Contents of This Section:

1. What is a brain aneurysm?

Like a steel cylindrical pipe, an artery is comprised of an inner space (the "lumen", filled with blood) enclosed by a wall ( you can go to the section on Brain Artery Structure by clicking here). The wall is made up of a number of layers, two of which are muscle tissue and elastic tissue. When a region of the blood vessel wall weakens, it can balloon out to form a sac-like structure. This structure is called an aneurysm (a word derived from the Greek, aneurysma - a widening), and the major problem associated with aneurysms is that they can rupture, an event which may be fatal.

At the outset, it should be noted that there are different types of brain aneurysms. They are usually classified as being either "true" or "false" aneurysms.

A true brain aneurysm is an expansion of a blood vessel wall involving all layers of the wall. The two most recognized types of true aneurysms are "saccular" and "fusiform", although a third much rarer type called "mycotic" is also recognized:

A false (or "pseudo-") brain aneurysm is an expansion of a blood vessel wall that does not involve all layers of the wall. Most commonly, it involves the outermost layers of the brain artery only, and usually follows injury or tearing of the vessel wall (referred to as a "dissection" or "laceration").

Please note that this section of the Website is concerned with the most common type of brain aneurysm, namely, the "berry" or "saccular" brain aneurysm.

Brain aneurysms can also be classified according to their size. The most common ones are "small" in that their diameter is 10 mm or less. "Giant" aneurysms are ones whose diameter is 25 mm or greater. In-between, i.e., from 11 to 15 mm and from 20 to 24 mm in diameter are the "large" and "near-giant" aneurysm sizes, respectively. There is a gray area of classification for brain aneurysms between 16 to 19 mm. Of all aneurysms, 95% are less than 25 mm in diameter; i.e., only 5% are "giant".

Interestingly, certain differences exist between brain aneurysms of these different sizes. For most purposes, small and large brain aneurysms (i.e., together, 15 mm or less in diameter) behave in similar ways in that they tend to grow and rupture. In fact, more than 90% of these present following rupture (i.e., following "subarachnoid hemorrhage"). On the other hand, 75% of patients with near-giant and giant brain aneurysms (together, 20 mm or larger in diameter) are admitted to hospital with effects due to compression or irritation of brain structures surrounding these aneurysms (i.e., with "mass effect", seizures, etc.); the remaining 25% of patients with near-giant and giant brain aneurysms are admitted following aneurysmal rupture. The risks of death and disability associated with bigger brain aneurysms, and particularly those in the back portion of the brain arteries (i.e., in the "posterior cerebral circulation"), are significantly higher than smaller aneurysms in the front part of the brain arteries ("anterior cerebral circulation").

Brain Arteries and Brain Aneurysm:

Figure 1 shows the under-surface of the brain. The major arteries in this region are shown in red. Together, they form a ring-like structure called the "Circle of Willis", a critical point of communication between the main arteries supplying the substance of the brain. The front part of this group of arteries (in the top part the figure) is referred to as the "anterior circulation", the back part (in the bottom part of this figure) is referred to as the "posterior circulation". All of these arteries lie in the "subarachnoid space" (SAS), a space normally filled with circulating cerebrospinal fluid.

The vast majority of brain aneurysms arise from the parent arteries (or their main branches) forming the circle of Willis, and more tend to occur in the anterior (front) part of the brain circulation. Figure 2 shows a sac-like brain aneurysm (A) arising from the wall of a brain artery (ba). It is well known that most brain aneurysms form near regions where an artery branches out (i.e., at so-called "arterial bifurcations"). It is at these regions where the turbulent forces exerted on the arterial wall by the flowing blood may be the greatest. Of course, we all have arterial bifurcations in the brain, but relatively few of us will ever develop a brain aneurysm (see 3., below).

2. How common is a brain aneurysm? ("Prevalence" and "Incidence")

This really depends on what you read! Some series have suggested that up to 5 to 10% of the general population may have one or more brain aneurysms (i.e., a "prevalence" of 5 to 10%), others have suggested this number may be less than half of 1%. In the U.S., with a population of approximately 275 million people, these percentages mean that between approximately 1.5 million people (in the best-case scenario) and 27.5 million (in the worst-case scenario) in this country may harbor a brain aneurysm. Either way, that's a lot of people! Most reports put them at a prevalence of somewhere between 1-5%.

