15/12/2025
Practical Points to Differentiate Inverted Papilloma (IP) vs Antrochoanal Polyp (ACP)
(Do not rely solely on radiology reports when making management decisions.Radiology findings are supportive, not decisive)
1.Patient & History
Adult patient (>40 years) favors IP
Child or young adult favors ACP
Male predominance suggests IP
Recurrent unilateral nasal mass after surgery suggests IP
Epistaxis or blood-stained discharge favors IP
ACP rarely causes bleeding
2.Nasal Endoscopy
Irregular, lobulated, cerebriform surface suggests IP
Smooth, pale, cystic mass suggests ACP
Firm consistency favors IP
Soft and mobile mass favors ACP
Broad-based attachment suggests IP
Narrow stalk suggests ACP
Easy bleeding on touch suggests IP
3.CT Scan Findings
Focal hyperostosis indicates the attachment site of IP
Bony remodeling or erosion favors IP
Irregular sinus opacification favors IP
Smooth maxillary sinus expansion favors ACP
ACP typically extends through the maxillary ostium into the choana
Absence of hyperostosis favors ACP
4.MRI Findings
Cerebriform (convoluted) pattern on T2 and post-contrast MRI is characteristic of IP
Homogeneous signal intensity favors ACP
Heterogeneous enhancement favors IP
5.Intra-operative Findings
Difficult dissection with firm attachment to bone favors IP
Easily avulsed mass favors ACP
Need for drilling of attachment site indicates IP
Frozen section may be needed in IP, not in ACP
6.Histopathology
Invagination of squamous epithelium into stroma confirms IP
Edematous respiratory mucosa confirms ACP
Dysplasia or carcinoma in situ may be seen with IP
No malignant potential in ACP
7.Prognosis & Follow-up
High recurrence rate in IP
Risk of malignant transformation (≈5–15%) in IP
Lifelong follow-up required for IP
Low recurrence and no malignant risk in ACP
-line Clinical Rule
Any unilateral nasal polyp in an adult should be considered inverted papilloma until proven otherwise.
IP case :
CT images of a patient with inverted papilloma.
A and B, Axial and coronal CT images show focal plaquelike hyperostosis in part of right ethmoid sinuses (arrows).
C, Although tumor extends to the right maxillary sinus and nasal cavity, no additional foci of hyperostosis are seen. Intraoperative endoscopic examination confirmed the limitation of tumor origin to the ethmoid sinuses.( Image from https://www.ajnr.org/content/28/4/618/F1)
