aneurysm: Definition and Much More from Answers.com
- ️Wed Jul 01 2015
Definition
Cerebral aneurysm is the enlargement, distention, dilation, bulging, or ballooning of the wall of a cerebral artery or vein. Aneurysms affect arteries throughout the body, including blood vessels in the brain (intracerebral aneurysm). Ruptures of intracerebral aneurysm result in stroke (loss of blood supply to tissue) and bleeding into the subarachnoid space). The most common aneurysm is an abdominal aneurysm.
Description
Dilations, or ballooning, of blood vessels to form an aneurysm are particularly dangerous because they increase the chance of arterial rupture and subsequent bleeding into brain tissues (a hemorrhagic stroke). Rupture of an aneurysm can lead to the leakage of blood into the tissues and spaces surrounding the brain. This leaked blood then clots to form an intracranial hematoma. Aneurysms that rupture can result in severe disability or death.
Common complications of cerebral aneurysms that leak include hydrocephalus (the excessive accumulation of cerebrospinal fluid) and persistent spasms of blood vessels that adversely affect the maintenance of arterial blood pressure.
Once they rupture or bleed, aneurysms have a tendency toward recurrent bleeding episodes. This tendency to rebleed is particularly high in the first few days following the initial bleed. Intracerebral bleeds are often accompanied by increases in cerebrospinal fluid and an increased intracranial pressure (hydrocephalus).
Once they occur, aneurysms are dynamic and can increase in size over time. The increase in size is not always linear and can advance sporadically until they expand to a critical size. As they grow, aneurysms begin to put pressure on surrounding tissues. In addition, as they grow, aneurysms usually result in progressively more difficult problems.
The larger the size of an aneurysm, regardless of location, the greater the chance it will ultimately bleed. Cerebral aneurysm ruptures usually lead to subarachnoid hemorrhage (SAH).
Demographics
Although more common in adults than children, cerebral aneurysms occur in all age groups. Cerebral aneurysms are more common—and the risk of aneurysm generally increases—with age.
Aneurysm sufferers are rarely young; the incidence of aneurysm is low in those under 20 years of age. In contrast, aneurysms are relatively common in people over 65 years of age. Risk indicators for some groups such as Caucasian males begin to increase at age 55. Some studies indicate that up to 5% of the population over 65 suffer some form of aneurysm.
Incidence of specific aneurysms varies, but in general within the United States they are occur less frequently in Caucasian women, and are relatively uncommon in African Americans.
Of those affected with an aneurysm anywhere in the body, the National Institute of Health (NIH) estimates that approximately 30,000 people in the United States will suffer an aneurysm rupture.
Cigarette smoking and excess alcohol use substantially increase the risk of aneurysm rupture.
Causes and symptoms
An aneurysm may be a congenital defect in the structure of the muscular wall of affected blood vessels (e.g., the intima of an artery), or arise secondary to trauma, atherosclerosis, or high blood pressure. The defect results in an abnormal thinning of the arterial or venous wall that makes the wall subsequently susceptible to aneurysm.
Research data appears to show that some individuals have a basic genetic susceptibility or predisposition to aneurysms. The genetic inheritance patterns resemble characteristics linked to an autosomal dominant gene. Within some families, rates of aneurysms can run as high as five to 10 times those found in the general population.
Direct causes of intracerebral aneurysms include infection, trauma, or neoplastic disease. If infection is the cause, the infection may be from a remote site. For example, an aneurysm in the brain may result from the loosed embolus such as plaque, fatty deposit, clot, or clump of cells, originating at an infection in another part of the body. The embolus is transported to the site of the future cerebral aneurysm by the bloodstream and cerebral circulation. An aneurysm formed in this manner is termed a mycotic aneurysm.
Prior to rupture, the symptoms associated with an aneurysm depend upon its location, size, and rate of expansion. A static aneurysm that does not leak (bleed) or adversely affect cerebral circulation or neighboring tissue may be asymptomatic (without symptoms). In contrast, larger aneurysms or aneurysms with a rapid growth rate may produce pronounced symptoms such as swelling, loss of sensation, blurred vision, etc.