Note that not all brain aneurysms cause problems. On average, there are 10 cases of brain aneurysmal rupture (i.e., bursting of the aneurysm sac, or "subarachnoid hemorrhage") per 100,000 of the general population per year (i.e., an "incidence" of 10 per 100,000 per year). Note that this statistic has often been misquoted. This does not mean that 10 out of 100,000 brain aneurysms rupture. Rather, it means that every year, for every 100,000 persons in the community-at-large, 10 persons can be expected to be hospitalized for a newly diagnosed "ruptured brain aneurysm." Therefore, in the U.S., this amounts to about 30,000 persons diagnosed with a ruptured brain aneurysm per year. Although it's not the most common of illnesses, it still is a very serious one, as brain aneurysmal rupture is associated with a high rate of death ("mortality") and serious disability ("morbidity").

The "natural history" of aneurysmal subarachnoid hemorrhage (i.e., the typical chain of events following the sudden rupture of a brain aneurysm, assuming no treatment is given) is often devastating for a patient. In the absence of treatment, half-to-two-thirds of all patients who suffer a brain hemorrhage from a ruptured brain aneurysm will not survive 6-months - in fact, most of the deaths occur between the time of rupture itself (approximate 10% instant mortality) and within a few weeks of the initial rupture. Half of the remaining survivors will not be able to return to work or maintain an independent life. Of course, with better community awareness, earlier diagnosis (including better imaging, and the prospect of a genetic test for brain aneurysm rupture risk), and more and improved treatment options (see below), the chances of a very good outcome are much higher now than ever before.

3. What are the risk factors that lead to brain aneurysm formation?

There are several risk factors that increase the likelihood of a brain aneurysm forming. It cannot be overstressed that smoking is an extremely important risk factor for brain aneurysm formation. A history of high blood pressure (hypertension), or a previous aneurysm in the same person, or a family history [i.e., one or more close (first-degree) relatives (i.e., a parent or sibling) with a brain aneurysm] are also important risk factors. In fact, 5-15% of persons diagnosed with a brain aneurysm have a positive family history for brain aneurysm (i.e., a close relative who also had a brain aneurysm). Age is a risk factor, in that persons above the age of 40 tend to present more commonly with brain aneurysms, and the majority of patients diagnosed with brain aneurysms are females. While the vast majority of brain aneurysms occur in adults, they can also occur in children, and so the symptoms and signs associated with a brain aneurysm (see below) should not be ignored in kids. Note that a person suffering from or having a first-degree relative with an inherited connective tissue disorder such as polycystic kidney disease, alpha-1 anti-trypsin deficiency, Marfan's syndrome and Ehlers-Danlos syndrome, or with Neurofibromatosis Type 1, is at a higher risk of forming a brain aneurysm. It is also thought that in persons born with abnormal blood vessel connections in the brain (i.e., "congenitally abnormal cerebrovascular anatomy"), or with a history of brain vessel injury (i.e., from head trauma), there may also be an increased risk of brain aneurysm formation later in life.

The bottom line is that each of the risk factors contributes to the weakening of a region of the wall of a brain artery, and this in turn permits a brain aneurysm to form.

Note that there are no solid scientific trends regarding "race" or ethnicity and brain aneurysm formation, with the exception of several published reports citing higher incidence of brain aneurysm rupture among Japanese persons. In other instances, racial differences detected between study groups may be the result of differences between the manner or pattern of referral to institutions, geographically-dependent brain aneurysm reporting/detection mechanisms, or to "confounding" factors such as subpopulation-dependent smoking and hypertension rates, etc.

