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 extensive ly reported to increase exposure in neurosurgical procedures. However, ther e have been few attempts to quantify the extent of additional exposure gain ed 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 tr anssylvian approach. Methods. The authors dissected five cadavers bilaterally. The area of expos ure provided by the frontotemporal transsylvian approach was determined by using a frameless stereotactic device. With the tip of a microdissector pla ced on targets deep within the exposure, the position of the end of the mic rodissector handle was measured in three-dimensional space as the microdiss ector was rotated around the periphery of the operative field. This maneuve r was performed via the frontotemporal approach alone as well as with orbit al rim and orbitozygomatic osteotomy approaches. After data manipulation, t he areas of exposure corresponding to the polygons used to define these han dle positions were calculated and directly compared. On average, the area o f exposure provided by the frontotemporal transsylvian approach was increas ed 26 to 39% (p < 0.05) by adding orbital rim osteotomy and an additional 1 3 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 produc ed less consistent gains. Both maneuvers may be expected to improve surgica l access. However, because larger and more consistent gains were afforded b y orbital rim removal, the threshold for removal of this portion of the orb itozygomatic complex should be lower.