Introduction: Treatment of basilar artery aneurysms is challenging. While endovascular techniques have dominated, there still remain circumstances where open surgical clipping is required or preferred. Minimally invasive “keyhole” approaches are being used more frequently to provide the durability of surgical clipping with a lower morbidity profile. With minimally invasive approaches, however, careful patient selection is required. The supraorbital “keyhole” approach has been described for the treatment of basilar artery aneurysms, but careful assessment of the basilar exposure is necessary to ensure proper visualization of the aneurysm and ability to obtain proximal vascular control. Various methods of estimating the basilar artery exposure in a supraorbital “keyhole” approach have been described, including the anterior skull base line and the posterior clinoid line, but both are unreliable and inaccurate. We propose a new method, the orbital roof-dorsum line, to simply and accurately predict the basilar artery exposure.

Methods: CT angiograms of twenty patients were reviewed. Three measurements were obtained: length of basilar artery above the anterior skull base (planum), length of basilar artery above the posterior clinoid, length of basilar artery above an oblique line that estimates the slope of the orbital roof. This was then compared to a "control" using neuronavigation to plan and map the anterolateral basilar artery exposure.

Results: The average length of basilar artery visualized using the anterior skull base line, the posterior clinoid, and the orbital roof was 1.7mm, 4.2mm, and 6.7mm, resepectively. The controls had an average basilar artery length of 7.2mm. The average difference between the anterior skull base, posterior clinoid, and orbital roof estimations and the control was 5.48m±2.37mm, 2.98mm±1.87mm, and 0.49mm±0.89mm, respectively. Differences between all estimations and control were statistically significant except for the orbital roof-dorsum line.

Conclusions: The orbital roof-dorsum line provides an accurate estimation of basilar artery exposure through a keyhole supraorbital exposure.

Patient Care: Neurosurgery as a discipline is constantly focusing on establishing and maintaining the highest quality of life for our patients; minimally invasive craniotomies are continuing to evolve in providing the best neurosurgical care. This research focuses on applying minimally invasive craniotomy as a solution to posterior circulation aneurysms; which is particularly needed when these aneurysms cannot be treated by endovascular methods.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the constraints on basilar artery exposure via a keyhole supraorbital approach 2) Describe the various methods of estimating length of basilar artery exposure via a keyhole supraorbital approach

References: Ma Y, Lan Q: Supraorbital keyhole approach to upper basilar artery aneurysms via the optico-carotid window: a cadaveric anatomic study and preliminary application. Minim Invasive Neurosurg 54:228-235, 2011 Sure U, Alberti O, Petermeyer M, Becker R, Bertalanffy H: Advanced image-guided skull base surgery. Surg Neurol 53:563-572; discussion 572, 2000