3D Navigation-Guided Volumetric and Angular Quantitative Analysis of Nasofrontal Trephination, Sublabial Contralateral Transmaxillary, and Subtarsal Contralateral Transmaxillary Approaches to the Skull Base and Upper Cervical Spine

Background: Recent advances in endoscopic skull base surgery have enabled access to difficult to access anatomy. While the sublabial contralateral transmaxillary (SL-CTM) approach is well established, the nasofrontal trephination (NFT) and subtarsal contralateral transmaxillary (ST-CTM) approaches offer novel corridors whose spatial reach and angular capacities remain undefined. Objective: To perform a 3D navigation-guided volumetric and angular analysis of NFT, SL-CTM, and ST-CTM approaches to quantify and compare their anatomical reach and assist surgical decision-making. Methods: Five latex-injected cadaveric heads were dissected using each approach. Pre-dissection CT imaging and a stereotactic navigation system facilitated precise annotation of reachable anatomical landmarks. Using 3D Slicer software, fiducial points were reconstructed into three-dimensional models to measure accessible volumes and instrument angulation in coronal and sagittal planes. Results: NFT approach achieved the highest mean accessible volume (156,643 mm 3 ), followed by SL-CTM (134,982 mm 3 ) and ST-CTM (111,458.5 mm 3 ). NFT also demonstrated the greatest vertical angular reach (113.64° ± 29.45°), while SL-CTM achieved the broadest horizontal angulation (109.4° ± 13.36°). SL-CTM provided superior [KW1] lateral access to the paramedian skull base, whereas NFT extended further caudally toward the odontoid and craniovertebral junction. ST-CTM offered intermediate performance in both dimensions. Conclusion: The NFT approach offers significant vertical access to midline caudal skull base lesions, making it a useful adjunct to endonasal routes. SL-CTM approach provides enhanced lateral reach, ideal for petrous apex and paramedian targets. This study introduces a reproducible navigation-based volumetric modelling methodology to guide approach selection and optimize operative planning. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany