Objective To investigate the MRI findings of sinonasal inverted papilloma so as to promote the diagnostic accuracy.Methods All 36 cases of sinonasal inverted papilloma were verified by pathology.Their MRI findings were analyzed retrospectively.Results The lesion occurred in the lateral nasal wall in 25 cases,in the maxillary sinus in 4 cases,in the ethmoid sinus in 2 cases,in the frontal and ethmoid sinuses in 2 cases, in the ethmoid and sphenoid sinuses in 2 cases and in the frontal sinus in one case.Of the 36 cases,11 cases had recurrent lesions and 3 cases were associated with malignant change.All lesions showed well-defined margin,with lobulate configuration in 26 cases and irregular shape in 10 cases.The diameter of the lesions ranged from 22 to 82 mm (mean,38 mm).On MR T1WI,sinonasal inverted papilloma revealed isointense signal compared to adjacent muscle in 32 cases and slight hyperintense signal in 4.On T2 WI,the lesions showed heterogeneous hyperintense signal in 34 cases and inhomogeneous isointense signal in 2 cases with malignant change.Postcontrast MR imaging demonstrated marked inhomogeneous enhancement compared with nasal septum mucosa in 34 cases.Regular fence-like pattern was found on MR T2WI and enhanced T1WI in 32 cases,while irregular ones were found in three cases with malignant change.The time-intensity curve (TIC)of dynamic contrast enhancement of MRI showed rapid enhancing and slow wash-out type in 7 cases,while rapid enhancing and wash-out pattern was detected in one ease with malignant change.Conclusion Regular fence-like pattern on MR T2WI or enhanced T1WI was reliable characteristics for the diagnosis of sinonasal inverted papilloma.Irregular ones may suggest malignant change.