Background: The purpose of this study was to analyze sphenoid sinus lateral pneumatization (SSLP), especially in Asian populations, and to identify cautionary items when using the endoscopic endonasal approach (EEA) for parasellar/lateral lesions. Methods: We analyzed SSLP and the width of SS (SSW) in 121 patients who had undergone EEA from 2008 to 2013 at the Division of Neurosurgery, Keio University Hospital. SSLP was defined as the distance between the SS lateral edge and the medial aspect of the pterygoid process on coronal reconstruction computed tomography. SSW was defined as the distance between the midline and lateral wall. We recorded SSLP and SSW for 242 sides. Further, we present two characteristic cases. Results: The average SSLP and SSW were 7.0 mm (-10.0-25.8 mm) and 21.8 mm (6.0-40.2 mm), respectively. No correlation between pneumatization and age was observed at age 15 or more. Sphenoid pneumatization was significantly wider in male than in female patients. There was no relationship between lateral and sagittal plane pneumatization. In a patient with recurrent chordoma who had an undeveloped SSLP, the tumor was removed via the medial space in the internal carotid artery. In another patient who had a giant pituitary adenoma and average SSLP, the tumor was located in the middle cranial fossa and was removed via the lateral internal carotid space through the left SSLP. Conclusions: Wide variations were observed in SSLP and SSW. For EEA, pneumatization is an instrument corridor. Preoperative assessment of SSLP is important, especially for parasellar lesions.
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