Surgical Anatomy of the Microscopic and Endoscopic Transorbital Approach to the Middle Fossa and Cavernous Sinus: Anatomo-Radiological Study with Clinical Applications

SIMPLE SUMMARY: The popularity that transorbital approaches (TOAs) gained in recent years has allowed their diffusion into skull base surgery. However, for their correct application, it is essential to know the potential and the limits of this group of transorbital routes, as well as the knowledge of anatomy from this relatively new surgical perspective. In this paper, the authors illustrate step-by-step the superior eyelid transorbital approach from a macroscopic and endoscopic perspective, highlighting the main anatomical relationships to understand the application of this surgical route for the treatment of skull base pathologies. Surgical cases are provided to illustrate indications for this approach. ABSTRACT: Background: The transorbital approaches (TOAs) have acquired growing notoriety, thanks to their ability to offer alternative corridors to the skull base. However, the limited access and the unfamiliarity with this surgical perspective make recognition of key landmarks difficult, especially for less experienced surgeons. The study wants to offer a detailed description of the anatomy to comprehend the potential and limitations of TOAs. Methods: Measurements of the orbit region and the surrounding areas were performed on two hundred high-resolution CT scans and thirty-nine dry skulls. Five specimens were dissected to illustrate the TOA, and one was used to perform the extradural clinoidectomy. Three clinical cases highlighted the surgical applications. Results: A step-by-step description of the key steps of the TOA was proposed and a comparison with the transcranial anterior clinoidectomy was discussed. The mean work distance was 6.1 ± 0.4 cm, and the lateral working angle increased 20 ± 5.4° after removing the lateral orbital rim. Conclusions: TOAs are indicated in selected cases when tumor involves the lateral portion of the cavernous sinus or the middle skull base, obtaining a direct decompression of the optic nerve and avoiding excessive manipulation of the neurovascular structures. Comprehension of surgical anatomy of the orbit and its surrounding structures is essential to safely perform these approaches.