Introduction: The interest in detailed anatomy of the sellar and parasellar region 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 sellar and parasellar region. The purpose of this project is to study and analyze the anatomical variations of the MCP in the general population using CT scans.

Methods: 150 maxillofacial CT scans were reviewed to characterize the MCP. Only adult patients with no pathology in sellar region that could potentially cause changes in the morphology of the MCP. Measurements were made in the axial and sagittal planes to determine maximum length, diameter, distances from key structures and angulation of the MCP.

Results: The prevalence of the MCP was 30.67% in males and 42.7% in females. Of subjects found to have an MCP, 41.82% were ring forming while 76.36% were pneumatized. Quantitatively the average base diameter was 4.6±1.4mm in the axial plane and 5.0±1.8mm in the sagittal plane, average maximum length was 4.7±1.7mm, average distance from midline was 5.9±2.3mm, average distance from the clival sellar angle was 10.5±3.4mm, average angle in the sagittal plane was 88.5±21.1º, and average angle in the axial plane was 45.2±15.5º. There were no significant differences in gender, age, ethnicity, race, or laterality.

Conclusions: A clear understanding of the sellar and parasellar anatomy is crucial for performing successful and safe expanded endoscopic approaches to treat skull base pathologies. This study provides a quantitative anatomical characterization of the MCP in the general population. Surgeons should obviously carefully review the CT scan of every patient to detect unusual variations and pathological involvement of the skull base.

Patient Care: This research provides surgeons with an improved understanding of the anatomy of the sella tursica, specifically the middle clinoid process. This better understanding will assist surgeons in providing safe and effective surgical intervention to patients with sella tursica pathology.

Learning Objectives: By conclusion if this session, participants should be able to: 1) Identify the middle clinoid process on CT scans, 2) Understand the basic morphology and variants of the middle clinoid process, 3) Understand how the presence and morphology of the middle clinoid process can impact the transphenoidal surgical approach.

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