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INTRODUCTION
Endovascular coil embolization of intracranial aneurysms is now widely used after initial validation was given by the International Subarachnoid Aneurysm Trial and by the International Study of Unruptured Intracranial Aneurysms (12). Improved protective devices and advanced coiling techniques, such as balloon remodeling and stenting, have enabled coil embolization of aneurysms with complex configurations (34567). Using dual microcatheters for coil embolization compared with stenting or balloon protection is advantageous in terms of procedural complications and post-procedural antiplatelet maintenance (89). In particular, this approach is considered safer for ruptured aneurysms, based on its relatively low complication rate. Dual microcatheters may be applied as follows: 1) both microcatheters dedicated to intrasaccular delivery of the coil (so-called "double microcatheter technique") (1011) or 2) one microcatheter placed within aneurysmal sac and the other advanced into a branching artery to prevent coil protrusion (so-called "microcatheter protective technique") (12). Because this strategy may be technically limited for some lesions with complex configurations, an additional microcatheter may be required to improve coil stability, to promote compact coil packing, or to enhance the protective effect. Herein, the clinical and radiological outcomes of endovascular coil embolization are detailed for simultaneous deployment of three microcatheters (triple microcatheter technique) in wide-necked aneurysms, and the technical aspects of such a treatment are addressed.
MATERIALS AND METHODS
Study Population
A total of 3349 intracranial aneurysms in 2898 patients were treated by endovascular coil embolization at our institution between January, 2006 and October, 2014. Of this population, multiple microcatheters (i.e., two or more) were utilized for coil embolization in 1064 aneurysms (31.8%), with microcatheter protection in 238 lesions. However, the simultaneous triple microcatheter technique was applied in just 38 patients (26 females and 12 males; mean age, 60.1 ± 9.6 years), whom we selected for this study. Six aneurysms subjected to dual microcatheters plus balloon protection and 18 aneurysms treated via dual microcatheters plus stent protection (i.e., microcatheter jailing) were excluded (Fig. 1). Non-saccular aneurysms (i.e., dissecting, fusiform, or blood blister-like aneurysms) and pseudoaneurysms were also excluded. All aneurysms (except three) were unruptured (seven recanalized after coiling), and nearly all lesions (except five) had wide necks, with depth-to-neck ratios < 1.0 (mean, 0.90 ± 0.38; range, 0.42-2.7; median, 0.82). All lesions (except three) had small diameters (< 10 mm maximum). Therapeutic decisions were rendered through consensus of two neurosurgeons and nonsurgical neurointerventionists, and informed consent was obtained from all patients after the treatment and related risks were adequately explained. This study was approved by the Institutional Review Board of our hospital. Clinical and radiographic features of the cohort are shown in Table 1.
Therapeutic Strategy
As illustrated in Figure 1, the tactical strategies for simultaneous triple microcatheter deployment were as follows: 1) dual microcatheter delivery of the coil within the aneurysmal sac, with a single microcatheter for protection; 2) triple microcatheters used only for delivering the coil within the aneurysm; and 3) single microcatheter coil delivery within the aneurysmal sac, plus dual microcatheter protection of both branching arteries.
The first option was useful in cases where a coil frame formed using a double microcatheter that repeatedly protruded into a branching artery (Fig. 2A, B), or where a coil frame formed was unstable using microcatheter protection (Fig. 2C, D). The second option was commonly applied if the initial coil frame configured by a double microcatheter was unstable (Fig. 3A, B) or if some portion of the sac went unfilled due to intrinsic complexities, such as trilobulation (Fig. 3C, D). The third and final option was applied sparingly if both branching arteries were broadly or evenly incorporated by the aneurysm and the coil protruded into unprotected branch arteries, despite use of microcatheter protection (Fig. 4A, B).
