Abstract
Background
Inventing an optimal curve on a microcatheter is required for successful intracranial aneurysm coiling. Shaping microcatheters for vertebrobasilar artery aneurysm coiling is difficult because of the vessel’s long, tortuous and mobile anatomy. To overcome this problem, we devised a new method of shaping the microcatheter by using the patient’s specific vessel anatomy and the highly shapable microcatheter. We report our preliminary results of treating posterior circulation aneurysms by this method.
Methods
An unshaped microcatheter (Excelsior XT-17; Stryker Neurovascular, Fremont, CA, USA) was pretreated by exposure to the patient’s vessel for five minutes. The microcatheter was placed in the vicinity of the targeted aneurysm and was left in contact with the patient’s vessel before extraction. This treatment precisely formed a curve on the microcatheter shaft identical to the patient’s vessel anatomy. Following the pretreatment, the tip of the microcatheter was steam shaped according to the long axis of the target aneurysm. Five consecutive vertebrobasilar aneurysms were treated using this shaping method and evaluated for the clinical and anatomical outcomes and microcatheter accuracy and stability.
Results
All of the designed microcatheters matched the vessel and aneurysm anatomy except in one case that required a single modification. All aneurysms were successfully catheterized without the assistance of a microguidewire, and matched the long axis of the aneurysm. All microcatheters retained stability until the end of the procedure.
Conclusions
A precise microcatheter shaping for a vertebrobasilar artery aneurysm may be achieved by using the patient’s actual vessel anatomy and the highly shapable microcatheter.
Keywords: Microcatheter shaping, intracranial aneurysm, coiling
Introduction
For a safe and effective intracranial aneurysm coiling, the microcatheter must be stably placed into the aneurysm.1–3 A well-designed microcatheter is crucial in achieving this, and may be accomplished by customizing the shape of the microcatheter to the patient’s vessel anatomy. A novel method to devise a patient-specific microcatheter using a patient-specific three-dimensional (3D) intracranial aneurysm model was recently published reporting favorable clinical results.3 We have adopted this method to our procedure, and found that microcatheters replicating the patient’s vessel anatomy were highly effective for catheterizing of anterior circulation aneurysms, particularly the paraclinoid internal carotid artery (ICA) aneurysms. However, in the posterior circulation aneurysms, designing a patient-specific curve with the 3D aneurysm model had not always resulted in an optimal aneurysm catheterization. The planned microcatheter often pointed oppositely from the target aneurysm and failed to catheterize the lesion. Reasons for the suboptimal results were presumed as follows: (a) unpredictable stretching of the vertebrobasilar artery by a microcatheter insertion resulted in deformation of the original vessel anatomy by which the catheter was designed; and (b) the extradural (V3) curve of the vertebral artery, which outranged the length of the shaping mandrel and therefore was difficult to reproduce, determined the overall direction of the microcatheter tip. To overcome these problems, we developed a new precision microcatheter shaping method. This method utilizes the patient’s true arterial anatomy and was enhanced by the highly shapable newer generation microcatheter. We aim to report on our initial experience with this method in posterior circulation aneurysm coiling.
Material and methods
Patient selection
This study was conducted in accordance with the Jichi Medical University Research Ethics Committee. Written consent was obtained for publication of patient information and images from all participating patients. Five consecutive patients undergoing endovascular coiling of saccular vertebrobasilar aneurysms between August 2016 and March 2017 at our institution were included in this study. Fusiform and partially thrombosed aneurysms were excluded.
Precision microcatheter shaping
Using the highly shapable new generation microcatheter (Excelsior XT-17; Stryker Neurovascular, Fremont, CA, USA), the microcatheter was shaped according to the patient’s true arterial anatomy in two steps. First, a straight microcatheter without catheter tip shaping was advanced just proximal to the target aneurysm. The microcatheter was left in contact with the patient’s arterial curve (Figure 1(a)) and body heat for five minutes before extraction. This treatment formed a 3D curve on the microcatheter that precisely reproduced the V3 and other curves including the deformed vessel course caused by the catheterization (Figure 1(b), arrows). Second, the tip of the microcatheter was steam shaped toward the long axis of the aneurysm according to the 3D anatomy of the vessel (Figure 1(c), arrow). The shaped microcatheter was then reinserted into the target vessel and aneurysm for coil embolization.
