What are coils, and how are they used to treat a brain aneurysm?
Coils are platinum spirals placed inside an aneurysm through a catheter, without opening the skull. Learn what they are intended to do, when they may be used, and what monitoring they require.
By Dr. Martin Roberto Casas MartínezSep 13, 20266 min read
In this article
Summary: Coils are very thin platinum wires, thinner than a strand of hair, that are placed inside a brain aneurysm through a catheter without opening the skull. By filling the sac, they encourage a blood clot and scar tissue to form, reducing blood flow into the aneurysm and the risk of rupture. They are not appropriate for every aneurysm and require imaging follow-up.
When a specialist recommends embolization, it’s natural to want to understand what coils are and how they’re used to treat a brain aneurysm before making a decision. Here, you’ll find a plain-language explanation of what they are, how they’re delivered, what the procedure aims to do, and what follow-up may be needed.
What exactly is a coil?
A coil (also called a spiral or microcoil) is a soft, very thin platinum wire wound into a small bundle. Its purpose is to fill the inside of the aneurysm so that blood no longer flows freely through it.
There are uncoated, coated, and bioactive coils; the medical team chooses the type based on the aneurysm. The term embolization describes the entire procedure: placing material inside a blood vessel to block or reduce blood flow; when coils are used, it is called coil embolization.
How does the coil reach the aneurysm?
Coils are delivered endovascularly, meaning from inside the blood vessels. The doctor inserts a catheter (a long, thin, flexible tube) through a small incision, usually in the groin, and guides it with real-time imaging to the artery in the brain where the aneurysm is located.
Once the tip of the catheter is inside the aneurysm sac, one or more coils are inserted and unfurled inside it. In some cases, a stent (a tubular metal mesh) is also placed in the artery across from the aneurysm’s neck to help keep the coils in place.
The procedure is performed under general anesthesia or with sedation, depending on the person. Like any procedure involving the arteries of the brain, it carries risks (bleeding, blood clot formation, or damage to the blood vessel), which the specialist explains before a decision is made.
What is the procedure intended to achieve?
The goal is to exclude the aneurysm from the bloodstream. When the coils fill the sac, blood stagnates, a clot forms, and the body responds by forming scar tissue around the coils. This process helps block blood from entering and reduces the risk of rupture.
The procedure does not remove the aneurysm or ensure that it will be completely closed in every case. The result depends on the aneurysm’s size, the shape of its neck (the area where it joins the artery), and the technique used. The care team assesses how it was treated and determines the follow-up plan.
A ruptured aneurysm is an emergency. The appropriate course is 911, not a scheduled appointment.
Are coils suitable for every aneurysm?
No. Coil embolization is an option for some aneurysms, but not all. The shape of the aneurysm, particularly its neck, affects whether coils can be placed securely. In some cases, a supporting stent or balloon, or a different device, may be needed.
Other factors include the aneurysm’s location and size, the person’s clinical condition, and whether it has ruptured before. For this reason, the choice between coils, surgical clipping (open surgery in which a clip is placed at the base of the aneurysm), or another option is made individually by the treating team based on imaging studies.
If a flow diverter (a more densely woven stent that redirects blood away from the aneurysm) has been recommended instead of coils, or in addition to them, that choice reflects specific features of your aneurysm.
Why is follow-up needed afterward?
Imaging follow-up is part of treatment after coil embolization. Over time, the coils may compact, leaving space for blood to flow back in. The aneurysm may grow again and require additional treatment.
If the neck was not completely closed, it is also monitored for changes. The care team determines the timing and type of imaging studies (angiography, CT angiography, or MR angiography—different ways of viewing the brain’s arteries) based on how the treatment turned out.
If you suddenly develop a severe headache that is different from your usual headaches, weakness on one side of your body, difficulty speaking, vision changes, or confusion after the procedure, call 911 immediately; do not wait for your next appointment.
Frequently asked questions
Do coils stay inside the head permanently?
Yes. Coils are permanent implants: they remain inside the aneurysm and are not removed later. The tissue that forms around them is part of the intended effect. Ask your care team if you have questions about compatibility with future imaging studies.
Can coils be used if the aneurysm has already ruptured?
Yes. Embolization is used for both ruptured and unruptured aneurysms. For a ruptured aneurysm, care begins in the emergency department, and the hospital team decides how to close it based on the person’s condition and the aneurysm’s characteristics.
What happens if the aneurysm fills with blood again after coil placement?
The coils may compact, allowing blood to flow into the aneurysm again. That is why follow-up imaging is ordered. If this happens, the care team will assess whether additional treatment is needed, which may involve another embolization or a different technique.
What should I ask before the procedure?
If you have sudden neurological symptoms, call 911 first. If you’re considering scheduled embolization, these questions may help during your consultation:
- •Why is coil embolization recommended in my case instead of another option, such as clipping?
- •Will only coils be used, or will a stent or another supporting device also be used, and what does that involve?
- •What risks does the procedure pose in my situation, and what follow-up tests will I need?
- •What signs should I watch for afterward, and when should I call 911?
For non-urgent questions or to request an individual assessment, you can contact the office.
Informational notice: This content is for informational purposes and does not replace a medical consultation or constitute a diagnosis.
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