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Balloon- and Stent-Assisted Endovascular Occlusion of Intracranial Aneurysms

  • Brian J. A. Gill
  • Jason A. Ellis
  • Philip M. Meyers
Chapter

Abstract

Endovascular approaches to the management of intracranial aneurysms have been employed since the early 1960s and usually involved the use of free coils or detachable balloons which were technically challenging and had limited safety and effectiveness in comparison to open surgical clipping of the lesion [1]. This remained the case until early 1990s, when two watershed moments would form the impetus for the development and widespread use of endovascular techniques for the treatment of intracranial aneurysms.

Checklist: Aneurysm Treatment with Adjuvant Devices

Administrative and pre-procedural nursing assessment

 • Confirm patient identity, procedure, and consent

 • Inquire about contrast allergies and pregnancy status if applicable

 • Creatinine level

 • Ensure intensive care unit inpatient bed availability

Technologist

 • RHV

 • Tubing

 • Choice of balloons, coils, and stents

 • Microcatheters

 • Guidewire

 • Dyna-CT protocol

Nursing

 • Heparinized saline

 • Protamine

 • Active type and screen

 • Platelets on call to the interventional suite

 • Desmopressin

 • Glycoprotein IIb/IIIa receptor inhibitor—abciximab or eptifibatide

 • Mannitol

 • Anticonvulsants

 • Call numbers to anesthesiology attending, neurosurgery resident on call, and CT scanner

Anesthesia

 • Endotracheal intubation equipment

 • Intracranial pressure monitoring equipment

Neurosurgery

 • External ventricular drain kit

Neurointerventionalist

 • Pre-procedural neurological exam

 • Ensure all equipment is available prior to start of procedure

 • Identify contrast extravasation from the aneurysm fundus

– Ask nursing and anesthesia teams to reverse anticoagulant/antiplatelet agents

– Tell technologist to prepare for possible Dyna-CT

– Keep microcatheter in place

– Deploy and inflate balloon via an additional RHV

– Rapidly coil ruptured aneurysm

– Post-op neurological exam and CT scan

 • Identify coil migration or prolapse into the parent artery

– Deploy balloon or SEIS through additional RHV to trap prolapsed coils in aneurysm fundus

– Consider use of retrieval devices to remove migrated coil

 • Identify stent misplacement or migration

– Consider placement of a second stent

– Evaluate functional neck size and consider coil embolization

– Consider staging the procedure to allow for endothelialization

 • Identify local thrombus formation

– Evaluate antegrade flow in parent and branching vessels

– Ask the nursing or anesthesia teams to determine the activated clotting time

– Administer local infusions of GP IIb/IIIa

– Post-op neurological exam

– Post-op platelet inhibition testing

– Consider a post-procedural heparin or GP IIb/IIIa drip

Complication Avoidance Flowchart

Complication

Cause

Management

Avoidance

Intraprocedural

Aneurysmal

Rupture

1. Iatrogenic—Injury secondary to microcatheter, guidewire, or coils

2. Morphological features of the aneurysm, e.g., the presence of a small basal outpouching, smaller aneurysms, may increase intraprocedural rupture risk

