Cerebral arteriovenous malformation
Encyclopedia
A cerebral arteriovenous malformation (AVM) is an abnormal connection between the arteries
and vein
s in the brain
.
s and seizure
s while at least 15% of the population at detection have no symptoms at all. Other common symptoms are a pulsing noise in the head, progressive weakness
and numbness and vision changes.
In serious cases, the blood vessels rupture and there is bleeding within the brain (intracranial hemorrhage
). Nevertheless in more than half of patients with AVM, hemorrhage is the first symptom. Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence
, and blurred vision, amongst others. Impairments caused by local brain tissue damage on the bleed site are also possible, including seizure, one-sided weakness (hemiparesis
), a loss of touch sensation on one side of the body and deficits in language processing (aphasia
). Minor bleeding can occur with no noticeable symptoms.
AVMs in certain critical locations may stop the circulation of the cerebrospinal fluid
, causing accumulation of the fluid within the skull and giving rise to a clinical condition called hydrocephalus
. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges
.
studies after a complete neurological and physical examination. Three main techniques are used to visualize the brain and search for AVM: computed tomography
(CT), magnetic resonance imaging
(MRI), and cerebral angiography
. A CT scan of the head is usually performed first when the subject is symptomatic. It can suggest the approximate site of the bleed. MRI is more sensitive than CT in the diagnosis of AVMs and provides better information about the exact location of the malformation. More detailed pictures of the tangle of blood vessels that compose an AVM can be obtained by using radioactive agents injected into the blood stream. If a CT is used in conjunction of dye this is called a computerized tomography angiogram while if MRI is used it is called magnetic resonance angiogram. The best images of an AVM are obtained through cerebral angiography
. This procedure involves using a catheter
, threaded through an artery up to the head, to deliver a contrast agent into the AVM. As the contrast agent flows through the AVM structure, a sequence of X-ray
images are obtained.
The risk of post-surgical neurological deficit (difficulty with language, motor weakness, vision loss) increases with increasing Spetzler-Martin grade.
enriched blood from the heart travels in sequence through smaller blood vessels going from arteries, to arterioles and then capillaries
. Oxygen is removed in the latter vessel to be used by the brain. After the oxygen is removed blood reaches venules and later veins which will take it back to the heart and lungs. On the other hand when there is an AVM blood goes directly from arteries to veins through the abnormal vessels disrupting the normal circulation of blood.
. This risk is difficult to quantify since many patients with asymptomatic AVMs will never come to medical attention. Small AVMs tend to bleed more often than do larger ones, the opposite of cerebral aneurysms. If a rupture or bleeding incident occurs, the blood may penetrate either into the brain tissue (cerebral hemorrhage) or into the subarachnoid space
, which is located between the sheaths (meninges
) surrounding the brain (subarachnoid hemorrhage
). Bleeding may also extend into the ventricular system
(intraventricular hemorrhage
). Cerebral hemorrhage appears to be most common.
One long-term study (mean follow up greater than 20 years) of over 150 symptomatic AVMs (either presenting with bleeding or seizures) found the risk of cerebral hemorrhage to be approximately 4% per year, slightly higher than the 2-3% seen in other studies. A simple, rough approximation of a patient's lifetime bleeding risk is 105 - (patient age in years). This equation assumes a 3% yearly bleeding risk. For example, a healthy 30 year old patient would have approximately a 75% lifetime risk of at least one bleeding event.
The treatment in the case of sudden bleeding is focused on restoration of vital function. Anticonvulsant medications such as phenytoin
are often used to control seizure; medications or procedures may be employed to relieve intracranial pressure. Eventually, curative treatment may be required to prevent recurrent hemorrhage. However, any type of intervention may also carry a risk of creating a neurological deficit.
