Preoperative simulation of a middle cerebral artery aneurysm clipping using a rotational three-dimensional digital subtraction angiography
- Department of Neurosurgery, Jichi Medical University, Shimotsuke, Tochigi, Tokyo, Japan
- Department of Neurosurgery, National Center Hospital, National Center of Neurology and Psychiatry, Kodaira, Tokyo, Japan
Department of Neurosurgery, Jichi Medical University, Shimotsuke, Tochigi, Tokyo, Japan
DOI:10.25259/SNI_934_2020Copyright: © 2020 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Yuiko Kimura1,2, Toshihiro Mashiko1, Eiju Watanabe1, Kensuke Kawai1. Preoperative simulation of a middle cerebral artery aneurysm clipping using a rotational three-dimensional digital subtraction angiography. 23-Feb-2021;12:70
How to cite this URL: Yuiko Kimura1,2, Toshihiro Mashiko1, Eiju Watanabe1, Kensuke Kawai1. Preoperative simulation of a middle cerebral artery aneurysm clipping using a rotational three-dimensional digital subtraction angiography. 23-Feb-2021;12:70. Available from: https://surgicalneurologyint.com/surgicalint-articles/10605/
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.
Keywords: Clipping, Intraoperative finding, Middle cerebral artery aneurysm
Clipping surgery for the treatment of cerebral aneurysm has recently become less common because of the development of endovascular intervention. The reduced opportunities for experience with clipping surgery emphasize the need for young neurosurgeons to improve their skills and knowledge during the few opportunities they have to perform this technique. Careful pre- and post-operative examinations and surgery simulation are important for improving the outcome of the surgical procedure.
The first author (Y.K.) has developed a method to obtain a thorough understanding of the anatomical relationships of a middle cerebral artery (MCA) aneurysm as follows: the anteroposterior view is obtained with a three-dimensional (3D) digital subtraction angiography (3D-DSA) or 3D computed tomography angiography (3D-CTA). The image is rotated from the horizontal plane by 30° to the affected side and 10° to the cranial side. This angle was defined as a tentative preoperative standard determined by the fixed head rotation angle.
However, the anatomical relationships between the aneurysm and blood vessels often unexpectedly differed from those in the preoperative simulation. A representative case of an unruptured right MCA aneurysm is shown in [
Differences between expected and actual views during clipping surgery for right middle cerebral artery (MCA) aneurysm. (a) Three-dimensional digital subtraction angiography image of the expected view of the aneurysm obtained at 30° from the anteroposterior axis to the affected side and 10° from the XY-plane to the cranial side. The origin of the branch (arrowheads) is hidden by the aneurysm. Asterisk shows the first segment of the MCA (M1). (b) Transparent view with almost the same angle as that in (a). The branch originates from behind the aneurysm. (c) Operative view during application of a clip (arrow). The aneurysm neck is clearly visible.
Therefore, the present study analyzed the differences between the expected and actual operative findings and attempted to determine the optimal 3D-DSA or 3D-CTA viewing angle to correspond with the actual surgical view. The actual view varies from moment to moment during surgery; therefore, the operative findings were defined as the microscope view immediately after the aneurysm was clipped. This study included patients who had undergone 3D-DSA because the viewing angle could easily be measured with this technique.
This study included 15 consecutive patients who underwent rotational 3D-DSA in preparation for an MCA aneurysm-clipping surgery. Rotational 3D-DSA (Allura Xper FD; Philips, Amsterdam, Netherlands) was performed using the Seldinger technique with a 12-mL (4.0 mL/s) injection of iohexol (Omnipaque 350; GE Healthcare, Princeton, NJ) into the internal carotid artery. The tentative preoperative standard view was orientated at a 30° angle between the anteroposterior axis and the affected side and at a 10° angle between the XY-plane and the cranial side. The surgery was video recorded through the operating microscope. After surgery, the differences between the expected and actual operative findings were analyzed. The origin of the coordinate system was defined as the center of the external acoustic meatus (middle point of the meatal–meatal line). The X-axis was set as a line parallel to the infra-orbitomeatal line, passing through the origin. The Y-axis was set as the meatal–meatal line orthogonal to the X-axis. The Z-axis was set on the line orthogonal to the XY-plane passing through the origin of the XY-plane.
The preoperative 3D-DSA image was then rotated and reconstructed to focus on a very small area that included the aneurysm and its parent arteries. The positional relationships between the aneurysm and parent arteries in this area were obtained by approximating the intraoperative findings just before clipping was performed. The virtual viewing direction of this image was determined.
The angle between the virtual viewing direction and the coordinate axis is denoted as the “virtual angle for clipping (VAC).” The angle between the X-axis and the virtual viewing direction in the XY-plane is denoted as VAC-XY, and the angle between the XY-plane and virtual viewing direction is denoted as VAC-Z. The VAC-XY was expressed as a positive value if the virtual viewing direction originated ipsilateral to the lesion and as a negative value if it originated contralaterally. Similarly, positive VAC-Z was expressed as positive with a cranial viewing angle and as negative with a caudal viewing angle.
Schema explaining the virtual angle for clipping (VAC). (a-c) Simple schema explaining VAC on the horizontal plane (VAC-XY). We mostly expected the “natural view,” as shown in a. Surgical manipulation results in arterial displacement, so the operator can visualize the aneurysm as shown in b. This view is an approximation of the image shown in c. We defined this angle as VAC-XY. (d) Three-dimensional concept of VAC. ∠A=VAC-XY; ∠B=VAC-Z. The X-axis was set as a line parallel to the infra-orbitomeatal line. The Y-axis was set as the meatal–meatal line orthogonal to the X-axis. The Z-axis was set orthogonal to the XY-plane and included the origin for the XY-plane.
