• Wei-Hsin Wang, Kumar Abhinav, Eric Wang, Carl Snyderman, Paul A Gardner, and Juan C Fernandez-Miranda.
• *Department of Neurological Surgery, University of Pittsburgh School of Medicine, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania; ‡Department of Neurosurgery, Neurological Institute, Taipei Veterans General Hospital, Taiwan; §School of Medicine, National Yang-Ming University, Taipei, Taiwan; ¶Department of Otolaryngology, University of Pittsburgh School of Medicine, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
• Neurosurgery. 2015 Nov 3.

BackgroundThe endoscopic endonasal approach provides a direct route to ventral foramen magnum (FM) lesions like meningiomas, which are difficult to access. Endonasal access at the FM is limited laterally by the occipital condyles and inferiorly by the C1 anterior arch and the odontoid process, which may need partial resection.ObjectiveWe investigated the surgical anatomy and technical nuances for endonasally increasing the surgical corridor at the FM region both laterally and inferiorly. Unique to our report, we quantified the amount of required medial condyle resection to obtain exposure of the lateral aspects of the FM.MethodsFive fresh human head silicone-injected specimens underwent endonasal inferior transclival, transcondylar approaches. The lateral limit of medial condyle resection was defined using a vertical line extending inferiorly from foramen lacerum and its intersection with the occipital condyle. The condylectomy was limited posteriorly by the cortical bone surrounding the hypoglossal canal. The volume of the resected condyle (cubic centimeters) for 10 sides was measured using the pre- and postdissection computed tomography-volumetric analysis.ResultsThe mean percentage condylar volume resected during a unilateral medial condylectomy was 18% (9.7%-28.3%). The surgical corridor was extended inferiorly in all specimens without violating the transverse ligament by drilling the superior aspects of C1 anterior arch and the exposed odontoid tip. These operative nuances were successfully applied in the operating room.ConclusionAnatomical landmarks can reliably guide an endonasal anteromedial condyle resection. Minimal condyle resection is required to widen lateral access at the FM, which minimizes the risk of craniocervical instability.AbbreviationFM, foramen magnum.

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