Surgical elimination of the blood vessels involved is the preferred curative treatment for many types of AVM. Surgery is performed by a neurosurgeon who temporarily removes part of the skull (craniotomy
), separates the AVM from surrounding brain tissue, and resects the abnormal vessels. While surgery can result in an immediate, complete removal of the AVM, risks exist depending on the size and the location of the malformation. The preferred treatment of Spetzler-Martin grade 1 and 2 AVMs in young, healthy patients is surgical resection due to the relatively small risk of neurological damage compared to the high lifetime risk of hemorrhage. Grade 3 AVMs may or may not be amenable to surgery. Grade 4 and 5 AVMs are not usually surgically treated.
Radiosurgery
has been widely used on small AVMs with considerable success. The Gamma Knife is an apparatus used to precisely apply a controlled radiation dosage to the volume of the brain occupied by the AVM. While this treatment does not require an incision and craniotomy (with their own inherent risks), three or more years may pass before the complete effects are known, during which time patients are at risk of bleeding. Complete obliteration of the AVM may or may not occur after several years, and repeat treatment may be needed. Radiosurgery is itself not without risk. In one large study, nine percent of patients had transient neurological symptoms, including headache, after radiosurgery for AVM. However, most symptoms resolved, and the long-term rate of neurological symptoms was 3.8%.
Embolization
is the occlusion of blood vessels most commonly with a glue-like substance introduced by a radiographically
guided catheter
. Such glue blocks the vessel and reduces blood flow into the AVM. Embolization is frequently used as an adjunct to either surgery or radiation treatment. Before other treatments it reduces the size of the AVM while during surgery it reduces the risk of bleeding. However, embolization alone may completely obliterate some AVMs.
of AVMs is approximately 1 per 100000 a year. The point prevalence
in adults is approximately 18 per 100000. AVMs are more common in males than females, although in females pregnancy
may start or worsen symptoms due the increase in blood flow
and volume
it usually brings.
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
and vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
s in the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
.
Signs and symptoms
The most frequently observed problems related to an AVM are headacheHeadache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
s and seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s while at least 15% of the population at detection have no symptoms at all. Other common symptoms are a pulsing noise in the head, progressive weakness
Weakness
Weakness is a symptom represented, medically, by a number of different conditions, including: lack of muscle strength, malaise, dizziness, or fatigue. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a...
and numbness and vision changes.
In serious cases, the blood vessels rupture and there is bleeding within the brain (intracranial hemorrhage
Intracranial hemorrhage
An intracranial hemorrhage is a hemorrhage, or bleeding, within the skull.-Causes:Intracranial bleeding occurs when a blood vessel within the skull is ruptured or leaks. It can result from physical trauma or nontraumatic causes such as a ruptured aneurysm...
). Nevertheless in more than half of patients with AVM, hemorrhage is the first symptom. Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence
Urinary incontinence
Urinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners...
, and blurred vision, amongst others. Impairments caused by local brain tissue damage on the bleed site are also possible, including seizure, one-sided weakness (hemiparesis
Hemiparesis
Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....
), a loss of touch sensation on one side of the body and deficits in language processing (aphasia
Aphasia
Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
). Minor bleeding can occur with no noticeable symptoms.
AVMs in certain critical locations may stop the circulation of the cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
, causing accumulation of the fluid within the skull and giving rise to a clinical condition called hydrocephalus
Hydrocephalus
Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...
. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
.
Diagnosis
An AVM diagnosis is established by neuroimagingNeuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
studies after a complete neurological and physical examination. Three main techniques are used to visualize the brain and search for AVM: computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
(CT), magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI), and cerebral angiography
Cerebral angiography
Cerebral angiography is a form of angiography which provides images of blood vessels in and around the brain, thereby allowing detection of abnormalities such as arteriovenous malformations and aneurysms....