3. Previous aneurysm rupture

1. Reverse antiplatelet/anticoagulants administered prior to or during the procedure

2. Keep systolic blood pressure less than 140

3. If present, inflate a balloon within the parent vessel to obtain hemostasis

4. Rapidly coil the ruptured aneurysm with coils

5. Open surgical management

6. CT scan to evaluate for hydrocephalus

7. Standard subarachnoid hemorrhage management

1. Careful positioning of the microcatheter into the fundus

2. Avoid overpacking the fundus during coil embolization

3. Consider staged embolization/leaving a neck remnant for recently ruptured aneurysms

Coil migration/malposition

1. Inappropriate positioning of the microcatheter

2. Premature coil deployment

3. Deployment of undersized coils

1. Coil retrieval using Merci devices, stent retrievers, alligator clips, or microwires

2. Administer intra-arterial abciximab if coil migration has led to thrombus formation

1. Stabilize microcatheter within the fundus to prevent kickout and possible coil malposition

Coil herniation

1. Displacement of the first coil after subsequent embolization

2. Excessive embolization

1. Deployment of a SEIS within the parent vessel to trap the prolapsed coils

2. Inflation of a balloon across the aneurysm neck

1. The use of longer and stiffer coils to form a stable initial basket

2. The use of shorter and softer coils in the later stages of endosaccular embolization

Stent misplacement/migration

1. Unstable delivery catheter position

2. Trans-stent manipulation of microcatheters, additional stents, etc. through the deployed stent

3. Tortuous anatomy of the parent vessel

1. Deployment of a second stent across the aneurysm neck to provide adequate neck protection

2. Coil embolization of the aneurysm if the misplaced stent reduces the functional neck size

3. Stent retrieval

1. Staged deployment of multiple stents or coil embolization to allow for stent endothelialization

2. Stable distal microwire access

Thromboembolic complications with intracranial stenting

1. Non-responders to first-line antiplatelet treatment

2. Medication noncompliance

1. Administer intra-arterial abciximab until the thrombus has dissolved or stabilized and antegrade flow in parent and branching vessels has resumed

1. Patients are loaded with dual antiplatelet medication prior to intervention

2. Full heparinization during the procedure with a goal ACT of 250–300 s

3. Preoperative platelet inhibition testing

Introduction

Endovascular approaches to the management of intracranial aneurysms have been employed since the early 1960s and usually involved the use of free coils or detachable balloons which were technically challenging and had limited safety and effectiveness in comparison to open surgical clipping of the lesion [1]. This remained the case until early 1990s, when two watershed moments would form the impetus for the development and widespread use of endovascular techniques for the treatment of intracranial aneurysms.

The first of these was the FDA approval of the Guglielmi detachable coil (GDC) in 1995. Unlike devices employed prior to its introduction, the GDC allowed for both the retrieval and repositioning of the coil in order to achieve complete occlusion of the fundus, while maintaining patency of the parent vessel [2, 3]. The second was the results of the international subarachnoid aneurysm trial (ISAT), a multicenter, prospective, randomized controlled trial that compared the results of open surgical clipping and endovascular coiling for patients with ruptured intracranial aneurysms. This trial was stopped ahead of schedule after a planned interim analysis demonstrated a better outcome for patients treated with endovascular therapy, with the rates of death or dependency at 1-year follow-up being 23.5% for the endovascular group and 30.9% for the surgical group [4].

While these results led to the increased use of coil embolization for intracranial aneurysms, interventionalists soon realized that the presence of a wide neck, dome to neck ratio less than 2.0, large-size tortuous vessels, and bifurcation aneurysms posed a greater challenge and were associated with a higher risk of incomplete fundus occlusion and recurrence. This has necessitated the development of several adjuncts to conventional endovascular therapy including balloon remodeling techniques, stent-assisted coiling, and flow-diverting stents. These techniques have simultaneously increased the armamentarium of the modern interventionalist and expanded the range aneurysms amenable to endovascular treatment. In this chapter we discuss the development, indications, safety, and efficacy of balloon remodeling and stent-assisted endovascular occlusion of intracranial aneurysms.

Procedural Overview

Balloon Remodeling Technique

Moret et al. described the balloon remodeling technique in 1997, and at that time, it was the first adjunct capable of facilitating the successful endovascular treatment of intracranial aneurysms with an unfavorable neck-to-dome ratio [5]. During this procedure, a nondetachable balloon is placed within the parent vessel across the neck of the aneurysm, while a second microcatheter is positioned within the fundus of the lesion. Following balloon inflation, coils are placed within the aneurysmal sac; the balloon is then deflated in order to test the stability of the coil within the lesion prior to coil detachment. The temporary inflation of the balloon results in obliteration of the neck and thus allows the coils to assume the shape of the lesion and ultimately prevents prolapse of the coil mass. Following the satisfactory occlusion of the aneurysm, the balloon is removed from the parent vessel.

Balloon remodeling offers several advantages : it prevents herniation of the coils, it forces the coils to assume the three dimensional shape of the aneurysm, thus increasing the density of the coil mass, and it provides a means of tamponade in the setting of intraprocedural aneurysm rupture [6, 7]. It does not require pre- or post-procedural dual antiplatelet therapy, which is particularly advantageous if this technique is pursued in patients who present following subarachnoid hemorrhage or suffer an intraprocedural rupture. Finally it conforms to the shape of the parent vessel, and in doing so, it delineates both the neck of the lesion and any adjacent vessels that protect them during the procedure [6].

