Cerebral Aneurysms

An aneurysm occurs when a weakness in the wall of an artery leads to the swelling, or “ballooning” of that artery. It is estimated that up to 5 million Americans have cerebral aneurysms, although most do not experience any symptoms.1 Aneurysms likely occur at a higher rate in women than men, and about 20% of people who have had an aneurysm will have at least one more develop at some point in their lives.

Most brain aneurysms —up to 85%—typically occur in the anterior or front part of the brain’s blood vessel system, whereas approximately 15% occur in the posterior or back section of the brain’s blood vessel network. Most aneurysms occur along vessels that comprise the “circle of Willis” or the set of collateral blood vessels that link right to left and front to back.

Risk factors for aneurysm development include smoking, obesity and hypertension. Some people may also be born with a predisposition to experience an aneurysm, although most people develop them after the age of 40. Certain genetic conditions that lead to familial aneurysm formation include fibromuscular dysplasia and polycystic kidney disease. Aneurysms can also occur due to infections, drug abuse, or head trauma.

When aneurysms develop along the arteries in the brain, they can rupture into the fluid spaces (subarachnoid space) that surround the brain with devastating results. This subarachnoid hemorrhage may cause stroke and, ultimately, death in a high percentage of patients if not treated expeditiously at expert treatment centers. Aneurysms may also press against the nearby brain tissues or cranial nerves causing neurological symptoms or even seizures. New neurological changes due to an aneurysm can be an ominous sign that the aneurysm is suddenly expanding and may rupture causing hemorrhage. Patients with new neurological deficits due to aneurysm should receive urgent medical attention in most cases.

Warning signs
The majority of people with aneurysms do not experience warning signs that they are at risk of having aneurysmal hemorrhage. About 40% of patients with aneurysms, however, may experience the following symptoms:

Nausea or vomiting
Pain above and behind the eye
Numbness or weakness
Neck pain
Headache confined to a specific area
Visual difficulties
Apeech difficulties
Memory problems
Seizures

Figure 2

When these symptoms are present, assessment procedures should include a computed tomography scan (CT) or magnetic resonance imaging (MRI). These techniques can help to identify aneurysms before they rupture. A more accurate diagnosis, however, is still typically made using catheter cerebral cerebral angiography. This involves the injection of dye into the blood vessels through a catheter or tube. These images define the anatomy and location of an aneurysm with great detail and form the basis on which treatment planning using either can be performed. Treatment using either open surgery with craniotomy and surgical clipping of the aneurysm or endovascular surgery with internal occlusion of the aneurysm can then be undertaken. There are benefits and risks to either approach and the treatment team must comprise members with expertise in both types of procedures in order to achieve optimal patient outcomes.

Descriptions of aneurysms
There are 3 different shapes of aneurysms:

Berry – the most common type of aneurysm, these are small and shaped like a blister, balloon, sac or even a little red “berry” appearance at the time of craniotomy and direct surgical exposure. These aneurysms most often arise at a blood vessel branch point or bifurcation where a relatively weak point is subject to high stress factors from the flowing blood.
Fusiform – this type of aneurysm is elongated and shaped like a spindle. I often liken the appearance to a snake that swallowed a rat. Rather than a balloon or bulge from one side of the blood vessel wall, the entire circumference of the blood vessel has become involved in the formation of a fusiform aneurysm.
Dissecting – this type of aneurysm occurs when blood passes through a tear in the inner layer of the blood vessel wall that causes the wall to split weakening its ability to contain the flow of blood. The result can be aneurysmal dilatation of the blood vessel, narrowing of the main flow channel for blood to reach the brain causing stroke, or even rupture through the weakened blood vessel wall causing subarachnoid hemorrhage.

Aneurysms are further characterized by size. A small aneurysm is considered to be less than 7-10 millimeters. An aneurysm between 10 and 25 millimeters is classified as large, and a giant aneurysm is greater than 25 millimeters.

Rupture of aneurysms
The rupture of aneurysms, also known as aneurysmal bleed or subarachnoid hemorrhage (SAH), is believed to occur at a rate of 1-2% per year and the risk is cumulative over time. The hemorrhage rate is the subject of ongoing debate based upon the available epidemiological data, but most physicians still agree on this range for hemorrhage risk. Various factors influence whether an aneurysm is at risk of rupture, including its size, type, location, and previous history of rupture. Common warning signs of a subarachnoid bleed include an extremely painful headache, drowsiness, and nausea or vomiting. We do not yet fully understand what causes aneurysms to form, grow, and rupture. Conditions over which we have control in an effort to prevent aneurysmal hemorrhage include strict control of high blood pressure and strict abstinence from all tobacco use or exposure.