Just prior to an aneurysm rupture, patients typically experience some symptoms commonly associated with stroke. Depending on the size and location of the aneurysm about to rupture, a patient may suffer a severe headache, deterioration or disturbances of hearing, and disturbances of vision such as double vision, severe nausea and vomiting, and syncopal episodes (periodic fainting or loss of consciousness).
A severe headache that is unresponsive to standard analgesics is the most common sign of a leaking or bleeding aneurysm. Many patients experience a series of sentinel (warning) headaches if the aneurysm begins to leak prior to rupture. A fully ruptured aneurysm presents with a severe headache that is frequently accompanied by fainting or temporary (transient) loss of consciousness, often with severe nausea, vomiting, and rapidly developing stiff neck (nuchal rigidity).
Aneurysms normally rupture while the patient is active and awake.
Diagnosis
The severe headache that accompanies a cerebral aneurysm is often the principle complaint upon which the diagnosis of aneurysm begins to build.
Angiography provides the most definitive diagnosis of an intracerebral aneurysm by determining the specific site of the aneurysm. A computed tomography (CT) scan can also diagnose a bleeding cerebral aneurysm. Arteriography is an x ray of the carotid artery taken when a special dye is injected into the artery.
The presence of blood in the cerebrospinal fluid withdrawn during a lumbar puncture is also diagnostic evidence for blood leaking into the subarachnoid space.
Magnetic resonance imaging (MRI) studies can also be useful in accessing the extent of damage to surrounding tissues and are often used to study aneurysms prior to leakage or rupture. MRI uses magnetic fields to detect subtle changes in brain tissue content. The benefit of MRI over CT imaging is that MRI is better able to localize the exact anatomical position of an aneurysm. Other types of MRI scans are magnetic resonance angiography (MRA) and functional magnetic resonance imaging (fMRI). Neurosurgeons use MRA to detect stenosis (blockage) of the brain arteries inside the skull by mapping flowing blood. Functional MRI uses a magnet to pick up signals from oxygenated blood and can show brain activity through increases in local blood flow.
Duplex Doppler ultrasound and arteriography are two additional diagnostic imaging techniques used to decide if an individual would benefit from a surgical procedure called carotid endarterectomy. This surgery is used to remove fatty deposits from the carotid arteries and can help prevent stroke. Doppler ultrasound is a painless, non-invasive test in which sound waves bounce off the moving blood and the tissue in the artery and can be formed into an image.
Treatment team
Management and treatment of aneurysms require a multi-disciplinary team. Physicians are responsible for caring for general health and providing guidance aimed at preventing a stroke. Neurologists and neurosurgeons usually lead acute-care teams and direct patient care during hospitalization and recovery from surgery. Neuroradiologists help pinpoint the location and extent of aneurysms.
Treatment
Treatment for ruptures of cerebral aneurysms includes measures to stabilize the emergency by assuring cardiopulmonary functions (adequate heart rate and respiration) while simultaneously moving to decrease intracranial pressure and surgically clip (repair and seal) the ruptured cerebral aneurysm.
Surgery is often performed as soon as the patient is stabilized; ideally within 72 hours of the onset of rupture. The goal of surgery is to prevent rebleeding. Surgery is performed to expose the aneurysm and allow the placement of a clip across a strong portion of the vessel to obstruct the flow of blood through the weakened aneurysm. Repeat surgical procedures to seal an aneurysm are not uncommon.
Treatment of unruptured aneurysms is certainly less dramatic, but presents a more deliberate and complex path. Microcoil thrombosis or balloon embolization (the insertion via the arterial catheter of a balloon or other obstruction that blocks blood flow through the region of aneurysm) are alternatives to full surgical intervention.
Other nonsurgical interventions include rest, medications, and hypertensive-hypervolemic therapy to drive blood around obstructed vessels.
Treatment decisions are made between the treatment team and family members with regard to the best course of treatment and the probable outcomes for patients suffering a severe aneurysm rupture with extensive damage to surrounding brain tissue.
Asymptomatic aneurysms allow the treatment team to more fully evaluate surgical and nonsurgical options.
Recovery and rehabilitation
The recovery and rehabilitation of patients suffering a cerebral aneurysm depend on the location and size of the aneurysm. The course of recovery and rehabilitation is also heavily influenced by whether the aneurysm ruptures.
