Endovascular thrombosis or embolization or Microcoil Thrombosis (coiling) is a procedure that was introduced in 1990 as a less invasive alternative to surgical clipping. It is similar to the cerebral angiogram but instead of simply taking pictures as the contrast medium (dye) is injected into the artery, the aneurysm is treated from the catheter inside the blood vessel by the insertion of coils into the aneurysm’s sac. The coils are packed into the aneurysm. They promote blood clotting within the aneurysm. Both coils and clotting fill the aneurysm closing it off and preventing blood from entering.

Balloon-assisted coiling involves a tiny balloon catheter which covers the neck or entrance to the aneurysm, holding the coils in place. Stent-assisted coiling involves a small cylindrical mesh tube which acts as a scaffolding within the aneurysm for the mass of coils. The development of supple, more flexible stents and balloons has allowed stent-assisted and balloon-assisted coiling of irregular fusiform and wide-necked aneurysms in some cases.

Angiogram: Many large coils in giant skull base aneurysm. Balloons have been detached below the coils to ensure the ICA interior communicating artery is closed.
Courtesy of Dr. Kieran Murphy, Johns Hopkins University, Department of Radiology

Coiling does not involve surgically opening the head and may be done under local or general anesthesia. Barring complications the hospital stay for the procedure is generally 1-2 days and the recovery usually takes 5-7 days (American Stroke Association).

3-D reconstruction with Vitrea software, computer enhanced red coloring of coiled aneurysm. - Click image for a larger view.
Courtesy of Dr. Kieran Murphy, Johns Hopkins University, Department of Radiology

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Coiling Procedure

Coiling is performed by a neuroradiologist or endovascular surgeon. The femoral artery is accessed through a tiny incision in the groin/inner thigh where a thin hollow tube or sheath is inserted into the artery wall to allow the introduction of a catheter which is inserted and guided by a guidewire through the artery and up towards the brain. This process is guided with the use of computer-aided X-ray scanners.

Once the catheter is in place, the guidewire is removed, leaving the catheter in place. A contrast dye is introduced via the catheter into the bloodstream in order to make the artery and the aneurysm clearly visible and to aid in obtaining clear radiographic images. The characteristics of the aneurysm, including shape, size and exact location, are determined and recorded. This portion of the procedure is similar to an angiogram.

A microcatheter is then introduced through the larger catheter and used to deliver coils through the neck and into the sac of the aneurysm. The platinum coils are shaped like springs and are approximately twice the thickness of a human hair. There are several types of coils which vary as to shapes, pliability and levels of softness. They are attached to the end of the microcatheter. The coils placed are of progressively smaller sizes. They are individually placed and detached from the microcatheter by a small electric current. Within the microcatheter the coils are straight but, after placement in the aneurysm, they bend in a helix shape and conform to the shape of the aneurysm walls.

They then form a mesh similar to steel wool. Eventually, blood cells are caught and clot on this mesh in a process called "thrombosis", effectively filling and sealing off the aneurysm from the artery circulation. Thus, as the procedure is completed, the interventional radiologist will see the aneurysm slowly darken and fade until it disappears into the surrounding brain material, effectively out of the blood circulation.

There is the possibility that a coil could protrude or be dislodged from the aneurysm and reintroduced into the artery, although this is rare in experienced hands. This could cause a clot or stroke. For this reason, neuroradiologists often rule out coiling for aneurysms with a large neck-to-dome (neck-to-sac) ratio. (Johnston et al, 2000). There is also the possibility of a small aneurysm remnant occurring at the neck to the aneurysm as a result of incomplete coiling. Again, this is less likely in experienced hands. What happens to such a remnant is still being researched by the medical community. However, there is a risk that a remnant could grow or allow coils to compact over time.

Possible complications include rupture of the aneurysm during treatment, damage to the artery and bleeding into the brain which could result in brain damage. This could lead to:

Weakness or paralysis of an arm or a leg
Difficulty with speech or understanding
Vision impairment
Confusion, memory loss and/or seizures

The anesthesia used during the procedure also has the associated risks:

Infection
Bleeding
Kidney damage from X-ray dyes

If there are complications or a hemorrhage event, the hospital stay could be 10-14 days or more.

See Treatment – Recovery and Treatment – Risks for more details.

Angiogram: DSA disgnostic angiogram of the previous case showing a successfully coiled aneurysm.
Courtesy of Dr. Kieran Murphy, Johns Hopkins University, Department of Radiology

Preparing for the Procedure

If treatment is undertaken following a rupture, it is likely that it will be done within a short time of your arrival in the hospital emergency room. It is important to have as thorough a discussion of treatment options with your doctor as your situation permits. If more time is available, as in the case where the aneurysm is discovered prior to rupture, you will have the opportunity to question the neuroradiologist or endovascular surgeon more closely about the risks and benefits of the treatment and what to expect during and after treatment. Important questions may include the frequency and success rate of the doctor and the hospital performing the procedure, potential complications, recovery time both in the hospital and at home, and the advisability of screening close family members for aneurysms.

Assuming an unruptured aneurysm, you will first attend a pre-operative appointment scheduled, usually the day before your surgery, wherein you will undergo testing (blood tests, EKG, chest X-ray, etc.). The doctor will explain the procedure, risks, and ask you to sign release forms. You should come prepared to discuss your medical history including any medications you are currently taking. Make sure you are aware of the guidelines for your hospital with respect to not eating before general anesthesia.

Also in the pre-operative appointment, an anesthesiologist will discuss the use of anesthesia during the procedure. General anesthesia is typically used in this procedure for patient comfort, to keep the head immobile and to assure the quality of the X-ray images. Let the doctor know ahead of time if you have a problem recovering from anesthesia. There are medications that can aid in recovery from anesthesia.

Present for procedure: Interventional neurologist, fellow (in academic medical institution), Anesthesiologist (stays whole procedure) for coiling, nurses, angiotechs (responsible for assisting with equipment, redording data). - Click image for a larger view.
Courtesy of Dr. Kieran Murphy, Johns Hopkins University, Department of Radiology

On the day of surgery catheter will be inserted to monitor urine production. An IV (intravenous) line will be inserted in order to monitor blood and deliver medications.

To gain access to your femoral artery, your groin is shaved, scrubbed and sterilized. The team decides whether to use one or both arteries based on the aneurysm characteristics and the tools necessary to treat it. Your body is then covered with sterile wraps, leaving only the groin area exposed.

The anesthesiologist will administer your anesthesia. Upon completion of the procedure, you will likely be moved to the ICU (Intensive Care Unit) where you will be monitored closely for 24 to 36 hours or so. The sheath will remain in place for 24 or more hours. You will likely feel quite drowsy and may experience mild nausea from the anesthesia.

You will be asked not to bend the leg with the sheath in place.