A 54-year-old woman had complained of left nasal obstruction for several years. A polypoid lesion filled the left nasal cavity (Figure 1A). Nasal CT revealed a soft tissue extending from the left nasal cavity to the ethmoid sinus (Figure 2A). Histological examination revealed an inflammatory polyp with an average eosinophil count of 130 in high magnification field view (x400), then diagnosis of eosinophilic chronic rhinosinusitis (ECRS) was made (Figure 3A). A peripheral eosinophil count was 6.5%. According to the Japanese epidemiological survey of refractory eosinophilic chronic rhinosinusitis criteria, she was diagnosed having ECRS. Endoscopic sinus surgery was performed, and polyps were removed. Postoperative pathology showed a papillary proliferation of high columnar cells with eosinophilic cytoplasm accompanied by intraepithelial microcysts. Diagnosis of an oncocytic papilloma was finally made (Figure 3B).

Four months later, papillomatous polyp arose again then grew larger (Figure 1B). CT revealed a lobulated mass was detected in the left nasal cavity, continuous with the middle turbinate. After 10 months, the second surgery was performed and tumour was totally removed with the part of middle turbinate (Figure 2B). A histology of tumour was consistent with oncocytic papilloma. After two years, no tumour recurrence was observed.

ECRS is a subgroup of chronic rhinosinusitis with nasal polyps and causes multiple bilateral nasal polyps through an allergic mechanism, resulting in intractable nasal obstruction and olfactory dysfunction. On the other hand, oncocytic papilloma is a very rare nasal tumour, accounting for only 3% of all paranasal sinus papillomas. Although their histological findings are characterized by eosinophilic infiltration, their pathology and treatment are different. In the present case, the pathology of the initial biopsy showed high eosinophilic infiltration without papillary proliferation. The peripheral part of the tumour may have shown atypical features of papilloma, leading to the misdiagnosis of eosinophilic sinusitis.