Inverted Papilloma (Sinonasal)

Inverted papilloma (also called Schneiderian papilloma, inverted type) is a benign neoplastic proliferation of the sinonasal epithelium characterized by endophytic (inverted) growth pattern in which hyperplastic respiratory or transitional epithelium grows downward into the underlying stroma rather than as exophytic projections. It is one of three Schneiderian papilloma subtypes (inverted, oncocytic, fungiform).

It comprises 0.5-4% of all sinonasal tumors with a male predominance (3-5:1) and peak incidence in the 5th-7th decades. The majority arise from the lateral nasal wall, maxillary sinus, or ethmoid sinuses, with the middle meatus being the most common attachment site. HPV (especially types 6, 11, and 16) has been detected in a subset of cases, but the etiology remains incompletely understood.

Characteristic features include unilateral nasal mass on examination and cerebriform/convoluted appearance on T2-weighted MRI, which helps differentiate from other sinonasal masses. CT shows opacification with sclerotic bone changes. Staging systems (Krouse T1-T4, Han I-IV) guide surgical approach. Treatment is complete endoscopic medial maxillectomy or appropriate endoscopic approach with drilling of the bony attachment to remove subperiosteal extension and prevent recurrence. Recurrence is 10-30% (mostly within 2-3 years); 5-15% harbor concurrent or develop metachronous squamous cell carcinoma. Long-term endoscopic surveillance is mandatory.