Early adopters of the balloon remodeling technique employed low-compliance nondetachable balloons glued onto microcatheters or balloon microcatheters with a guidewire running through it [5, 8]. Catheterization was easier with the latter construct; however the low compliance and oblong shape of these balloons meant that this technique was only amenable to wide-necked sidewall aneurysms as they were unable to effectively maintain the patency of the parent vessel or branching arteries when used for the management of more complicated bifurcation lesions. In an attempt to address such aneurysms with the balloon remodeling technique, interventionalists employed round high-compliance latex balloons that were glued to the tip of a flow-guided microcatheter. While temporary occlusion of the neck and maintaining the patency of the parent and branching vessels were feasible with this construct, the use of the flow-dependent microcatheter made stabilization of the balloon during the procedure challenging.

The development of high-compliant over-the-wire balloons such as the HyperForm (Medtronic/Covidien/Ev3), Ascent (Codman Neurovascular), and Scepter (Microvention) allowed for successful coil embolization of complex bifurcation aneurysms using the balloon remodeling technique while maintaining vessel patency. The high compliance of these balloons allows them to change their shape on inflation in order to conform to the neck of the aneurysm and the adjacent branching vessels. Additionally the use of a guidewire as opposed to a flow-dependent microcatheter enables stable positioning of the balloon throughout the procedure [9].

Modifications of the balloon remodeling technique may be employed to treat more challenging cerebral aneurysms. The double-balloon remodeling technique described by Arat and Cil may be used to treat bifurcation aneurysms with necks greater than the length of the balloon catheter [10]. Two compliant balloon catheters are placed in the parent and branching vessels in a Y configuration, while a third catheter is used to deploy the coils into the fundus of the aneurysm. However such techniques require a dual femoral approach; additionally the presence of multiple microcatheters and balloon inflations increases the risk for thromboembolism and vascular injury secondary to overinflation.

Based on most published series, BRT provides comparable or superior anatomic results than standard coiling. The ATENA and CLARITY prospective trials looked at outcomes for unruptured and ruptured aneurysms that underwent endovascular management. In the ATENA series, immediate complete aneurysm occlusion was seen in 59.8% of both the standard coiling and BRT groups [11]. In the CLARITY series, immediate complete aneurysm occlusion was seen in the 46.9% of aneurysms subject to standard coiling and 50.0% of aneurysms treated by BRT [12]. The meta-analyses performed by Shaprio et al. demonstrated that BRT was superior to standard coiling with 73% of aneurysms treated by the former method achieving complete occlusion immediately after intervention as opposed to 49% in the standard coiling group [13]. Similar rates of occlusion were seen at follow-up.

Stent-Assisted Endovascular Occlusion

The impetus for the development of stent-assisted coiling of intracranial aneurysms was twofold. First, while the advent of the balloon remodeling technique increased the armamentarium of the neurointerventionalist, the approach was considered by many to be technically demanding and lacked an effective plan if coils prolapsed into the parent artery. Furthermore a large percentage of wide-necked intracranial aneurysms still remained unsuitable for coiling, as their morphology would not permit the retention of coils within the fundus.

Endovascular stents have been used in the clinical setting since the 1960s in attempt to address and prevent the propagation of dissection after angioplasty, to force asymmetric plaques into a cylindrical shape in the vessel lumen, and to prevent vessel collapse. However it wasn’t until 1997 when Higashida et al. reported the use of a balloon-mounted coronary stent in combination with Guglielmi detachable coils for the management of a fusiform vertebrobasilar junction aneurysm [14]. Following this there were several case reports describing the use of balloon-expandable coronary stents to address cerebral aneurysms, intracranial atherosclerosis, and coil prolapse after the embolization of cerebral aneurysms [15, 16, 17, 18, 19].