Key to recovery is the prevention of aneurysm rebleeding, the management of swelling in the ventricular system (hydrocephalus), seizures, cardiac arrhythmias, and vasospasm. The onset of vasospasm within the first two weeks of the initial bleeding incident is the major cause of death in those who survive the initial rupture of the aneurysm.
Ventricular drains are used to control the buildup of cerebrospinal fluid in the ventricular system.
Clinical trials
As of May 2004, current studies sponsored by the National Institute of Neurological Disorders and Stroke (NINDS) include a study on the effect of the drug ProliNO on brain artery spasms after aneurysm rupture and a study of the role of genetics on the development of intracranial aneurysms (Familial Intracranial Aneurysm Study). Further information is available at .
Prognosis
The overall prognosis for a patient with a cerebral aneurysm depends on several factors including the size, location, and stability of the aneurysm. Facets of the patient's general health, neurological health, age, and familial history must also be evaluated in forming a prognosis.
Although each patient is different, and each aneurysm must be individually evaluated, in general, the prognosis for patients who have suffered a bleed is guarded at best, with mortality rates up 60% within a year of the initial bleeding incident. Approximately half of the survivors suffer some long-lasting disability. Patients with cerebral aneurysm can, however, fully recover with no long-lasting disorder.
Data regarding the prognosis for unruptured aneurysms is more tentative and not specific for cerebral aneurysms. Some long-term studies give evidence that only 10% of patients might suffer leakage or bleeding from their aneurysm over a period of 10 years and only about a quarter of patients would experience bleeding from the aneurysm over a period of 25 years.
Special concerns
Intracerebral aneurysms are sometimes associated with other diseases such as fibromuscular hyperplasia or other disorders such as high blood pressure (although aneurysms also occur in persons with normal blood pressure.
Other physiological stresses such as pregnancy have not been demonstrated to have a correlation to the rupture of cerebral aneurysm.
Resources
BOOKS
Bear, M., et al. Neuroscience: Exploring the Brain. Baltimore: Williams & Wilkins, 1996.
Goetz, C. G., et al. Textbook of Clinical Neurology. Philadelphia: W.B. Saunders Co., 1999.
Goldman, Cecil. Textbook of Medicine, 21st ed. New York: W.B. Saunders Co., 2000.
Guyton & Hall. Textbook of Medical Physiology, 10th ed. New York: W.B.Saunders Co., 2000.
Wiebers, David. Stroke-Free for Life: The Complete Guide to Stroke Prevention and Treatment. New York: Harper, 2002.
OTHER
"Stroke Risk Factors." American Stroke Association. April 20, 2004 (May 22, 2004). http://www.strokeassociation.org/presenter.jhtml?identifier=4716.
ORGANIZATIONS
American Stroke Association: A Division of American Heart Association. 7272 Greenville Avenue, Dallas, TX 75231-4596. (214) 706-5231 or (888) 4STROKE (478-7653). strokeassociation@heart.org. http://www.strokeassociation.org/.
Brain Aneurysm Foundation. 12 Clarendon Street, Boston, MA 02116. (617) 723-3870; Fax: (617) 723-8672. information@bafound.org. http://www.bafound.org.
National Stroke Association. 9707 East Easter Lane, Englewood, CO 80112-3747. (303) 649-9299 or (800) STROKES (787-6537); Fax: (303) 649-1328. info@stroke.org. http//www.stroke.org/.
Paul Arthur
Classification & external resources
| ICD-10 | I72. |
|---|---|
| ICD-9 | 442 |
| DiseasesDB | 15088 |
| MedlinePlus | 001122 |
An aneurysm (or aneurism) is a localized, blood-filled dilation (bulge) of a blood vessel caused by disease or weakening of the vessel wall.[1] Aneurysms most commonly occur in arteries at the base of the brain (the circle of Willis) and in the aorta (the main artery coming out of the heart), a so-called aortic aneurysm. The bulge in a blood vessel can burst and lead to death at any time. The larger an aneurysm becomes, the more likely it is to burst. Aneurysms can usually be treated.
Classification
Aneurysms may involve arteries or veins and have various causes. They are commonly further classified by shape, structure and location.