Main Risk Factors for Brain Aneurysm Formation:

4. How does a brain aneurysm develop? ("Pathophysiology")

Like most diseases, brain aneurysms develop for reasons that may be "congenital" (i.e., the person was born with some defect in the brain artery wall, or an abnormal communication in the brain circulation or, e.g., a hereditary disease which lead to and worsened a defect in a brain vessel wall) or "acquired" (i.e., the person was not born with any such defect, but some event or illness during life lead to the development of the brain aneurysm). Although the congenital theory was thought to be more important in the past (and it still is in cases of persons with inherited connective tissue diseases which weaken the artery wall from the beginning), it is now thought that acquired reasons are the main ones underlying the development of brain aneurysms. Perhaps the most significant of the acquired reasons are smoking (which is associated with injury to the blood vessel wall, particularly the endothelium; take me to Brain Artery Structure now) and high blood pressure (systemic hypertension; which causes additional stress on the blood vessel wall).

How and why brain aneurysms develop really relate to properties of the wall of the blood vessel. As reviewed elsewhere ( take me to Brain Artery Structure now), the artery wall is made up of a number of layers, each of which plays an important role in the overall strength and resilience (flexibility) of the vessel. In particular, there is only one elastic layer in the brain artery (there are two elastic layers in arteries elsewhere in the body), which itself tends to have many normal openings (perforations), and anything that damages this layer will predispose to a brain aneurysm forming in this region of the artery. Also, the smooth muscle layer of brain arteries has certain naturally occurring defects (isolated regions where the layer may be thinned out or absent), particularly where artery branch points (arterial bifurcations) occur. This makes aneurysms more likely to occur in such regions. In addition, at arterial bifurcations, the forces exerted by the flow of blood (hemodynamic forces) tend to be increased relative to other segments along the artery, and any condition which increases blood flow pressure and turbulence (such as high blood pressure and high cholesterol) will aggravate the tendency for this part of the artery to balloon out as a brain aneurysm.

The sequence of events from early brain aneurysm formation, growth, and eventual rupture is shown in Figures 3-8, below.

Sequence of Brain Aneurysm Formation:

Figure 3 shows a normal brain artery branch point with normal blood flow (arrows) in the artery. No brain aneurysm is present. An aneurysm then starts to develop from one side of the wall (Figure 4; green arrow), and with time it continues to expand (Figure 5; green arrows).

As the brain aneurysm gets larger, a "neck" may become apparent (Figure 6; green arrow heads), and the blood flow in the "body" or sac of the brain aneurysm (Figure 6; curved arrows) becomes more and more turbulent. This leads to progressive weakening of the brain aneurysm wall, especially at the "dome" of the brain aneurysm (Figure 7; arrows). Rupture eventually occurs (Figure 8) and blood gushes out of artery (arrow) and enters the space surrounding the vessel (the "subarachnoid space") where it forms a clot (see Figure 9, below). For this reason, this event is referred to "subarachnoid hemorrhage".

5. What are the symptoms of a brain aneurysm? ("Clinical presentation")

Most brain aneurysms are silent, the person totally unaware of a problem till the time of rupture. This is the pattern of events in approximately 90% of all brain aneurysm patients. At this point, i.e., the time of rupture, the person experiences one or more of the following: a sudden, extremely severe headache [which may be described as "the worst headache in (the person's) life", or as a "sledge-hammer headache which struck like a bolt of lightening"], vomiting, neck stiffness, collapse (loss of consciousness), sudden loss of function in one or more parts of the body (like a classic "stroke"), or a "fit" (seizure). In the remainder of patients, the brain aneurysm is either found by chance (i.e., incidentally; found this way in 3% of all brain aneurysm patients) during investigation for some other reason, or presents with symptoms due to its relatively large size or "mass" (where it may compress or irritates surrounding brain structures; seen in 7% of all brain aneurysm patients). In these instances of so-called "mass effect", the symptoms may be continuous morning headaches, nausea, loss of function in one or more of one of the nerve bundles in the brain or spinal cord (e.g., leading to facial muscle weakness, double vision, impaired balance or hearing, tongue deviation, and weakness in the limbs, etc.). Of course, these symptoms may also occur in conditions not related to brain aneurysms (e.g., brain tumors), so careful evaluation by a physician is required.