Intracranial stents promote changes in the vascular endothelium and blood flow at the aneurysm parent vessel interface that facilitate embolization of the aneurysm fundus. Following deployment the stent reduces blood flow into the aneurysm and in turn decreases the peak pulsatile velocity and maximum shear strength on the wall of the fundus [20, 21]. The reduced regional blood flow and shear stress in addition to the scaffold provided by the stent allow for endothelialization of the device within the parent vessel and, most importantly, across the neck of the aneurysm [22]. This will ultimately allow for endoluminal reconstruction of the parent vessel.

Currently there are two types of stents available—balloon-expandable coronary stents (BECS) and self-expanding intracranial stents (SEIS). Balloon-expandable coronary stents (BECS) were the first type of stent utilized in the endovascular treatment of intracranial aneurysms. Initially designed for the revascularization of coronary vessels in the setting of coronary artery disease, their rigid structure made them resistant to intraprocedural damage or migration. However this feature also made them unsuitable for navigating tortuous cerebral vasculature. Furthermore their deployment requires inflation of a high-pressure balloon increasing the risk of vessel rupture. These characteristics ultimately precluded the widespread use of BECS for the management of intracranial aneurysms.

Self-expandable intracranial stents (SEIS) became commercially available in 2001 after the Food and Drug Administration (FDA) authorized the Neuroform microstent (Boston Scientific/Stryker) use for the treatment of intracranial aneurysms via a humanitarian device exemption. These stents were made from nitinol and far more flexible than their balloon-mounted predecessors, thus enabling navigation for a wider variety of landing zones within the cerebral vasculature. Its open-cell design allowed each segment to act as a separate fixation point, thus accounting for its superior vessel wall apposition in comparison to closed-cell designed stents (Fig. 25.1).
Fig. 25.1

(a–f) A 70-year-old woman with neck pain, right internal carotid aneurysm incidentally found on cervical MRI scan. (a) Right internal carotid angiogram in frontal projection shows tandem aneurysms (arrows), with distal aneurysm projecting into subarachnoid space. (b) Digital road map image of the right internal carotid artery following placement of treatment catheters across aneurysms. (c) Diagram depicting placement of balloon catheter across the neck, or face, of aneurysm while coil delivery catheter projects into aneurysm fundus. (d) Right internal carotid angiogram in the same frontal projection demonstrates placement of multiple detachable platinum coils into each aneurysm using balloon neck remodeling technique. Note that the coils conform to the balloon margin during inflation (not shown) and the wall of the artery (small arrows). (e) Fluororadiograph obtained during angiography shows subsequent placement of self-expanding nitinol stent into the right internal carotid artery across both aneurysms (white tip arrows). (f) Surveillance angiography 6 months later shows complete occlusion of both aneurysms and patency of the right internal carotid artery without stenosis

Despite this some technical difficulties with deployment still remained with the first iteration of the Neuroform. The stent was preloaded onto a delivery microcatheter making navigation to the landing zone difficult. Interventionalists have circumvented this problem by using a standard microcatheter and microwire to access the site of interest. The microcatheter is then removed over a 300 cm exchange microwire positioned distal to the target site; finally the Neuroform stent delivery microcatheter system is navigated over the exchange microwire [23]. This final maneuver was still technically difficult as the guidewire was prone to distal migration thus placing the involved vessels at risk for perforation. The more recent iterations of the Neuroform stent—the Neuroform EZ stent system—may be delivered via a standard microcatheter removing the need for the exchange maneuver.

The Enterprise (Cordis Neurovascular/Johnson and Johnson) system was the second commercially available SEIS, and unlike the Neuroform, it has a closed-cell design which allows it to be partially delivered, resheathed, and repositioned prior to its final delivery. Additionally navigation and deployment of the Enterprise stent are less technically challenging than the initial Neuroform stent. The collapsed device is premounted on a microwire which is loaded into a delivery catheter after the target zone has been reached, thus removing the need for an exchange microwire and thus reducing the risk of distal vessel perforation during the exchange process [24]. The major disadvantage of the Enterprise system is that its closed-cell design also reduces its ability to conform to tortuous vessels and the resultant reduced wall apposition may decrease the ability of the stent to protect the parent vessel.

