Abstract
OBJECTIVE: The mini-pterional (MP) approach is widely adopted as the standard exposure for middle cerebral artery (MCA) aneurysms, whereas the eyelid transorbital (TOA) approach has recently emerged as a minimally invasive alternative. This cadaveric study aims to quantitatively compare the anatomical exposure and working geometry of the mini-pterional and microscopic transorbital approaches to the MCA bifurcation, with implications for approach selection and skull base microsurgical planning. METHODS: Five latex-injected human cadaveric heads were dissected via either the MP (n = 5) or TOA (n = 5) approach. Standardized microsurgical techniques of eyelid transorbital and mini-pterional approaches were used to access the MCA bifurcation. Key surgical parameters including access depth, access angle (M1 angle) to first segment of MCA (M1), and horizontal and vertical angles of attack to the MCA bifurcation were evaluated quantitatively using neuronavigation. Statistical analysis was performed using the Wilcoxon Rank Sum test with a significance threshold of p < 0.05. RESULTS: Both approaches provided adequate exposure to the MCA bifurcation and its branches. The working distance is similar in both approaches (MP 26.9 ± 7.48 mm vs. TOA 31.0 ± 7.49 mm, p = 0.24). The MP approach offered significantly wider vertical angle of attack (86.1 ± 34.82° vs. 45.3 ± 32.11°, p = 0.02) while the horizontal angle (25.0 ± 8.56° vs. 33.6 ± 15.33°, p = 0.42) was comparable in both approaches. The TOA approach demonstrates a more perpendicular M1 angle (54.3 ± 17.37° vs. 32.7 ± 17.2°, p = 0.03), which may be anatomically favorable for proximal control. CONCLUSION: The MP approach remains advantageous for broader exposure and maneuverability; however, the microscopic TOA offers distinct anatomical exposure characteristics. These findings define the geometric differences between the two routes and may inform surgical planning in selected MCA bifurcation aneurysm cases.