PURPOSE: Several kinds of nasal cavity lesions located in the region of the infundibulum on CT. At such time,the visualization of these lesions is very sinilar. The purpose of this study was to differentially diagnose thesenasal cavity lesions through evaluation of the MR findings. MATERIALS AND METHODS: In 51 cases of pathologicallyproven nasal cavity masses which on CT showed infundibular widening, we retrospectively evaluated the MR findings.The cases involved prolapsed antral mucosa from sinusitis(n=15), inverted papilloma(n=10), antrochoanalpolyp(n=10), aspergillosis(n=9), and nasal polyp(n=7). All patients underwent both CT and MR. imaging. RESULTS: In all cases, CT findings were similar ; soft tissue masses filling the maxillary sinus and nasal cavity wereassociated with infundibular widening caused by pressure on the uncinate process, leading to erosion. Differentialdiagnosis by CT was very difficult ; MR T2 weighted imaging was most effective for differential diagnosis of thesenasal cavity masses. Prolapsed antral mucosa showed central inhomogeneous mixed signal intensity, with aperipheral rim of hyperintensity along the sinus wall and nasal component. Antrochoanal polyps showed homogeneousbright signal intensity of the antral and nasal component. Aspergillosis showed central dark signal foci. Invertedpapillomas showed mixed intermediate and high intensity mixed with high signal intensity. Nasal polyps showedstriation mixed of intermediate and high signal intensity, while nasal polyp showed striation of intermediate andhigh intensity. On Gd-enhanced T1 weighted images, prolapsed antral mucosa and antrochoanal polyp showedperipheral rim enhancement of the antral and nasal component. In contrast, inverted papilloma and nasal polypshowed intense enhancement of the mass and can be separate from the sinus inflammatory disease. CONCLUSION: Various nasal cavity masses showing infundibular widening on CT can be differentiated on MR images, especially ofthese are T2 weighted or contrast enhanced T1 weighted.