Shape
A saccular aneurysm resembles a small bubble that appears off the side of a blood vessel. The innermost layer of an artery, in direct contact with the flowing blood, is the tunica intima, commonly called the intima. Adjacent to this layer is the tunica media, known as the media and composed of smooth muscle cells and elastic tissue. The outermost layer is the tunica adventitia or tunica externa. This layer is composed of tougher connective tissue. A saccular aneurysm develops when fibers in the outer layer separate allowing the pressure of the blood to force the two inner layers to balloon through.
A fusiform aneurysm is a bulging around the entire circumference of the vessel without protrusion of the inner layers. It is shaped like a football or spindle.
These aneurysms can result from hypertension in conjunction with atherosclerosis that weakens the tunica adventitia, from congenital weakness of the adventitial layer (as in Marfan syndrome) or from infection.
Structure
In a true aneurysm the inner layers of a vessel have bulged outside the outer layer that normally confines them. The aneurysm is surrounded by these inner layers.
A false- or pseudoaneurysm does not primarily involve such distortion of the vessel. It is a collection of blood leaking completely out of an artery or vein, but confined next to the vessel by the surrounding tissue. This blood-filled cavity will eventually either thrombose (clot) enough to seal the leak or it will rupture out of the tougher tissue enclosing it and flow freely between layers of other tissues or into looser tissues. Pseudoaneurysms can be caused by trauma that punctures the artery and are a known complication of percutaneous arterial procedures such as arteriography or of arterial grafting or of use of an artery for injection, such as by drug abusers unable to find a usable vein. Like true aneurysms they may be felt as an abnormal pulsatile mass on palpation.
Location
Most non-intracranial aneurysms (94%) arise distal to the origin of the renal arteries at the infrarenal abdominal aorta, a condition mostly caused by atherosclerosis. The thoracic aorta can also be involved. One common form of thoracic aortic aneurysm involves widening of the proximal aorta and the aortic root, which leads to aortic insufficiency. Aneurysms occur in the legs also, particularly in the deep vessels (e.g., the popliteal vessels in the knee). Arterial aneurysms are much more common, but venous aneurysms do happen (for example, the popliteal venous aneurysm).
- While most aneurysms occur in an isolated form, the occurrence of berry aneurysms of the anterior communicating artery of the circle of Willis is associated with autosomal dominant polycystic kidney disease (ADPKD).
- The third stage of syphilis also manifests as aneurysm of the aorta, which is due to loss of the vasa vasorum in the tunica adventitia.
Risks
Rupture and blood clotting are the risks involved with aneurysms. Rupture leads to drop in blood pressure, rapid heart rate, and lightheadedness. The risk of death is high except for rupture in the extremities.
Blood clots from popliteal arterial aneurysms can travel downstream and suffocate tissue. Only if the resulting pain and/or numbness are ignored over a significant period of time will such extreme results as amputation be needed. Clotting in popliteal venous aneurysms are much more serious as the clot can embolise and travel to the heart, or through the heart to the lungs (a pulmonary embolism). Risk factors for an aneurysm are diabetes, obesity, hypertension, tobacco smoking, and alcoholism.
Formation
Most frequent site of occurrence is in the anterior cerebral artery from the circle of Willis. The occurrence and expansion of an aneurysm in a given segment of the arterial tree involves local hemodynamic factors and factors intrinsic to the arterial segment itself.
The human aorta is a relatively low-resistance circuit for circulating blood. The lower extremities have higher arterial resistance, and the repeated trauma of a reflected arterial wave on the distal aorta may injure a weakened aortic wall and contribute to aneurysmal degeneration. Systemic hypertension compounds the injury, accelerates the expansion of known aneurysms, and may contribute to their formation.
Aneurysm formation is probably the result of multiple factors affecting that arterial segment and its local environment.
Hemodynamically, the coupling of aneurysmal dilation and increased wall stress is approximated by the law of Laplace. Specifically, the Laplace law states that the (arterial) wall tension is proportional to the pressure times the radius of the arterial conduit (T = P X R). As diameter increases, wall tension increases, which contributes to increasing diameter. As tension increases, risk of rupture increases. Increased pressure (systemic hypertension) and increased aneurysm size aggravate wall tension and therefore increase the risk of rupture. In addition, the vessel wall is supplied by the blood within its lumen in humans. Therefore in a developing aneurysm, the most ischemic portion of the aneurysm is at the farthest end, resulting in weakening of the vessel wall there and aiding further expansion of the aneurysm. Thus eventually all aneurysms will, if left to complete their evolution, rupture without intervention. In dogs, collateral vessels supply the vessel and aneurysms are rare.