. A CT scan of the head is usually performed first when the subject is symptomatic. It can suggest the approximate site of the bleed. MRI is more sensitive than CT in the diagnosis of AVMs and provides better information about the exact location of the malformation. More detailed pictures of the tangle of blood vessels that compose an AVM can be obtained by using radioactive agents injected into the blood stream. If a CT is used in conjunction of dye this is called a computerized tomography angiogram while if MRI is used it is called magnetic resonance angiogram. The best images of an AVM are obtained through cerebral angiography
Cerebral angiography
Cerebral angiography is a form of angiography which provides images of blood vessels in and around the brain, thereby allowing detection of abnormalities such as arteriovenous malformations and aneurysms....
. This procedure involves using a catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
, threaded through an artery up to the head, to deliver a contrast agent into the AVM. As the contrast agent flows through the AVM structure, a sequence of X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
images are obtained.
Grading
A common method of grading cerebral AVMs is the Spetzler-Martin grade. This system was designed to assess the patient's risk of neurological deficit after open surgical resection, based on characteristics of the AVM itself. Based on this system, AVMs may be classified as grades 1 - 5.| AVM size | Adjacent eloquent cortex | Draining veins |
|---|---|---|
| Under 3 cm = 1 | Non-eloquent = 0 | Superficial only = 0 |
| 3-6 cm = 2 | Eloquent* = 1 | Deep veins = 1 |
| Over 6 cm = 3 |
- Such as sensory or motor cortex, language or visual areas, brain stem, etc.
The risk of post-surgical neurological deficit (difficulty with language, motor weakness, vision loss) increases with increasing Spetzler-Martin grade.
Pathophysiology
AVMs are an abnormal connection between the arteries and veins in the human brain. Arteriovenous malformations are most commonly of prenatal origin. The cause of AVMs remains unknown. In a normal brain oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
enriched blood from the heart travels in sequence through smaller blood vessels going from arteries, to arterioles and then capillaries
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
. Oxygen is removed in the latter vessel to be used by the brain. After the oxygen is removed blood reaches venules and later veins which will take it back to the heart and lungs. On the other hand when there is an AVM blood goes directly from arteries to veins through the abnormal vessels disrupting the normal circulation of blood.
Prognosis
The main risk is intracranial hemorrhageIntracranial hemorrhage
An intracranial hemorrhage is a hemorrhage, or bleeding, within the skull.-Causes:Intracranial bleeding occurs when a blood vessel within the skull is ruptured or leaks. It can result from physical trauma or nontraumatic causes such as a ruptured aneurysm...
. This risk is difficult to quantify since many patients with asymptomatic AVMs will never come to medical attention. Small AVMs tend to bleed more often than do larger ones, the opposite of cerebral aneurysms. If a rupture or bleeding incident occurs, the blood may penetrate either into the brain tissue (cerebral hemorrhage) or into the subarachnoid space
Subarachnoid space
In the central nervous system, the subarachnoid cavity is the interval between the arachnoid membrane and pia mater....
, which is located between the sheaths (meninges
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
) surrounding the brain (subarachnoid hemorrhage
Subarachnoid hemorrhage
A subarachnoid hemorrhage , or subarachnoid haemorrhage in British English, is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain...
). Bleeding may also extend into the ventricular system
Ventricular system
The ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord.-Components:The system comprises four ventricles:* right and left lateral ventricles* third ventricle...
(intraventricular hemorrhage
Intraventricular hemorrhage
An intraventricular hemorrhage , often abbreviated "IVH," is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space...
). Cerebral hemorrhage appears to be most common.
One long-term study (mean follow up greater than 20 years) of over 150 symptomatic AVMs (either presenting with bleeding or seizures) found the risk of cerebral hemorrhage to be approximately 4% per year, slightly higher than the 2-3% seen in other studies. A simple, rough approximation of a patient's lifetime bleeding risk is 105 - (patient age in years). This equation assumes a 3% yearly bleeding risk. For example, a healthy 30 year old patient would have approximately a 75% lifetime risk of at least one bleeding event.
