Endovascular treatment of intracranial aneurysms with Guglielmi Detachable Coils: emphasis on new techniques

Journal of Clinical Neuroscience (2000) 7(3), 244–253 © 2000 Harcourt Publishers Ltd DOI: 10.1054/ jocn.1999.0211, available online at http://www.idealibrary.com on

Technical note

Endovascular treatment of intracranial aneurysms with Guglielmi Detachable Coils: emphasis on new techniques Frank C. Tong MD, Harry J. Cloft MD PhD, Jacques E. Dion MD FRCP (C) Department of Radiology and Neurosurgery Emory University Hospital, Atlanta, Georgia, USA

Summary Endovascular therapy for intracranial aneurysms has evolved since Serbinenko pioneered embolisation with latex balloons in the 1970s. The focus of modern endovascular therapy has shifted to the use of Guglielmi Detachable Coils (GDC; Boston Scientific Corporation, Natick, MA, USA) which are retrievable until the operator is satisfied with placement and they are detached. GDC therapy has been shown to be most efficacious in smaller aneurysms with relatively large dome:neck ratios which allow maximal coil packing within the aneurysm lumen. Wide neck aneurysms with dome:neck ratios of less than 2.0 and large aneurysms have a significantly lower incidence of complete treatment, with higher rates of repeat rupture following GDC therapy. The geometry of wide neck aneurysms is less favourable for retention of coils within the aneurysm lumen, resulting in greater risk of parent vessel compromise from coil herniation and difficulty obtaining maximal coil packing. This chapter will summarise GDC therapy for intracranial aneurysms including newer techniques designed to address the problem of wide neck aneurysms. © 2000 Harcourt Publishers Ltd Keywords: balloon dilatation/instrumentation, cerebral aneurysm/radiography/therapy, electrolysis/instrumentation, embolisation, therapeutic/instrumentation, subarachnoid haemorrhage/radiography/therapy, stents

INTRODUCTION Endovascular therapy for intracranial aneurysms was pioneered by Serbinenko who utilised detachable latex balloons in the 1970s.1 Since then the focus of endovascular therapy has shifted to embolisation with retrievable coils. The Guglielmi Detachable Coil (GDC; Boston Scientific Corporation, Natick, MA, USA) was developed in 1989 as an endovascular approach to cerebral aneurysm therapy.2,3 This technology was approved by the United States Food and Drug Administration in 1995 and has been increasingly utilised. Other retrievable coil systems available outside the US include the tungsten Spirales (Balt, Montmorency, France) and the Interlocking Detachable Coil (IDC; Boston Scientific Corporation, Natick, MA, USA).4 This chapter focuses on intracranial aneurysm therapy with GDC, including newer techniques that may increase the versatility and effectiveness of this treatment modality. The basic principle of the retrievable coil is that it is deployed percutaneously into the aneurysm lumen through a microcatheter. The coil is not detached from the pusher wire until the operator is satisfied with coil placement. If coil position is suboptimal, it can be retrieved and redeployed, or removed and replaced by a more appropriate one. The GDC is a platinum coil that is fused to a stainless steel pusher wire. Following satisfactory placement of the coil in the aneurysm, the fused detachment zone is electrolysed by a small electrical current (2–4 volts, 1 milliamp), thus separating the coil from the pusher wire. These platinum coils are relatively soft, adapting to the configuration of the aneurysm, and are available in a variety of diameters, lengths, configuration, wire gauges and softness. Received 19 August 1999 Accepted 24 September 1999 Correspondence to: Frank C. Tong MD, Department of Radiology, Emory University Hospital, 1364 Clifton Road, NE, Atlanta, GA 30322, USA. Tel.: + 001 (404) 712–4991; Fax: + 001 (404) 712–0293; E-mail: [email protected]

