Objective:To investigate the changes of sphenoid sinus and related risk factors of sphenoid sinusitis after microscopic transsphenoidal pituitary adenoma resection.Methods:The clinical and imaging data of 106 patients with large pituitary adenoma in 900 Hospital of the PLA Joint Logistics Team between August 2012 and March 2015 were continually collected. The changes of accumulated blood and fluid, inflammation, mucocele, mucosa remodeling in sphenoid sinus cavity at preoperative and postoperative different time points were observed through the analysis of magnetic resonance imaging (MRI). Binary logistic multiple factors regression model was used to analyze the independent risk factors for postoperative sphenoid sinusitis.Results:MRI results showed that the blood and fluid accumulated in sphenoid sinus cavity were absorbed and dissipated 3 months after the surgery, and the saddle bone windows were covered by new mucous membrane at this time, but they were not complete; the remaining tumors in the saddle all sank into the saddle to different degrees. The reconstruction of sphenoid sinus mucosa was basically complete 6 months after the surgery. There were 7 (6.6%) cases of mucocele in sphenoid sinus and 26 (24.5%) cases of sphenoid sinusitis 3 months after the surgery among 106 patients. The results of multivariate analysis showed that growth hormone adenoma ( OR = 2.981, 95% CI 1.480-26.207, P = 0.014), preoperative sphenoid sinusitis ( OR = 12.392, 95% CI 2.927-52.462, P = 0.001), frequency of multiple transsphenoidal surgery ( OR = 14.758, 95% CI 2.431-89.584, P = 0.003) and perioperative cerebrospinal fluid leakage ( OR = 11.644, 95% CI 2.175-62.344, P = 0.004) were independent risk factors for postoperative sphenoid sinusitis. Conclusions:The evolution of sphenoid sinus cavity contents has its own rules after microscopic transsphenoidal pituitary adenoma resection. Patients with growth-hormone pituitary adenoma, sinusitis before surgery, multiple transsphenoidal surgery and cerebrospinal fluid leakage during the surgery should receive enhanced anti-infection treatment and nasal care in perioperative period to reduce the possibility of sphenoid sinusitis after surgery. The staged time of reoperation for pituitary adenoma resection by transsphenoidal approach should be about 3 months after the previous operation.