Joe Niekro Foundation - Knuckling Up for Aneurysm Research

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 incidence of reported ruptured aneurysm is about 10 in every 100,000 persons per year (about 27,000 patients per year in the US), most commonly in people between ages 30 and 60 years.

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:

The "saccular" or "berry" 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 (see Figure 4, below). Most of these have a "neck" region (see Figure 6, below), 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 (Figures 3 - 7, below) and rupture (hemorrhage; see Figure 8, below).
The "fusiform" aneurysm, less common than the berry aneurysm, is not a saccular aneurysm. Unlike the saccular aneurysm, a fusiform aneurysm looks like the blood vessel is expanded (i.e., "ectatic") 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") aneurysm, very rare, 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 (i.e., "hematogenous spread").

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")

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 (i.e., in the "posterior cerebral circulation"), are significantly higher than smaller aneurysms in the front part of the brain arteries ("anterior cerebral circulation").


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 incidence of reported ruptured aneurysm is about 10 in every 100,000 persons per year (about 27,000 patients per year in the US), most commonly in people between ages 30 and 60 years. 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: The "saccular" or "berry" 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 (see Figure 4, below). Most of these have a "neck" region (see Figure 6, below), 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 (Figures 3 - 7, below) and rupture (hemorrhage; see Figure 8, below). The "fusiform" aneurysm, less common than the berry aneurysm, is not a saccular aneurysm. Unlike the saccular aneurysm, a fusiform aneurysm looks like the blood vessel is expanded (i.e., "ectatic") 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") aneurysm, very rare, 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 (i.e., "hematogenous spread"). 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") 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 (i.e., in the "posterior cerebral circulation"), are significantly higher than smaller aneurysms in the front part of the brain arteries ("anterior cerebral circulation").





Factors that doctors and researchers believe contribute to the formation of brain aneurysms: • Smoking • Hypertension • Traumatic Head Injury • Use of Alcohol • Use of Oral Contraceptives • Family History of Brain Aneurysms Other Inherited Disorders: Ehler's Syndrome, Polycystic Kidney Disease, and Mar fan's Syndrome



Aneurysms 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.





Most cerebral aneurysms do not show symptoms until they either become very large or burst. Small, unchanging aneurysms generally will not produce symptoms, whereas a larger aneurysm that is steadily growing may press on tissues and nerves. Symptoms may include pain above and behind the eye; numbness, weakness, or paralysis on one side of the face; dilated pupils; and vision changes. When an aneurysm hemorrhages, an individual may experience a sudden and extremely severe headache, double vision, nausea, vomiting, stiff neck, and/or loss of consciousness. Patients usually describe the headache as "the worst headache of my life" and it is generally different in severity and intensity from other headaches patients may experience. "Sentinel" or warning headaches may result from an aneurysm that leaks for days to weeks prior to rupture. Only a minority of patients have a sentinel headache prior to aneurysm rupture. Other signs that a cerebral aneurysm has burst include nausea and vomiting associated with a severe headache, a drooping eyelid, sensitivity to light, and change in mental status or level of awareness. Some individuals may have seizures. Individuals may lose consciousness briefly or go into prolonged coma. People experiencing this "worst headache," especially when it is combined with any other symptoms, should seek immediate medical attention.



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. 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. For this reason, this event is referred to "subarachnoid hemorrhage".