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The primary advantage of endovascular GDC therapy of intracranial aneurysms is that it is less invasive than surgical clipping. The size and configuration of the aneurysm are key factors with regard to the success of GDC therapy. Complete aneurysm thrombosis can be obtained in 57–85% of aneurysms with a neck diameter less than 4 mm with an average of 71%.5,6 On the other hand, the total occlusion rate of aneurysms with a neck greater than 4 mm is only 15–35%.5,6 Although the long term efficacy of GDC therapy remains to be determined, the incidence of rebleeding from treated aneurysms is reduced from approximately 30% to 4% over the first 6 months.7,8 In 100 patients followed over an intermediate period of 2–6 years (mean=3.5 years), the rehaemorrhage rate was 0% for small aneurysms (<1.5 cm), 4% for large aneurysms (1.5–2.5 cm) and 33% for giant aneurysms (>2.5 cm).9 INDICATIONS FOR GDC THERAPY In our institution, surgical clipping remains the primary treatment modality for ruptured and unruptured intracranial aneurysms. Our indications for endovascular therapy include 1) aneurysm configuration deemed unclippable by the neurosurgeon, 2) patient inability to tolerate surgery due to poor clinical grade (Hunt & Hess IV or V) or other medical condition, 3) partially clipped aneurysm and 4) patient refusal of surgery. The configuration of the aneurysm is a key factor in determining whether a patient is a good candidate for endovascular therapy. Generally speaking, GDC is best suited for small aneurysms with small necks, while giant and large necked aneurysms generally respond less well. PATIENT PREPARATION Patients should undergo complete cerebral angiography on a preoperative basis. Although MRA and CTA have greatly improved in their ability to demonstrate vascular detail, traditional cerebral angiography remains irreplaceable in terms of delineating the aneurysm anatomy and identifying other cerebral aneurysms. The angiogram is used to provide essential information regarding the

Endovascular treatment of intracranial aneurysms with Guglielmi Detachable Coils 245

Fig. 1 GDC embolisation technique.

location of the aneurysm, size and configuration of the aneurysm including the neck, and the relationship of the aneurysm neck to the surrounding parent vessels. The identification of the aneurysm neck, separating the aneurysm from the parent vessel, is a prerequisite in assessing whether the aneurysm may be appropriate for GDC embolisation. Rotational angiography may facilitate determination of the working projection, which is necessary for optimal visualisation of the aneurysm neck. More recently, three-dimensional angiography technologies have been developed that depict the angiographic information as a three-dimensional data set, allowing viewing of the aneurysm neck in multiple projections from a single contrast injection. This working projection must clearly separate the aneurysm neck from the parent vessel if coils are to be placed into the aneurysm without parent vessel compromise. At our institution, general anaesthesia is usually utilised for patients undergoing GDC therapy. Its advantages include: 1) decreased patient motion, which allows improved visibility of the aneurysm and better control over the placement of endovascular devices; 2) improved patient comfort; 3) increased control over the patient’s cardiopulmonary status; and 4) better management of complications, including iatrogenic aneurysm perforation. The trade offs include cost, inability to perform neurological assessments during the procedure, and the risks of general anaesthesia. If general anaesthesia is not used, the patient must be able to remain reliably motionless with intravenous sedation. The patient’s condition and physician’s assessment of these factors determine the type of anaesthesia to be used. ENDOVASCULAR PROCEDURE Catheterising the Aneurysm The process of GDC embolisation for intracranial aneurysms is depicted in Figure 1. A femoral sheath is placed and continuously infused with heparinised saline. A guide catheter is placed into the internal carotid artery or vertebral artery leading to the aneurysm. Angiograms are obtained in the working projection, optimising visualisation of the aneurysm neck by separating the aneurysm from the parent vessel. The large bore guide catheter allows digital roadmap imaging and angiograms to be performed during catheterisation and embolisation of the aneurysm. A two-marker microcatheter is placed over a microguidewire through the guide catheter. Under digital roadmap imaging, the tip of the microguidewire is carefully placed into the aneurysm lumen. The microcatheter is slowly advanced over the microguidewire into © 2000 Harcourt Publishers Ltd

Fig. 2 Balloon remodeling GDC embolisation technique.

