Cerebral AV Malformations - An Overview

Introduction:

Arteries carry blood that is rich in oxygen, from the heart to other parts of the body. Veins carry blood that has decreased oxygen content from various parts of the body to the heart for reoxygenation. Abnormalities in the arteriovenous connections disturb the usual blood transport of the arteries and veins. Even though arteriovenous malformation can occur anywhere in the body, the common sites include the brain and spinal cord. In most of the cases with cerebral arteriovenous malformations, the abnormality may be present since birth. However, some people may develop the abnormality shortly after birth.

What Is Cerebral Arteriovenous (AV) Malformation?

Cerebral arteriovenous malformation is the tangling of blood vessels that link the arteries and veins of the brain. This leads to the abnormal functioning of the arteries and veins of the brain. The tangling of blood vessels causes a direct connection between the arteries that carry the oxygen-rich blood from the heart and the veins that carry the oxygen-deficient blood from other body parts into the heart. Cerebral arteriovenous malformations can reduce the amount of oxygen entering the brain and spinal cord. This is often referred to as a “steal” effect due to the fact that the blood is being stolen from its actual path of flow.

What Are the Causes of Cerebral Arteriovenous (AV) Malformations?

The exact cause of cerebral arteriovenous malformation is not known. However, the possible causes suggested by the researchers are listed below. They are:

• Most cerebral arteriovenous malformations are congenital (an abnormality that has been present since birth).

• Cerebral arteriovenous malformations may occur as a result of the combined effect of change in some genes and the physiological process of new blood vessel formation from the old vessels.

• Cerebral arteriovenous malformations may occur as a result of head injury or certain injuries and infections of the brain.

• Rarely, cerebral arteriovenous malformations are thought to result from hereditary aspects.

What Are the Symptoms of Cerebral Arteriovenous (AV) Malformations?

• Intracranial hemorrhage (bleeding which occurs in the area between the brain and the skull or within the brain). Even though intracranial hemorrhage cannot be seen externally, it presents signs like loss of consciousness, severe headache, nausea (uneasiness of the stomach with an urge to vomit), and vomiting.

• Seizures (sudden uncontrolled disturbances inside the brain which cause changes in behavior, movements, and levels of consciousness).

• Loss of sensation in one half of the body.

• Disturbances in vision.

• Weakness of muscles may make the person feel tired.

• Numbness or tingling sensation in one side of the body.

• Difficulty in speaking.

• Loss of balance while moving from one place to another.

• Confused mental state.

• Dizziness (feeling unsteady).

• Reduced hearing abilities.

• Fingers and toes may turn blue or cold.

• Decrease in memory and social abilities that are needed to carry out the tasks in daily life.

How Are Cerebral Arteriovenous (AV) Malformations Diagnosed?

The ways to diagnose cerebral arteriovenous (AV) malformations are as follows:

• Medical History: The doctor takes a detailed history of the symptoms of the patient. A thorough physical examination of the patient is done to find out any abnormalities in the vision, speaking, hearing, and movement abilities of the person.

• Cerebral Angiography: It is the most reliable test to diagnose cerebral arteriovenous malformations. During this test, a thin tube (catheter) is inserted into an artery of the wrist or groin (hip area present in between the upper part of thighs and lower part of the stomach) and is connected to the brain. A dye is injected into the blood vessels of the brain, and X-rays are taken. Clear images which give details about the location and nature of the malformed blood vessels are obtained. This test helps to find out the blood vessels involved in cerebral arteriovenous malformations that help to formulate the correct treatment plan.

• Cerebral Magnetic Resonance Angiography (MRA): This test uses magnets and radio waves to give a clear and detailed image of the blood vessels in and around the brain. Sometimes, a dye is injected to view the blood circulation inside the brain.

• Transcranial Doppler Ultrasound: This test uses sound waves to calculate the blood flow inside the brain.

• Magnetic Resonance Imaging (MRI): This test uses radio waves and powerful magnets to obtain detailed and clear images of the brain. It gives information about the precise location of the cerebral arteriovenous malformation and any other bleeding which may be present in the brain.

• Computed Tomography (CT) Scan: A computed tomography scan uses several x-rays to produce a cross-sectional image of the brain. It is similar to magnetic resonance imaging, except that magnets are not used in computed tomography.

How Are Cerebral Arteriovenous (AV) Malformations Treated?

The treatment options for cerebral arteriovenous malformations depend on the location and size of the abnormality. There is no specific medication that cures cerebral arteriovenous malformation. Hence treatment mainly focuses on relieving the symptoms. The various treatment options are as follows:

• Medical Therapy: This mode of treatment is done in patients who do not experience any symptoms, and the location of the arteriovenous abnormality in the brain is at a risky site. In such cases, surgery cannot be done. The patient is asked to avoid over-exercising and to avoid the usage of blood thinners (medications taken to prolong the time taken by the body to form blood clots).

• Surgery: The surgical method using high-powered microscopes is preferred in patients who have cerebral arteriovenous malformation that has either caused bleeding inside the skull or is located at a site that is easily accessible during the surgery. During the surgery, the surgeon makes an incision on the skull to reach the area of arteriovenous malformation. The arteries and veins located nearby are sealed off using special clips, and the arteriovenous malformation is removed carefully. The connection between the arteries and veins is corrected, and the blood flow is returned to normal. Finally, the incision in the scalp is closed. Surgery is avoided in patients who have the risk of developing seizures and arteriovenous malformations that are located in the deeper areas of the brain.

• Sclerotherapy: In this procedure, the doctor uses x-rays and ultrasound (an imaging test that uses sound waves to obtain images of the structures present in the body) to locate the arteriovenous malformation. In sclerotherapy, a liquid medicine is injected into the arteriovenous malformation. The blood vessels present in the malformation are destroyed, which may either reduce or stop the blood flow through the arteriovenous malformation. This method does not remove the malformation completely but reduces the symptoms and size of the malformation. If the arteriovenous malformation expands in size over time, this process has to be repeated a few times throughout the patient’s life.

• Embolization: In this method, a catheter (thin tube) is inserted into an artery present in the wrist or hip area, which is connected to the blood vessels inside the brain. Glue-like substances, coils, or plugs are injected through the catheter into the artery, which supplies the arteriovenous malformation. This creates a block in the artery which in turn reduces or stops the blood flow inside the arteriovenous malformation. This method does not remove the arteriovenous malformation completely but reduces its size. It is performed mostly before surgery to reduce the blood flow in the arteriovenous malformation, thereby preventing excessive bleeding during surgery. It is also performed in cases where the arteriovenous malformations are large with a lot of blood flow and to reduce stroke-like symptoms.

• Stereotactic RadioSurgery (SRS): This procedure involves the destruction of arteriovenous malformation using highly focused radiations. The radiation directed towards the arteriovenous malformation damages, shrinks, and scars the blood vessels. The scarred blood vessels of the arteriovenous malformation get dissolved within a period of a few years. Scans should be taken at regular intervals to monitor if the malformation has dissolved completely. This procedure is best suited for arteriovenous malformations that are small in size and do not pose the risk of bleeding.

Conclusion:

Although arteriovenous malformations can occur anywhere in the body, those present in the brain are highly dangerous due to the risk of bleeding of the blood vessels inside the brain leading to neurological (related to the nervous system) damage. However, through proper treatment, a person can be free from the symptoms and lead a normal life. Hence it is very important to respond quickly to the symptoms and take the proper treatment from a doctor.