Cerebral Aneurysm Coiling: Techniques, Advances, and Long-Term Outcomes

Cerebral aneurysms represent a significant health concern, affecting approximately 3-5% of the general population. These balloon-like dilations of cerebral blood vessels pose a substantial risk of rupture, leading to devastating subarachnoid hemorrhage with high mortality and morbidity rates. While surgical clipping was historically the mainstay of treatment, endovascular coiling has revolutionized aneurysm management over the past three decades. This comprehensive review explores the evolution, current techniques, clinical evidence, and future directions of cerebral aneurysm coiling.

Historical Evolution of Aneurysm Treatment

From Surgical Clipping to Endovascular Coiling

The journey toward modern aneurysm treatment has been marked by significant milestones:

For most of the 20th century, surgical clipping represented the gold standard for cerebral aneurysm treatment. This approach, pioneered by Walter Dandy in 1937, involves placing a metal clip across the neck of the aneurysm, effectively excluding it from circulation while preserving the parent vessel. Surgical techniques evolved significantly over decades, with the introduction of the operating microscope in the 1960s representing a particularly important advance.

Despite refinements in microsurgical techniques, surgical clipping carried significant limitations:
– Invasiveness requiring craniotomy
– Difficulty accessing certain aneurysm locations (e.g., basilar tip)
– Manipulation of brain tissue and vessels
– Prolonged recovery periods
– Higher complication rates in elderly or medically compromised patients

The concept of endovascular treatment emerged in the 1970s, with early attempts using detachable balloons. However, the true revolution began in 1991 when Guglielmi introduced detachable platinum coils (Guglielmi Detachable Coils or GDCs), which received FDA approval in 1995. This innovation allowed controlled deployment of soft platinum coils into the aneurysm sac, inducing thrombosis and isolating the aneurysm from circulation.

The landmark International Subarachnoid Aneurysm Trial (ISAT), published in 2002, demonstrated improved one-year clinical outcomes with endovascular coiling compared to surgical clipping for ruptured aneurysms amenable to both treatments. This pivotal study led to a paradigm shift in aneurysm management, with endovascular coiling becoming the preferred treatment for many aneurysms, particularly in centers with neurointerventional expertise.

Evolution of Coiling Techniques and Devices

Endovascular coiling has undergone remarkable evolution since its introduction:

First-generation coiling involved the deployment of bare platinum coils into the aneurysm sac. While effective for small, narrow-necked aneurysms, this approach had limitations for complex aneurysm morphologies, including:
– Coil compaction and aneurysm recurrence
– Difficulty treating wide-necked aneurysms
– Risk of coil protrusion into the parent vessel
– Incomplete occlusion rates

These challenges drove the development of adjunctive techniques and advanced coil designs:

Adjunctive Techniques:
– Balloon-assisted coiling (1997): Temporary balloon inflation across the aneurysm neck during coil deployment to prevent coil herniation
– Stent-assisted coiling (early 2000s): Deployment of self-expanding stents across the aneurysm neck to create a scaffold for coil retention
– Flow diversion (2008 onwards): Use of densely braided stents to divert flow away from the aneurysm while maintaining parent vessel patency

Advanced Coil Designs:
– 3D shaped coils: Designed to create a basket-like framework within the aneurysm
– Bioactive coils: Coated with materials to enhance thrombus formation and healing
– Hydrogel-coated coils: Expand when in contact with blood to increase packing density
– Softer finishing coils: Designed for safer filling of small spaces between denser coils

The field has subsequently evolved to incorporate increasingly sophisticated devices and techniques, establishing endovascular coiling as the first-line treatment for many cerebral aneurysms, with surgical clipping reserved for specific anatomical configurations or after failed endovascular attempts.