the aneurysm lumen. Finally, the microguidewire is removed. Both the guide catheter and microcatheter are continuously infused with heparinised saline (4000 µ/1000 cc) through rotating haemostatic valves to minimise the risk of thromboembolic complications. Perfusion of the microcatheter is essential to protect the coil from static blood in the microcatheter, which can increase friction and cause damage and/or unraveling of the GDC coil. Superselective angiograms of the aneurysm lumen and adjoining branches may be obtained through the microcatheter to further delineate the anatomy. Coil Deployment The two-marker microcatheter is manufactured with the distal markers separated by 3 cm. A similar marker exists on the GDC pusher wire, which is 3 cm proximal to the fusion point of the platinum coil and the pusher wire. Alignment of the catheter and coil markers indicates that the detachment zone of the GDC system is at the tip of the catheter in a manner suitable for detachment. The GDC coils are available in two versions: a 0.010 inch nominal diameter (GDC-10) and 0.018 inch nominal diameter (GDC-18). Both GDC-10 and GDC-18 coils come in a variety of lengths and coil diameters. Also available is a more deformable soft version which allows tighter, less traumatic packing of the aneurysmal cavity. Stretch resistant coils have been developed to better resist damage or unraveling when withdrawn from the aneurysm. Journal of Clinical Neuroscience (2000) 7(3), 244–253

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Fig. 3 55 year old female with small wide neck right ICA superior hypophyseal aneurysm with neck:dome ratio approaching 1.0. A: Lateral view demonstrating superior hypophyseal aneurysm; B: Roadmap image with microcatheter in aneurysm lumen and uninflated balloon positioned over aneurysm neck in the parent artery; C: Inflation of balloon in parent artery across aneurysm neck; D: Placement of GDC coils through microcatheter with balloon inflated

Angiographic assessment of the configuration of the aneurysm (size, shape and neck anatomy) is necessary for the selection of the initial GDC coil. The diameter of the initial coil should approximate

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the aneurysm diameter and should always be wider than the aneurysm neck to prevent herniation of the coil into the parent artery. The first coil is selected for appropriate size and softness with

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Endovascular treatment of intracranial aneurysms with Guglielmi Detachable Coils 247

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Fig. 3 cont E: Deflation of balloon following GDC coil placement; F: Final lateral angiogram demonstrating satisfactory GDC coil placement.

the goal of forming a basket of loops within the aneurysm, forming an outer framework for the subsequent placement of additional coils of progressively smaller diameter. Some loops from the initial coil should cross the aneurysm neck in order to prevent subsequent coils from entering the parent vessel, and optimise endothelialisation across the aneurysm neck after treatment. The retrievable coil system is unique in that it can be withdrawn into the microcatheter and redeployed if initial placement is not satisfactory. Both the speed of deployment and the orientation of the microcatheter affect the configuration of the deployed coil. As long as there is no friction, the coil can be withdrawn and redeployed as necessary until the configuration of the coil basket is satisfactory or the operator is convinced that the coil selected is not suitable for the aneurysm. Once satisfactory placement of the coil has been achieved, the marker on the pusher wire is aligned with the proximal marker on the microcatheter. This ensures that the detachment zone is just beyond the catheter tip and ready for detachment. A ground electrode is connected to the patient (a #22 gauge needle placement in the soft tissues or a shoulder patch). This electrode is connected to the negative lead of the GDC Power Supply (Boston Scientific Corporation, Natick, MA, USA) and the positive lead is connected to the proximal end of the GDC delivery wire. The power supply unit is activated, adjusting the voltage across the leads to maintain a fixed 1 milliamp current through the coil (other choices include 0.5 mA and 0.75 mA). The detachment zone is electrolytically lysed by this current, separating the coil from the pusher wire. This is then removed under fluoroscopic guidance. Additional coils are placed into the aneurysm and detached as described. Care is taken not to dislodge previously placed coils within the aneurysm during the placement or withdrawal of addi-

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tional coils. The endpoint for coil placement is when the operator is satisfied that the aneurysm is maximally packed with coils such that no additional coils can safely be placed. The microcatheter is slowly withdrawn under fluoroscopy so as not to displace the coils. A control angiogram is finally obtained through the guide catheter to assess the distal vessels for possible thromboembolism and exclusion of the aneurysm. POTENTIAL COMPLICATIONS The morbidity and mortality for GDC embolisation of intracranial aneurysms is reported to be 6–9%.5,8,10 The primary potential complications include aneurysm perforation and thromboembolic complications. Aneurysm perforation occurs in 2.7% of ruptured aneurysms treated with GDC.5 The rate of perforation for previously unruptured aneurysms is significantly lower, likely less than 0.5% based upon meta-analysis of multiple published series.11–17 Precautions against perforation include careful access of the aneurysm with minimal contact between the aneurysm wall and the microcatheter/microguidewire. Perpendicular contact between the aneurysm wall and the wire, catheter and coil should also be avoided. Thromboembolic complications can occur when thrombus forms on the catheters, guidewires or coils during or after coil placement. Overall there is a 2.5–5.5% incidence of thromboembolic complications in GDC cases.5,9 A patient with an unruptured aneurysm should be systemically anticoagulated with heparin. As mentioned, ruptured aneurysms are at increased risk of bleeding compared to unruptured aneurysms. Strategies for ruptured aneurysms include full anticoagulation, partial anticoagulation or

