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Endovascular Treatment (Coiling) of Cerebral Aneurysms

Until the early 1990s, the only treatment for a cerebral (brain) aneurysm has been opening the head (craniotomy, see Craniotomy) and placing a special clip across the neck of the aneurysm. In an acutely ill patient with a ruptures aneurysm and swollen brain, craniotomy is a formidable task fraught with many problems. In up to 70-90% of patients, an alternative is coiling of the aneurysm, which may spare the patient neurological complications that sometimes occurs with open surgery. Coiling involves placing a fine platinum wire into the aneurysm through a small catheter. The wire causes the aneurysm to clot off from the cerebral circulation, negating the risk of rupture in most cases,

Anatomy and Physiology

  • Blood leaving the heart enters the aorta, the main central artery of the body
  • The first arterial branches off of the aorta are the innominate artery (also called the brachiocephalic trunk), left common carotid artery and the left subclavian artery. The innominate artery gives rise to the right common carotid and subclavian arteries (Figure 1)
  • In the neck the common carotid arteries branch into the internal and external carotid arteries, the internal carotid arteries extending upwards in the front of the neck. The vertebral arteries on each side pass upwards in the back of the neck
  • The right and left internal carotid arteries divide into the anterior and middle cerebral arteries and feed blood to the front part of the brain including the frontal, parietal and temporal lobes (Figure 1). The right and left vertebral arteries come together to form the basilar artery, which then divides into the posterior cerebral arteries to feed the back part of the brain. (See Craniotomy for anatomy of the brain)
  • The wall of the arteries is made up of an inner layer, the endothelium, an elastic layer, a muscle layer and a thin outer layer, the adventitia.
Figure 1 - Arterial anatomy from the aorta to the arteries of the head. © P. Montelone

Pathology

  • An aneurysm forms because of a break in the elastic and muscle layer of the artery allowing the artery to balloon out. Occasionally a patient is born with the defect and the aneurysm is seen in a relatively young patient, but this is rare. More often the aneurysm forms in the later years due to degeneration (break down) of the muscle layer
  • The defect in the muscle is almost always at the angle formed by a branching in artery. This causes the thin endothelium and adventitia to balloon out like a berry on a branch of a tree, thus the term berry aneurysm (Figure 2)
  • The other form of aneurysm occurs when a larger section of artery degenerates causing the artery to balloon out like a sausage. This is called a fusiform aneurysm (Figure 3)
  • Various factors may contribute the formation of an aneurysm
    1. Smoking and alcohol use appear to accelerate degeneration of arteries
    2. There also appears to be a correlation between the use of oral contraceptives and aneurysm formation
    3. A family history of cerebral aneurysm
    4. Certain other inherited diseases such as Polycystic Kidney Disease, Fibromuscular dysplasia, Ehler's Syndrome and Marfan's Syndrome
    5. High blood pressure (hypertension) is commonly associated with aneurysms
    6. Artherosclerosis (hardening of the arteries) may also be a factor
    7. Aneurysms larger than 10 mm (slightly over one fourth inch) have a greater tendency to rupture
    8. With any head injury, an artery may be injured with formation of an aneurysm
Figure 2 - Berry aneurysm. Courtesy Michigan Stoke Network. © T. Graves Figure 3 - Fusiform aneurysm. Courtesy Michigan Stoke Network. © T. Graves

History and Examination

  • Aneurysms that have not ruptured
    1. Headache is usually not a symptom of an unruptured aneurysm. While a patient with an unruptured aneurysm may have headaches, the headache is rarely related to the aneurysm
    2. In some patients, a severe headache that goes away may precede by days or weeks the rupture of an aneurysm. This is called a sentinel headache. The exact cause is unknown but may be due to a very small leak of blood
    3. An unruptured aneurysm may press on one of the nerves that control eye movement and the size of the pupil of the eye. This causes double vision and the pupil to be dilated. This may also be associated with pain above and behind the eye
    4. Pressure on the optic nerve may cause loss of vision
  • Ruptured aneurysms
    1. The sudden onset of a very severe headache ("The worst headache I have ever had.") is typical of a ruptured aneurysm. This is caused by blood in the fluid that bathes the brain and spinal cord (cerebrospinal fluid). This is called a subarachnoid hemorrhage (SAH)
    2. Nausea and vomiting
    3. Stiff neck
    4. Sensitivity to light
    5. Rarely the patient does not have a headache but complains of chest pain simulating a heart attack
    6. Rupture of an aneurysm is more common in women
    7. Rupture of an aneurysm increases with increasing age. It is most common around 60 years of age
    8. All the signs of a stroke can be caused by a ruptured aneurysm including paralysis, loss of feeling, loss of vision and loss of speech

