomas arising in the paranasal sinuses without nasal involvement also occur. Nasal obstruction is the most common presenting symptom. Other manifestations include nasal drainage, epistaxis, anosmia, headaches, proptosis, and diplopia. Morphologically, it is composed of hyperplastic ribbons of basement membrane-enclosed epithelium that grow endophytically into the underline stroma. Although it is histologically a benign tumor, it has an unlimited growth potential and, if neglected, can cause considerable morbidity or even death by extending into contiguous structures. The preferred treatment for most lesions is a lateral rhinotomy and medial maxilectomy with meticulous removal of all mucosa in the ipsilateral paranasal sinuses (WHO, 2005).</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>