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Fig. 4 Stent assisted GDC embolisation technique.

delayed anticoagulation. At our institution, we fully anticoagulate patients from the procedure onset. Coil unraveling occurs most commonly when the distal aspect of the coil is tethered and the proximal end is pulled, resulting in stretching and loss of the coil winding. Other causes include torquing the pusher wire and using excessive force when deploying or retrieving the coil. This is problematic because the unraveled portion of the coil assumes the characteristics of a thin wire with loss of directional control and pushability. A more extreme case is coil fracture where the distal aspect of the coil becomes disconnected from the proximal end. This also usually results from excessive coil stress. The microcatheter lumen and type should be matched to the coil such that T-18 catheters are used with T-18 coils and T-10 catheters with T-10 coils. This minimises friction between the catheter and the coil. Additionally, the catheter is perfused with continuous heparinised saline flush to minimise thrombus formation and friction. Endovascular techniques or surgery may be required to retrieve the damaged coil. Alternatively, the coil can implanted in certain situations. Parent artery compromise occurs when a portion of the detached coil mass herniates through the aneurysm neck into the parent vessel. For ruptured aneurysms there is a 3% rate of unintentional parent artery occlusion associated with GDC therapy.5 Isolated coil loops within the parent vessel not resulting in significant luminal compromise may require anticoagulation with heparin and aspirin to protect from distal thromboemboli. Malpositioned coils can also be treated with endovascular retrieval techniques including snares and the Attractor (Boston Scientific, Natick, MA, USA), which is an endovascular coils retrieval device. The Attractor is designed to adhere to previously detached GDC coils allowing them to be retrieved into the guide catheter. Neurosurgery may also be required to relieve parent vessel compromise and complete aneurysm therapy. If there is adequate collateral circulation, permanent occlusion of the vessel can be considered to minimise the risk of distal thromboemboli. Permanent occlusion can be performed with placement of additional endovascular coils or detachable silicone balloons. LIMITATIONS OF ENDOVASCULAR GDC THERAPY The objective of endovascular therapy is dense placement of coils in the aneurysm neck and sac to achieve exclusion of the lumen from the circulation. Generally, coils are placed in the aneurysm lumen until the operator determines that no additional coils can safely be