Current Techniques and Approaches

Patient Selection and Imaging

Appropriate patient selection is crucial for optimal outcomes in aneurysm coiling:

Clinical Considerations:
– Aneurysm status (ruptured vs. unruptured)
– Patient age and comorbidities
– Previous treatments and complications
– Antiplatelet/anticoagulation status
– Allergies to contrast media
– Renal function

Aneurysm Characteristics Affecting Treatment Decision:
– Size: Small (<7mm), medium (7-12mm), large (12-25mm), giant (>25mm)
– Location: Anterior vs. posterior circulation, proximity to branch vessels
– Neck width: Narrow-necked (dome-to-neck ratio >2) vs. wide-necked (dome-to-neck ratio <2)
– Morphology: Saccular, fusiform, dissecting, blister, pseudoaneurysm
– Presence of intraluminal thrombus
– Incorporation of branch vessels
– Parent vessel anatomy and access

Imaging Modalities:
– Digital Subtraction Angiography (DSA): Gold standard for detailed aneurysm evaluation
3D rotational angiography provides comprehensive assessment of aneurysm morphology
Allows dynamic assessment of flow patterns
Essential for precise measurements and treatment planning
– CT Angiography (CTA): Excellent for initial detection and follow-up
Widely available and less invasive
Modern multidetector CTA approaches DSA accuracy for detection
Limited in assessing very small aneurysms or those near bone
– MR Angiography (MRA): Useful for screening and follow-up
No radiation exposure
Time-of-flight and contrast-enhanced techniques
Limited spatial resolution compared to CTA and DSA

Advanced Imaging Techniques:
– Computational fluid dynamics: Assesses flow patterns and hemodynamic stress
– Virtual reality and 3D printing: Enhances pre-procedural planning
– Vessel wall imaging: Evaluates aneurysm wall inflammation and stability

The evolution from simple anatomical assessment to comprehensive multimodal evaluation represents a significant advance in aneurysm treatment planning, allowing more personalized approaches based on individual patient and aneurysm characteristics.

Verfahrenstechniken

Modern aneurysm coiling encompasses several technical approaches:

Basic Coiling Technique:
1. Femoral artery access with appropriate sheath (typically 6F)
2. Navigation of guide catheter to appropriate cervical vessel
3. Advancement of microcatheter into the aneurysm sac under roadmap guidance
4. Sequential deployment of framing, filling, and finishing coils
5. Angiographic assessment of occlusion and parent vessel patency
6. Removal of devices and hemostasis

Balloon-Assisted Coiling (BAC):
– Indicated for wide-necked aneurysms or those with unfavorable dome-to-neck ratio
– Temporary balloon inflation across aneurysm neck during coil deployment
– Allows denser packing and prevents coil herniation
– Requires dual antiplatelet therapy
– Technique variations:
Single-catheter technique with balloon and microcatheter through same guide
Dual-catheter technique with separate access for balloon and microcatheter
Compliant vs. non-compliant balloons based on vessel anatomy

Stent-Assisted Coiling (SAC):
– Indicated for wide-necked aneurysms, particularly sidewall aneurysms
– Self-expanding stent deployed across aneurysm neck creates scaffold for coils
– Requires dual antiplatelet therapy (typically aspirin and clopidogrel)
– Technique variations:
“Jailing” technique: Microcatheter placed in aneurysm before stent deployment
“Trans-cell” technique: Microcatheter navigated through stent struts after deployment
“Semi-jailing” technique: Partial stent deployment during coiling
“Y-stenting” and “X-stenting” for bifurcation aneurysms

Flow Diversion:
– Indicated for large/giant, wide-necked, or fusiform aneurysms
– Dense mesh stent diverts flow away from aneurysm while maintaining branch patency
– Induces progressive thrombosis and endothelialization
– Requires dual antiplatelet therapy (typically for 3-6 months)
– May be used with adjunctive coiling for large aneurysms or in ruptured setting

Intrasaccular Flow Disruption:
– Newer approach using self-expanding devices deployed within the aneurysm
– Examples include Woven EndoBridge (WEB) device and Medina Embolization Device
– Particularly useful for wide-necked bifurcation aneurysms
– May require less or shorter duration antiplatelet therapy than stent-assisted approaches

Technical Considerations:
– Coil selection based on aneurysm size, shape, and location
– Sequential coiling from larger to smaller diameter coils
– Packing density (>20-25%) correlates with lower recurrence rates
– Careful attention to coil loop positioning to avoid parent vessel compromise
– Management of intraprocedural complications (thromboembolism, perforation)

The field continues to evolve with refinements in technique, device design, and approaches to challenging anatomy. The optimal approach varies based on specific aneurysm characteristics, patient factors, and operator experience.