Tests

  • Computerized Axial Tomogaphy (CAT Scan) - Occasionally an unruptured aneurysm may be seen on a CAT scan obtained for another reason such as following a minor head injury. Following an SAH, a CAT scan is usually the first imaging study since in almost all cases blood can be seen in the subarachnoid space
  • Magnetic Resonance Imaging (MRI) - An MRI can also demonstrate an unruptured aneurysm though usually with better clarity than an CAT scan
  • Lumbar puncture (spinal tap) - A needle is placed into the spine and cerebrospinal fluid is removed to look for evidence of blood. This test is usually done when SAH is suspected but the CAT scan fails to demonstrate blood
  • CTAngiogram (CTA) - An CTA is a computer reconstruction of the blood vessels of the brain by CAT scan after the patient is given intravenous a dye containing iodine, which outlines the vessels. This test can accurately show the relationships of the aneurysm to surrounding vessels
  • MRAngiogram (MRA) - Computer reconstruction of the cerebral vessels can also be obtained by MRI and show an aneurysm
  • Femerocerebral Angiogram (FCA) - The standard for defining an aneurysm is an FCA. A catheter is placed into the femoral artery in the groin and guided under fluoroscopy (a special type of X-ray) into the carotid artery. An iodine containing dye is then injected into the artery and serial images obtained of the cerebral vessels. This test gives the clearest image of the aneurysm and allows mapping of the neck and flow of blood into the aneurysm in three dimensions. This test always precedes endovascular coiling of an aneurysm
  • Before endovascular coiling, the patient is evaluated with complete blood count, blood clotting tests, blood electrolyte content, urine analysis, electrocardiogram (ECG) and chest X-ray

Indications

  • Endovascular coiling of an aneurysm has the same indications as for surgical clipping of an aneurysm whether the aneurysm has ruptured or not
  • In most institutions there is a close relationship between the neurosurgeon and the endovascular surgeon. In general, about 70% of aneurysms can be coiled. When, in the opinion of the endovascular surgeon, the aneurysm cannot be coiled the patient is transferred to the care of the neurosurgeon for surgical clipping
  • Endovascular coiling has the distinct advantage that it can be used even when the patient is not a candidate for surgery due to age or significant medical conditions

