Ossifying inverted papilloma and ossifying polyp of the sinonasal tract: comparison of CT and MRI features.

Aim: To investigate the key imaging points in distinguishing ossifying inverted papilloma (IP) from polyps.

Materials And Methods: The native computed tomography (CT), conventional and enhanced MRI manifestations of 20 ossifying IPs and eight polyps, which were confirmed histopathologically, were retrospectively evaluated by two doctors majoring in head and neck imaging.

Results: A significant difference was detected between the two entities for the involved sites (p<0.05). Although two lesions had similar CT findings, the MRI features differed significantly (p<0.05). Twenty ossifying IPs demonstrated heterogeneously isointense with moderate gadolinium enhancement, and a convoluted "cerebriform" configuration. Seven ossifying polyps revealed low T1 and high T2 signal, with marginal enhancement, and one showed isointense with moderate enhancement. The ossification appeared as oval or striped bone-like high attenuation, which consisted of peripheral hyperattenuating cortical bone and central fat-like attenuation of the medullary cavity. The corresponding MRI findings of the ossifying regions were peripherally low signal and centrally high signal on both T1- and T2-weighted images. The occurrence of two key MRI features of cystic appearance and the "cerebriform" sign were significantly different between two entities (p<0.05).

Conclusions: CT can better detect intralesional ossification, but MRI is the optimal imaging technique for discriminating between two disease entities.