Periprocedural Management

Comprehensive care extends beyond the coiling procedure itself:

Pre-procedural Considerations:
– Antiplatelet management:
Unruptured aneurysms: Dual antiplatelet therapy (typically aspirin and clopidogrel) for 5-7 days before stent-assisted procedures
Platelet function testing to ensure adequate response
Ruptured aneurysms: Loading doses immediately before procedure if stenting required
– Hydration and nephroprotection for patients with renal impairment
– Groin preparation and access site planning
– Anesthesia considerations:
General anesthesia typically preferred for precise control and patient immobility
Conscious sedation acceptable in selected cases
– Baseline neurological assessment
– Informed consent discussing risks, benefits, and alternatives

Intraprocedural Management:
– Systemic heparinization (typically 70-100 units/kg) to achieve ACT 250-300 seconds
– Continuous hemodynamic monitoring
– Maintenance of normothermia
– Judicious fluid management
– Neurophysiological monitoring in selected cases
– Management of intraprocedural complications:
Thromboembolic events: Intra-arterial thrombolytics, glycoprotein IIb/IIIa inhibitors
Aneurysm rupture: Reversal of heparinization, balloon tamponade, additional coiling
Vasospasm: Intra-arterial vasodilators (nimodipine, verapamil)

Post-procedural Care:
– Immediate post-procedure imaging to assess for complications
– Neurological monitoring in intensive care or step-down unit
– Blood pressure management:
Ruptured aneurysms: Careful control to prevent rebleeding
Unruptured aneurysms: Avoidance of extreme hypertension
– Antiplatelet management:
Stent-assisted procedures: Dual antiplatelet therapy for 3-6 months, then aspirin indefinitely
Standard coiling: Antiplatelet therapy individualized based on procedure
– Hydration and monitoring of access site
– Early mobilization when stable
– Patient education regarding warning signs and symptoms

Management of Complications:
– Thromboembolic events (occur in 2-8%):
Clinical assessment and imaging
Consideration of rescue endovascular treatment
Anticoagulation or antiplatelet adjustment
– Intraprocedural rupture (occurs in 2-5%):
Immediate coil deployment to secure rupture site
Reversal of anticoagulation
Management of increased intracranial pressure
Ventricular drainage if hydrocephalus develops
– Groin complications:
Pseudoaneurysm or hematoma management
Ultrasound-guided compression or thrombin injection
Surgical repair for significant complications

Follow-up Protocol:
– Initial imaging at 3-6 months (MRA or DSA)
– Subsequent imaging at 12-18 months
– Long-term surveillance based on occlusion status and risk factors
– Clinical follow-up to assess neurological status and recovery

Optimal periprocedural management requires a multidisciplinary approach involving neurointerventionalists, neurointensivists, anesthesiologists, and specialized nursing care. Protocols for rapid assessment, treatment, and management of complications are essential to maximize good outcomes.

Klinische Nachweise und Ergebnisse

Landmark Trials

A series of pivotal trials established the efficacy of endovascular coiling:

ISAT (International Subarachnoid Aneurysm Trial):
– Published in 2002, with long-term follow-up in 2009
– Randomized 2,143 patients with ruptured aneurysms suitable for both clipping and coiling
– Primary outcome: death or dependency at one year
– Results:
Absolute risk reduction of 7.4% in death or dependency at one year (23.5% vs. 30.9%)
NNT = 13.5 to prevent one death or dependent outcome
Early survival advantage maintained at long-term follow-up
Higher rebleeding rates in coiled aneurysms but still very low overall (0.2% per year)
– Impact: Established coiling as preferred treatment for many ruptured aneurysms

BRAT (Barrow Ruptured Aneurysm Trial):
– Published in 2012, with 6-year follow-up in 2015
– Randomized 471 patients with subarachnoid hemorrhage to intent-to-treat with clipping or coiling
– Results:
Significantly lower poor outcomes in coiling group at 1 year (23.2% vs. 33.7%)
Difference no longer significant at 3 years but trend favored coiling
Crossover rate: 38% from coiling to clipping arm (anatomical unsuitability)
Higher retreatment rates in coiled aneurysms

ISUIA (International Study of Unruptured Intracranial Aneurysms):
– Observational study published in 1998, with treatment outcomes in 2003
– Evaluated natural history and treatment outcomes of unruptured aneurysms
– Results:
Surgical morbidity and mortality: 12.6% at one year
Endovascular morbidity and mortality: 9.8% at one year
Rupture risk varied by size and location
– Impact: Provided data on risks of treatment vs. observation for unruptured aneurysms

