2025 Proffered Presentations
S095: ANATOMICALLY-BASED STRATEGIES TO PREVENT ABDUCENS NERVE INJURIES IN THE RETROSIGMOID ROUTE: INSIGHTS FROM A CADAVERIC ANALYSIS
Fabio Torregrossa, MD1; Amedeo Piazza, MD1; Yuki Shinya, MD, PhD1; Luciano Leonel, PhD1; Steven Graepel1; Giovanni Grasso, MD, PhD2; Giuseppe Lanzino, MD1; Michael J. Link, MD, PhD1; Maria Peris-Celda, MD, PhD1; 1Mayo Clinic, Rochester, MN (USA); 2Neurosurgical Unit, Department of Biomedicine, Neurosciences and Advanced Diagnostics (BiND), University of Palermo, Palermo, Italy
INTRODUCTION: Lesions of the cerebellopontine angle and petroclival region represent a challenging surgical target due to the complex anatomy of the involved neurovascular structures. In this scenario, cranial nerve VI (CN VI) is particularly exposed to potential injuries due to its deep-seated location and consequent encasing and displacement caused by lesions (Fig. 1).
OBJECTIVE: This study aims to provide reliable operative guidance for preventing injuries to CN VI during the retrosigmoid approach to address cerebellopontine (CP) angle and petrotentorial lesions.
METHODS: Four formalin-fixed, latex-injected anatomical specimens were dissected to highlight and investigate the relevant anatomy of the CP angle and petroclival region during the retrosigmoid approach (Fig. 2).
Additionally, 50 sides of non-injected formalin-fixed specimens were dissected for morphometric evaluation. Associations between the petrotentorial junction, internal acoustic meatus (IAM), and trigeminal impression with the entry point of CN VI into Dorello’s canal were evaluated. To verify if the path followed by the petrotentorial junction was parallel to the line connecting the lower edge of the IAM to the entrance of CN VI into Dorello’s canal, we measured the distances from Dorello’s canal (A) and the lower edge of the IAM (E) to the petrotentorial junction perpendicularly (A-C & E-D) (Fig. 3).
A three-dimensional anatomical model generated through the photogrammetry scanning technique was described.
RESULTS: The distance from the petrotentorial junction to the entry point of CN VI into Dorello’s canal and to the inferior edge of the IAM was 9.5 ± 1.4 mm (A-C) and 10.2 ± 0.9 mm (E-D) (p > 0.05), respectively (Fig. 3). Thus, the outlined trajectory of the petrotentorial junction was parallel to the line passing through the inferior edge of the IAM to the entrance of Dorello’s canal. The latter, measured as 21.4 ± 1.3 mm (Fig. 3, E-A). Moreover, the entrance point of CN VI into Dorello’s canal was estimated at 6.2 ± 1.2 mm (Fig. 3, B-A) from the anterior edge of the trigeminal impression in a trajectory perpendicular to the petrotentorial junction. The obtained results demonstrate two surgical strategies to locate Dorello’s canal during the retrosigmoid approach: (1) Moving parallel to the petrotentorial junction from the inferior edge of the IAM; (2) Starting from the anterior edge of the trigeminal impression and moving inferiorly, perpendicular to the petrotentorial junction (Fig. 4).
CONCLUSION: The defined operative landmarks provide reliable anatomical guidance to locate Dorello’s canal within the retrosigmoid route. This knowledge can enable neurosurgeons to perform petroclival microsurgery with greater precision and confidence, thereby reducing the risk of abducens nerve palsy and improving patient outcomes.