IP occurs when the Schneiderian membrane of the nose and paranasal sinuses inverts into the stroma in a pattern of endophytic growth.30'31 Microcysts are often trapped within the epithelium. The Schneiderian membrane is composed of ciliated pseudostratified columnar epithelium. It starts 1 to 2 cm posterior to the nares at the mucocutaneous junction and is found in the nasal cavity and paranasal sinuses. The membrane is of ectodermal origin, unlike the nasopharyngeal mucosa, which is endodermal, but similar in appearance. Fungiform (usually from the nasal septum) and cylindrical cell papillo-mas are histologic variants of Schneiderian papillomas, managed similarly to IP.32 The data reported by Hyams1 showed recurrence in roughly one-half of patients with IP, regardless of the type.

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