Quantitative Comparison of Endoscopic Approaches to the Paramedian Skull Base: A Preclinical Study

Introduction: The paramedian skull base has been considered a challenging region to approach surgically, especially for the management of extradural lesions, with significant risks for the neurovascular structures that run in that region. Recently, some authors have underlined the need to add anterior approaches that are characterized by a more lateral entry point (e.g., the contralateral transmaxillary approach), as compared to transnasal approaches, if the target in the skull base is paramedian. Objectives: A quantitative anatomical study, using a dedicated neuronavigation system that defines each surgical approach, was performed: the aim was to investigate ipsilateral endoscopic transnasal EEA, extended contralateral EEA, and endoscopic contralateral transmaxillary CTM (with its variations) features in the controlled, preclinical setting of the anatomy laboratory of the Catholic University School of Medicine (SURGEM). Methods: Three adult fresh-frozen cadaver heads (six sides) were dissected. A unilateral and contralateral expanded endonasal approach (eEEA) and a contralateral transmaxillary approach (CTM) were performed so as to expose the three main regions of the paramedian skull base: the parasellar region, the petrous apex, and the hypoglossal region. A quantitative comparison of the surgical pyramids described by each approach was obtained for each region by means of GtxEyesII-ApproachViewer, using two different modalities of quantification: crossing modality, which represents maximum reachable deep surface, moving the pointer freely, aiming to execute the largest movement possible to delimitate each structure, and non-crossing modality, which indicates the surgical pyramid with the highest surgical manoeuvrability, keeping the passive probe pointer always perpendicular to the target, describing circles and cylinders to delimit the structures. The quantification procedure was repeated six times for each approach. Results: Analyzing the results regarding the parasellar region, the EEA contralateral crossing and CTM crossing approach offered a statistically significant wider exposure than the non-crossing approaches, respectively ( p = 0.028) and ( p = 0.0001). For the petrous apex region, statistical significance was reached only for the ipsilateral ( p = 0.021) and contralateral ( p = 0.025) EEA and for the CTM after inferior turbinectomy ( p = 0.00003), while it was not confirmed for the CTM after middle turbinectomy ( p > 0.05). The manipulation of the neurovascular structures was required when EEAs were used. Analyzing the hypoglossal region, the CTM and the ipsilateral EEA were shown to grant a similar exposure in the crossing modality. The addition of an inferior turbinectomy allowed for significantly widening the exposure of the petrous apex and hypoglossal region both for crossing and non-crossing modalities. Conclusion: The EEA provides a straightforward surgical route, requiring the surgeon to circumvent the neurovascular structures. On the other hand, the CTM approach minimizes the need for complex and risky endoscopic maneuvers, offering greater exposure to the paramedian skull base for the management of extradural lesions. Publication History Article published online: 07 February 2025 © 2025. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany

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