Endovascular Procedure
All endovascular procedures were performed under general anesthesia. All patients underwent cerebral angiography and rotational angiography with three-dimensional image reconstruction using the Integris V (Philips Medical Systems, Best, the Netherlands) and Innova IGS 630 (General Electric, Milwaukee, WI, USA) biplane systems. All patients were managed with an antiplatelet agent before coiling in a relatively consistent scheme at our institution. A 300 mg loading dose of clopidogrel was given the day before the procedure for all patients with unruptured aneurysms, and an additional 75 mg clopidogrel was given in the morning of the day of the procedure. A 300-mg loading dose of aspirin was added for inpatients with a poor response to clopidogrel, based on the VerifyNow P2Y12 assay (Accumetric, Elizabethtown, KY, USA) (i.e., P2Y12 reactivity units > 285) (13). Dual-agent antiplatelet therapy was administered if stent protection was anticipated. Cilostazol was added in patients with a poor response to clopidogrel. After placing a femoral sheath, systemic heparinization was started with a 3000 IU loading dose and was maintained with a 1000 IU dose on an hourly basis. Antiplatelet medication was not administered prior to the procedure in patients with an acutely ruptured aneurysm. In these cases, systemic heparinization was initiated shortly after adequate protection of the aneurysm. It was mandatory to place a 7-Fr guiding catheter in the internal carotid artery in cases when triple microcatheters were expected to be applied simultaneously. If possible, use of three different microcatheters was used to distinguish each microcatheter. After the procedure, antiplatelet medications were not prescribed routinely for maintenance except in cases of stent protection, coil protrusion, composite atherosclerotic narrowing, and procedural thromboembolism.
Angiographic Outcomes and Follow-Up
Immediate angiographic results after coil embolization were evaluated by two experienced neurointerventionists. Therapeutic outcomes were classified as follows using the 3-point Raymond scale: complete occlusion (no residual filling of the aneurysm with contrast medium), residual neck (limited residual contrast at the base of the aneurysm), or residual aneurysm (any contrast filling of the aneurysmal sac) (14).
Clinical outcomes were scored using the Glasgow outcome scale (GOS), which was applied throughout the hospitalization period and at the last available clinical follow-up. Magnetic resonance angiography (MRA) with three-dimensional reconstruction and/or plain radiography was recommended for all patients 6, 12, 24, and 36 months after coil embolization. Conventional angiography was recommended when aneurysmal recanalization was suspected by a noninvasive evaluation, such as MRA or plain radiography, to decide if further treatment was necessary.
Anatomic outcomes at follow-up were categorized as follows based on the Raymond scale: complete occlusion, minor recanalization, or major recanalization (15). Repeat embolization was advocated for patients showing major recanalization.
RESULTS
Selective endovascular coil embolization was performed successfully using three microcatheters simultaneously in patients with saccular aneurysms of the posterior communicating artery (n = 13), middle cerebral artery (MCA) (n = 10), basilar tip (n = 7), anterior cerebral artery (n = 5), and internal carotid artery (n = 3). In one patient with a basilar tip aneurysm, dual guiding catheters were deployed due to a limited vertebral arterial diameter. A combination of dual microcatheter coil delivery/single microcatheter protection was primarily applied (n = 24), followed by inserting the coil via all three microcatheters (n = 11), and single microcatheter coil delivery/dual microcatheter protection (n = 3) (Figs. 2, 3, 4). After building a proper coil frame through using triple microcatheters, additional coils were inserted via the microcatheter(s) in each instance; stents were placed in four patients and a balloon in one patient during this process. Immediately following coil embolization, 34 aneurysms were occluded satisfactorily (eight complete occlusion and 26 neck remnant), and four retained small residual sacs. No procedure-related morbidity or mortality was observed, although an asymptomatic thrombus occurred in two patients. The thrombotic incidents were related to protruding coils (not directly related to the triple microcatheter technique), and they resolved after intra-arterial infusion of tirofiban. All patients were neurologically intact (GOS 5) at the time of discharge. Thirty-six patients (excluding two treated recently) underwent follow-up evaluations at > 6 months (mean, 30.2 ± 22.7 months; median, 36 months), including magnetic resonance and conventional angiography. Twenty-six maintained stable coil configurations, whereas the remaining 10 showed minor (n = 3) or major recanalization (n = 7). None of the patients experienced delayed complications (i.e., thromboembolic infarction or hemorrhage).
Illustrative Cases
Case 1
A 68-year-old female was admitted for endovascular treatment of an unruptured basilar tip aneurysm detected during investigation of headache. Conventional angiography revealed a wide-necked aneurysm (Fig. 5A), so a 6-Fr guiding catheter was placed in the cervical segment of the left vertebral artery (VA). Our initial plan called for a microcatheter protective technique, positioning one catheter within the sac to deliver the coil and passing the other into right posterior cerebral artery (PCA) for protection (Fig. 5B). An initial coil frame was formed through persistent efforts without the coil protruding into the parent artery; however, it appeared unstable (Fig. 5C). Another 5-Fr guiding catheter was advanced into the right VA, and a third microcatheter was placed within the sac (Fig. 5D). A frame coil was then added to intermix with the existing framing coil to enhance its stability. Later, an errant loop of the filler coil protruded into the left PCA (Fig. 5E). One of the two microcatheters was subsequently withdrawn from the sac and was passed into the left PCA for protection (Fig. 5F). An additional coil was added under dual microcatheter protection of the PCA (bilaterally) (Fig. 5G) to occlude the aneurysm (Fig. 5H). The patient was discharged the next day without complications.