For example, in the case shown in [
We measured the M1 length of all 15 cases. The difference between the average VAC and the measured VAC is called VAC discrepancy. We checked if there was a correlation between M1 length and VAC discrepancy using a Pearson test.
Finally, we investigated how to obtain the optimum VAC. This study has been approved by the ethics committee of the institute and informed consent was obtained from patients.
A 65-year-old woman was diagnosed with a right MCA aneurysm by follow-up magnetic resonance imaging (MRI) after undergoing clipping surgery for a left internal carotid-posterior communicating artery aneurysm. A small arterial branch was located behind the aneurysm [
Case 1: Unruptured right middle cerebral artery aneurysm. (a and b) A small arterial branch (arrowhead) emerges from behind the aneurysm (a). We predicted that the branch origin would be difficult to observe. The initial view of the actual surgery was almost identical to the expected view (b), but moving the microscope and shifting the main trunk (M1, asterisk) allowed the operator to visualize the aneurysm neck. (c) Reconstructed image based on the operative view. The origin of the small branch is visible. virtual angle for clipping (VAC)-XY is –22°, and VAC-Z is +8°.
A 60-year-old woman had an unruptured left MCA aneurysm that was revealed by MRI during the follow-up examination for a lacunar infarction. The aneurysm was 7 mm in diameter and had a broad neck and a bleb. Based on the tentative preoperative standard view, we expected the M2 inferior branch to hide the M1 and anticipated that the aneurysm neck was located on the side of the superior branch of M2 [
Case 2: Unruptured left middle cerebral artery (MCA) aneurysm with a broad neck and a bleb. Asterisk shows M1; ◇,superior branch of the second segment of the MCA (M2). (a) Expected operative view showing that the inferior branch of the M2 (◆) is hidden behind the aneurysm. (b) During surgery, the aneurysm neck was easily detected without detaching the bleb in the temporal lobe. (c) Reconstructed image based on the operative view. The origin of the inferior branch of the MCA is visible. Virtual angle for clipping (VAC)-XY is +68°, and VAC-Z is +18°.
A 70-year-old woman complained of dizziness. An MRI indicated a left MCA aneurysm with several blebs. A clipping surgery was performed. Based on the tentative preoperative standard view, we expected the M2 inferior branch to be hidden behind the aneurysm [
Case 3: Unruptured left middle cerebral artery aneurysm with several blebs. (a) Expected operative view indicates the inferior branch of the M2 (◆) is hidden behind the aneurysm. Asterisk shows M1. (b) Actual intraoperative view easily allows for visualization of the aneurysm neck. (c) Reconstructed image based on the operative view. The origin of the inferior branch of the M2 is visible. Virtual angle for clipping (VAC)-XY was +73°, and VAC-Z was +25°.
VAC-XY ranged from –43° to +73° (mean, +27°) in the 15 cases [
The correlation coefficient between M1 length and VAC-XY discrepancy was 0.013 with a significance probability of 0.964 and that between M1 length and VAC-Z discrepancy were –0.444 with a significance probability of 0.098.
Various head positions have been recommended for clipping surgery for MCA aneurysm, such as “the head is rotated 20– 30° toward the opposite side, tilted slightly downwards,”[
However, the operative findings are often different from the expected operative view because of the movement of the microscope, brain shift, brain retraction, or deformation of the arteries caused by surgical manipulation. Therefore, it is not easy for young surgeons to predict the operative findings actually observed during aneurysm clipping. Several simulators have been developed to predict the operative findings.[
Neither the relationships between the aneurysm and its parent arteries nor the aneurysm shape and clip application angle were identical to those predicted from the tentative preoperative standard view in this study. For example, we usually expected VAC-Z to be positive. In fact, VAC-Z was often negative, suggesting that the required perspective was needed from the caudal side. VAC-XY was also negative in two cases, contrary to our expectation. Mean VAC-XY was +27°, which would approximate the expected operative findings. However, VAC-XY ranged from +68° to –43°. VAC-Z ranged from +25° to –34° (mean, –5.5°). The difference between VAC-XY and the mean value was significantly larger in cases with hidden branches behind the aneurysm, as predicted. This discrepancy has important implications.
Other factors, such as the degree of fixation and orientation of the parent arteries, may affect VAC discrepancy. However, there was no correlation between M1 length and the degree of VAC discrepancy. It is worth noting that differences in the degree of fixation of the parent arteries due to the presence of branch arteries or adhesions, rather than M1 length, might have affected the VAC.
The discrepancy between the VAC and the expected operative view may be due to substantial displacement of the parent arteries by surgical manipulation to visualize the aneurysm neck in the presence of hidden branches. An actual-size model of an aneurysm and parent artery to simulate clipping suggested that the parent artery deviation had the biggest effect on the discrepancy between the estimated and actual operative findings.[
During the initial stage of surgery, the operative view was almost the same as the expected view but the operative view changed during the procedure. Finally, just before clipping, the operative view allowed visualization of the aneurysm neck. The angle of this final view corresponded to the working angle for intravascular surgery. Therefore, a preoperative image should be obtained from this “working angle” as well as from the standard oblique angle because the former often resembles the true operative findings, particularly in the case of an aneurysm with a hidden branch.
Preoperative 3D-DSA should include an image visualizing the neck of the aneurysm together with an image taken from the standard oblique angle. We conclude that the preoperative views should be prepared as follows: (1) standard oblique angle (30° rotated to the affected side and 10° to the cranial side); (2) specific angle visualizing the neck of the aneurysm; and (3) several views at angles between (1) and (2). These additional views may be important for preoperative simulation.
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