• Pierre-Olivier Champagne, Georgios A Zenonos, Eric W Wang, Carl H Snyderman, and Paul A Gardner.
• Department of Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.
• World Neurosurg. 2022 Dec 1; 168: e269e277e269-e277.

BackgroundTranscranial removal of the anterior clinoid process (ACP) provides access to the clinoidal segment of the internal carotid artery as well as superolateral decompression of the optic canal. Endoscopic endonasal approaches (EEAs) can access the entire medial and inferior portions of the optic canal, but no data exist to support what proportion of the anterior clinoid could be safely resected via an EEA.MethodsA cadaveric anatomical study was performed with removal of the ACP in 3 major steps in order of difficulty and risk. At each step, the removal was stopped when no more bone of the ACP could be seen without traction on neural structures. After each step, a CT scan was performed to allow volumetric measurement of the remaining ACP.ResultsTwenty ACPs in 10 cadaveric heads were removed to various degrees using the described stepwise technique. The mean portion of the ACP resected by each step was 21%, 46%, and 27%, respectively. Cumulated ACP removal at the end of step 3 was 94%, with complete removal achieved in 35% of the specimens.ConclusionsUsing the safe route above the optic canal, removal of 21% of the ACP can be achieved via EEA. Although substantially more of the ACP can be drilled by accessing the optic strut, the benefits of pursuing additional removal must be weighed against the significant risks of drilling in this narrow corridor bordered by the internal carotid artery, the third cranial nerve, and the optic nerve.Copyright © 2022 Elsevier Inc. All rights reserved.

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