Transorbital Endoscopic Approach to the Middle and Inner Ear: An Anatomical Feasibility Study

Background: Various approaches have been devised for managing diseases of the middle and inner ear. The TOEA was recently introduced as a complementary gateway to the skull base. The anatomical nuances and applicability of the TOEA for reaching the middle and inner ear have not been elucidated previously.

Objective: To assess the feasibility of the TOEA to the middle and inner ear and provide a detailed description of its surgical anatomy.

Methods: Lateral TOEAs to the middle cranial fossa were performed in five adult cadaveric heads (10 sides), under image-guidance. A lateral rim osteotomy was performed in all cases to facilitate a wider lateral access. The tegmen tympani, labyrinth, internal acoustic canal (IAC), and petrous apex, were unroofed and their underlying structures reached. Anatomic relationships relevant to surgery were studied from a ventral view-point.

Results: Anatomical structures, including the Eustachian tube, tympanic and mastoid cavities, internal carotid artery, cochlea, geniculate ganglion, the superior and lateral semicircular canals, IAC contents, and sigmoid sinus, among others, were exposed and visualized. The crista ovale, middle meningeal artery, Eustachian tube, greater superficial petrosal nerve, subarcuate artery, and arcuate eminence served as the major landmarks during dissection. Minimal eyeball and brain retraction were necessary during the approach.

Conclusion: Access to the middle and inner ear, through the lateral transorbital corridor, is feasible in the cadaver. The TOEA grants a direct view of key middle fossa landmarks for identifying critical neurovascular structures. A comprehensive understanding of the compact temporal bone anatomy, from a ventral perspective, is paramount in this approach. Further studies are warranted to determine its clinical value.