There are several operative strategies that may be employed when pursuing stent-assisted coil embolization of intracranial aneurysms. In the trans-stent technique, the stent may be deployed first, and the microcatheter may be placed inside the fundus through the struts of the stent. It is not uncommon for interventionalists to perform this procedure 1–2 months after the stent has been deployed. This delay allows for endothelialization of the stent which should make it more stable and less prone to migration during trans-stent coiling. Alternatively in the jailed-catheter technique, the microcatheter responsible for coil deployment is positioned inside the fundus of the aneurysm; the stent is then deployed across the neck of the aneurysm prior to coiling. This method is somewhat less susceptible to kickback of the microcatheter during coiling than the trans-cell technique. In the stent-jack technique, a coil delivery microcatheter is placed in the fundus, and an undeployed stent is placed across the neck of the aneurysm. The first coil is then delivered into the fundus and allowed to take the shape of the aneurysm, and subsequently the stent is deployed. Finally stents may be used as a rescue device in the setting of herniation of a coil mass into the parent vessel in order to maintain vessel patency and decrease embolic risk.

Unlike sidewall aneurysms, wide-necked bifurcation aneurysms are not always adequately addressed with a single stent. In these cases a single stent may not be able to provide adequate parent or branching artery protection from the coil mass. In this setting two stents may be placed in a “Y” configuration, with the one stent deployed through the interstices of the first. This allows for reconstruction of the parent and branching vessels while preventing herniation of the coil mass. This technique has been successfully applied to basilar tip, anterior communicating, and middle cerebral artery bifurcation aneurysms [25, 26, 27].

Endovascular stents require dual antiplatelet therapy (DAPT) to prevent thrombosis in the hyperacute, acute, and chronic periods following stent deployment. Aspirin a cyclooxygenase-1 inhibitor which blocks the production of thromboxane 2 and clopidogrel a thienopyridine derivative which prevents platelet activation by irreversibly inhibiting the P2Y12 ADP receptors are usually used for this purpose. Patients are typically given loading doses of aspirin and clopidogrel 3–5 days prior to the procedure, followed by 6 weeks of DAPT and maintained on ASA 81 thereafter. Alternatively a single loading dose of clopidogrel can be given 1 day prior to the procedure. In the setting of unplanned stent deployment in order to achieve adequate embolization or to maintain parent artery patency following prolapse, the glycoprotein IIb/IIIa inhibitor abciximab can be used to achieve rapid platelet inhibition. Following stent deployment and satisfactory positioning, a 0.25 mg/kg bolus is administered followed by a 12 h infusion. Alternatively, instead of a 12 h infusion, the patient may be given loading doses of aspirin and clopidogrel following administration of the loading dose of abciximab [28]. Given the need for DAPT) , patients with ruptured cerebral aneurysms are not generally a candidate for stent-assisted coiling; additionally the need for potential adjuvant surgical and invasive procedures including external ventricular drain, shunt placement, lumbar puncture, central line, tracheostomy, percutaneous endoscopic gastrostomy, or angioplasty for cerebral vasospasm often precludes the need for long-term antiplatelet therapy.

Complication Avoidance and Management

The most common complications of the BRT are thromboembolism and intraprocedural rupture.

The risk of thromboembolic events when employing the balloon remodeling technique theoretically increases due to the presence of multiple catheters within the arteries and temporary occlusion of parent and or branching vessels, with repeated inflation and deflation of the balloon [29]. These events are not always symptomatic and may only be detected after follow-up diffusion imaging [30]. However meta-analysis performed by Shaprio et al. has shown that there is no statistically significantly increased risk of thromboembolism associated with BRT in comparison to the unassisted deployment of Guglielmi detachable coils [13]. Furthermore several single center series and randomized trials have shown that the rate of thromboembolism in BRT is no different than that encountered with standard coiling [31, 32, 33, 34].

BRT also carries a theoretical increased risk of aneurysmal rupture as the microcatheter may impinge against the wall of the aneurysm with inflation which may itself result in rupture of the aneurysm or the subsequent deployment of coils while the microcatheter is impinged against the wall may result in rupture. Reported intraprocedural rupture rates associated with BRT range from 1.7 to 4%, and depending on the series, this rate exceeded, was comparable to, or was less than the intraprocedural rupture rate associated with standard coiling [13, 35].

