Inverted papillomas

• Convoluted cerebriform pattern on T2 and contrast-enhanced T1 MRI—alternating lines of high and low signal intensity
• Mass arising from lateral nasal wall near middle turbinate, middle meatus, or maxillary ostium
• Focal cone-shaped hyperostosis at the point of tumor origin on CT

• MRI shows the distinctive convoluted cerebriform pattern on both T2-weighted and contrast-enhanced T1-weighted images, appearing as alternating lines of high and low signal intensity resembling cerebral gyrations, seen in 50-100% of cases.
• T1-weighted signal is isointense to muscle; T2-weighted signal is generally hyperintense to muscle with alternating hypointense lines; post-gadolinium enhancement is heterogeneous with alternating hypointense lines.
• Mass typically originates from the lateral nasal wall, most commonly near the middle turbinate, middle meatus, or maxillary ostium, with frequent extension into the maxillary antrum.
• CT demonstrates soft tissue density mass with heterogeneous enhancement and bony remodeling/resorption patterns similar to squamous cell carcinoma; intralesional calcifications representing residual bone fragments are present in approximately 40% of cases.
• Focal, cone-shaped hyperostosis on CT correlates with the point of tumor origin and is useful for diagnosis and surgical planning.
• Plain radiographs show a nasal mass with opacification of the adjacent maxillary antrum but are no longer routinely used for sinonasal assessment.
• DSA angiography demonstrates that these tumors are mostly avascular and has no significant role in diagnosis.
• Impaired maxillary sinus drainage is common due to mass location, though mucocele formation is rare.

• Sinonasal carcinoma and inverted papilloma with malignancy—imaging cannot reliably distinguish these entities; malignant transformation occurs in ~10% of cases as keratinizing or non-keratinizing squamous cell carcinoma.
• Antrochoanal polyp—typically non-enhancing with possible peripheral mucosal enhancement, unlike the heterogeneous enhancement pattern of inverted papillomas.
• Inflammatory polyp—non-enhancing with peripheral mucosal enhancement, lacking the characteristic cerebriform pattern.
• Juvenile nasopharyngeal angiofibroma (JNA)—highly vascular on imaging, whereas inverted papillomas are avascular or minimally enhancing.
• Olfactory neuroblastoma—arises from olfactory epithelium at cribriform plate, different location and imaging characteristics.
• Paranasal sinus mucocele—non-enhancing, loculated fluid collections distinguished from solid enhancing papillomas.

Describe the characteristic convoluted cerebriform pattern (alternating bands of hyperintense and hypointense signal on T2 and post-contrast T1 images) and specify the location of origin (lateral nasal wall, middle turbinate/meatus, or maxillary ostium), noting any focal hyperostosis and extent of bony remodeling or resorption to guide surgical planning and assess for potential complications.

• Confusing inverted papillomas with primary sinonasal carcinoma or inverted papilloma with malignant transformation, as imaging features overlap significantly and cannot reliably distinguish these entities—histopathology is required.
• Missing the focal hyperostosis on CT that localizes the site of tumor origin, which is essential for surgical planning and reducing recurrence risk.
• Underestimating the potential for malignant transformation; approximately 10% of inverted papillomas undergo transformation to squamous cell carcinoma, either synchronously or metachronously.
• Attributing the cerebriform pattern to other sinonasal masses; while distinctive, it is not pathognomonic and must be interpreted in conjunction with tumor location and clinical context.