Participants and setting
Patients who underwent ESS for CRS and SFB were identified using automated and manual chart reviews, as described below. We conducted an automated search of the histopathology database of our institute between 2005 and 2018. We then manually reviewed the chart records of the identified patients to confirm the study groups. A total of 6195 ESS procedures were identified during the study period; 713 patients with SFB were selected from the database based on the exclusion criteria, which included patients with allergic fungal rhinosinusitis or invasive FRS (Figure 1) . In order to evaluate the incidence of SFB, the ratio of the number of ESS procedures for SFBs to the total ESS procedures was calculated for each year.
Since clinical features differ according to the location of the SFB, and unilateral MSFB constituted the majority16, 592 patients with unilateral MSFB were identified for analysis. Among them, CT scan images of four patients were not available for review; we therefore evaluated the CT findings of 588 patients for the presence of complete or partial opacification and manifestations of IH. Odontogenic etiology was determined based on the clinical history and CT findings of adjacent maxillary odontogenic lesions including periapical lucency, periodontal bone loss, oroantral fistula, and exogenous dental reconstructive/restorative materials (Figure 2 ).17