Figure 1.
(a) A basilar tip aneurysm pointing anteriorly in case 3. An Excelsior XT-17 microcatheter was left in contact with this vessel for five minutes. (b) After contact with the vessel for five minutes, the microcatheter has formed the curve of the vertebrobasilar artery. Note the extradural vertebral artery curve replicated on the microcatheter (arrows). (c) The tip of the microcatheter is steam shaped anteriorly to align the long axis of the aneurysm (arrow).
Endovascular intracranial aneurysm coiling and clinical and angiographic outcomes
The technique for endovascular intracranial aneurysm coiling has been previously described.4,5 All cases were performed under general anesthesia using high-resolution biplane digital subtraction angiogram. The patients were started on a dual antiplatelet regimen (aspirin 100 mg and clopidogrel 75 mg) 2 weeks prior to the procedure. Systemic anticoagulation with heparin was added during the procedure extending the activated clotting time to over 250 seconds.
The aneurysm was coiled as densely as possible with coils of the surgeon’s preference. The adjunctive technique, such as balloon neck remodeling, stent assist and double microcatheter, was adopted singularly or in combination as required. Intravenous heparin at 500 IU/h was continued for 24 hours post-operatively. Complication was defined as any clinical adverse event related to the procedure. Immediate aneurysm occlusion was evaluated using the method reported by Roy et al. (complete occlusion, residual neck, residual aneurysm).6 Clinical outcome was assessed by the modified Rankin Scale (mRS) at 1 month post-procedure follow-up in the clinic.
Accuracy of the microcatheter shape
Accuracy of the microcatheter shape was assessed by two parameters: catheterizing method and axial alignment with the aneurysm. The microcatheter shape was considered accurate when the aneurysm was catheterized by microcatheter shifting.1,3 This was based on the hypothesis that an accurately shaped microcatheter would fit into an aneurysm without the aid of a microguidewire. Alignment of the microcatheter tip should match the long axis of the aneurysm (alignment).
The catheterizing method was graded as either successful or unsuccessful depending on the usage of a microguidewire. The alignment of the microcatheter was graded as accurate when the catheter tip matched the long axis of the aneurysm without modification. The alignment was graded as moderate when the microcatheter shape required modification.
Stability of the microcatheter
Stability of the microcatheter was assessed toward the end of the procedure. Stable catheterization was defined as follows: coiling completed without premature prolapse of the microcatheter.
Results
Anatomical and clinical outcomes
Table 1 summarizes the data on the patient, aneurysm demographics, treatment details, and clinical and angiographic outcomes. Five aneurysms in the vertebrobasilar circulation were treated: three basilar artery (BA) tip, one BA-superior cerebellar artery (SCA) and one BA trunk aneurysm. Case 2 presented with Hunt and Hess grade 3 subarachnoid hemorrhage (SAH), case 4 with mass effect, and three patients with enlarging unruptured aneurysms. Four aneurysms were small (<12 mm), and one was large (>12 mm). The adjunctive technique was employed as shown in the table. Complete occlusion of the aneurysm was achieved in four patients, and the aneurysm for one patient resulted in residual neck.
Table 1.
Patient and aneurysm characteristics, treatment method, and clinical and angiographic outcomes.
| Case | Sex | Age | Presentation | AN location | AN size (mm3) | Neck (mm) | Adjunctive technique | Complication | Clinical outcome (mRS) | AN occlusion |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | M | 80 | Incidental | BA trunk | 3.8 × 4.7 × 5.8 | 4.7 | Stenting | No | 0 | CO |
| 2 | F | 70 | SAH | BA tip | 6.3 × 4.0 × 4.2 with a 1.7 × 1.3 × 1.1 bleb at the base | 3.4 | Double micro | Symptomatic vasospasm | 3 | CO |
| 3 | F | 73 | Incidental | BA tip | 5.6 × 4.3 × 5.2 | 3.9 | Stenting | No | 0 | RN |
| 4 | F | 69 | Mass effect | BA-SCA | 20 × 19 × 18 | 14 | Stenting Double micro | No | 2 | CO |
| 5 | F | 59 | Flow related (moyamoya) | BA tip | 7.4 × 6.0 × 7.6 | 5.1 | Simple converted to double micro | No | 0 | CO |
AN: aneurysm; BA: basilar artery; CO: complete occlusion; micro: microcatheter; mRS: modified Rankin Scale; RN: residual neck; SAH: subarachnoid hemorrhage; SCA: superior cerebellar artery.