Treatment of Aneurysms
Historically, the treatment of arterial aneurysms has been surgical intervention, or watchful waiting in combination with control of blood pressure. Recently, endovascular or minimally invasive techniques have been developed for many types of aneurysms.
Treatment of Brain Aneurysms
Currently there are two treatment options for brain aneurysms: surgical clipping or endovascular coiling. Surgical clipping was introduced by Walter Dandy of the Johns Hopkins Hospital in 1937. It consists of performing a craniotomy, exposing the aneurysm, and closing the base of the aneurysm with a clip. The surgical technique has been modified and improved over the years. Surgical clipping remains the best method to permanently eliminate aneurysms. Endovascular coiling was introduced by Guido Guglielmi at UCLA in 1991. It consists of passing a catheter into the femoral artery in the groin, through the aorta, into the brain arteries, and finally into the aneurysm itself. Once the catheter is in the aneurysm, platinum coils are pushed into the aneurysm and released. These coils initiate a clotting or thrombotic reaction within the aneurysm that, if successful, will eliminate the aneurysm. In the case of broad-based aneurysms, a stent is passed first into the parent artery to serve as a scaffold for the coils ("stent-assisted coiling").
At this point it appears that the risks associated with surgical clipping and endovascular coiling, in terms of stroke or death from the procedure, are the same. The major problem associated with endovascular coiling, however, is the high recurrence rate and subsequent bleeding of the aneurysms. For instance, the most recent study by Jacques Moret and colleagues from Paris, France, (a group with one of the largest experiences in endovascular coiling) indicates that 28.6% of aneurysms recurred within one year of coiling, and that the recurrence rate increased with time. (Piotin M et al., Radiology 243(2):500-508, May 2007) These results are similar to those previously reported by other endovascular groups. For instance Jean Raymond and colleagues from Montreal, Canada, (another group with a large experience in endovascular coiling) reported that 33.6% of aneurysms recurred within one year of coiling. (Raymond J et al., Stroke 34(6):1398-1403, June 2003) The long-term coiling results of one of the two prospective, randomized studies comparing surgical clipping versus endovascular coiling, namely the International Subarachnoid Aneurysm Trial (ISAT) are turning out to be similarly worrisome. In ISAT, the need for late retreatment of aneurysms was 6.9 times more likely for endovascular coiling as compared to surgical clipping. (Campi A et al., Stroke 38(5):1538-1544, May 2007)
Therefore it appears that although endovascular coiling is associated with a shorter recovery period as compared to surgical clipping, it is also associated with a significantly higher recurrence and bleeding rate after treatment. Patients who undergo endovascular coiling need to have annual studies (such as MRI/MRA, CTA, or angiography) indefinitely to detect early recurrences. If a recurrence is identified, the aneurysm needs to be retreated with either surgery or further coiling. The risks associated with surgical clipping of previously-coiled aneurysms are very high. Ultimately, the decision to treat with surgical clipping versus endovascular coiling should be made by a cerebrovascular team with extensive experience in both modalities. At present it appears that only older patients with aneurysms that are difficult to reach surgically are more likely to benefit from endovascular coiling. These generalizations, however, are difficult to apply to every case, which is reflected in the wide variabilty internationally in the use of surgical clipping versus endovascular coiling.
Treatment of peripheral aneurysms
For aortic aneurysms or aneurysms that happen in the vessels that supply blood to the arms, legs, and head (the peripheral vessels), surgery involves replacing the weakened section of the vessel with an artificial tube, called a graft. More recently, covered metallic stent grafts can be inserted through the arteries of the leg and deployed across the aneurysm.
See also
- Aortic aneurysm
- Aortic dissection
- Cerebral aneurysm
- Charcot-Bouchard aneurysms
- Rasmussen's aneurysm
- Aneurysm of sinus of Valsalva
References
External links
- Addressing the Challenges Faced as a Result of Brain Haemorrhage
- Brain Blood Vessel Disorder Help & Info Site
- @neurIST - Integrated Biomedical Informatics for the Management of Cerebral Aneurysms
- Story of Aneurysm Survival
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