Inverted Papilloma (IP)

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Diagnosis Definition

IPs (a subtype of Schneiderian Papillomas) are benign, locally aggressive lesions composed of pseudostratified respiratory epithelium that account for 0.4-4% of nasal cavity masses
They typically originate from the lateral wall of the nasal cavity, although they may also arise from the paranasal sinuses, and grow inward and into the underlying bone
IPs are often resected, as up to 10% undergo malignant transformation, most commonly into squamous cell carcinoma
The rate of recurrence after resection is between 2 and 15%

Imaging Findings

Imaging is insufficiently specific to reliably differentiate an IP from other benign (inflammatory or antrochoanal polyps) and malignant (sinonasal carcinoma) masses
On CT, IPs appear as an enhancing nasal or sinus mass, which may widen the maxillary infundibulum; identification of a hyperostotic stalk favors IP over other sinonasal masses and can help direct the surgical approach
On MRI, IPs classically demonstrate a “cerebriform” or “brainlike” appearance, seen as heterogeneous alternating hypointense and hyperintense bands on T2-weighted and contrast-enhanced T1-weighted images

Pearls

Classic features on CT (hyperostotic stalk) and MRI (cerebriform T2 signal) favor the diagnosis of IP

References

Chawla A, Shenoy J, Chokkappan K, Chung R. Imaging features of sinonasal inverted papilloma: a pictorial review. Current Problems in Diagnostic Radiology 2016; 45(5):347-53
Ojiri H, Ujita M, Tada S, Fukuda K. Potentially distinctive features of sinonasal inverted papilloma on MR imaging. American Journal of Roentgenology 2000; 175:465-468

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