Quantification of increased exposure resulting from orbital rim and orbitozygomatic osteotomy via the frontotemporal transsylvian approach

Object. Use of orbital rim and orbitozygomatic osteotomy has been extensively reported to increase exposure in neurosurgical procedures. However, there have been few attempts to quantify the extent of additional exposure gained by these maneuvers. Using a novel laboratory technique, the authors have attempted to measure the increase in the 'area of exposure' that is gained by removal of the orbital rim and zygomatic arch via the frontotemporal transsylvian approach. Methods. The authors dissected five cadavers bilaterally. The area of exposure provided by the frontotemporal transsylvian approach was determined by using a frameless stereotactic device. With the tip of a microdissector placed on targets deep within the exposure, the position of the end of the microdissector handle was measured in three-dimensional space as the microdissector was rotated around the periphery of the operative field. This maneuver was performed via the frontotemporal approach alone as well as with orbital rim and orbitozygomatic osteotomy approaches. After data manipulation, the areas of exposure corresponding to the polygons used to define these handle positions were calculated and directly compared. On average, the area of exposure provided by the frontotemporal transsylvian approach was increased 26 to 39% (p < 0.05) by adding orbital rim osteotomy and an additional 13 to 22% (not significant) with removal of the zygomatic arch. Conclusions. Significant and consistent increases in surgical exposure were obtained by using orbital osteotomy, whereas zygomatic arch removal produced less consistent gains. Both maneuvers may be expected to improve surgical access. However, because larger and more consistent gains were afforded by orbital rim removal, the threshold for removal of this portion of the orbitozygomatic complex should be lower.