Computer-aided three-dimensional reconstruction and measurement of the optic canal and intracanalicular structures

Objective: To reconstruct the human optic canal and its inner structures an d to provide detailed knowledge of this region for optic nerve decompressio n. Methods: Six optic canals and their inner structures were reconstructed using a computer-aided three-dimensional reconstruction system. Quantitativ e measurement of the canal wall thickness, bony canal transverse area, opti c nerve transverse area, dural sheath transverse area, subarachnoid space t ransverse area, and subarachnoid space volume was done using the computer m orphometric analysis system. The detailed spatial relationship. among intra canalicular structures was also carefully identified on the three-dimension al models, Results The thinnest portion of the canal was the middle part of the medial wall (0.45 +/- 0.14 mm) and the narrowest space was in the midd le part of the optic canal (the transverse area was 18.21 +/- 1.20 mm(2)). The volume of subarachnoid space that can be considered the compensatory sp ace for distention incurred by the hemorrhage, optic nerve edema, or hemato ma was 21.16 +/- 4.31 mm(3). At the cranial opening, the middle part, and t he orbital opening, its transverse area was 4.45 +/- 0.46 mm(2), 2.68 +/- 0 .54 mm(2), and 1.23 +/- 0.34 mm(2) respectively. Conclusions: Because the c ompensatory space was limited, even a tiny amount of blood or swelling of t he nerve may cause optic nerve compression, Because the compensatory space for distention gradually decreases from cranial end to orbital end, the mid dle part and the anterior part of the optic canal and dural sheath are crit ical in optic nerve decompression.