When a rupture of a brain aneurysm does occur, the blood typically seeps into the fluid space closely surrounding the brain called the subarachnoid space. The subarachnoid space is filled with cerebrospinal fluid and is mostly one continuous area although filamentous bands of fibrous tissue may compartmentalize certain parts of the subarachnoid space and limit flow from one part to another. Blood may also travel directly into the brain substance, although this is less common. In more severe hemorrhages, blood may back up into the ventricles or caverns deep within the brain where the spinal fluid is originally produced.

It cannot be overstated that the rupture of a brain aneurysm is a true medical emergency and warrants immediate medical attention; it is estimated that 25% of patients with this condition will die before arrival in the emergency room, and that 45% of patients will die within 30 days of the bleed.2 Furthermore, once an aneurysm has ruptured, it is at greater risk for additional bleeding in the first minutes, to hours, and days following the initial hemorrhage. In hindsight, some patients who experience subarachnoid hemorrhage will recall a back headache days to weeks before the big hemorrhage. This is often referred to as a “sentinel” headache and is thought to represent an early small hemorrhage that went unrecognized.

A CT scan can usually diagnosis bleeding in the brain and subarachnoid area. If necessary, a lumbar puncture, commonly referred to as a spinal tap, may also be conducted to examine if blood is present in fluid around the brain. In this procedure, a thin needle is inserted into the lower part of the spinal column to obtain a small fluid specimen to examine for evidence of bleeding not apparent on the CT scan. Lumbar puncture is required in the vast minority of patients who have experienced acute subarachnoid hemorrhage.

Treatment of aneurysm
In the past, treatment of brain aneurysm has entailed a surgical procedure.. First, a small opening in the skull called a craniotomy is made so that the surgeon can dissect away the tissues surrounding the aneurysm and apply a clip to the aneurysm. A clip looks somewhat like a tiny clothes pin that pinches the walls of the blood vessel together at the base of the aneurysm and prevents flowing blood from access to the aneurysm. If the flowing blood cannot get into the aneurysm, then it also cannot leak out. Although this procedure can be effective, it is invasive, requiring exposure and retraction of the brain. Newer methods of treating aneurysm are always in development. One relatively newer method of treatment is known as endovascular embolization or occlusion of the aneurysm from within the blood vessel. In the same way that the surgical clip pinches closed an aneurysm preventing flowing blood from access to the aneurysm, tiny platinum coils can be placed into the aneurysm that also prevent flowing blood from access to the aneurysm and allow aneurysm healing.

Endovascular aneurysm treatment from start to finish
Prior to undergoing an endovascular surgery, patients are expected to sign a consent form and will have the opportunity to have any questions answered. The anesthesiologist will administer medications and fluids through the use of an intravenous line (IV) into a vein in the hand or arm. Usually, endovascular procedures are also performed under general anesthesia not so much for pain control but rather so that the patient will be completely still for the entire procedure. Aneurysms are very small and measured in millimeters. The treatment coils are also small, delicate, and measured in millimeters. Precision is very important for the success of the endovascular procedure, and general anesthesia facilitates this success. Otherwise, the procedure is essentially painless.

Blood pressure can be monitored through the catheters used to perform the aneurysm treatment. An electrocardiogram (EKG) will monitor heart rate and rhythm and a pulse oxymeter monitors oxygen levels. A specific type of catheter known as a Foley catheter will be placed through the urethra into the bladder to allow urine to drain. Anesthesiologists often monitor urine output as a simple indicator that the body’s major systems are functioning well.

Very simply, endovascular treatment of a cerebral aneurysm is an extension of the diagnostic arteriogram used to diagnose the aneurysm. Special training is required to perform this type of treatment procedures, however. For the diagnostic arteriogram, the catheter is passed into the arteries that lead to the brain, but the catheter is usually positioned within the blood vessel around the level of the collar bones or voice box. The x-ray contrast material is injected through the catheter into the blood vessels in the neck, and x-ray images are obtained over the head as blood flows through brain arteries.

Endovascular treatment requires passage of a tiny, “hair-like” catheter through a supporting catheter positioned within the blood vessels in the neck. The tiny catheter is then navigated through the brain blood vessels on high resolution “road-map” images. These images obtained from two different directions allow the physician to monitor the progress of the catheter toward the aneurysm and control its ever movement. Finally, the tiny catheter is positioned in the orifice or hole leading into the aneurysm.

Again, under high resolution road-map imaging, the physician carefully passes delicate detachable platinum-base coils into the aneurysm. For a number of years, there was only one type and one vendor of cerebral aneurysm coils: Guglielmi Detachable Coils (GDC) by Target Therapeutics, Inc. Now, there are an increasing variety of coils with unique properties suited to aneurysm treatment. Each coil is carefully sized to the specific aneurysm under treatment based upon three-dimensional computer reconstructions of the aneurysm. Once placed into the aneurysm, each coil is carefully detached from its delivery device, and the aneurysm is progressively filled with a succession of smaller coils until it is completely occluded. When the coils are inserted, the aneurysm becomes tightly packed to prevent blood from flowing into it, with the ultimate goal of preventing the aneurysm from rupturing. The newest coils approved by the FDA for aneurysm treatment even appear to promote aneurysm healing for durable and long-lasting results.

