What Is the Best Approach? A Cadaver-Based Anatomic Comparison of the Ipsilateral and Contralateral Approach to Superior Hypophyseal Artery Aneurysms

Introduction: Superior hypophyseal artery (SHA) aneurysms are proximal inferomedially projecting intracranial internal carotid artery aneurysms. Although the SHA provides the major blood supply to the intracranial optic nerve, visualization of the SHA branch via an ipsilateral approach to an SHA aneurysm is usually suboptimal but may be improved using a contralateral approach. The objective of this study is to compare the contralateral and ipsilateral approaches to the SHA region.

Methods: Using five formalin-fixed, latex-injected cadaver heads, we performed a standardized pterional approach to the contralateral SHA branches of eight carotid arteries working between the two optic nerves. We used a frameless stereotactic workstation to quantify the deep working area and approach angle freedom. We recorded the number of SHA branches visible and evaluated the feasibility of clip placement for a hypothetical SHA aneurysm. Following anterior clinoidectomy and opening the falciform ligament, we assessed the ipsilateral approach.

Results: On average, the deep working area was 1.7 ± 0.5 times larger (P < 0.01, paired t-test), and the approach angle freedom was 2.3 ± 0.7 times larger (P < 0.001) for the ipsilateral approach over the contralateral approach. However, only 60% (9/15) of SHA branches were seen via the ipsilateral approach, and the origin of the SHA branches was never seen without significant manipulation of the supraclinoid carotid artery. Therefore, clips placed for hypothetical aneurysms via an ipsilateral approach risked incorporating the SHA branch. Although 3 of 5 specimens harbored a prefixed optic chiasm narrowing the contralateral deep working area, we determined that by varying clip choice and length it would be anatomically feasible to clip smaller aneurysms in this location via a contralateral approach without excessive optic nerve manipulation while preserving the SHA branch origin.

Conclusion: Although the contralateral approach to the SHA origin narrows the approach corridor and reduces the deep working area each by about one half, clipping aneurysms in this location seems to be feasible despite optic chiasm configuration and may reduce the risk of optic nerve ischemia by allowing clip placement under direct vision to ensure protection of SHA perforators. During a contralateral approach, proximal control would require cervical carotid exposure.