Pre- versus Post-Anterior Clinoidectomy Measurements of the Optic Nerve, Internal Carotid Artery, and Opticocarotid Triangle: A Cadaveric Morphometric Study

OBJECTIVE: Published morphometric data supporting the microsurgical advantages of anterior clinoidectomy are scant. The goal of this study was to quantify, with direct measurements, the improved exposure of the optic nerve, internal carotid artery (ICA), and opticocarotid triangle (OCT) after extradural removal of the anterior clinoid process. METHODS: Ten formalin-fixed adult cadaver heads were dissected bilaterally, and measurements were made both before and after anterior clinoidectomy. Twenty sets of pre- and post-anterior clinoidectomy measurements were collected, consisting of: 1) optic nerve length from the optic chiasm to the optic canal (pre) and to the anulus of Zinn (post); 2) ICA length from the ICA bifurcation to the distal limit of the anterior clinoid process (pre) and to the ICA distal dural ring (post); 3) OCT width, the widest in situ distance between the optic nerve and the ICA (pre) and the analogous measurement with allowable retraction on the mobilized ICA and optic nerve (post); and 4) OCT length from the point where the A1 segment crosses the optic chiasm to the optic canal (pre) and to the anulus of Zinn (post). RESULTS: The right and left combined mean values +/- standard error of the mean before and after removal of the anterior clinoid process, respectively, were: optic nerve length, 10.28 +/- 2.30 mm and 22.83 +/- 2.54 mm; ICA length, 10.48 +/- 2.39 mm and 14.78 +/- 3.02 mm; OCT width, 3.93 +/- 1.16 mm and 12.95 +/- 2.61 mm; and OCT length, 10.38 +/- 2.84 mm and 23.55 +/- 2.79 mm. CONCLUSION: Anterior clinoidectomy can provide a twofold increase in exposure of the optic nerve length and the OCT length, as well as a three- to fourfold increase in the maximum OCT width. This dramatically improves surgical exposure in the suprasellar and periclinoid regions.