There are two other aspects of brain aneurysm symptoms that are well worth mentioning. First, many physicians recognize the occurrence of a "warning leak" in brain aneurysms, where some don't frankly rupture, but instead tear a little and release a small amount of blood. A warning leak occurs in somewhere between 15 to 30% of truly "ruptured" brain aneurysm patients. Leak frequently results in a severe headache and some degree of neck stiffness and, as the term implies, the leak typically occurs at some time (not precisely known) prior to the actual "main bleed". Again, not all headache and neck stiffness episodes are warning leaks from brain aneurysms. Second, the American Heart Association and its Stroke Council coined the catchy term "brain attack" ( take me to the Brain Attack section) to describe the brain equivalent of the common "heart attack". This term is an important one, aimed at increasing community awareness of this important and potentially life-threatening brain condition. The term encompasses the symptoms of a stroke (many of which were mentioned above), although the stroke itself may arise from blood vessel blockage (which is the most common cause), or from the rupture of a brain aneurysm.

Based on the neurological presentation of the patient, the World Federation of Neurological Societies (WFNS) has designated a grading system for patients following aneurysmal SAH. This has implications for prognosis. The WFNS SAH grading system is as follows (Grade 1 is best, Grade 5 is worst; GCS = Glasgow Coma Score - made up of a combination of eye opening, vocalization, and peripheral motor response). Deficit is defined here as hemiparesis or aphasia. WFNS SAH:

1. (Grade 1) GCS = 15, no focal deficit
2. (Grade 2) GCS = 13-14, no focal deficit
3. (Grade 3) GCS = 13-14, focal deficit present
4. (Grade 4) GCS = 7-12, with or without deficit
5. (Grade 5) GCS = < 7, with or without deficit

What are the complications of a brain aneurysm?

For any brain aneurysm, the main problem or dangerous consequence (i.e., "complication") is that it may grow and rupture. If a brain aneurysm ruptures, the main complications are death and serious disability from the initial rupture itself or due to events occurring after the initial rupture. Of these events, the most important two are "rebleeding" of the brain aneurysm (i.e., it re-ruptures and bleeds again), and permanent brain tissue injury (i.e., "infarction") from "cerebral vasospasm" (i.e., where, following hemorrhage, brain arteries go into severe spasm; i.e., they shut down, depriving the nearby brain tissue of oxygen and other nutrients; see Figure 9, below). These major complications are discussed elsewhere ( take me to the section on Aneurysmal Rebleeding or Cerebral Vasospasm now).

Spasm of Arteries Neighboring Ruptured Brain Aneurysm:

Following rupture of a brain aneurysm (see Figure 8, above), blood gushes out of artery and enters the subarachnoid spacewhere it forms a clot (Figure 9; green arrows). This clot releases substances that can cause spasm (Figure 9; arrow heads) of the neighboring brain arteries. This event is referred as cerebral vasospasm, and causes death and serious disability in about one in five patients with ruptured brain aneurysms ( take me to the separate section on Cerebral Vasospasm now).

In persons surviving the above complications, other complications may arise. For example, there may be some degree of obstruction (or blockage) of normal cerebrospinal fluid (CSF) flow in the brain (i.e., resulting in high-pressure build up in the brain referred to as "hydrocephalus"; see Figure 9B). This is caused by the blood clot or blood products clogging up the CSF drainage system following brain aneurysm rupture, and it can lead to progressive, permanent brain injury. Also, following brain aneurysm rupture, parts of the brain can become electrically irritated, resulting in seizures. Finally, it should be noted that the rupture of a brain aneurysm can, in some patients, cause "cardiac stunning" (a heart attack or arrhythmia that can even be fatal).

Hydrocephalus:

The figure to the right depicts CSF flow and the development of hydrocephalus. The brain contains fluid-filled spaces called ventricles (drawn as light blue spaces in center of brain, above). The fluid that fills these spaces is known as cerebrospinal fluid (CSF). CSF, which is produced by structures collectively referred to as the choroid plexus (drawn as light red structures within brain, right), circulates throughout the brain (blue arrows). It exits the brain near the brainstem and makes its way either over the surface of the brain (in the subarachnoid space; light blue spaces around the brain, above), or into and around the spinal cord (light blue space within and around spinal cord, above). Note that in the lowest part of the spine, just above the level of the tailbone, is a generous CSF-filled cavity known as the lumbar cistern, which is the site from which CSF is drawn during a “spinal tap” or lumbar puncture. CSF is mostly absorbed at the very top surface of the brain in structures called arachnoid granulations (drawn as the three dark red stuctures on the top surface of the brain, above).

