Surgical examination of vascular anatomy in transorbital approach

Introduction: Minimally invasive skull base approaches have developed considerably in recent years. Lesions that were thought to be accessible only through open surgery can now be accessed by new approaches such as transnasal or transorbital route. Endoscopic or endoscope-assisted approaches can reduce morbidity, and new surgical techniques that access the orbit and intracranial cavity have been named transorbital neuroendoscopic surgery (TONES) in recent years. The superior eyelid route as a TONES corridor has proven to be clinically feasible as a route to selected anterior and middle skull base pathologies. In our study, we aimed to define the vascular structures that can be accessed by the superior eyelid endoscopic approach. Materials and Methods: The superior eyelid approach was performed in 8 orbits in 4 silicone-stained cadavers obtained from Dokuz Eylül University Anatomy Department and the vascular structures reached were recorded. Results: In our study, the superior orbital fissure was identified after inferomedial extraction of the orbital contents using the upper eyelid approach. Then, the greater and lesser sphenoid wings and orbital roof were drilled and craniectomy was performed and access was provided to the basal frontal lobe, temporal pole and sylvian fissure was obtained. After dissecting the sylvian fissure, the M1 segment of the middle cerebral artery located posterior to the lesser sphenoid wing was reached. Following this segment medially, access to the proximal M1, the lenticulostriate arteries originating from the posterosuperior aspect of M1, the mesial temporal lobe and the oculomotor nerve was obtained. It was observed that the supraclinoid segment of the internal carotid artery and the opticocarotid cistern could be reached if the craniectomy was extended medial to the superior orbital fissure and towards the optic canal, But it was noted that an angled endoscope should be used for visualisation of this region and orbital retraction should be increased. After following the M1 segment laterally from the craniectomy, the genu of the middle cerebral artery from the level of the limen insula to the posterior was observed and the bifurcation of the middle cerebral artery, superior and inferior branches of the M2 segment, limen insula and anterolateral part of insula were visualised. Conclusion: Endoscopic superior eyelid approach can be considered as a novel approach for different pathological scenarios. Our study showed that the M1 and M2 segments of the middle cerebral artery and the branches originating from it are accessible with a 0-degree endoscope after an appropriate and careful dissection.