All patients were treated without procedure-related complications. Case 2 presenting with SAH developed symptomatic vasospasm resulting in mild right hemiparesis and word finding problem, and case 4 was left with preexisting mild right hemiparesis and truncal ataxia that did not worsen post-operatively.
Accuracy and stability of the microcatheter
Figure 2 shows the accuracy and stability of the microcatheter. Cases 1 to 5 correspond to Figure 2(a) to (e), respectively. Arrowheads in Figure 2 show the trajectory of the microcatheters. After steam shaping the tip of the microcatheter, the catheter was readvanced just proximal to the aneurysm with the aid of a microguidewire. The microguidewire was then pulled back into the microcatheter and the catheter was pushed (shifted) into the aneurysm. All the aneurysms were successfully catheterized in this fashion at the first attempt, except in one patient (case 5, Figure 2(e)). In this case, the microcatheter tip required readjustment according to the vessel anatomy and the degree of microcatheter deviation, resulting in successful shifting at the second attempt.
Figure 2.
Accuracy (upper row) and stability (lower row) of the microcatheters. The upper row of each figure shows the accuracy of the microcatheter in two different views except in (d). The lower row shows the stability of the microcatheter at the end of the coiling. (a) to (e) correspond to cases 1 to 5, respectively. Arrowheads in each figure demonstrate the trajectory of the microcatheter. (a) A basilar trunk aneurysm in case 1. Arrowheads in the upper and lower rows show accuracy and stability of the microcatheter. (b) A basilar tip aneurysm in case 2. Arrows in the upper row show the bleb at the base of the aneurysm. Note the second microcatheter accurately pointing toward the bleb at the beginning and the end of the coiling. (c) A basilar tip aneurysm in case 3. Arrowheads in each figure demonstrate the accuracy (upper row) and stability (lower row) of the microcatheter. (d) A left superior cerebellar (SCA) aneurysm in case 4. Arrow in the upper figure points to the origin of the SCA arising from the aneurysmal dome. Arrowheads demonstrate the tip of the microcatheter facing the SCA orifice. Arrow in the lower figure shows the precise coil placement at the SCA origin to prevent occlusion of the artery. (e) A basilar tip aneurysm in case 5. Arrowheads show the trajectory of the microcatheter. Note the slight microcatheter deviation to the left. The anteroposterior direction of the microcatheter matched the long axis of the aneurysm throughout the coiling (right column).
Alignment of the microcatheter was accurate in all cases as demonstrated in Figure 2 (upper row), except in case 5. In case 5, the alignment of the microcatheter slightly deviated to the left of the aneurysm axis (Figure 2(e)).
Stability toward the end of the procedure was excellent in all cases except in case 4, with no microcatheters flipping out of the aneurysm (Figure 2(a) to (e), lower row). In case 4 (Figure 2(d) and Figure 3), the precision microcatheter shaping was applied to accurately place a protection coil at the orifice of the SCA. As a consequence, the stability was not assessed (see details in the Illustrative cases and Figure 3).
Figure 3.
(a) A three-dimensional rotational angiogram in oblique view demonstrating a large basilar left superior cerebellar artery (SCA) aneurysm incorporating the basilar artery trunk and the origin of the SCA (arrow). Note the extremely tortuous vertebrobasilar artery preventing subtle microcatheter manipulation and unpredictable microcatheter tip direction. (b) Cone beam computed tomography with contrast injection after microcatheter and stent placement. An Excelsior 1018 microcatheter is inserted in the aneurysm and half-jailed with an LVIS Jr stent. A precisely designed Excelsior XT-17 microcatheter (arrowheads) is placed at the orifice of the SCA (arrow) to prevent occlusion of this artery. Note that the tip of the microcatheter is pointing toward the orifice of the SCA. (c) Extraction of the protection coil under roadmap imaging. The mass of the protection coil that had been temporarily placed at the SCA orifice is indicated by the arrow. The removed coil is seen in the microcatheter (arrowheads). Note the precise coil placement at the SCA origin. (d) Post-coiling angiogram demonstrates complete occlusion of the aneurysm as well as preservation of the SCA (arrowheads).
