A Classification of Unruptured Middle Cerebral Artery Bifurcation Aneurysms that can Help in Choice of Clipping Technique

Numerical simulation of flow-diverting stent: comparison between branches in bifurcation brain aneurysm

The usage of flow-diverting stents in the treatment of intracranial aneurysms is widespread due to their high success and low complication rates. However, their use is still not officially recommended for bifurcation aneurysms, as there is a risk of generating ischemic complications due to the reduced blood flow to the jailed branch. Many works utilize computational fluid dynamics (CFD) to study how hemodynamic variables respond to flow diverter placement, but few seem to use it to verify flow variation between branches of bifurcation aneurysms and to aid in the choice of the best ramification for device placement. This investigation was performed in the present work, by comparing wall shear stress (WSS) and flowrates for a patient-specific scenario of a middle cerebral artery (MCA) aneurysm, considering device placement on each branch. A secondary objective was to follow a methodology that provides fast results, envisioning application to daily medical practice. The device was simplified as a homogeneous porous medium, and extreme porosity values were simulated for comparison. Results suggest that stent placement on either branch is both safe and effective, significantly reducing WSS and flow into the aneurysm while maintaining flow to the different ramifications within acceptable thresholds.

VR-based training of craniotomy for intracranial aneurysm surgery

PURPOSE

Intracranial aneurysms can be treated micro-surgically. This procedure involves an appropriate head position of the patient and a proper craniotomy. These steps enable a proper access, facilitating the subsequent steps. To train the access planning process, we propose a VR-based training system.

METHOD

We designed and implemented an immersive VR access simulation, where the user is surrounded by a virtual operating room, including medical equipment and virtual staff. The patient's head can be positioned via hand rotation and an arbitrary craniotomy contour can be drawn. The chosen access can be evaluated by exposing the aneurysm using a microscopic view.

RESULTS

The evaluation of the simulation took place in three stages: testing the simulation using the think-aloud method, conducting a survey and examining the precision of drawing the contour. Although there are differences between the virtual interactions and their counterparts in reality, the participants liked the immersion and felt present in the operating room. The calculated surface dice similarity coefficient, Hausdorff distance and feedback of the participants show that the difficulty of drawing the craniotomy is appropriate.

CONCLUSION

The presented training simulation for head positioning and access planning benefits from the immersive environment. Thus, it is an appropriate training for novice neurosurgeons and medical students with the goal to improve anatomical understanding and to become aware of the importance of the right craniotomy hole.

Distance and force visualisations for improved simulation of intracranial aneurysm clipping

Purpose

The treatment of cerebral aneurysms shifted from microsurgical to endovascular therapy. But for some difficult aneurysm configurations, e.g. wide neck aneurysms, microsurgical clipping is better suited. From this combination of limited interventions and the complexity of these cases, the need for improved training possibilities for young neurosurgeons arises.

Method

We designed and implemented a clipping simulation that requires only a monoscopic display, mouse and keyboard. After a virtual craniotomy, the user can apply a clip at the aneurysm which is deformed based on a mass–spring model. Additionally, concepts for visualising distances as well as force were implemented. The distance visualisations aim to enhance spatial relations, improving the navigation of the clip. The force visualisations display the force acting on the vessel surface by the applied clip. The developed concepts include colour maps and visualisations based on rays, single objects and glyphs.

Results

The concepts were quantitatively evaluated via an online survey and qualitatively evaluated by a neurosurgeon. Regarding force visualisations, a colour map is the most appropriate concept. The necessity of distance visualisations became apparent, as the expert was unable to estimate distances and to properly navigate the clip. The distance rays were the only concept supporting the navigation appropriately.

Conclusion

The easily accessible surgical training simulation for aneurysm clipping benefits from a visualisation of distances and simulated forces.

Clinical and radiological outcomes in relation with the anatomical orientation of clipped middle cerebral artery bifurcation aneurysms

BACKGROUND

The middle cerebral artery (MCA) bifurcation represents the most frequent location for intracranial aneurysms. Often, the aneurysmal dome can hide the origin of perforating arteries from the M1 segment during the surgical clipping causing ischemic lesions and worse clinical outcome. The aim of this paper is to analyze the association between the orientation of the aneurysm sac and the clinical and radiological outcomes after surgical clipping.

METHODS

Data from 50 MCA bifurcation clipped aneurysms in 47 patients were collected retrospectively. Three different groups were identified according to the aneurysmal sac orientation: anterior-inferior, posterior and superior. A possible association between the aneurysmal sac projection and the outcome was searched through a univariable logistic regression analysis.

RESULTS

Statistical analysis showed significant correlation between the radiologic evidence of post-operative ischemia in the posterior group (p = 0.046, RR = 1.65) and an increased risk in the superior orientation group (p = 0.145, RR = 1.38). The anterior-inferior group was, instead, significantly associated with no evidence of radiologic ischemia (p = 0.0019, RR = 0.58).

