BACKGROUND: Endoscopic endonasal approaches (EEAs) are an efficient way to manage skull base lesions
however, studies regarding postoperative rhinosinusitis are limited. This study analyzed the incidence of postoperative rhinosinusitis, the associated risk factors, microbial species, and antibiotic usage in patients who underwent EEA. METHODS: Patients who underwent EEAs at a tertiary referral hospital between July 2015 and May 2019 were retrospectively evaluated. Postoperative rhinosinusitis was defined as the presence of a purulent nasal discharge on postoperative endoscopic examination. The mucopus was aspirated and subjected to bacterial culture analysis. The culture results of various groups were analyzed. RESULTS: This study included 300 patients, and the incidence of post-EEA rhinosinusitis was 59.7%. History of endonasal surgery was an independent predictive factor for post-EEA rhinosinusitis (odds ratio [OR]: 2.54 [1.28-5.05], p = 0.007). Lesions in the anterior skull base were associated with prolonged use of antibiotics for rhinosinusitis during postoperative care (OR: 3.91 [1.32-11.52], p = 0.013). Staphylococcus aureus was the most common causative pathogen (52.3%), followed by methicillin-resistant S. aureus (MRSA) (20.7%), Pantoea dispersa (14.4%), and Pseudomonas aeruginosa (52.3%). P. aeruginosa was more significant in the complex reconstruction group than in the control group. While most patients with post-EEA rhinosinusitis experienced a transient clinical course, one female patient underwent endoscopic sinus surgery (ESS) for prolonged rhinosinusitis. CONCLUSION: Rhinosinusitis is common in the postoperative stage of the EEA. As it usually lasts for a short duration and is treatable with proper medication, aggressive nasal care during the postoperative period is required to prevent related nasal morbidities.