When a brain aneurysm ruptures, the blood, which should be on the inside of blood vessels, now enters the subarachnoid space and eventually makes its way to the arachnoid granulations. Cells and debris in the blood can clog up and damage these granulations. This leads to obstruction of CSF absorption. This damage may be short term, or permanent. CSF now accumulates, like a dam effect, and results in hydrocephalus (water in the head), i.e., enlargement of the ventricles (green arrows, above). This causes pressure to build up in the brain, and it manifests in one or more of the following: headache, nausea, vomiting, blurred or double vision, increasing drowsiness, even coma and death. The way to treat this is to divert the CSF, at first temporarily through a special drainage tube placed either into the ventricles (an “external ventricular drain”) or into the lumbar cistern (a “lumbar drain”). CSF will intermittently be drained via this tubing over several days and then an attempt made to gradually clamp off (wean”) the drain in order to see if the natural pathways for CSF absorption have recovered. If so, good, the drain will be removed. If a drain can't be weaned successfully (i.e., the patient gets symptomatic from hydrocephalus each time the drain is clamped), then a “shunt” usually needs to be placed by the neurosurgeon. Formal shunting requires a separate operation and carries its own short and long term risks. The literature reflects that one in three ruptured brain aneurysm patients will develop hydrocephalus, and many of these will require placement of a permanent shunt. Therefore, from the get go, I prefer to be fairly aggressive about CSF diversion techniques in patients with ruptured brain aneurysms, with the aim to avoid the development of hydrocephalus and therefore avoid the patient needing a shunt.

7. How is a brain aneurysm detected? ("Investigation")

Sadly, most brain aneurysms are detected only after they have ruptured. As mentioned above, in less than 10% of patients, the brain aneurysm is detected by chance (3%) or, in the case of bigger brain aneurysms, due to symptoms arising from compression of brain structures (7%).

The gold-standard for detection of a brain aneurysm is cerebral angiography. Here, a contrast dye is first injected through a catheter device inserted usually in a thigh (femoral) artery. From here, the dye eventually enters one or more of the main brain arteries, where it is X-ray imaged. It typically provides a detailed roadmap of the brain circulation. An aneurysm appears as an expansion of the vessel. If there is no clot (thrombus) in the brain aneurysm, it will light up like a sac coming off the parent artery. If the lumen (or inner space) of the brain aneurysm is packed with clot (this is more common in bigger brain aneurysms due to slowing of blood flow in the lumen), then sometimes the real extent of the brain aneurysm may not be seen by this method.

Other X-ray based advanced imaging methods for detecting brain aneurysms are magnetic resonance imaging (MRI) and its associated method referred to as magnetic resonance angiography (MRA). The advantages of these methods are that they are less invasive than cerebral angiography, in that they do not involve femoral (thigh) artery puncture and insertion and navigation of a long catheter through the arteries. However, they may not detect the smallest of brain aneurysms as well as cerebral angiography can, and (due to problems with magnetic attraction and interference; ferromagnetism) are not able to be used in certain patients in whom metallic hardware has been placed. Of course, some patients with certain metallic (nonferromagnetic, e.g., titanium) hardware can still be safely and effectively imaged by this method. Check with your physicians first.

Ordinary computer-assisted tomographic (CAT or CT) scanning with a limited injection of contrast dye is another way to detect brain aneurysms, but not a very good way (note that without injection of contrast, an ordinary CT scan is almost useless unless the brain aneurysm is very large, calcified or ruptured). Even when used as part of CT angiography (see below), this method is not as sensitive (i.e., can't quite pick up the smallest brain aneurysms or some aneurysms located around the brainstem) or as specific (i.e., can't really be sure it's a brain aneurysm that's been detected) compared with cerebral angiography. Note that if an aneurysm has ruptured, the amount of blood on the CAT scan can be prognostic in terms of the likelihood a patient will experience cerebral vasospasm ( take me to the separate section on Cerebral Vasospasm now). The more the blood (i.e., the higher the "Fisher Grade"), the more likely it will be that a patient will experience cerebral vasospasm, but exceptions exist of course. Fisher SAH Grade 1 means no blood seen on the CT scan, while Fisher Grade 2 means very little blood seen on the CT scan. These first two grades are not associated with a high risk of cerebral vasospasm. Fisher grades 3 & 4 imply that a significant amount of blood is seen on the CT scan and, of these, Fisher Grade 3 seems to be the grade most strongly associated with vasospasm occurrence.

