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Brain AVM (Arteriovenous Malformation)

Definition


Disease: Brain AVM (Arteriovenous Malformation) Brain AVM (Arteriovenous Malformation)
Category: Neurological diseases
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Disease Definition:

When someone has brain AVM (arteriovenous malformation), the normal flow of blood between the arteries and veins is interrupted due to an abnormal connection between them. Although a congenital AVM usually develops in the brain or spine, but it could occur anywhere in the body.
A brain AVM can occur in any part of the brain and it looks like tangles of normal and dilated blood vessels.

The cause of brain AVM is not clear, and the only way to know that someone has it is through its symptoms which could include headaches or seizures. The blood vessels rupture in some serious cases, and ends up causing hemorrhage (bleeding in the brain). However, a diagnosed brain AVM is usually successfully treated.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

Until a person's AVM ruptures and causes hemorrhage they might not experience any signs or symptoms.

Some of the signs and symptoms of a brain AVM are:

  • Headache
  • Seizures
  • Pulsing noise in the head, a condition called pulsatile tinnitus
  • Progressive weakness or numbness
  • A whooshing sound (bruit) that can be heard during an examination of the skull with a stethoscope.


When hemorrhage occurs, the signs and symptoms that a person experiences will be similar to those of a stroke, such as:

  • Difficulty speaking
  • Weakness or numbness
  • Severe unsteadiness
  • Sudden and severe headache
  • Vision loss
  • Inability to understand others


A bleeding brain AVM requires emergency medical treatment because it is life-threatening.

Although the symptoms could begin at any age, however, a person is more likely to experience them before age 50. Over time, brain AVM could damage the patient's brain tissue and its effects build up slowly, in some cases causing symptoms in early adulthood. However, a brain AVM tends to remain stable and is less likely to cause any symptoms once the person reaches middle age.

Pregnancy could start or worsen the symptoms of brain AVM due to increased blood flow and blood volume.

Someone should get immediate medical help in case they notice any signs or symptoms of a brain AVM.

Causes:

Although its cause is unknown, however, it is believed that a brain AVM develops during fetal development.

Oxygen-rich blood is sent from the heart to the brain through arteries that branch into smaller arterioles and subsequently to capillaries, which are the smallest blood vessels. This oxygen is then removed from blood in the capillaries and used by the brain. After this, the oxygen-depleted blood passes into small venules and then into larger veins that drain blood from the brain and return it to the heart and lungs in order to get more oxygen.

In the case of a brain AVM, the blood passes directly from the arteries to the veins via abnormal vessels, disrupting the normal process of blood’s circulation through the brain.

Complications

Complications:

Some of the complications of a brain AVM are:

Reduced oxygen to brain tissue:
When someone has a brain AVM, blood bypasses the network of capillaries and flows directly from arteries to veins and because it isn’t slowed down by channels of smaller blood vessels, it rushes through the altered path quickly, leading to the inability of the surrounding brain tissue to absorb oxygen easily due to its fast-flow. Without enough oxygen, the brain tissues could weaken or even die off, resulting in stroke-like symptoms including severe unsteadiness and difficulty speaking.

Brain damage:
Over time, more arteries might be “recruited” in order to supply blood to the fast-flowing AVM, resulting in its enlargement, which moves or compresses portions of the brain. This could prevent protective fluids from flowing freely around the hemispheres of the brain. This fluid build-up can push brain tissue up against the skull, which is a condition known as hydrocephalus.

Hemorrhage:
An AVM puts extreme pressure on the walls of the affected arteries and veins because no capillaries are available to slow down the blood, resulting in the thinning of these walls, which could cause hemorrhage. Although a microscopic hemorrhage causes limited damage to the surrounding tissues and is not likely to cause noticeable symptoms, however, a large hemorrhage can cause brain damage and a hemorrhagic stroke.

Thin or weak blood vessels:
An aneurysm, which is a bulge in a blood vessel wall, could develop and become susceptible to rupture, because an AVM puts extreme pressure on the thin and weak walls of the blood vessels.

Treatments:

Brain AVM treatment options include a number of procedures depending on the size and location of the abnormal blood vessels. In order to treat related symptoms, such as seizures or headaches, medications could be used. Some of these treatment options include:

Resection or surgical removal:
In this procedure, a section of the skull is removed temporarily in order to gain access to the AVM, and with the help of a high-powered microscope, the AVM is sealed off with special clips and carefully removed from surrounding brain tissue. In some cases, this procedure is done with a laser. Then, the skull bone is reattached and the scalp is closed with stitches. This procedure is relatively safe for a small brain AVM.

To prevent hemorrhage or seizures, resection is usually done when the AVM can be removed with acceptable risks. However, other treatments are considered for AVMs that are in deep regions of the brain because they carry a higher risk of complications.

Stereotactic radiosurgery:
In this procedure, a precisely focused radiation is used to destroy the AVM. The radiation will cause the AVM vessels to slowly clot off in the months or years following the treatment. Usually, this type of treatment works best for AVMs that have not caused a life-threatening hemorrhage and for small AVMs.

Endovascular embolization:
In this procedure, a catheter is inserted into a leg artery and threaded through the body to the brain arteries. Then, this catheter is positioned in one of the feeding arteries to the AVM, and to block the vessels and reduce blood flow into the AVM, small particles of a glue-like substance are injected.

To reduce the size of the AVM, endovascular embolization could be done before other treatments; it could also be done during surgery in order to reduce the chance of bleeding during the operation. By redirecting blood back to normal brain tissue, endovascular embolization could reduce stroke-like symptoms in some large brain AVMs.

Prognosis:

Not Available

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