Endoscopic 360° vision of the orbit: A comparative anatomical study of endonasal and transorbital approaches.

Background and objective: Treatment of lesions located within and surrounding the orbit pose considerable surgical challenges, due to the presence of critical neurovascular structures in such deep, confined spaces. Historically, transcranial and craniofacial approaches have been widely used to deal with orbital pathologies. However, in recent decades we have witnessed the emergence of minimally invasive techniques to reduce morbidity and hospitalization times. Among these techniques are the endoscopic endonasal approach (EEA) and the subsequently developed endoscopic transorbital approach (ETOA). This anatomical study aims to compare and combine the surgical view offered by these two endoscopic pathways to achieve a circumferential access to the orbit.

Methods: Anatomic dissections were performed at the Laboratory of Surgical NeuroAnatomy (LSNA) of the Human Anatomy and Embryology Unit, University of Barcelona (Barcelona, Spain) on five cadaveric specimens (10 sides), whose arterial and venous systems were injected with red and blue latex respectively. Dissections were made with microsurgical instruments and a surgical endoscope.

Results: After careful removal of the intraorbital fat, all the extraocular muscles were exposed and dissected, as well as the optic nerve, the ophthalmic artery, and the lacrimal gland. Special emphasis was given to dissecting the nerves' course from the cavernous sinus to their muscle innervation: oculomotor and its branches, trochlear, abducent and ophthalmic nerve with its branches (frontal, nasociliary and lacrimal nerve). Each of the two endoscopic pathways provided a different perspective of the orbit and its structures. After both corridors were completed, a communication between the surgical pathways was highlighted, in a so-called connection area.

Conclusions: The combination of the EEA and ETOA provides a 360° view of the orbit and its contents. The EEA offers an inferior and medial view of the orbit, through the lamina papyracea of the ethmoid in the first case and through the roof of the maxillary sinus in the latter. At the same time, the ETOA shows a lateral perspective, removing the lateral rim of the orbit, allowing great maneuverability inside the orbit and a wide visualization. This study provides a detailed overview of the surgical neuroanatomy of the orbit, which is an essential and didactic baseline in preparation for practical clinical applications. Overall, EEA and ETOA seem adequate to gain optimal exposure of the orbit and can be adapted to treat a wide range of pathologies. Yet, surgical case series are necessary to establish the true clinical value of these endoscopic approaches in orbital and peri-orbital surgery. However, the limited number of specimens analyzed (5 cadavers, 10 sides) must be acknowledged as a limitation.