Microinvasive Fungal Rhinosinusitis: Proposal of a New Subtype in the Classification

Background: Fungal rhinosinusitis (FRS) with mucosal invasion is not classified by the current criteria, and clinical reports on the topic are limited. The aim of this study was to present our 25-year experience on fungal balls with mucosal invasion that do not appear in the FRS classification. Methods: Of 1318 patients who underwent endoscopic surgery with paranasal FRS between November 1994 and July 2019, 372 underwent mucosal biopsies. Medical chart and pathology review were performed on 13 patients diagnosed as having fungal balls with mucosal invasion without accompanying tissue invasion. Results: Histopathologic findings identified all fungi as belonging to the Aspergillus species. In 13 patients, 7 fungal balls were located in the maxillary sinus, 3 in the sphenoid sinus, and 3 in both the maxillary and ethmoid sinuses. The median age at diagnosis was 67 years (interquartile range (IQR): 62-72), and the sex ratio was 1:2 (4 men and 9 women). Five patients had comorbidities-three with diabetes mellitus and two with hematologic malignancy-all of whom received postoperative antifungal therapy. The median duration of antifungal treatment was 13 weeks (IQR: 8-17). No recurrences occurred during the median follow-up period of 30 months (IQR: 22-43). Conclusions: Patients who have been clinically diagnosed with a fungal ball and showed mucosal invasion but no vascular invasion, based on pathologic findings after surgery, may need a new FRS classification category, such as microinvasive FRS, and adjuvant antifungal treatment may be needed for immunocompromised patients with microinvasive FRS. Key points: Fungal rhinosinusitis with mucosal invasion is different from fungal ball and invasive fungal rhinosinusitis and may be classified in a separate category as microinvasive FRS.