Biomechanical Bases to the Mobilization of the Transcavernous Oculomotor Nerve during Basilar Aneurysm Surgery

Introduction: The transcavernous approach adds a significant exposure advantage in basilar aneurysm surgery. However, one of its frequently reported side effects is postoperative oculomotor nerve palsy. We present the technique of mobilizing the oculomotor nerve throughout its intracranial course and we assess its biomechanical consequences on cadaveric specimens. Methods: The oculomotor nerve is mobilized from its mesencephalic origin to the superior orbital fissure. Its degree of mobility, related to the imposed pulling force, was measured in 11 cadaveric nerves. Tension was mathematically deduced and compared before and after mobilizing the cavernous segment. A total of 104 patients treated for basilar aneurysms using the orbitozygomatic pretemporal transcavernous approach were followed for a 1-year period and evaluated for postoperative oculomotor nerve palsy. Results: Releasing the transcavernous segment compared with cisternal mobilization alone resulted in a significant increase in freedom of mobility from 4 to 7.9 mm (p < 0.001) and in a significant decrease of tension from 0.8 to 0.5 N (p = 0.006). Overall 99% of aneurysms treated using this technique were amenable to neck clipping, and a total 84% of patients had a good postoperative outcome (mRS 0-2). All patients showed direct postoperative palsy, however 97% had a complete recovery by 9 months. Only three patients had a persistent diplopia on medial gaze which was corrected with prism glasses. Conclusion: The mobilization of the transcavernous oculomotor nerve results in better maneuverability and less tension on the nerve, which leads to successful surgical treatment and favorable oculomotor outcome.