Ultrasound (e.g., Duplex-Doppler) plays no real role in the detection of brain aneurysms in clinical practice, although it is more useful for detecting spasm of arteries following rupture of an aneurysm. Common X-rays are not used for aneurysm detection, although highly calcified brain aneurysms may show up as curvilinear lesions on a plain skull x-ray (and in neurosurgery resident examinations!).

A combination of CT scanning and angiography (referred to as CT-angiography, CTA; where a larger amount of intravenous dye is introduced into the patient at the time of CT scanning) is currently gaining popularity as a very good means of detecting brain aneurysms, and may one day replace conventional cerebral angiography (with the obvious advantages that CT-angiography is so much quicker, cheaper, and less invasive compared with conventional angiography). The ability to create high-resolution and color 3-dimensional images with CTA is very useful for surgeons planning to operate these lesions.

Lumbar puncture is frequently used to determine whether or not a brain aneurysm that may have been detected by one or more of the above methods has ruptured. This involves the insertion of a spinal needle into the lower part of the back, and examination of the cerebrospinal fluid for blood pigments ("xanthochromia") whose signature is first present from around 6 hours after the hemorrhage and may linger for weeks).

At present there is no single blood test that can reliably predict "sporadic" brain aneurysm formation or rupture. However, researchers have been working on developing such a test, although they are still waiting for validation through a larger clinical trial ( take me to the section on Genetic Test for Brain Aneurysm Rupture). It should be noted that certain genetic (hereditary) diseases may have genetic fingerprints that can be detected in the blood or after an appropriate tissue biopsy which, if found, may indicate that a person is at increased risk of developing a brain aneurysm.

8. Who should be screened for a brain aneurysm, and when?

Note that the possible benefits of screening and any risks associated with screening procedures should be discussed with your local physician or attending neurologist or neurosurgeon.

Screening for brain aneurysms refers to the attempt to detect a brain aneurysm in a person who has had no symptoms related to, or previous diagnosis of, brain aneurysmal disease. At present, there are no hard and fast rules regarding brain aneurysm screening. Some physicians recommend that if two or more first degree relatives (i.e., close relatives such as a person's siblings or parents) are known to have (or have had) brain aneurysms, then the person in question should be a strong candidate for screening. Some patients with certain inherited connective tissue diseases are also considered by some physicians as good candidates for brain aneurysm screening, particularly if they have had problems in other parts of their body related to their connective tissue disorder.

Screening is carried out using an imaging device which scans the brain, such as a magnetic resonance imaging (MRI) scanner, particularly in its magnetic resonance angiography (MRA) mode. MRA scanning is regarded as a safe and acceptable way of detecting brain aneurysms, although some very small aneurysms may be difficult to detect by this scanning technique. Ordinary CT (or "CAT") scanning is not a good way to detect unruptured brain aneurysms (because unless they are large in size, ordinary CT scanning isn't sensitive enough in detecting their presence). However, a newer mode of CT scanning referred to as "CT-angiography" (CTA; described above) is showing promise as being a good alternative to MRA for brain aneurysm screening. Referring docs should ask for "high-resolution CTA with multiplanar views". CTA is quicker, less expensive, and is less claustrophobic than MRA, however, clinical studies are still required to conclusively compare the methods of MRA and CTA as effective screening tools for unruptured brain aneurysms.

Cerebral angiography (see above) may be regarded by some as an alternative method for screening. Although this procedure is the best (most accurate; "gold standard") method known for detecting brain aneurysms, it carries certain risks when compared with, say, MRA or CTA. For example, angiography may cause local bleeding at the femoral artery catheter entry site or in other more distant arteries in the body during navigation of the catheter itself. There is also a small (1%) risk of stroke during cerebral angiography. Also, some patients may be allergic to the contrast material, although more modern contrasts have been developed to reduce this risk. Owing to its complexity and need for an experienced interventional radiologist, cerebral angiography is also a relatively costly form of imaging compared with MRA and CTA.