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placed. The denser the coil pack, the higher is the probability of aneurysm thrombosis and the lower the risk of coil compaction or recanalisation. The annual risk of rehaemorrhage in ruptured aneurysms is directly dependent upon the degree of aneurysm occlusion following GDC therapy. A recent study described the annual aneurysm rebleeding risk as 0% for complete treatment, 1.4% for near complete treatment and 7.3% for incomplete treatment.16 Complete aneurysm thrombosis is more easily accomplished in small aneurysms with small necks, and more difficult in aneurysms with relatively large necks. GDC embolisation is very effective for aneurysms with dome to neck ratios >2. Aneurysms with dome to neck ratios in the 1–2 range demonstrate intermediate long term success, while wide neck aneurysms with neck to dome ratios approaching 1.0 remain difficult to treat. Wide neck aneurysms are difficult to maximally pack because the coils are less well contained by the aneurysm neck and have increased propensity to herniate into the parent vessel. This results in a relatively loose coil pack, as fewer coils can be placed without risking parent vessel compromise. New techniques that attempt to address the relative shortcomings of GDC in wide neck aneurysms have recently been described. BALLOON REMODELING The balloon remodeling technique involves combining the use of GDC with a temporary endovascular balloon to protect the coils from herniating into the parent vessel. Moret et al.18 first described this technique for treating difficult wide neck aneurysms. Since then, multiple case reports have described it in patients with wide neck aneurysms not suitable for conventional GDC therapy.10,19,20 The purpose of the balloon is to provide temporary mechanical displacement of the coils away from the parent vessel as they are deployed into the lumen of the aneurysm. This effectively protects the coils from herniating into the parent vessel, also allowing denser coil packing. The indications for the remodeling technique include treatment of wide neck (dome:neck ratio <1.5) or irregularly shaped aneurysms that are not suitable for conventional GDC treatment, incompletely clipped aneurysms or patients with recurrent or incompletely treated aneurysms following GDC therapy.10 Theoretically, the balloon remodeling technique may also be used to protect the parent vessel where the neck of the aneurysm cannot be clearly delineated from the parent vessel angiographically; this is not done at our institution. Attention to systemic anticoagulation is of utmost importance with the balloon remodeling technique which is schematically demonstrated in Figure 2. After obtaining the working projection, the uninflated balloon catheter is placed through a large bore guide catheter in the feeding vessel across the aneurysm neck. The microcatheter is then placed into the lumen of the aneurysm under roadmap imaging. This requires either bifemoral puncture with placement of two guide catheters (both 6 French) or a single femoral puncture and a larger guide catheter (typically 7 French). The balloon catheter is placed first to minimise the chance of aneurysm perforation by the microcatheter during balloon placement. Initial placement of the ballon when using a single guide catheter also takes advantage of the initially larger uncompromised lumen. The heparin flush through the microcatheter is temporarily suspended and the balloon is inflated just to the point of stasis within the parent artery. Temporary suspension of the heparin flush is required to prevent increasing intra-aneurysmal pressure within the now ‘closed’ space during balloon inflation. The GDC coil is advanced through the microcatheter into the aneurysm lumen while the balloon is inflated. If the coil configuration is not satisfactory it can be removed and redeployed with the

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Endovascular treatment of intracranial aneurysms with Guglielmi Detachable Coils 249

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Fig. 5 69 year old male status post prior right ICA endarterectomy with recurrent stenosis at the surgical site, and distal tandem lesion with associated sidewall pseudoaneurysm. A: Lateral angiogram of right carotid bifurcation demonstrating two ICA stenoses with associated pseudoaneurysm of the distal stenosis; B: Lateral image demonstrating placement of guidewire across both stenoses and stenting of the proximal lesion; C: Superselective injection following stenting of distal stenosis with placement of microcatheter through the stent struts into the pseudoaneurysm; D: Placement of GDC coils through the microcatheter into the pseudoaneurysm using the stent to protect the parent vessel; E: Final post embolisation angiogram demonstrating thrombosis of the pseudoaneurysm and no luminal compromise of the parent vessel.

Fig. 6 Three-dimensional (3D) GDC coil configuration.

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Fig. 7 49 year old female with wide neck basilar tip aneurysm. A&B: Initial AP and lateral angiograms demonstrating wide neck basilar tip aneurysm; C&D: AP and lateral angiograms showing basket formation across aneurysm neck following placement of 3D GDC coil

balloon inflated. The balloon is typically not inflated for more than one or two minutes at a time. Prior to coil detachment, the balloon is deflated and the coil pack observed under fluoroscopy to determine whether there is any change in configuration, which might Journal of Clinical Neuroscience (2000) 7(3), 244–253

indicate instability, possibly resulting in coil migration and herniation into the parent artery following detachment. The heparinised saline flush within the microcatheter should be restarted immediately to minimise the opportunity for thrombus formation within © 2000 Harcourt Publishers Ltd

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Fig. 7 cont E&F: Final AP and lateral angiograms obtained following placement of additional conventional GDC coils within the initial 3D GDC coil.