CONCLUSION

The orientation of the aneurysmal dome and sac represents a fundamental feature to be considered during the surgical clipping of the MCA aneurysms. Indeed, its posterior and superior projection is associated with a higher incidence of radiologic ischemic lesions due to the origin of perforating arteries from M1 segment behind the aneurysmal sac. The anterior-inferior orientation, on the contrary, is associated with a lower risk.

Bipolar Coagulation Aneurysm Dome Remodeling (Aneurysmorrhaphy) for Middle Cerebral Artery Aneurysms

Adequate visualization of the proximal and distal vessels and clip reconstruction of the bifurcation with complete aneurysm neck exclusion are often difficult in the setting of bulbous small- and moderate-sized middle cerebral artery (MCA) aneurysms. We describe our experience with bipolar aneurysm dome remodeling in the setting of bulbous MCA aneurysms. The charts of the senior author's (Aaron Cohen-Gadol) patients who underwent clip ligation of their MCA aneurysm (220 patients), and more specifically those whose aneurysm clipping was facilitated through bipolar coagulation remodeling (8 patients), were reviewed. Patient demographics, aneurysm characteristics, and postoperative angiographic results were analyzed. Eight patients with eight MCA aneurysms were treated through this technique over a six-year period. Their mean age was 53 years, and six of the eight patients were women. Two involved the anterior temporal artery, and the rest were at the M1 bifurcation or trifurcation. Three of the eight were ruptured; the mean aneurysm maximum diameter was 7 mm. Postoperative angiography demonstrated complete aneurysm obliteration in seven of eight patients; one patient had an asymptomatic mild stenosis of her anterior temporal artery's origin, and another had a small neck remnant in the setting of a highly atherosclerotic neck. On the basis of this experience, dome coagulation remodeling of small- and moderate-sized bulbous aneurysms in the setting of poor proximal and distal vessel visualization was found to be safe for facilitating aneurysm clipping and offers more desirable clip deployment.

Stent-Assisted Coil Embolization of MCA Bifurcation Aneurysms at a Hypoplastic M1 Branch by Use of Hook Technique

BACKGROUND

We describe the Hook technique enabling coil embolization in unfavorable M1 bifurcation aneurysms and analyze the morphologic variations in M1 bifurcation to evaluate how often such aneurysms can be seen.

METHODS

Among 42 MCA aneurysms treated by stent-assisted coil embolization, aneurysms arising at the acute-angled hypoplastic M1 branch (n = 14) were treated by the Hook technique, in which a short stent was deployed only to protect the aneurysm neck after microcatheter selection of the hypoplastic M2, followed by subsequent coiling of the aneurysm. Outcome was evaluated, including Raymond classification, coil packing density, final modified Rankin Scale (mRS), and recurrence. Separately, 100 middle cerebral artery (MCA) bifurcation aneurysms were analyzed to assess the proportion of such unfavorable aneurysms.

RESULTS

Procedural success of the Hook technique was obtained in 13 of 14 patients (93%). A mean packing density of 30% was achieved. Magnetic resonance angiographic follow-up at a median 4 months (range, 1-26 months) showed complete occlusion in 11 patients and residual neck filling in 3 patients. There was no clinical event (mRS = 0) over a median 17 months (range, 2-26 months) of clinical follow-up. One patient had a thrombotic occlusion during the procedure, which was resolved after tirofiban infusion, without evidence of an infarct or deficit. Of the 100 MCA bifurcation aneurysms, aneurysm arising in asymmetric hypoplastic M2 division was the most common type (48%).

CONCLUSIONS

The Hook technique enabled stent-assisted coiling of M1 bifurcation aneurysm with extension along the asymmetric hypoplastic M2 division and also securing the M2 branch.

Middle Cerebral Artery Aneurysm "Neck Overhang": Decreased Postclipping Residual Using the Intersecting Clipping Technique

BACKGROUND

Middle cerebral artery (MCA) aneurysms continue to be viewed by many as primarily surgical entities.

OBJECTIVE

To introduce a new, easily measurable dimension termed "neck overhang," defined as the amount of the aneurysm that extends proximal to the 2 dimensionally defined "neck" and to evaluate the utility of the intersecting clipping technique (use of straight clip and intersecting fenestrated clip) to adapt to this overhanging segment's specific dimensions and achieve better obliteration of the MCA aneurysms.

METHODS

We reviewed retrospectively 100 MCA aneurysms treated surgically over the last 10 yr at our institution. We identified the clipping technique that was performed (intersecting vs "standard" technique) and we evaluated the presence of a postoperative remnant. We then correlated these with the aneurysm's overhanging neck length.