Procedure

A thorough neurological examination is carried out before the procedure

  • Hours prior to the procedure the patient is given intravenous fluids to be sure the patient is well hydrated
  • If there is a lot of blood in the CSF and/or there is evidence of increased pressure in the head, a catheter may be placed into the fluid spaces inside the brain (ventricles) to remove some of the blood and reduce the pressure
  • A urinary catheter is inserted
  • The patient is placed on dexamethasone (cortisone-like medication) and nimodipine (a medication that reduces spasm in the arteries)
  • The patient is placed on a special X-ray table in a special suite designed for this purpose
  • Blood pressure, ECG and blood oxygen are continuously monitored during the procedure
  • Medication for control of blood pressure are kept immediately available
  • It absolutely necessary that the patient not move during the procedure. In patients that are fully cooperative, intravenous sedation medication is given. In patients that cannot cooperate fully, a general anesthetic is necessary
  • Both groins are shaved and prepped with an antiseptic solution and sterilely draped
  • A special needle is inserted into the femoral artery in the groin. A guide wire is placed into the artery and the needle removed after which an introducer catheter is inserted into the artery
  • The patient is given heparin to prevent blood clotting
  • The various special catheters necessary for the procedure are then place through the introducer catheter and guided through the aorta (large central artery in the body) into the carotid or vertebral artery and then toward and into the aneurysm
  • First a fine guide wire is placed into the neck of the aneurysm (Figure 4). Then a thin (1-2 mm) catheter is inserted into the neck of the aneurysm and the wire removed (Figure 5)
  • The special coil wire is then placed through the catheter (Figure 6). This coil wire is composed of a special platinum wire designed to cause clotting in the aneurysm. Some wires are coated with material that increases clotting
  • The wire is packed as tightly as possible into the aneurysm
  • If the neck of the aneurysm is narrow, the coil generally does not bulge into the artery. It is important that the coil not narrow the artery since this may cause the artery to block and cause a stroke
  • The coil wire is finally detached by passing a small electrical current that cuts the wire (Figure 7) leaving the platinum coil in place (Figure 8).
  • The wire, catheter and introducer catheter are removed and the artery plugged at the point of catheter entrance
  • In wider necked aneurysms, a stent may be placed across the mouth of the aneurysm and the coil placed through one of the side openings of the stent into the aneurysm (Figure 9). The stent prevents the coil from falling into the artery
  • The blood thinner is reversed and a final angiogram obtained to evaluate the effect of the coiling
  • The patient is then carefully watched in the intensive care unit to be sure there is no bleeding from the femoral puncture site and for any evidence of neurological change
Figure 4 - Guide wire placed in narrow neck aneurysm. Courtesy Michigan Stoke Network. © T. Graves Figure 5 - Catheter moved into aneurysm. Courtesy Michigan Stoke Network. © T. Graves
Figure 6 - Guide wire removed and platinum wire for coiling placed in aneurysm and packed as tight as possible. Courtesy Michigan Stoke Network. © T. Graves Figure 7 - Platinum wire detached by passing small electrical current. Courtesy Michigan Stoke Network. © T. Graves
Figure 8 - Catheter removed leaving coil in aneurysm. Courtesy Michigan Stoke Network. © T. Graves Figure 9 - With wide neck aneurysm, a stent is placed across the aneurysm neck to prevent the platinum wire from falling into the artery. Platinum wire is inserted into the aneurysm through one of the openings in the stent. Courtesy Michigan Stoke Network. © T. Graves

Complications

  • The aneurysm may rupture during the procedure
  • The artery leading to the aneurysm may block and cause a stroke. Should a stroke happen it is necessary to take the patient back for angiography. If there is a clot in the artery, a catheter can be placed in the artery and medication infused that may break up the clot in the artery
  • The coil may migrate into the artery and cause a stroke
  • The artery leading to the aneurysm may tear causing bleeding
  • The coil may not clot the aneurysm and the aneurysm may continue to grow requiring an additional coiling procedure
  • There may be hemorrhage at the femoral puncture site
  • Because there is blood in the CSF from the ruptures aneurysm, the arteries of the brain may go into spasm causing a stroke, which can be massive. The spasm usually occurs between 4 and 10 days after the aneurysm ruptures. In most instances the spasm may be managed with medications

Post Operative Care

  • The patient is placed in the intensive care unit and carefully watched particularly as regards the neurological condition of the patient
  • The patient's blood pressure is carefully monitored and controlled as best as possible
  • If the patient is unconscious, an endotracheal tube is placed in the windpipe and the patient's respiration is controlled
  • MRI and CAT scans may be necessary as needed
  • Angiography is usually repeated at 1 and 3 days after the coiling to determine the degree of clotting in the aneurysm. Additional coiling may be required
  • The presence of a stent may require the use of blood thinner medication for months or years
  • A special ultrasound test called Transcranial Doppler may be used to determine if vasospasm is developing. If so, treatment for this problem is started

After Care

  • The patient is usually brought back after one year for angiography to evaluate the aneurysm
  • Stop smoking
  • Control high blood pressure
  • Neurological rehabilitation may be necessary if the patient has had a stroke
  • Follow up with your doctor at regular intervals