Endoscopic Transorbital and Retrosigmoid Approaches to the Pre-meatal and Ambient Area: An Anatomical and Quantitative Comparative Study with Surgical Applications

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BACKGROUND: The study aims to quantitatively compare the transorbital approach (TOA) and the retrosigmoid approach (RSA) in terms of surgical exposure and maneuverability, assessing whether these approaches are complementarity or competitive in accessing the pre-meatal area (PMA) and ambient cistern following tentorial incision. METHODS: Six sides of formalin-fixed cadaveric specimens were analyzed. Two parameters were measured using neuronavigation: (1) Area of Exposure (AoE), defined as the anatomical area accessible via a given approach, and (2) Surgical Freedom (SF), representing an estimation of the range of motion for the surgeon's hands. These parameters were evaluated under standard conditions and following tentorial incision extension to improve exposure of the ambient cistern, middle tentorial incisura, the cerebellopontine angle (CPA). RESULTS: Pre-extension analysis revealed that the TOA provided a grater AoE than the RSA, although the difference was not statistically significant (P = 0.22), while SF was greater with the TOA (P = 0.008). After tentorial incision, the RSA achieved a larger AoE compared with the TOA. Both approaches offered similar exposure of the ambient cistern (P > 0.05), demonstrating that surgical extension mitigates the initial differences in exposure between the two techniques. A representative clinical case was also described. CONCLUSION: The TOA offers greater surgical freedom, potentially improving maneuverability during neurovascular dissection within the PMA. However, following tentorial extension, RSA achieves a larger AoE in the PMA region, indicating its advantage in cases requiring broader surgical exposure. These findings highlight the importance of selecting an appropriate approach to optimize the surgical trajectory toward the middle tentorial incisura and the CPA angle. Depending on the lesion extent and anatomical complexity, both TOA and RSA may be used either individually or as components of a multiportal surgical strategy.

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