the catheter. If the coil herniates into the parent vessel following balloon deflation, it is removed and redeployed. Attempting to ‘push’ a coil loop back into the aneurysm with balloon inflation can result in increased tension on the aneurysm walls, risking perforation. Following satisfactory placement and observation for stability, the coil is detached in the usual fashion and the pusher wire removed. The cycle is then repeated with suspension of saline flush through the microcatheter, balloon inflation, coil deployment, balloon deflation, resumption of saline flush and coil detachment. Once again, the operator determines the endpoint when he/she feels that no additional coils can safely be placed within the aneurysm. The balloon may be inflated again to prevent coils from being displaced into the parent artery while withdrawing the microcatheter. The microcatheter and balloon are removed and a final control angiogram is obtained through the guide catheter to document absence of thromboembolism, and the final appearance of the embolised aneurysm. A clinical example of the balloon remodeling technique is shown in Figure 3. Treatment results using the remodeling technique demonstrate improved ability to treat aneurysms that would otherwise be unsuitable for GDC therapy. In the largest published series of 56 wide neck aneurysms, total occlusion was achieved in 77%, subtotal occlusion in 17% and incomplete occlusion in 6%.10 Because of its increased complexity, the remodeling technique is reserved for those cases requiring a higher degree of parent vessel protection in wide neck lesions, rather than a first line treatment for all aneurysms. In the above series, there was a 5.5% incidence of angiographic evidence of thrombus and a 5.5% incidence of aneurysm rupture.10 The potential complications of the balloon remodeling technique are numerous. In addition to the risks of conventional GDC

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treatment, there are additional risks of balloon inflation within the cerebral vasculature. These include parent vessel rupture, dissection, vasospasm, balloon related thrombus and occlusion of adjacent perforators.19 In addition, there is theoretically an increased risk of aneurysm rupture because the coils are deployed in a ‘closed space’ without the aneurysm neck as an outlet for coil decompression. Delayed migration of coils into the parent artery is also a theoretical risk of this technique but was not observed in the largest published series.10 The risk of coil migration can be minimised by placing the largest initial coil possible within the aneurysm to obtain the most stable coil basket possible. INTRAVASCULAR STENT PLACEMENT PRECEDING GDC PLACEMENT This recently described treatment method involves placement of a stent into the parent vessel, bridging the ostium of the aneurysm neck prior to GDC coil placement. Here the stent serves a similar purpose to the balloon in the remodeling technique by mechanically deflecting coil loops away from the parent vessel. Following placement of the stent, the microcatheter is placed through the stent struts into the aneurysm lumen and the aneurysm is coiled in the standard fashion. This also allows for a denser coil pack in aneurysms with irregular shapes or relatively wide necks. The application of this technique is limited to those vessels where an intravascular stent can safely be navigated and placed. Stents are presently used to maintain luminal diameter following percutaneous angioplasty. Recent advances in coronary stent technology make the placement of intracranial stents increasingly feasible. Described applications include lateral aneurysms or fusiform basilar artery aneurysms not suitable for surgery or conventional GDC therapy,21,22 in addition to sidewall dissecting Journal of Clinical Neuroscience (2000) 7(3), 244–253

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Fig. 8 Double microcatheter GDC embolisation technique.

pseudoaneurysms.23 Bifurcation aneurysms are not appropriate for treatment using this method. Given the increased technical complexity, GDC with stenting is limited to patients who are not candidates for surgery or conventional GDC therapy. This technique is diagrammed in Figure 4. Angiograms of the parent artery and aneurysm are initially obtained for evaluation of the aneurysm neck and sizing of the parent artery. A guide catheter is then placed into the feeding artery and a guidewire is placed across the aneurysm neck into the distal parent artery. Anticoagulation is required, given the thrombogenicity of the stent and vessel surface. Stent selection depends upon the diameter and tortuosity of the parent vessel in addition to the size of the aneurysm neck. The stent should exert minimal radial force upon the parent vessel and the interstices of the deployed stent should be wide enough to allow perforator perfusion and catheterisation of the aneurysm. The stent is deployed in the parent vessel, bridging the neck of the aneurysm. A microcatheter is placed over a microguidewire through the struts of the stent into the aneurysm lumen. GDC coil embolisation is then performed in the usual fashion. Following aneurysm packing the microcatheter is removed and follow up angiograms are obtained through the guide catheter. A clinical example of this technique applied to a cervical carotid pseudoaneurysm is shown in Figure 5. At our institution patients are temporarily anticoagulated following the procedure prior to receiving antiplatelet therapy. This consists of clopidogrel 75 mg qd for 6 weeks and aspirin 325 mg qd permanently. Because this method has only been described in isolated case reports and animal studies, information regarding treatment results or long term follow up data are limited. The potential complications include the usual risks of GDC therapy in addition to stentassociated risks. Although no long term data for intracranial stents are available, the described risks of stent placement likely apply including undesirable stent location, incomplete stent expansion, vessel rupture, acute and delayed thrombosis and intimal hyperplasia. This method is technically feasible but should be reserved as a last resort for patients with no other treatment options, given higher relative risk and short track record. THREE-DIMENSIONAL (3D) GDC COILS Another approach to wide necked aneurysms consists of using a coil which is inherently less prone to herniating into the parent vessel. While conventional GDC coils have a helical configuration, three-dimensional GDC coils (Boston Scientific Corporation,