Some aneurysms have relatively wide apertures or holes leading into the aneurysm. These present a challenge to coil placement because it can be difficult to place the coils within the aneurysm without blocking the blood vessel from which the aneurysm arises. To facilitate endovascular treatment of these aneurysms, adjunctive tools and techniques have been developed. In some cases, a small balloon is used to create a temporary buttress to help hold the coils in the aneurysm during their deployment. In these cases, the coils develop a stable configuration that does not require any further support following occlusion of the aneurysm. In a small number of cases, the aneurysm orifice is too broad even for balloon remodeling. In these cases, the FDA approved a specialize brain stent that allows placement of a tiny stent in the brain artery that acts as a permanent scaffolding to hold the artery open while the aneurysm is occlude with coils outside the confines of the stent.

Once the procedure is complete, the patient will be transferred from the operating room to either the Neurological Intensive Care Unit (NICU) or the Post-Anesthesia Care Unit (PACU). In the intensive care setting, patients are carefully monitored for any neurological changes that might require urgent medical attention. For patients who underwent treatment of a ruptured aneurysm, their stay in the NICU often lasts for up to two weeks as they recover from their hemorrhage. For patients who undergo treatment of an unruptured or incidental aneurysm, the hospitalization is often as short as one day. Some patients can even be discharged home right from the intensive care unit on the morning after endovascular surgery.
Follow-up procedures may include an x-ray, MRI, or angiogram to assess the effectiveness of the procedure. Although there is no absolute concensus, arteriographic surveillance is usually performed for two main reasons. 1.) Surveillance arteriography allows the treating physician to confirm durable occlusion of the aneurysm or plan further treatment if necessary. Over time in a small minority of aneurysms, the coil mass can compact itself so that a portion of the aneurysm reopens. A brain aneurysm is a very delicate structure and so are the coils used to occlude the aneurysm. The treating physician can only push so many coils into an aneurysm before the risk of rupturing the aneurysm increases dramatically. After treatment, however, continuous blood flow and beating of the heart and pack or compress the coils into a smaller bundle than at the time of the original treatment procedure. In these cases additional coils can be added to refill the aneurysm. If retreatment is required, a few extra coils is all that is necessary to permanently block the aneurysm. The newest coils that promote aneurysm healing are meant to preclude this problem by encouraging scar formation in the aneurysm and permanently sealing off the aneurysm orifice or hole. 2.) We have said that up to 20% of patients will develop a second or multiple aneurysms during the course of their lives. This is another way of saying that whatever conditions caused the development of an aneurysm at one location, these same conditions exist at many other branch points in the blood vessel network. Surveillance arteriography also allows the treating physician to evaluate for development of other aneurysms that could pose a risk to the patient and may require treatment or periodic observation. Medication may also be prescribed in the form of aspirin or other blood thinner after treatment.

Once at home, certain activities such as heavy lifting and driving must be avoided until the physician provides approval. Most patients, however, can begin resuming normal activity after a relatively brief period.

Although the GDC method was once only used to treat high-risk aneurysms only, its high success rate has led to its recent approval for use in treating all types of brain aneurysms. It is also linked to a reduction in the incidence of future episodes of bleeding.3 Age is believed to be a factor that influences the outcome of treatment. The younger the patient, the more likely surgical treatment is to be successful.2 Smaller aneurysms are also associated with better outcomes. If aneurysmal bleeding has occurred, recovery is most closely tied to the degree of injury caused by the hemorrhage or any further bleeding episodes.

The International Subarachnoid Aneurysm Trial (ISAT) was a multinational study comparing surgical clipping with endovascular aneurysm occlusion in patients with subarachnoid hemorrhage. In summary, ISAT found that patients who underwent endovascular treatment of their aneurysms recovered far better (up to 25% better in the first year) than patients who underwent surgical clipping of comparable aneurysms. In fact, the safety monitoring committee prematurely terminated the study because the primary endpoint (neurological outcome) was reached before the required number of patients were enrolled in the study.4 As time continues since the end of the difference in outcomes between the surgical and endovascular groups continues to increase. Similar differences have been suggested by other smaller trials for both ruptured and unruptured aneurysms. This is not to say that all aneurysms should be or can be treated by endovascular methods. The decision to treat an aneurysm and the method by which treatment will be performed requires the recommendation of neurosurgeons skilled at skull base and cerebrovascular surgery and endovascular surgeons skilled at endovascular procedures performed under x-ray fluoroscopic guidance.