What is a brain aneurysm coil?

Brain Aneurysm Coil: An Endovascular Treatment Device

A brain aneurysm coil is a thin platinum wire that is inserted into a cerebral aneurysm through minimally invasive endovascular techniques to prevent rupture by promoting blood clot formation within the aneurysm sac, effectively excluding it from circulation and reducing the risk of hemorrhagic stroke. 1

What Are Brain Aneurysm Coils?

Brain aneurysm coils (most commonly known as Guglielmi Detachable Coils or GDCs) are medical devices used in the endovascular treatment of cerebral aneurysms. These coils have several key characteristics:

• Made primarily of platinum
• Available in various sizes and lengths
• Can form complex shapes when deployed within an aneurysm
• Detachable from a delivery wire using electrical current
• Introduced through a microcatheter via femoral artery access
• FDA approved since 1995 for treating surgically unclippable aneurysms 1

How Coiling Works

The coiling procedure involves several steps:

1. A microcatheter is navigated through the arterial system to the aneurysm
2. Platinum coils are sequentially deployed into the aneurysm sac
3. The first coil creates a mesh framework
4. Additional softer coils of decreasing diameter are packed into the aneurysm
5. The coils induce blood stagnation and thrombus formation
6. Over time, tissue grows over the coils, permanently excluding the aneurysm from circulation 1, 2

Types and Advancements in Coil Technology

Since their introduction, coil technology has evolved significantly:

• Standard platinum coils (original GDCs)
• Multidimensional coils for safer initial placement
• Softer coils for better packing density
• Biologically active coils to improve efficacy (though efficacy remains unproven)
• Various sizes to accommodate different aneurysm dimensions 1, 3

Effectiveness and Outcomes

Coiling has demonstrated significant benefits for treating cerebral aneurysms:

• The International Subarachnoid Aneurysm Trial (ISAT) showed endovascular coiling resulted in better outcomes than surgical clipping for ruptured aneurysms
• 22.6% relative risk reduction in death or disability at 1 year compared to surgical clipping
• Lower rate of seizures compared to surgical clipping
• Survival advantage maintained up to 7 years after treatment 1

However, important limitations exist:

• Complete occlusion is achieved in only about 54% of aneurysms on initial treatment
• Approximately 17.4% of coiled aneurysms require retreatment (compared to 3.8% for clipped aneurysms)
• Follow-up angiography and potential additional coiling are often necessary 1

Adjunctive Techniques

For complex aneurysms, especially those with wide necks, additional techniques may be used:

• Balloon-remodeling: temporary balloon inflation during coil deployment
• Stent-assisted coiling: permanent stent placement to prevent coil herniation
• Pipeline stents for giant aneurysms
• Combined approaches using both coils and flow-diverting stents 1, 4

Clinical Considerations and Patient Selection

The decision to use coiling versus surgical clipping depends on several factors:

• Aneurysm location: posterior circulation and cavernous segment aneurysms are often better suited for coiling
• Aneurysm size: very small (<3mm) and very large aneurysms present challenges for coiling
• Neck width: narrow-necked aneurysms (neck <5mm and ratio of neck to dome <0.5) are ideal for coiling
• Patient factors: age, medical comorbidities, and contraindications to contrast agents 1

Safety Profile

Endovascular coiling has demonstrated favorable safety outcomes:

• Procedural mortality rate of approximately 1.3%
• Morbidity rate around 2.6%
• Most patients with complications can still achieve independent functioning 5

Common Pitfalls and Limitations

Important considerations when evaluating coiling as a treatment option:

• Incomplete occlusion requiring follow-up imaging and potential retreatment
• Aneurysm recurrence, particularly in large and giant aneurysms
• Need for long-term angiographic follow-up
• Technical challenges with wide-necked or complex aneurysms
• Requirement for anticoagulation during the procedure 1, 2

Brain aneurysm coils represent a significant advancement in the treatment of cerebral aneurysms, offering a minimally invasive alternative to open surgical clipping with demonstrated benefits for patient outcomes in appropriately selected cases.