A Case of Sinonasal Inverted Papilloma Suspected as Postoperative Recurrence of Eosinophilic Chronic Rhinosinusitis.

Chronic rhinosinusitis (CRS) is a persistent inflammatory disease affecting the nasal and paranasal sinus tissues, classified into two main categories: one associated with nasal polyps (CRSwNP) and one without them (CRSsNP). A particular form of CRSwNP, known as eosinophilic CRS (ECRS), is distinguished by the excessive presence of eosinophils in the affected tissues. While surgical intervention and corticosteroids are the standard treatments, high relapse rates have led to increasing interest in biological treatments. Inverted papilloma (IP), a benign yet recurrent tumor with potential for malignancy, often complicates diagnosis when concurrent inflammation is present. We present a case of a 56-year-old man with a long-standing history of ECRS, initially suspected to have experienced a recurrence. Imaging suggested the possibility of IP, but biopsy results showed a marked increase in eosinophil levels. Following surgery, the diagnosis of IP was confirmed, and no malignancy was found. A year after surgery, the patient remained free of recurrence. This case emphasizes the difficulty of differentiating ECRS from IP due to their overlapping histological features. To ensure accurate diagnosis, a thorough evaluation combining radiological, endoscopic, and pathological methods is crucial.