In general, a screening method should be least risky, relatively cost-effective, yet should provide good and accurate information. In this context, MRA may be the best method for brain aneurysm screening at present, although CTA may be an upcoming acceptable method, too. Again, the possible benefits of screening and any risks associated with screening procedures should be discussed with your local physician or attending neurologist or neurosurgeon.

Lastly, it should be noted that one of the biggest questions that needs to be addressed in screening for brain aneurysms is this: "What will YOU do if you are found by screening to have a brain aneurysm, yet had no symptoms related to it?" Will you be prepared to undergo the necessary investigations and possible treatment? This issue certainly makes the issue of screening more complex. Certainly, some brain aneurysms that are discovered by screening may be at a higher risk of rupture (particularly if they are 7-10 mm or greater in diameter, or found to be growing in consecutive studies). However, smaller brain aneurysms (i.e., those less than 10 mm in diameter) may also rupture. So, if an aneurysm that has been causing no symptoms has been found "incidentally" by screening then,...should it be treated? when? how? These are issues that require considerable discussion between the patient and a team of physicians including a neurosurgeon, neurologist, and neuroradiologist.

9. How is a brain aneurysm treated?

If a brain aneurysm is detected, but hasn't ruptured, the choice of treatments is very controversial at the moment. Some physicians have found that a brain aneurysm diameter (size) of 10 mm may be the critical number after which there is a significantly increased risk of brain aneurysm rupture. Others, however, have found that rupture occurs in even smaller brain aneurysms (e.g., 3 to 6 mm in diameter), and therefore advocate that the 10 mm size "threshold" is not valid for determining risks and deciding on close observation (which means not actually treating the brain aneurysm, but rather following the patient every so often with repeated scans to see if the brain aneurysm is enlarging) versus actual treatment. The bottom line is that each case of brain aneurysm should be treated on an individualized basis, taking into consideration the age of the patient, copresence of significant medical conditions, the site and size and shape of the brain aneurysm, whether there is a history of previous aneurysmal hemorrhage in that patient, the experience of the treating physician or surgeon, and the type and risk(s) of treatment option most suitable for that brain aneurysm and person.

The picture is more clear if the brain aneurysm has ruptured. Here, the options are either surgery (which is generally recommended for as early as possible after the hemorrhage) or a nonsurgical (neuroradiological) intervention [i.e., involving insertion of a catheter (a long, thin, flexible, tube-like device) into an artery (usually the femoral artery in the thigh), and navigating the catheter through the artery up into the brain to the region of the brain aneurysm itself].

Immediate and early medical management of patients presenting following aneurysm rupture includes:

• Assessment of ABCD (airway, breathing, circulation, "deficit") -- some SAH patients present comatose, others may have significant cardiorespiratory issues secondary to the SAH ("cardiac stunning", "arrythmia", "myocardial ischaemia", and "neurogenic pulmonary oedema" can occur following SAH)
• Appropriate laboratory studies [complete blood count, electrolytes, creatinine, "coags"(APTT, PT/INR), electrocardiogram, chest x-ray, blood type & screen or "group and hold"]
• Keeping the patient in a relatively quite and (if photophobic) dim-lit environment
• Tight blood pressure control (aiming to keep systolic 120-140 mmHg max, and MAP around 85-90 mmHg max)
• Monitoring serum sodium and urine output ("cerebral salt wasting" is common in SAH patients) - usually seen in the 2-7 days after the ictus/SAH itself.
• Neurosurgical stat consultation
• Watch level of consciousness, if declines, need for intubation likely; inform intensive care and neurosurgical teams
• Postoperative management and management issues in comatose patients are complex and discussed elsewhere
• Medical management of patients experiencing cerebral vasospasm is discussed elsewhere