Case 2
A 68-year-old female was admitted for endovascular treatment of an unruptured aneurysm, located at the MCA bifurcation. The aneurysm broadly incorporated the orifice of the inferior division, originating at an acute angle (Fig. 6A). In this setting, passing a microcatheter to deliver a stent seemed technically difficult. A 7-Fr guiding catheter was placed in the cervical segment of the left internal carotid artery, and dual microcatheters were placed in the inferior portion of the aneurysm to deliver the coil (Fig. 6B). Two coils were inserted, and a coil frame formed with considerable effort that did not protrude into the inferior division (Fig. 6C, D). Unfortunately, the superior segment of the aneurysm lacked an initial coil frame (Fig. 6E), so another microcatheter was placed within the void (Fig. 6F). A third coil was ultimately delivered to blend with the existing coils. Thereafter, one microcatheter was removed and additional filling coils were inserted via dual microcatheters. The lesion was satisfactorily occluded (Fig. 6G) without complication. Conventional angiography performed at the 6-month follow-up revealed stable occlusion of the aneurysm (Fig. 6H).
DISCUSSION
Improvements in protective devices and coiling techniques, including balloon remodeling and stent protection have rendered many previously ineligible aneurysms with difficult configurations amenable to selective endovascular treatment (16). However, angio-anatomic complexities, including extreme vessel tortuosity or intricate vascular arrangements occasionally prohibit using these techniques (17). Dual microcatheter coil embolization, pioneered by Baxter et al. (10), may be a viable alternate technical strategy for challenging wide-neck intracranial aneurysms (11121819), although two microcatheters are occasionally insufficient to form a stable coil frame without protrusion or to protect the parent artery from impingement. Hence, a third microcatheter may be added for these purposes. Three microcatheters may also help to meticulously fill every nook of an aneurysm with a coil for optimal compaction through even distribution when used in some large-sized or trilobulated lesions. Indeed, the triple microcatheter technique may be helpful and effective in aneurysms where customary dual microcatheters or microcatheter protective measures have failed or are inadequate to construct a proper coil frame. In addition, balloons or stents may be avoided in some aneurysms with prohibitive angio-anatomic features (i.e., arterial tortuosity and small arterial size). In contrast, thromboembolic risk is heightened by this number of microcatheters within a parent artery or a guiding catheter. To reduce this threat, each microcatheter is withdrawn once its contribution to proper, stable coil frame configuration (without protrusion or voids) is completed.
Kwon et al. (11) were the first to report coil embolization using three or more microcatheters. According to their description, deploying multiple microcatheters was used only to deliver the coil; thus, enhancing stability of the coil frame. Our series demonstrates that strategic variations may easily be adopted to accommodate specific angio-anatomic restrictions, including utilization of one or two microcatheters as protective devices. Such variations may be necessary to compensate for deficiencies in coil embolization.
Although uncommon, limitations of this triple microcatheter technique include distal aneurysms with small-sized parent arteries or crowding within guiding catheters or parent arteries that hampers control of microcatheter tension. In one of our patients with a distal anterior communicating artery (ACA) aneurysm, triple microcatheters posed no problem due to an azygous-ACA A2 segment of sufficient caliber. Another patient required a dual guiding system (via double femoral punctures) because flow in the dominant VA could not be maintained with a 7-Fr guiding catheter in place. Throngs of a guiding microcatheters and parent arteries may also increase the chance for thromboembolic complications during the procedure. Thus, we recommend that each microcatheter be withdrawn after serving its purpose, such as stabilizing or protecting the coil. Finally, interlocking or stretching coils may be problematic when multiple coils are manipulated (11), although this did not occur in the present cohort.
This technique is not recommended as a first-line strategy. However, collective outcomes in this small series of patients suggest that coil embolization via three microcatheters may be safely and effectively implemented after tailored technical modifications for some wide-necked saccular aneurysms, where circumstances are not conducive to stent or balloon protection (i.e., complex angio-anatomic configurations or rupture). The clinical and anatomic outcomes are particularly encouraging.
In conclusion, this triple microcatheter technique may have value in settings where traditional remodeling or protective techniques are precluded by aneurysmal configuration and vascular anatomy and where traditional coiling in wide-necked shallow aneurysms proves difficult through technical strategies that address such angio-anatomic challenges. Long-term study of a larger patient series is needed to confirm the preliminary safety and efficacy seen here.
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