Computer-aided 3-D 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 for further understanding on the pathologic mechanisms of indirect optic nerve injury. Methods Six optic canals and their inner structures were reconstructed usin g a computer-aided 3-dimensional reconstruction system. Quantitative measur ement of the canal wall thickness, bony canal transverse area, optic nerve transverse area, dural sheath transverse area, subarachnoid space transvers e area, and subarachnoid space volume were done by means of the computer mo rphometric analysis system. The detailed spatial relationship among intraca nalicular structures were also carefully identified on the 3-D models. Results The thinnest portion of the canal was the middle part of the medial wall (0.45 +/- 0.35 mm) and the narrowest space was in the middle part of the optic canal (the transverse area was 18.21 +/- 2.50 mm(2))(.) The volum e of subarachnoid space which can be considered the compensatory space for distention incurred by the hemorrhage, optic nerve edema, or hematoma was 2 1.16 +/- 4.31 mm(3). At the cranial opening,the middle part and orbital ope ning, its transverse area was 4.45 +/- 1.12 mm(2), 2.68 +/- 1.32 mm(2) and 1.23 +/- 0.83 mm(2) , respectively. Conclusions Since the compensatory space was limited, even a tiny amount of blood or swelling of the nerve may cause optic nerve compression. Because the narrowest space was in the middle part of the optic canal and the compe nsatory space for distention gradually decreases from cranial end to orbita l end, the middle part and the anterior part of the optic canal and dural s heath are critical in optic nerve decompression.