Anterior Clinoid Process Pneumatisation and the Optic Nerve

Background: The anterior clinoid process of the sphenoid bone exhibits intricate anatomical relationships with the optic nerve, internal carotid artery, and oculomotor nerve, with considerable variations including pneumatisation, bony bridges, and dehiscence. These variations carry significant surgical implications, as anterior clinoidectomy procedures carry visual morbidity risks ranging from 4.8% to 20%. Understanding population-specific anterior clinoid process anatomy is paramount for preoperative risk assessment and surgical planning in endoscopic skull base approaches. The aim is to determine the prevalence of anterior clinoid process pneumatisation and its association with optic nerve. 2.To assess the distribution and laterality of anterior clinoid process pneumatisation stratified by age and sex. Material and Methods: This retrospective cross-sectional study was conducted over 18 months at the Department of Anatomy and Radiodiagnosis, Government Medical College, Kottayam, Kerala, India. CT images of head, paranasal sinuses, and orbits from 300 adults (≥20 years) were analysed using a 128-slice GE Optima 660 multidetector CT scanner with multiplanar reconstructions in bone window (width 2000 HU; level 300 HU). The anterior clinoid process was analysed and pneumatisation noted.Theprevalence of anterior clinoid process pneumatisation and its association with optic nervewas also studied. Results: Among 300 participants (175 males, 125 females; mean age 45–69 years in 59.7%), anterior clinoid process pneumatisation prevalence was 11.0% (right), 13.0% (left), and 7.0% bilaterally. ACP pneumatization was strongly associated with Type 3 optic nerve configuration: 75.8% of right-sided and 74.4% of left-sided Type 3 cases exhibited ACP pneumatization (χ² = 159.945, p < 0.001 right side; χ² = 206.115, p < 0.001 left side). No Type 1 cases demonstrated ACP pneumatization. Conclusion: Anterior clinoid process pneumatisation is significantly associated with surgically hazardous Type 3 optic nerve configurations in this South Indian population, providing a predictive framework for preoperative risk stratification. High-resolution CT with multiplanar reconstruction is essential for all patients undergoing sphenoid sinus or anterior clinoidectomy procedures to identify at-risk anatomical variants and enhance surgical safety.

Keywords: Anterior Clinoid Process, Pneumatisation, Optic Nerve, Sphenoid Sinus.