Early Visualization of Optic Canal for Safe Anterior Clinoidectomy: Operative Technique and Supporting Computed Tomography Findings

Abstract

Anterior clinoidectomy is considered difficult because important structures are adjacent to but hidden behind the anterior clinoid process (ACP). We sought to make anterior clinoidectomy a simpler procedure. A modification of anterior clinoidectomy is presented. To obtain a radiologic basis, original images from 357 consecutive sets of computed tomography angiography data were assessed. Anterior clinoidectomy was performed in 77 consecutive patients, as follows. By making a small window in the lateral wall of the ACP and curetting out the content inside, the lateral wall of the optic canal was easily exposed and functioned as a landmark for removal of the remaining bone. In addition, by removing the posterior edge and thinning the lateral part, the ACP was fractured and removed. The optic canal was opened if needed. No complications due to anterior clinoidectomy were observed. Among the 689 sides evaluated, 641 sides showed cancellous bone and 29 showed well-developed pneumatization inside the ACP. In each ACP examined, we observed the presence of compact bone facing the optic nerve, which constitutes the lateral wall of the optic canal. On 180 sides, part of the compact bone between the clinoid process and the internal carotid artery was absent; in other cases, thin compact bone was present. Visualizing the optic canal in the early stage of the procedure allows anterior clinoidectomy to be performed safely.