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Natick, MA, USA) are wound in a configuration with outer diameters of alternating size to resemble a sphere when deployed in the aneurysm (Figure 6). The ability to form a spherical basket without herniation into the parent vessel provides a stable foundation into which additional coils can be placed. Placement of three-dimensional GDC coils is technically similar to placement of conventional GDC coils. Once again the coil is sized to approximate the diameter of the aneurysm. The primary difference in coil placement is that the coil may exhibit a ‘tumbling’ behaviour as it is deployed, such that the configuration of the partially deployed coil may differ significantly from its appearance when fully deployed. The three-dimensional coil may be withdrawn and redeployed until a satisfactory basket is formed, but has a higher propensity to unravel. Conventional GDC coils are then typically placed inside the initial three-dimensional coil to achieve maximal coil density. A clinical example is shown in Figure 7. Early data at our institution suggest that the use of three-dimensional GDC coils can facilitate the treatment of wide neck aneurysms not amenable to treatment with conventional GDC techniques. One advantage of the three-dimensional coil is that is does not increase the technical demands of the case by requiring placement of a temporary balloon or stent. Because three-dimensional coils have only recently become available, further evaluation of this technology will help to characterise the efficacy of treating aneurysms with this method. DOUBLE MICROCATHETER TECHNIQUE One concern with placing coils in wide neck aneurysms is that even if the initial coil can be placed to achieve a basket, subsequent coils may displace the detached initial coil through the wide neck into the parent vessel. A solution to this problem is to place two coils into the aneurysm prior to detaching either coil. This requires the catheterisation of the aneurysm with two microcatheter systems such that two coils can be deployed without detaching them. The advantage of deploying both coils prior to detachment is that both remain retrievable if the second coil should displace the first. Additionally, the bracing characteristic of two coils results in a more stable mesh configuration prior to placement of additional coils. This approach is depicted in Figure 8 and requires either bifemoral punctures or placement of a single large guide catheter into the artery feeding the aneurysm. Two microcatheters are sequentially placed into the aneurysm lumen over microguidewire systems. The first coil is then placed through one microcatheter in a satisfactory configuration and not detached. A second coil is then placed through the other microcatheter into the aneurysm. The coils can be withdrawn and redeployed until a stable configuration is achieved. At this point the coils are sequentially detached. Additional coils are placed conventionally until the operator determines that the aneurysm is maximally packed. In a recent case report, two patients were treated with this method. One patient demonstrated complications of upper extremity weakness and the other experienced no clinical sequelae from embolisation with the dual microcatheter approach.24 The placement of two microcatheters increases the risk of aneurysm perforation and thromboemboli associated with this technique. However, this method is potentially more versatile, theoretically allowing treatment of aneurysms not amenable to balloon remodeling or stent placement. CONCLUSION Endovascular therapy with GDC is a proven method of treating intracranial aneurysms. This method is most effective for small

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aneurysms with favourable dome to neck ratios (greater than 2:1). With conventional GDC methods, the ability to treat wide neck (dome:neck <2:1) and large aneurysms is limited by the amount of coil that can be placed in the aneurysm lumen without risking parent vessel compromise. Newer methods of GDC placement include supporting the coils with a temporary balloon or stent to protect the parent vessel. Other approaches target stabilisation of the coil mass by inherently stabilising the coil with three-dimensional spherical coils and interlocking coils with the dual microcatheter technique. These innovative methods of GDC placement may facilitate denser GDC packing in hope of achieving greater efficacy and lower rates of aneurysm recurrence. Further study will ultimately determine the effectiveness of these adjunctive techniques.

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