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Research
WHAT IS AN ANEURYSM?
The Four types of Cerebral AneurysmsA 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: saccular
fusiform
Mycotic
Pseudo
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, 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; 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 ( "posterior cerebral circulation"), are significantly higher than smaller aneurysms in the front part of the brain arteries ("anterior cerebral circulation"). FACTORS OF AN ANEURYSMA person may inherit the tendency to form aneurysms, or aneurysms may develop because of hardening of the arteries (atherosclerosis) and aging. Some risk factors that can lead to brain aneurysms can be controlled, and others can't. The following risk factors that doctors and researchers believe may increase your risk of developing an aneurysm or, if you already have an aneurysm, may increase your risk of it rupturing: AtherosclerosisAtherosclerosis is a condition in which fatty materials collect along the walls of the arteries. This fatty material thickens, hardens, and may eventually block the arteries.
ArteriosclerosisArteriosclerosis is a condition where arteries become thick, blocked and inelastic as a result of a film of fat (atheromas) forming on their walls. Arteriosclerosis hinders effective blood circulation depriving the body's organs of oxygenated blood. HypertensionHypertenstion, or high blook pressure, is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. Ehlers-Danlos syndromeA group of inherited disorders marked by extremely loose joints, hyperelastic skin that bruises easily, and easily damaged blood vessels. Polycystic Kidney DiseaseA kidney disorder passed down through families in which multiple cysts form on the kidneys, causing them to become enlarged. SYMPTOMS OF A BRAIN ANEURYSMMost brain aneurysms cause no symptoms and may only be discovered during tests for another, usually unrelated, condition. In other cases, an unruptured aneurysm will cause problems by pressing on areas within the brain. When this happens, the person may suffer from severe headaches, blurred vision, changes in speech, and neck pain, depending on the areas of the brain that are affected and the severity of the aneurysm. Symptoms of a ruptured brain aneurysm often come on suddenly. They may include:
If you have any of the above symptoms or notice them in someone you know, see a health professional immediately. DANGERS OF A BRAIN ANEURYSMAneurysms may burst and bleed into the brain, causing serious complications including hemorrhagic stroke, permanent nerve damage or death. Once it has burst, the aneurysm may burst again and rebleed into the brain, and additional aneurysms may also occur. More commonly, rupture may cause a subarachnoid hemorrhage - bleeding into the space between the skull bone and the brain. A delayed but serious complication of subarachnoid hemorrhage is hydrocephalus, in which the excessive buildup of cerebrospinal fluid in the skull dilates fluid pathways called ventricles that can swell and press on the brain tissue. Another delayed post-rupture complication is vasospasm, in which other blood vessels in the brain contract and limit blood flow to vital areas of the brain. This reduced blood flow can cause stroke or tissue damage. HOW DOES A BRAIN ANEURYSM DEVELOP?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; and high blood pressure (ystemic 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, 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. HOW IS A BRAIN ANEURYSM DIAGNOSED?If you have a sudden, severe headache or other symptoms possibly related to a ruptured aneurysm, you will undergo a test or series of tests to determine if you have had bleeding into the space between your brain and surrounding tissues (subarachnoid hemorrhage) or another type of stroke. If bleeding has occurred, then your emergency care team will determine if a ruptured aneurysm is the cause. If you have symptoms of an unruptured brain aneurysm — such as pain behind the eye, changes in vision, and paralysis on one side of the face — you will likely undergo the same tests. Diagnostic tests include
WHAT IS AN AVM? An arteriovenous malformation (AVM) is a complex tangle of abnormal arteries and veins linked by one or more direct connections called fistulas or shuts. This tangle of abnormal arteries and veins is referred to as a nidus. Normally, as the high-pressure arterial blood is pumped through a capillary bed there is a gradual decrease in blood pressure before reaching the venous system. With an AVM, the capillary bed is absent and the high-pressure arterial blood bypasses normal brain tissue and is pumped directly into the normally low-pressure venous system.There is typically high blood flow through the nidus of the AVM, but it is not known whether the flow is a cause or effect of the abnormal blood vessels, or both. One thought is that the high-pressure blood from the arterial system gravitates towards the path of least resistance. Another thought is that the AVM itself recruits blood vessels.
Ultimately, the arterial blood rushes through the AVM, instead of working through available capillary beds, which feed the surrounding brain tissue, increasing blood flow through the nidus. This re-direction of the arterial blood away from the brain tissue and through the AVM is referred to as shunting.
Over time, the high blood flow and shunting of high-pressure arterial blood through the AVM causes the feeder arteries and veins making up the AVM to dilate or expand. This dilation weakens veins making them susceptible to hemorrhage and the arteries susceptible to aneurysms,
AVMs are thought to be congenital, arising from developmental derangements at the embryonic stage of vessel formation, at the fetal stage. However, this has never been clearly established and they may arise after birth. AVMs are usually single, except when associated with hereditary hemorrhagic telangiectasia (HHT).
* The information provided is not intended for medical advice nor should it substitute medical advice. We suggest contacting your physicians when seeking medical advice. This is not intended to take the place of qualified medical personnel.
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A cerebral aneurysm (also known as an Intracranial or intracerebral aneurysm) is a weak or thin spot on a blood vessel in the brain that balloons out and fills with blood. The bulging aneurysm can put pressure on a nerve or surrounding brain tissue. It may also leak or rupture, spilling blood into the surrounding tissue (called a hemorrhage). Some cerebral aneurysms, particularly those that are very small, do not bleed or cause other problems. Cerebral aneurysms can occur anywhere in the brain, but most are located along a loop of arteries that run between the underside of the brain and the base of the skull. Brain aneurysms can occur in anyone, at any age. They are more common in adults than in children and slightly more common in women than in men. 
The "saccular" or "berry" (A) aneurysm is the most common type of aneurysm, and it's the one we refer to when we think of "brain aneurysms" in general. Berry aneurysms are ones that look like sacs or berries sticking out of a side of a blood vessel wall. Most of these have a "neck" region, although sometimes a neck cannot be readily defined in this type of aneurysm, even at the time of surgery. Berry aneurysms are associated with growth and rupture.
The "fusiform" aneurysm, (B) less common than the saccular aneurysm, looks like the blood vessel is expanded in all directions. This type is typically associated with fatty plaques or streaks in the artery (i.e., atherosclerosis), or with cuts in the blood vessel wall (i.e., arterial dissections). Fusiform aneurysms don't have a "neck" region, and they seldom rupture. 
The "mycotic" or "infectious" (C) aneurysm is very rare and is a saccular aneurysm that arises from an artery that has had a certain part of the wall affected by a source of infection usually originating from somewhere else in the body (e.g., the heart) and spreading to the brain blood vessel by the blood stream.
A false or “pseudo-aneurysm" (D) 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").