RESULTS

Forty-three aneurysms were treated with the intersecting clipping technique. The overall rate of remnant was 16%. In the standard group, the rate of remnant was 23%, whereas with intersecting clipping that was 7% (P = .029). Within the standard clipping group, we found that the optimum threshold for length of the neck overhang was ≥1.9 mm in order to predict the occurrence of residual. Applying this threshold to the intersecting clipping technique group resulted in a reduction in remnant from 35% in the standard group to 9%.

CONCLUSION

Neck overhang >1.9 mm is associated with a higher chance of postclipping residual aneurysm in MCA aneurysms. The intersecting clipping technique is a versatile technique that can conform to various aneurysms' geometry and can reduce the rate of post clipping residual for aneurysms with high neck overhang.

Surgical exclusion of unruptured middle cerebral artery aneurysms: experience of 126 cases

A group of 126 surgical patients with 143 unruptured MCA aneurysms was evaluated in order to determine the risks of treatment and possible adjuncts for safer surgery. The precise location and size of the aneurysms were determined in each case; 21 aneurysms were located on the M1 tract, 109 on the main division - which consisted of more than two branches in 10 cases and was proximally located in 12 cases - and 13 were distal; 36 aneurysms were small (<7 mm), 90 standard, and 17 large or giant (>15 mm); 45 patients harbored multiple aneurysms (12 on the ipsilateral MCA). The aneurysms were excluded by clip in most cases, with the assistance of intraoperative flowmetry in 78 patients. Temporary proximal vessel occlusion was used in 57 patients (>10 min in 8 cases), without significant effects on radiological or clinical outcome. After surgery, newly occurring minor deficits were observed in 5 patients and significant deficits in 4; one patient died from an intractable coagulopathy. The low rate (3.9 %) of unfavorable results (modified Rankin Score > 2) linked to surgery justifies serious consideration for treatment in these patients, especially when facing the high disability rate after the rupture of aneurysms in this anatomical location.

Middle cerebral artery bifurcation aneurysms: an anatomic classification scheme for planning optimal surgical strategies

BACKGROUND

Changing landscapes in neurosurgical training and increasing use of endovascular therapy have led to decreasing exposure in open cerebrovascular neurosurgery. To ensure the effective transition of medical students into competent practitioners, new training paradigms must be developed.

OBJECTIVE

Using principles of pattern recognition, we created a classification scheme for middle cerebral artery (MCA) bifurcation aneurysms that allows their categorization into a small number of shape pattern groups.

METHODS

Angiographic data from patients with MCA aneurysms between 1995 and 2012 were used to construct 3-dimensional models. Models were then analyzed and compared objectively by assessing the relationship between the aneurysm sac, parent vessel, and branch vessels. Aneurysms were then grouped on the basis of the similarity of their shape patterns in such a way that the in-class similarities were maximized while the total number of categories was minimized. For each category, a proposed clip strategy was developed.

RESULTS

From the analysis of 61 MCA bifurcation aneurysms, 4 shape pattern categories were created that allowed the classification of 56 aneurysms (91.8%). The number of aneurysms allotted to each shape cluster was 10 (16.4%) in category 1, 24 (39.3%) in category 2, 7 (11.5%) in category 3, and 15 (24.6%) in category 4.

CONCLUSION

This study demonstrates that through the use of anatomic visual cues, MCA bifurcation aneurysms can be grouped into a small number of shape patterns with an associated clip solution. Implementing these principles within current neurosurgery training paradigms can provide a tool that allows more efficient transition from novice to cerebrovascular expert.

Two indices affecting the directions of the sylvian fissure dissection in middle cerebral artery bifurcation aneurysms

OBJECTIVE

This study proposes more objective methods for deciding the appropriate direction of the sylvian fissure dissection during surgical clipping in middle cerebral artery (MCA) bifurcation aneurysms.

METHODS

We reviewed data of 36 consecutive patients with MCA bifurcation aneurysms. We measured 2 indices preoperatively on 3-dimensional computed tomography angiography (3D-CTA). Analysis of the calculated data allowed us to select the appropriate direction of sylvian fissure dissection for ease of proximal control of M1. Statistically, Mann-Whitney test was used.

RESULTS

We classified subjects into 2 groups based on the technical level of M1 exposure during surgical clipping. When it was difficult to expose M1, subjects were assigned to Group I, and Group II were subjects in whom M1 exposure was easy. The mean difference between the distances extending from the limbus sphenoidale (LS) line to the internal carotid artery bifurcation and extending from the LS line to the MCA bifurcation was 1.00 ± 0.42 mm in group I and 4.39 ± 2.14 mm in group II. The mean M1 angle was 9.36 ± 3.73° in the group I and 34.05 ± 16.71° in the group II (M1 slope gap p < 0.05, M1 angle p < 0.05).

CONCLUSION

We have found an objective method for preoperatively verifying ease of exposure of M1 artery during surgical clipping. Therefore, we suggest use of the preoperative M1 slope gap and M1 angle as indicators in 3D-CTA selecting the direction of sylvian fissure dissection for easy proximal control of M1.