Comparative analysis of endoscopic endonasal far-medial, far-lateral transcondylar and combined approaches to the foramen magnum region: volumetric analysis and quantitative insights on surgical exposure and maneuverability

Abstract Background Surgical access to the anterior craniovertebral junction (CVJ) and foramen magnum region remains technically challenging due to dense neurovascular anatomy and limited working corridors. Although the far-lateral transcondylar and endoscopic far-medial approaches are both employed clinically, direct quantitative comparisons of maneuverability and volumetric exposure are still lacking. Objective To quantitatively assess and compare surgical maneuverability, anatomic limits and volume of exposure of the endoscopic far-medial, far-lateral, and combined approaches. Methods Five latex-injected cadaveric heads underwent dissection via an endoscopic endonasal far-medial approach (EEFM), contralateral far-lateral transcondylar approach (FL), and a combined approach. Surgical freedom, horizontal and vertical angles of attack, and volumetric exposure were measured using neuronavigation and 3D CT-based segmentation. Site-specific measurements were obtained at the hypoglossal canal, jugular foramen, and vertebrobasilar junction. Statistical comparisons were made using Wilcoxon rank-sum tests. Results The FL demonstrated significantly greater surgical freedom (363 mm 2 vs. 6.8 mm 2 , P = .01), horizontal angle of attack (99° vs. 8.1°, P = .01), and vertical angle of attack (78° vs. 15.4°, P = .01) compared to the EEFM. The EEFM yielded the smallest mean total volume (5.53 ± 2.01 cm 3 ), primarily concentrated in the anteromedial compartment (4.70 ± 1.67 cm 3 ). The FL offered a significantly larger mean total exposure (15.12 ± 1.93 cm 3 , p < 0.001), dominated by posterolateral access (12.60 ± 2.16 cm 3 , p < 0.001). The combined approach provided the greatest overall exposure volume (18.76 ± 3.58 cm 3 ), with substantial access to both the posterolateral (12.90 ± 2.32 cm 3 ) and anteromedial (5.86 ± 1.95 cm 3 ) compartments. Conclusion The far-lateral approach offers superior surgical freedom and posterolateral exposure, while the far-medial endoscopic approach provides a direct but limited midline corridor predominantly anteromedial foramen magnum lesions. The combined approach maximizes volumetric access and should be considered for extensive foramen magnum lesions particularly engulfing or anterior to neurovascular structures.