What is Intracranial Artherosclerosis?
Intracranial Artherosclerosis is a narrowing of an artery in the brain due to buildup of plaque inside the artery wall. This buildup reduces blood flow to the area of the brain that the affected vessels supply. This process of plaque buildup is known as atherosclerosis, or “hardening” of the arteries, and is similar to carotid stenosis in the neck. Atherosclerosis that is severe enough to cause symptoms carries a high risk of stroke, which can lead to brain damage and death.
It is important to understand the circulatory system of the brain in order to have a better understanding of arterial stenosis. Blood is carried to the brain by two paired arteries, the internal carotid arteries and the vertebral arteries. The internal carotid arteries supply the front areas and the vertebral arteries are responsible for the back areas of the brain. After passing through the skull, the right and left vertebral arteries join together to form a single basilar artery. The basilar artery and the internal carotid arteries “communicate” with each other in a ring at the base of the brain called the Circle of Willis. The arteries that are most commonly affected by stenosis are the internal carotid artery (ICA), the middle cerebral artery (MCA), the vertebral arteries, and the basilar artery.
The three ways in which intracranial artherosclerosis can result in a stroke include the following:
- Plaque continues to grow larger, severely narrowing the artery and further reducing the blood flow to the brain, to the point where the artery will eventually be completely blocked (occluded).
- Plaque can roughen and deform the artery wall, which causes blood clots to form, thereby blocking blood flow to the brain.
- Plaque can break away from the inner artery wall, traveling downstream where it can get lodged in a smaller artery and block blood flow to the brain.
Causes of Intracranial Artherosclerosis
Atherosclerosis is a major cause. Atherosclerosis begins with damage to the inner wall of the artery caused by high blood pressure, diabetes, smoking, and elevated “bad” cholesterol. Other risk factors include obesity, heart disease, family history, moyamoya disease, radiation-induced vessel damage, and advanced age. Atherosclerosis can begin in early adulthood but most patients do not notice symptoms until decades later. It also progresses at varied rates.
Who is affected?
Eight to ten percent of strokes in the United States are caused by intracranial stenosis. Researchers have shown this disease to affect African Americans, Asian Americans, and Hispanics more than other ethnic groups. Patients with intracranial artery disease tend to be younger than those with carotid artery disease in the neck.
Diagnosing Intracranial Artherosclerosis
In order to diagnose intracranial artherosclerosis, the physician takes into account the current symptoms, current and previous medical problems, current medications, family history, and physical exam, along with a series of diagnostic imaging tests. This information will allow the physician to detect narrowing of the intracranial arteries, come up with a probable cause of the stensosis, and determine the best treatment options.
MRI (magnetic resonance imaging) produces images of body structures using magnetic fields and computer technology. These images clearly show various types of nerve tissue and clear pictures of the brain stem and posterior brain. MRI of the brain can also help to determine whether there are signs of prior mini-strokes (TIA’s). MRI shows the location and extent of brain injury in the same way that a CT would, however, the image produced by MRI is sharper and more detailed than a CT. This is what makes MRI the scan of choice when diagnosing small, deep injuries.
MRA (magnetic resonance angiogram) is a noninvasive study also conducted in a magnetic resonance imager. The only difference is that this study provides an image of the arteries in your head and neck and can help detect blockage and aneurysms.
NOVA software is a flow analysis system that works with MRA to produce a 3D model of the vasculature, allowing the anatomy to be viewed from all angles. NOVA is the first system to offer fast, accurate, and non invasive determination of volumetric flow rates, velocity, waveforms, and flow direction. MRI and MRA with NOVA sequencing are almost always ordered when patients are suspected of stroke. Together these tests allow the physician to diagnose the problem and come up with the best treatment option. These are both noninvasive tests, although some patients may experience claustrophobia in the imager. It is important to let the office know if you are claustrophobic when they call to schedule your scan.
Computed tomography (CT or CAT scan) is a diagnostic image created after a computer reads x-rays. In some cases, iodine solution is injected through a vein in order to highlight brain structures. Bone, blood, and brain tissue have very different densities that can easily be distinguished on a CT scan. A CT scan is a useful diagnostic test for hemorrhagic strokes because blood can easily be seen. However, damage from an ischemic stroke may not be revealed on a CT scan for several hours or days and the individual arteries in the brain cannot be seen. CTA (CT angiography) allows clinicians to see blood vessels of the head and neck by injecting a contrast agent into the blood stream.
Doppler ultrasound is another test used to help detect plaque, blood clots, or other problems with blood flow in the arteries. A water-soluble gel is placed on the skin where the transducer (a handheld device that directs the high-frequency sound waves to the arteries being tested) is then placed. The gel helps transmit the sound to your skin surface. There is a “swishing” sound on the Doppler if the venous system is normal. Both the superficial and deep venous systems are evaluated in this test. There are no known risks in either of these tests, and they are noninvasive and painless.
Please also see section on diagnostic cerebral angiogram. The physician may recommend this procedure (based on the scans) in order to more thoroughly evaluate the arteries of the brain and determine whether or not surgery is necessary.
Treatments aim to reduce the risk of stroke by controlling or removing plaque buildup and by preventing blood clots. The treatment options for intracranial artery disease vary, depending on the severity of the narrowing and whether or not the patient is experiencing stroke-like symptoms. Patients may first be treated with medications and encouraged to make lifestyle changes to reduce their risk of stroke. Surgery is required if the stenosis has reached a certain severity or if the patient is having symptoms that don’t seem to be responding to medication, including high cholesterol and blood pressure medication. Diabetic patients are advised to maintain control of their blood sugar through a healthy diet and careful monitoring. Aspirin and Plavix (blood thinners) are given to patients one week before their procedure to allow the blood to pass through the narrowed arteries more easily, and prevent clotting. Please see Neurointerventional Procedures for more information on treatment of intracranial artherosclerosis.
The operative procedure for intracranial artherosclerosis is the cerebral artery bypass. In this procedure, the physician reroutes the blood supply around the plaque-blocked area. This procedure requires making an opening in the skull, called a craniotomy (please see Operative procedures for more details on this procedure). A donor artery from the scallop is detached from its original position on one end, redirected to the inside of the skull, and connected to an artery on the surface of the brain. The scalp artery is now able to supply blood to the brain and bypasses the blocked vessel. Complications from bypass can include stroke, vasospasm, and clotting in the donor vessel. Bypass is typically recommended when the artery is 100% blocked and angioplasty is not possible. Results of artery bypass vary widely, depending on the location and type of bypass. Ask your surgeon what results you can expect.
Results and Prevention
Despite treatment with medication, patients who have had a previous stroke or TIA due to intracranial artherosclerosis have a 12-14% risk of recurrent stroke during the 2 years following the initial stroke.
Re-stenosis occurs in about 7%-34% of patients and is usually not symptomatic. It is important to understand that atherosclerosis is a progressive disease and there are many preventative measures that patients can do to decrease their risks of stroke. These include:
- Quitting smoking
- Limiting alcohol consumption
- Maintaining good blood-sugar control (if diabetic)
- Lowering your cholesterol
- Taking medications as prescribed.