In the event of an intraprocedural aneurysm rupture , protamine should be administered in order to normalize the activated clotting time (ACT), the balloon is temporarily inflated within the parent vessel in order to achieve hemostasis, and the anesthesiologist is immediately informed of the situation and asked to keep the systolic blood pressure less than 140 mm Hg. The fundus of the aneurysm is then rapidly packed with coils. At the end of the procedure, a CT scan is obtained to evaluate for hydrocephalus, and an external ventricular drain may be necessary depending on the patient’s neurological exam after the procedure.

Herniation of the coil mass may precipitate thrombus formation or cause parent vessel occlusion. This problem is usually seen with wide-necked aneurysms and typically occurs at the end of the procedure, whereby excessive embolization, or the over-deployment of coils into the aneurysm, fundus promotes their subsequent prolapse. This can be avoided by using shorter and softer coils toward the end of coil embolization and careful removal of the microcatheter following coil detachment. The use of a longer and stiffer coil at the start of the procedure to form a stable initial basket also prevents subsequent displacement by other coils.

Various approaches can be used to address herniated and or migrated coils. A stent or balloon may be deployed across the neck of the aneurysm to trap the prolapsed coils within the fundus of the aneurysm. Stent retrievers, Merci devices, or alligator clips may also be employed to retrieve the prolapsed or migrated coil [36]. The displaced coils may precipitate local thrombus formation which should be addressed with a local low-dose intra-arterial glycoprotein IIb/IIIa receptor inhibitor [28, 37].

The most common complications seen with stenting are thromboembolic and include in-stent thrombosis, delayed parent vessel, or stent occlusion. These complications may result in an ischemic stroke, or they can be asymptomatic and discovered on routine follow-up imaging. Such complications are often due to incomplete platelet inhibition which may in turn be the result of patient noncompliance or poor patient response to the administered antiplatelet regimen. In this setting the patient should undergo platelet function testing to determine patient responsiveness and the need for alternative antiplatelet regimens. Intraprocedural thrombus formation may be treated with a local low-dose intra-arterial glycoprotein IIb/IIIa receptor inhibitor.

Unlike their balloon-mounted predecessors, self-expandable intracranial stents are more prone to misplacement and migration as they exert lower levels of outward radial force on the involved vessel. Trans-stent manipulation of microcatheters, guidewires, and additional stents may also cause stent migration. Should this occur during the procedure, the interventionalist may elect to proceed with coiling should the functional neck width preclude herniation of the coil mass. If neck coverage is determined to be insufficient for further treatment a second stent may be placed to enhance coverage.

Shapiro et al. published meta-analyses in 2012 which investigated the complications and clinical and angiographic outcomes of stent-assisted coiling of intracranial aneurysms. They reported a 61% rate of complete aneurysm occlusion at variable time points. Twenty-three percent of these aneurysms were judged to have been incompletely treated but progressed to complete occlusion on follow-up imaging. They found an overall complication incidence of 19%; of these thromboembolic complications were the most prevalent (9.6%) followed by stent-related technical complications (9.3%) including failed delivery and stent migration. Hemorrhagic complications were seen in 2.2% of cases but accounted for 43% of the periprocedural mortality observed. It is somewhat difficult to interpret these results given the heterogeneity of the data utilized in the analyses; comparatively single center series often report lower complication rates and a higher incidence of aneurysm occlusion [38].

Few studies have been published comparing outcomes in balloon remodeling and stent-assisted coiling of intracranial aneurysms. However the single center analysis done by Consoli et al. and Chalouhi et al. reached similar conclusions, namely, that stent-assisted coiling achieved higher rates of aneurysm occlusion with similar rates of periprocedural morbidity [39, 40].

Ultimately complication avoidance is the result of meticulous preparation, patient selection and careful selection of the treatment modality to be employed.

Conclusion

Balloon remodeling and stent-assisted coiling have allowed for the endovascular treatment of previously untreatable intracranial aneurysms. Both adjunctive devices and the techniques associated with them are safe and capable of providing durable embolization of aneurysms.

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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Brian J. A. Gill
    • 1
  • Jason A. Ellis
    • 1
  • Philip M. Meyers
    • 1
  1. 1.Department of Neurological SurgeryColumbia University Medical CenterNew YorkUSA

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