1. Surgical options for a brain aneurysm:

These include: (i) placing a metallic clip across the neck of the brain aneurysm ("direct clipping"; see Figure 10, below), regarded as the best and most sure (definitive) method of treating a brain aneurysm; (ii) placing a metallic clip across the artery feeding the brain aneurysm ("proximal" or "Hunterian" ligation) thereby allowing the brain aneurysm to clot off and hopefully shrink; (iii) placing a metallic clip across all arteries feeding and draining the brain aneurysm ("trapping"; see Figure 11below); and (iv) "surgical reconstruction" of the aneurysmal portion of the artery (where the brain aneurysm is surgically cut out, and the vessel thereafter repaired using an end-to-end resuturing technique or a natural or synthetic vessel graft). These types of procedures are carried out according to the individual patient's brain aneurysm and the experience of the neurosurgeon. As with any neurosurgical procedure, there are risks of injury to other vessels or brain structures in the vicinity of the operation field (which can result in a stroke-like picture), the possibility of bleeding or rebleeding from the brain aneurysm, and brain tissue or wound infection. There is also the risk that the brain aneurysm can recur (or an entirely new brain aneurysm can develop) despite surgery; this is very rare, however. Together, the risk profile depends on the size and location of the brain aneurysm, the age and general health of the patient, whether the brain aneurysm is ruptured or unruptured, the time between rupture and treatment, and the experience of the surgeon. The risk of rupture from an untreated unruptured brain aneurysm, or the risk of death or disability from the initial rupture itself, or from rerupture or delayed vasospasm from a ruptured brain aneurysm, may far outweigh the risks of surgery, but again, these are factors determined on an individual basis. It should be noted that in the most risky aneurysms, the surgeon may (on rare occasions) elect or need to carry out part of the procedure with the patient on heart (cardiopulmonary) bypass, and cooled to relatively low temperatures (profound hypothermia).

2. Neuroradiological options for a brain aneurysm:

The neuroradiological (catheter-based or endovascular) nonsurgical procedures include: (i) placement of metallic (e.g., titanium) microcoils or a "glue" (or similar composite) in the lumen of the brain aneurysm (in order to slow the flow of blood in the lumen, encouraging the aneurysm to clot off (be excluded) from the main artery and hopefully shrink; see Figure 12 below); (ii) placement of a balloon with or without microcoils in the parent artery feeding the brain aneurysm (again, with the intention of stopping the flow of blood into the brain aneurysm lumen, encouraging it to clot off and hopefully shrink); (iii) insertion of a synthetic hollow bridge (a stent) across the aneurysmal part of the artery to effectively cut off blood supply to the brain aneurysm, or to allow coiling through openings in the stent, without stopping blood flow across the open stent (see Figure 12 below); and (iv) a combination of the previous three procedures. The advantages of a neuroradiological procedure is that it doesn't require surgery, and yet may be as beneficial (esp. for small brain aneurysms). In certain brain aneurysms which are difficult to get to surgically, the interventional procedures have the added advantage of access to the brain aneurysm. However, there are complications associated with the neuroradiological approaches; these include the possibility of rupture of the brain aneurysm, stroke during the procedure, injury to the parent or another artery during navigation of the catheter, the possibility of incomplete stoppage of blood flow to (or within) the brain aneurysm thereby allowing the brain aneurysm to continue to grow and eventually rupture, and the possibility that the hardware can accidentally migrate away from the brain aneurysm, and cause a stroke by cutting off brain blood supply from further along the artery. It should be noted that a clotted brain aneurysm is not necessarily a safe one.

In the ideal circumstance, the decision as to how to best treat a brain aneurysm is made in joint consultation between the patient, a neurosurgeon and a neuroradiologist, taking into careful consideration the specific circumstances of the patient and the brain aneurysm itself.

Some Techniques for Treating a Brain Aneurysm:

Figure 10 shows a directly clipped brain aneurysm, the clip being placed across the brain aneurysm neck, thereby effectively removing (isolating) the brain aneurysm from the circulation. Figure 11 shows trapping of a brain aneurysm, with surgical clips being placed on the artery sections feeding and draining the brain aneurysm. Figure 12 shows a hollow stent (S) placed by a catheter across the region of the vessel that opens into the lumen of the brain aneurysm, again, isolating the brain aneurysm from the circulation (although this depends on the type of stent). Metallic microcoils (C) can also be placed in the lumen of the brain aneurysm to slow down and eventually clot off its internal flow. See above text for details.