Comparative Analysis of the Far-Medial and Far-Lateral Approaches to Clipping Proximal PICA Aneurysms

Introduction: Posterior inferior cerebellar artery (PICA) aneurysms are rare—they comprise only 3% of all intracranial aneurysms, and most arise at the vertebral artery (VA)–PICA junction. The far-lateral approach (FLA) has been the most commonly cited technique to reach these aneurysms, largely due to it affording wide-exposure of the ventromedial aspect of the brainstem. Nevertheless, reaching PICA aneurysms using FLA requires careful identification of IX, X, XI, XII cranial nerves, damage to which can cause serious neurological deficits. The Far Medial Approach (FMA) has often been used to reach lesions in the ventral lower clivus, but only one case of its use in the clipping of a PICA aneurysm has been reported in the literature. The objective of this study is to assess the feasibility of reaching the PICA origin through FMA and to compare its surgical freedom and exposure to the FLA.

Methods: Ten FMA and 10 FLA were performed in 5 cadaveric specimens, and a navigation system was used to acquire measurements. Measurements included (1) angle of attack at various points, (2) area of surgical freedom, and (3) linear distances between relevant landmarks. Subsequent statistical analysis was conducted to compare the results of the two approaches.

Results: The PICA origin was reached in 10 out of 10 FLA, but only in 6 out of 10 FMA. The angle attack at the origin of PICA was similar between FMA and FLA: 82.0 ± 22.1 degrees and 83.4±31.4 degrees, respectively. Length of VA exposed was similar with both approaches: 23.06±6.8 mm with FMA and 23.9±3.3 mm with FLA. Area of exposure was similar between both approaches: 229.6 ± 43.8 mm² with FMA, 237.8 ± 55.9 mm² with FLA.

Conclusion: While the FMA allowed wide exposure of the brain stem in the ventromedial compartment, anatomical variations of the course of VA yielded lower accessibility to the PICA origin compared with the FLA. Area of exposure and length of VA exposed did not differ significantly between the two approaches, and VA could be clipped proximally and distally to the PICA origin in both approaches. These findings suggest that the FMA is a potentially viable approach to proximal PICA aneurysms. However, preoperative angiography and CTA scans should be carefully referenced-as aneurysms arising posteriorly and laterally can be incompatible with the FMA.