HELPS (HydroCoil Endovascular Aneurysm Occlusion and Packing Study):
– Published in 2011
– Randomized 499 patients to hydrogel-coated vs. bare platinum coils
– Results:
No significant difference in major recurrence at 18 months
Hydrogel coils showed lower minor recurrence and higher procedural complications

MAPS (Matrix and Platinum Science Trial):
– Published in 2014
– Randomized 626 patients to Matrix bioactive coils vs. bare platinum coils
– Results:
No significant difference in target aneurysm recurrence at 12 months
No difference in adverse events

These landmark trials established endovascular coiling as an effective treatment for both ruptured and unruptured aneurysms, with lower procedural morbidity but higher recurrence rates compared to surgical clipping. They also demonstrated that advanced coil designs did not necessarily provide superior outcomes to conventional platinum coils in terms of recurrence rates.

More recent trials have focused on comparing different endovascular techniques:

BRANCH (Braided Aneurysm Embolization Device for Intracranial Aneurysm Treatment):
– Evaluated safety and efficacy of the Pipeline Embolization Device for large/giant aneurysms
– High technical success and occlusion rates with acceptable safety profile

WEBCAST (WEB Clinical Assessment of Intrasaccular Aneurysm Therapy):
– Evaluated safety and efficacy of the WEB device for wide-necked bifurcation aneurysms
– Demonstrated high technical success and adequate occlusion rates with low morbidity

These trials have expanded the endovascular armamentarium beyond traditional coiling to include flow diversion and intrasaccular flow disruption for more complex aneurysms.

Real-World Outcomes

Implementation of aneurysm coiling in clinical practice has generally validated trial results:

Effectiveness in Clinical Practice:
– Multiple national and international registries have demonstrated outcomes comparable to clinical trials
– Complete or near-complete occlusion achieved in 80-95% of cases initially
– Long-term complete occlusion rates of 70-85%
– Procedural mortality 0.5-1.5% for unruptured aneurysms, 1-3% for ruptured aneurysms
– Permanent neurological morbidity 3-7% for unruptured aneurysms, 5-10% for ruptured aneurysms

Factors Affecting Outcomes:
– Aneurysm characteristics:
Size: Larger aneurysms have higher recurrence rates
Neck width: Wide-necked aneurysms more challenging to treat
Location: Certain locations (e.g., basilar tip) associated with higher complication rates
Previous rupture: Ruptured aneurysms have higher procedural risks
– Patient factors:
Age and comorbidities impact complication rates and recovery
Hunt-Hess grade in ruptured aneurysms strongly predicts outcome
– Technical factors:
Packing density >20-25% associated with lower recurrence
Complete initial occlusion predicts long-term durability
Use of adjunctive techniques (balloon, stent) may improve occlusion rates but increase procedural risks

Long-term Durability:
– Recurrence rates 15-30% overall, with approximately 10-15% requiring retreatment
– Major recurrence more common in:
Large and giant aneurysms
Wide-necked aneurysms
Initially incompletely occluded aneurysms
Ruptured aneurysms
– Retreatment generally safe with low complication rates
– Rebleeding rates very low after complete occlusion (0.1-0.3% per year)

Quality of Life Outcomes:
– Faster recovery and return to normal activities compared to surgical clipping
– Cognitive outcomes appear favorable compared to surgical approaches
– Long-term quality of life comparable between coiling and clipping in most studies
– Economic analyses generally support cost-effectiveness of coiling despite higher initial costs

The translation of clinical trial results to real-world practice has been largely successful, though challenges remain in ensuring optimal patient selection and long-term follow-up. The higher recurrence rates compared to surgical clipping remain a limitation, but must be balanced against the lower procedural morbidity and mortality of endovascular approaches.

