Classification of Endoscopic Transnasal Lateral Skull Base Approaches: Anatomical Study

Abstract

Objective: Endoscopic transnasal approaches (ETAs) to the ventrolateral skull base are commonly classified according to coronal planes or anatomical structures. Our goal is to simplify the description of the ETA to lateral skull base regions in a sequential dissection with correlation to computed tomography, helping in preoperative planning and efficient surgical exposure, and exposing the surgical anatomy limitations. Methods: Five freshly injected cadaver heads were dissected using an extended ETA to the lateral skull base. Each specimen underwent a high-resolution computed tomography scan. A classification of the lateral skull base based on well-defined zones was proposed. Results: We divided the lateral target into four different zones, in a craniocaudal orientation: zone 1 is the space lying between the orbital floor superior and the level of the sellar floor inferior, zone 2 is on the coronal plane, located between the level of the sellar floor and the vidian canal, zone 3 is the area lateral to the anterior limb of the petro-occipital fissure, located between the vidian canal and the carotid canal, and zone 4 is the space located between the carotid canal and the extracranial opening of the hypoglossal canal, lateral to the anterior part of the posterior limb of petro-occipital fissure. Conclusions: Multiple previous works have described and classified the coronal plane and its lateral extensions. Our classification system for the proposed lateral zones enables preoperative planning to select a suitable approach. The craniocaudal orientation facilitates the understanding of surgical corridors and tailored exposure.