Illustrative cases
Case 2
This 70-year-old female patient presented with Hunt and Hess grade 3 SAH due to rupture of a 6.3-mm BA tip aneurysm. The coiling was complicated by a 1.7-mm bleb existing at the neck of the aneurysm (Figures 2(b), arrows). The double microcatheter technique was adopted for the coiling with the first microcatheter designed to select the aneurysmal dome, and the second, the bleb. With the precision microcatheter shaping, the targeted aneurysm and the bleb were successfully catheterized (Figure 2(b), upper row). The second microcatheter with an inserted microguidewire is precisely pointing toward the bleb (arrowheads). Both microcatheters demonstrated excellent stability until the end of the procedure (Figure 2(b), lower row, arrowheads) resulting in complete occlusion of the aneurysm.
Case 4
A 69-year-old female patient presented with progressively worsening double vision and dizziness caused by a 20-mm BA left SCA aneurysm compressing the midbrain. The aneurysm incorporated the origin of the SCA and the BA trunk making the procedure challenging (Figure 2(d), small arrow; Figure 3(a), arrow). Additionally, the extremely tortuous vertebral and basilar arteries hampered subtle microcatheter manipulation (Figure 3(a)). To preserve the origin of the SCA and the BA trunk, coil protection and stent-assisted techniques were adopted, respectively.7 An Excelsior 1018 preshaped J microcatheter (Stryker Neurovascular Fremont, CA, USA) for coil placement was half-jailed with an LVIS Jr stent (Terumo MicroVention; Tokyo, Japan) (Figure 3(b)). With the precision microcatheter shaping, a second microcatheter (Excelsior XT-17) was placed adjacent to the SCA orifice (Figure 2(d) and Figure 3(b), arrowheads). The purpose of this second microcatheter was to place a temporary 2-mm coil at the SCA orifice to provide protection to the SCA orifice from being covered by the coils inserted in the aneurysmal dome (Figure 2(d), large arrow). Extraction of the 2-mm protection coil under roadmapping near the end of the procedure shows precise placement of the coil at the SCA origin (Figure 3(c), arrow). The post-coiling angiogram demonstrated complete occlusion of the aneurysm with the preservation of the left SCA (Figure 3(d)).
Discussion
This preliminary small study of precision microcatheter shaping utilizing the patient’s actual arterial anatomy proposes a feasible and effective method for posterior circulation aneurysm coiling. The accuracy and stability of the microcatheter and the anatomical and clinical results were promising in our experience.
