Surgical anatomy of the deep lateral orbital wall

PURPOSE: To determine the exact anatomic location and volume of the thickest section of the greater wing of the sphenoid bone (trigone), which is removed during deep lateral orbital wall decompression. METHODS: Eighteen dried skulls were used to determine the exact anatomic location and computed tomography (CT) images of 20 patients (10 male, 10 female) were used for volumetric calculations. RESULTS: Mean values were 14.5 mm for the orbital rim to inferior orbital fissure distance, 23.3 mm for rim to trigone distance, 13.0 mm for width of the trigone base, 5.8 mm for trigone to orbital apex distance, and 12.3 mm for trigone height. The width of the narrowest section of the trigone was 5.2 mm. The trigone was found to have a lower segment (0.92 cc) neighboring the inferior orbital fissure, and an upper segment (0.32 cc) adjoining the thick substance of frontal bone. The narrowest part between these two segments was located just at the superior border of the lateral rectus muscle. CONCLUSIONS: The authors recommend avoiding the thin rectangular portion located in the inter-fissural area adjacent to the superior orbital fissure. A high intersubject variability underscores the need for individualized preoperative analysis by imaging studies.