Treatment
Treatment depends on the location and size of the AVM and whether there is bleeding or not.The treatment in the case of sudden bleeding is focused on restoration of vital function. Anticonvulsant medications such as phenytoin
Phenytoin
Phenytoin sodium is a commonly used antiepileptic. Phenytoin acts to suppress the abnormal brain activity seen in seizure by reducing electrical conductance among brain cells by stabilizing the inactive state of voltage-gated sodium channels...
are often used to control seizure; medications or procedures may be employed to relieve intracranial pressure. Eventually, curative treatment may be required to prevent recurrent hemorrhage. However, any type of intervention may also carry a risk of creating a neurological deficit.
Surgical elimination of the blood vessels involved is the preferred curative treatment for many types of AVM. Surgery is performed by a neurosurgeon who temporarily removes part of the skull (craniotomy
Craniotomy
A craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often a critical operation performed on patients recording, brain imaging, and for neurological manipulations such as electrical stimulation and chemical...
), separates the AVM from surrounding brain tissue, and resects the abnormal vessels. While surgery can result in an immediate, complete removal of the AVM, risks exist depending on the size and the location of the malformation. The preferred treatment of Spetzler-Martin grade 1 and 2 AVMs in young, healthy patients is surgical resection due to the relatively small risk of neurological damage compared to the high lifetime risk of hemorrhage. Grade 3 AVMs may or may not be amenable to surgery. Grade 4 and 5 AVMs are not usually surgically treated.
Radiosurgery
Radiosurgery
Radiosurgery is a medical procedure that allows non-invasive treatment of benign and malignant tumors. It is also known as stereotactic radiotherapy, when used to target lesions in the brain, and stereotactic body radiotherapy when used to target lesions in the body...
has been widely used on small AVMs with considerable success. The Gamma Knife is an apparatus used to precisely apply a controlled radiation dosage to the volume of the brain occupied by the AVM. While this treatment does not require an incision and craniotomy (with their own inherent risks), three or more years may pass before the complete effects are known, during which time patients are at risk of bleeding. Complete obliteration of the AVM may or may not occur after several years, and repeat treatment may be needed. Radiosurgery is itself not without risk. In one large study, nine percent of patients had transient neurological symptoms, including headache, after radiosurgery for AVM. However, most symptoms resolved, and the long-term rate of neurological symptoms was 3.8%.
Embolization
Embolization
Embolization is a non-surgical, minimally-invasive procedure performed by an interventional radiologist and interventional neuroradiologists. It involves the selective occlusion of blood vessels by purposely introducing emboli.-Therapeutic applications:...
is the occlusion of blood vessels most commonly with a glue-like substance introduced by a radiographically
Radiology
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...
guided catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
. Such glue blocks the vessel and reduces blood flow into the AVM. Embolization is frequently used as an adjunct to either surgery or radiation treatment. Before other treatments it reduces the size of the AVM while during surgery it reduces the risk of bleeding. However, embolization alone may completely obliterate some AVMs.
Epidemiology
The annual new detection rate incidenceIncidence (epidemiology)
Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...
of AVMs is approximately 1 per 100000 a year. The point prevalence
Point prevalence
In epidemiology, point prevalence is a measure of the proportion of people in a population who have a disease or condition at a particular time, such as a particular date. It is like a snap shot of the disease in time. It can be used for statistics on the occurrence of chronic diseases...
in adults is approximately 18 per 100000. AVMs are more common in males than females, although in females pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
may start or worsen symptoms due the increase in blood flow
Blood flow
Blood flow is the continuous running of blood in the cardiovascular system.The human body is made up of several processes all carrying out various functions. We have the gastrointestinal system which aids the digestion and the absorption of food...
and volume
Blood volume
Blood volume is the volume of blood in the circulatory system of an individual.-Humans:A typical adult has a blood volume of approximately between 4.7 and 5 liters, with females generally having less blood volume than males....
it usually brings.