Endoscopic Anatomical Study of the Skull Base with Poor Pneumatization: A Quantitative Analysis Based on Cadaveric Specimens

Background: The endoscopic endonasal approach (EEA) has been widely applied in the surgical treatment of skull base tumors. However, poor pneumatization of the skull base—such as inadequate sphenoid sinus pneumatization and dense clival bone—can severely obscure key anatomical landmarks, significantly increasing surgical risks. Systematic quantitative studies on endoscopic anatomical landmarks under conditions of poor pneumatization remain limited to date. Methods: Using 10 lightly embalmed adult cadaveric head specimens with red-blue silicone injection, we performed a stepwise dissection of the nasal cavity; sphenoid sinus; cavernous sinus (CS); upper, middle, and lower clivus; craniovertebral junction (CVJ); and lateral skull base regions via the expanded endoscopic EEA with a 0° rigid endoscope. Particular emphasis was placed on observing variations in the landmarks within the sphenoid sinus under conditions of poor pneumatization, and morphometric measurements were obtained for key structures, including the clivus and its adjacent areas, occipital condyles (OC), hypoglossal canal (HC), petrous apex (PA), and vidian canal (VC). Results: In poorly pneumatized specimens, the clival recess (CR) within the sphenoid sinus is often not observable, and the optic nerve prominence and the internal carotid artery (ICA) prominence are indistinct. Quantitative data showed that the total length of the clivus was 28.7 ± 2.1 mm, with gradual widening from superior to inferior (upper clivus: 20.8 ± 2.0 mm; middle clivus: 22.7 ± 2.8 mm; lower clivus: 29.2 ± 3.9 mm). The average drillable area of the entire clivus was 8.6 ± 1.1 cm2, and the PA could be safely drilled by approximately 45–48% (about 1.0 cm3) via the EEA. The length of the VC ranged from 17.1 to 17.8 mm, and its distance from the foramen rotundum (FR) was approximately 7.8–8.0 mm, which may serve as a useful anatomical reference for localizing the horizontal petrous segment of the ICA. Conclusions: In cases of poor pneumatization of the skull base, the osseous and vascular prominences are often obscured under EEA, necessitating coordinate-based localization using quantitative anatomical data. The present study provides segmental clival widths, three-dimensional measurements of the OC-HC complex, the VC-FR interval, and the safe drillable volume of the PA, thereby furnishing a quantitative reference for precise and safe surgery in the poorly pneumatized skull base.