Zukünftige Richtungen

Expanding Indications and Novel Devices

The frontier of aneurysm treatment continues to evolve:

Expanding Applications:
– Previously Challenging Aneurysms:
Blister aneurysms: Flow diversion emerging as preferred treatment
Blood-blister like aneurysms: Combination of stenting and coiling or flow diversion
Fusiform aneurysms: Flow diversion or flow disruption
Dissecting aneurysms: Parent vessel sacrifice or flow diversion
– Distal Aneurysms:
Development of smaller microcatheters and softer coils
Increasing experience with distal access techniques
Novel devices designed specifically for distal locations
– Recurrent Aneurysms:
Strategies for retreatment after failed coiling
Flow diversion as salvage therapy
Intrasaccular flow disruptors for recurrent wide-necked aneurysms

Novel Devices and Approaches:
– Next-Generation Flow Diverters:
Surface modifications to reduce thrombogenicity
Improved visibility under fluoroscopy
Variable porosity designs
Flow diverters with integrated coils
Bifurcation-specific flow diverters
– Advanced Intrasaccular Devices:
Second-generation WEB device with improved deployment
Medina Embolization Device with three-dimensional design
LUNA AES (Aneurysm Embolization System)
Artisse Neck Bridge Device
– Bioactive and Surface-Modified Implants:
Endothelial cell-promoting surfaces
Antiplatelet drug-eluting coatings
Hydrogel technologies with improved properties
Biodegradable materials for temporary support

Biological Approaches:
– Cellular Therapies:
Endothelial progenitor cell-capturing stents
Stem cell delivery to promote healing
– Molecular Targets:
Inhibitors of matrix metalloproteinases
Modulators of inflammation
Growth factors to promote endothelialization
– Gene Therapy:
Targeted delivery of genes promoting vessel healing
Inhibition of pathways involved in aneurysm formation

These advances aim to address current limitations in aneurysm treatment, including:
– Improving long-term durability and reducing recurrence rates
– Reducing the need for long-term antiplatelet therapy
– Enabling treatment of more complex aneurysm morphologies
– Minimizing procedural complications
– Promoting biological healing of the aneurysm and parent vessel

The rapid pace of innovation in this field promises continued improvements in procedural success and patient outcomes, though careful clinical evaluation will be necessary to determine which advances provide meaningful clinical benefits.

Imaging and Computational Advances

Technological progress is enhancing aneurysm evaluation and treatment planning:

Advanced Imaging Techniques:
– High-Resolution Vessel Wall Imaging:
MRI sequences to visualize aneurysm wall inflammation
Identification of unstable or rupture-prone aneurysms
Potential for risk stratification beyond size and location
– 4D Flow MRI:
Non-invasive assessment of complex flow patterns
Evaluation of hemodynamic stress on aneurysm wall
Monitoring changes after partial treatment
– Intravascular Imaging:
Optical coherence tomography for vessel wall assessment
Intravascular ultrasound for device positioning
Assessment of endothelialization after treatment
– Molecular Imaging:
Targeted contrast agents for inflammation
PET tracers for metabolic activity in aneurysm walls
Early detection of aneurysm instability

Computational Modeling:
– Patient-Specific Computational Fluid Dynamics (CFD):
Prediction of flow patterns before and after treatment
Optimization of device selection and positioning
Assessment of rupture risk based on hemodynamic factors
– Virtual Device Deployment:
Simulation of different treatment strategies
Prediction of technical challenges
Optimization of device sizing and configuration
– Artificial Intelligence Applications:
Automated aneurysm detection and measurement
Prediction of rupture risk based on imaging features
Decision support for treatment selection
Automated follow-up assessment

Procedural Guidance Technologies:
– Augmented Reality:
Overlay of 3D aneurysm models during procedures
Integration of multiple imaging modalities
Enhanced spatial understanding of complex anatomy
– Robotic Assistance:
Precise catheter manipulation
Reduction in radiation exposure
Potential for remote procedures in underserved areas
– Real-time Flow Assessment:
Intraoperative assessment of flow modification
Immediate feedback on treatment efficacy
Optimization of device positioning

These technological advances aim to address current challenges in aneurysm management:
– Improving patient selection for intervention vs. observation
– Enhancing risk stratification beyond traditional factors
– Optimizing device selection for individual aneurysm characteristics
– Reducing radiation exposure during procedures
– Providing more precise assessment of treatment success

The integration of advanced imaging, computational modeling, and procedural guidance technologies promises to make aneurysm treatment more personalized, precise, and effective, though implementation in routine clinical practice will require validation of clinical benefit and cost-effectiveness.

