Preoperative simulation of a middle cerebral artery aneurysm clipping using a rotational three-dimensional digital subtraction angiography.

Background: In recent years, young neurosurgeons have had few opportunities to gain experience with clipping surgeries. The first author was sometimes surprised that she could not predict the anatomical relationships between the aneurysm and vessels during actual surgery. This study investigated the differences between the expected and actual operative findings during clipping surgery for aneurysms of the middle cerebral artery.

Methods: Medical records for 15 patients who underwent rotational three-dimensional (3D) digital subtraction angiography (3D-DSA) before the clipping surgery were analyzed after the surgery. The anatomical relationships between the aneurysm and parent arteries were defined by the intraoperative findings just before clipping. The viewing direction to obtain this definitive perspective (virtual viewing direction) was measured. The angle between this viewing direction and the coordinate axis was denoted as the "virtual angle for clipping (VAC)."

Results: The VAC between the X-axis and viewing direction on the XY-plane (VAC-XY) ranged from -43° to +73° (mean, +27°), and the angle between the XY-plane and viewing direction (VAC-Z) ranged from +25° to -34° (mean, 5.5°). The difference between the VAC-XY and mean angle was significantly larger in cases with hidden branches behind the aneurysm. In these cases, the virtual viewing direction visualized the neck of the aneurysm. There is no correlation between M1 length and VAC-XY or VAC-Z discrepancy.

Conclusion: 3D-DSA or 3D computed tomography angiography images visualizing the neck of the aneurysm should be obtained in combination with images obtained from the standard oblique angle.