• Christopher Miller, Roukoz Chamoun, and David Beahm.
• Department of Neurosurgery, The Uni-versity of Kansas School of Medicine, Kansas City, Kansas.
• Oper Neurosurg (Hagerstown). 2017 Feb 1; 13 (1): 124-130.

BackgroundThe interest in detailed anatomy of the sella and parasellar regions has resurged recently due to the wide clinical applications of the expanded endoscopic approaches to the skull base. The middle clinoid process (MCP) is a bony structure that can affect wide endoscopic exposure of the sella and parasellar region.ObjectiveTo study and analyze the anatomic variations of the MCP in the general population using computed tomography scans.MethodsA total of 150 maxillofacial computed tomography scans were reviewed to characterize the MCP. Only adult patients without intracranial or nasal pathology were included. Measurements were made in the axial and sagittal planes to determine the maximum diameter, length, angulation, and location of the MCP.ResultsThe prevalence of the MCP was 30.7% in male and 42.7% in female patients. Of the MCPs, 41.8% were ring forming, whereas 76.4% were pneumatized. Quantitatively, the average axial base diameter was 4.6 ± 1.4 mm, the average sagittal base diameter was 5.0 ± 1.8 mm, the average length was 4.7 ± 1.7 mm, the average midline distance was 5.9 ± 2.3 mm, the average distance from the sellar-clival junction was 10.6 ± 3.3 mm, the average sagittal angle was 91.0 ± 21.1°, and the average axial angle was 45.2 ± 15.5°. A significant increase was found in the prevalence of MCPs in white patients compared with black patients, and a significantly greater midline distance and axial angle were found in male compared with female patients.ConclusionA clear understanding of the sellar and parasellar anatomy is crucial for successful and safe expanded endoscopic approaches. This study provides a quantitative anatomic characterization of the MCP in the U.S. population with demographic data analysis.Copyright © 2016 by the Congress of Neurological Surgeons

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