Personalized Medicine Approaches

The future of aneurysm management lies in tailoring treatment to individual patient characteristics:

Risk Stratification Beyond Anatomy:
– Genetic Factors:
Identification of genetic variants associated with aneurysm formation and rupture
Familial aneurysm syndromes (polycystic kidney disease, Ehlers-Danlos, etc.)
Pharmacogenomic approaches to optimize antiplatelet therapy
– Molecular Biomarkers:
Circulating markers of inflammation and vascular remodeling
MMP-9, IL-6, and other inflammatory mediators
Potential for blood tests to assess rupture risk
– Advanced Imaging Biomarkers:
Aneurysm wall enhancement on MRI
Irregular shape and daughter sacs
Flow patterns and wall shear stress
Growth dynamics over time

Tailored Treatment Selection:
– Decision Support Algorithms:
Integration of multiple risk factors
Prediction of rupture risk vs. treatment risk
Recommendation of optimal treatment modality
– Device Selection Based on Aneurysm Biology:
Matching device properties to aneurysm wall characteristics
Consideration of flow dynamics in device selection
Personalized antiplatelet regimens based on patient factors
– Precision in Unruptured Aneurysm Management:
Moving beyond size-based decision making
Incorporating multiple risk factors for individualized recommendations
Shared decision making with fully informed patients

Long-term Management Strategies:
– Personalized Follow-up Protocols:
Risk-based surveillance intervals
Selection of optimal imaging modality
Duration of follow-up based on occlusion status and risk factors
– Targeted Medical Therapies:
Medications to stabilize aneurysm walls
Anti-inflammatory approaches
Modulation of hemodynamic stress
– Lifestyle Modifications:
Smoking cessation programs
Blood pressure management
Other modifiable risk factor interventions

The personalized medicine approach aims to move beyond the “one-size-fits-all” paradigm in aneurysm management, recognizing the heterogeneity in aneurysm biology, patient characteristics, and treatment responses. This approach promises to optimize the risk-benefit ratio of interventions by ensuring that each patient receives the most appropriate treatment at the most appropriate time.

Implementation challenges include the need for large datasets to validate predictive models, integration of multiple data sources in clinical decision making, and demonstration of cost-effectiveness compared to current approaches. However, the potential benefits in terms of improved patient outcomes and resource utilization make this an important direction for future research and clinical practice.

Medizinischer Haftungsausschluss

Wichtiger Hinweis: This information is provided for educational purposes only and does not constitute medical advice. Cerebral aneurysm coiling requires specialized training, equipment, and expertise. The techniques described should only be performed by qualified healthcare professionals with appropriate training in neurointerventional procedures. Patient selection and management decisions should be made on an individual basis considering all relevant clinical factors. This article is not a substitute for professional medical judgment, diagnosis, or treatment. Patients with suspected or confirmed cerebral aneurysms should consult with qualified healthcare providers for appropriate evaluation and management.

Schlussfolgerung

Endovascular coiling of cerebral aneurysms represents one of the most significant advances in neurovascular treatment in recent decades, offering a minimally invasive alternative to traditional surgical approaches. The evolution from the introduction of detachable coils to the current era of sophisticated devices and techniques has dramatically expanded treatment options for patients with both ruptured and unruptured aneurysms.

The overwhelming evidence from randomized controlled trials and large observational studies has established endovascular coiling as the first-line treatment for many cerebral aneurysms, with lower procedural morbidity and mortality compared to surgical clipping, though at the cost of somewhat higher recurrence rates. The development of adjunctive techniques such as balloon and stent assistance, along with newer approaches like flow diversion and intrasaccular flow disruption, has further expanded the range of aneurysms amenable to endovascular treatment.

Current techniques continue to evolve, with ongoing refinements in device design, procedural approaches, and periprocedural management. The real-world implementation of coiling has generally validated trial results, though challenges remain in ensuring optimal patient selection and long-term durability.

The future of aneurysm treatment lies in expanding indications to include more complex aneurysm morphologies, technological innovations to improve procedural success and durability, advanced imaging and computational techniques to enhance treatment planning, and personalized approaches tailored to individual patient characteristics. As these advances continue, the devastating impact of aneurysmal subarachnoid hemorrhage may be significantly reduced for an ever-growing number of patients worldwide.

The field of cerebral aneurysm treatment exemplifies the power of multidisciplinary collaboration, technological innovation, and rigorous clinical research to transform patient care and outcomes. The continued evolution of endovascular techniques promises further improvements in the management of this challenging neurovascular condition.