Although advances in endovascular technology such as balloon remodeling and stent-assisted techniques have significantly expanded the boundary of intracranial aneurysm coiling,8,9 accurate aneurysm catheterization remains the basic premise of a successful procedure. Without a properly positioned stable microcatheter in the aneurysm, safe and effective delivery of coils is impossible. Microcatheter shaping is one of the fundamental factors that affect stable catheterization of the aneurysm. Nevertheless, reports on the methods of shaping a microcatheter have been sparse and presumably have relied largely on the surgeon’s experience.1,2 Recently, a few studies reported that microcatheters shaped in accordance with the patient’s vessel anatomy were effective in achieving an optimal catheterization.3,10,11
An interesting report on the method of microcatheter shaping was based on the enhanced understanding of the 3D vessel anatomy through a patient-specific 3D printing aneurysm model.3 We have applied this method to our practice and saw acceptable clinical and anatomical results. However, in our subsequent experience, application of this method to posterior circulation aneurysms has not always resulted in the accurate catheterization for two reasons. First was the deformation of the vertebrobasilar artery caused by insertion of the microcatheter. The vertebrobasilar artery travels a long distance in the unsupported subarachnoid space compared to the ICA which is well attached to the bony and dural structures.12 This anatomical plasticity resulted in stretching of the vertebrobasilar artery with the insertion of a microcatheter, deforming the vessel from its original structure. As a consequence, the curve of a microcatheter designed on a patient-specific 3D printing aneurysm model paradoxically did not match the actual curve of the vertebrobasilar artery after catheterization. Second, the direction of the microcatheter tip was affected by the V3 curve of the vertebral artery. The long distance between the tip of the microcatheter and the V3 curve outranged the length of the shaping mandrel. Because of this, the 3D printing aneurysm model was not effective in the designing of the microcatheter. Additionally, the wide and tortuous V3 curve was difficult to replicate on the microcatheter even with the aid of the 3D printing aneurysm model. To overcome these problems, we developed a new precision microcatheter shaping method. The method utilizes the patient’s actual vessel anatomy in the shaping of a microcatheter, and was made possible with the use of the highly shapable new generation microcatheter (Excelsior XT-17). By inserting the shapable microcatheter into the patient’s artery, the body heat formed a precise patient-specific curve on the microcatheter. This curve included the V3 curve as well as curves of the stretched vertebrobasilar artery. Subsequent microcatheter tip shaping resulted in an accurate and stable microcatheter, resulting in favorable and anatomical posterior circulation aneurysm coiling. Recently, Yamaguchi et al. reported a similar microcatheter shaping method in various intracranial aneurysms, resulting in favorable microcatheter catheterization.11 The result of their publication is in line with ours. However, we specifically aimed to design the microcatheter shape in the vertebrobasilar artery aneurysms that was not amenable to the previous microcatheter shaping methods.
We believe that the new generation highly shapable microcatheter, such as the Excelsior XT-17 which we used in our procedure, may aid in the application of this method. This microcatheter has the feature of strong shape retention ability that replicated the vessel shape in a short contact time, even with the heat of the body temperature (Figure 1(b)).
Although the number in our report is small, we consider that the precision microcatheter method may be generalizable for the following reasons. First, because the method directly utilizes the patient’s actual vessel anatomy, the shape is accurate. The shape of the microcatheter includes the stretching of the target vessel that is unpredictable by studying the angiogram or a 3D aneurysm model. Also, a complicate curve outranging the length of a shaping mandrel can be replicated on the microcatheter. Second, the method is simple and the shaping can be achieved in approximately 10 minutes. The shaping of the microcatheter shaft takes five minutes with the catheter in contact with the target vessel. Then, another five minutes is required to shape the tip of the microcatheter in accordance with the axis of the aneurysm. Third, the method can be applied in the acute settings. The method using a 3D aneurysm model requires time to fabricate the vessel, and therefore is unsuitable in emergency cases.
Our study has a number of limitations. First, obviously, the number of the aneurysms treated is too small to draw any solid conclusions. Second, our study lacks the appropriate control to demonstrate the efficacy of the proposed method. Third, the assessment of the microcatheter accuracy and stability was a subjective judgment of the surgeon and may suffer from bias. Fourth, our study was carried out on the Excelsior XT-17 microcatheter and may not be applicable to other microcatheters with different features. However, there is a single report using a similar shaping method with Excelsior SL-10 microcatheters (Stryker Neurovascular, Fremont, CA, USA), suggesting the generality of this method.11 Fifth, because the microcatheter shape was formed with little forward tension applied to the catheter, the shape may not be optimal when the catheter is exposed to tension during coil insertion. In our experience, the stability of the microcatheter was fairly sufficient until the end of the procedure, suggesting the adequacy of the microcatheter shape. However, as mentioned above, this was a subjective judgment that requires demonstration. Finally, longer follow-up and a larger number of patients are needed to evaluate the true benefit of this method. Further studies are needed to clarify these shortcomings.
Conclusions
A precise microcatheter shaping for the vertebrobasilar artery aneurysms may be achieved by the precision microcatheter shaping method. This method makes use of the patient’s actual vessel anatomy and may be facilitated by the highly shapable new generation microcatheter.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
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