Advantages and limitations of orbital rim resection in transorbital endoscopic approach: an anatomical study

Background Endoscopic transorbital approach (eTOA) has been recently proposed as an alternative skull base approach. However, its feasibility for deeper lesions can be hampered by a reduced surgical maneuverability. Aim of this study is to consider how its extension through orbital rim resection can overcome this limitation, and to compare two different techniques for its removal. Methods Both sides of seven cadaveric fresh frozen head were dissected. Three different surgical approaches were performed consequentially (standard eTOA, its expansion with lateral orbital rim hinge removal, and with its complete resection). Distance to target and angle of attack have been measured for superior orbital fissure (SOF), lateral wall of cavernous sinus (LWCS), anterior clinoid process (ACP), foramen rotudum (FR) and foramen ovale (FO). Results The angle of attack to the SOF ( p = 0.01), to the LWCS ( p = 0.001), to the ACP ( p = 0.01), to the FR ( p = 0.01) and to FO ( p = 0.01) resulted larger in extended approaches with orbital rim resection, as well as the distance to target of LWCS ( p = 0.04). Particularly, we observed that hinge lateral orbital rim removal improved the angle of attack to SOF ( p = 0.02), APC ( p = 0.01), FR ( p = 0.01 and FO ( p = 0.01) in comparison to the standard eTOA. Conclusion Our study confirms that the lateral orbital rim resection could significantly expand the surgical room and the instruments maneuverability for the considered target skull base targets. Its hinge removal could balance the clinical outcome with the increase of the angles of attack for the more medial and deeper structures.