Microsurgical landmarks for safe removal of anterior clinoid process.

OBJECTIVE: The microsurgical and radiological anatomy of the clinoid process were studied to give surgeons more details about the anterior clinoid process and its relations to the vascular and nervous neighbourhood during intradural and extradural clinoidectomy, thus making the operative procedures safer.
METHODS: Seven formalin-fixed (14 sides) and two fresh cadavers (four sides) were studied to reveal the surgical anatomy of the anterior clinoid process and related landmarks during intradural and extradural drilling techniques of clinoid process. Furthermore, aeration of the anterior clinoid process was investigated in 100 paranasal tomography (200 sides) scans.
RESULTS: Careful drilling of the anterior clinoid process is mandatory to avoid damage to the extremely important adjacent structures. The anterior clinoid process must not be removed in one piece. Clinoid folds and the frontotemporal fold should be exposed adequately. The falciform ligament must be cut to visualize the optic nerve and ophthalmic artery clearly. Preoperative radiological assessment of clinoid process variations should be done. In computerized tomography scans, pneumatization of the right anterior clinoid process was found in 12%, of the left anterior clinoid process in 7% and bilaterally pneumatization was present in 9%.
CONCLUSIONS: Removal of the ACP is one of the most critical procedures to the successful and safe management of ophthalmic segment aneurysms and tumors located in the paraclinoid region and cavernous sinus. Special attention should be paid to the anatomic landmarks indicating the relationship between the anterior clinoid process and adjacent structures. Beside that, pneumatization of the anterior clinoid process should be evaluated preoperatively with computed tomography to avoid complications such as rhinorrhea and pneumocephalus.