AVM (Arteriovenous Malformation)

What is AVM?

An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels in the brain or spinal cord, resembling a "bag of worms" due to the intertwining of vessels. Normally, blood flows from the heart through large arteries throughout the body. The arteries branch into smaller ones and eventually become capillaries (which are one cell thick). In an AVM, arteries connect directly to veins without passing through the capillary bed, leading to the formation of a shunt (an abnormal channel) or fistula (an abnormal canal) with high pressure. The veins are unable to withstand the blood pressure coming directly from the arteries, so they become stretched and enlarged to accommodate the excess blood. Weakened blood vessels can rupture and bleed, and there is also a risk of forming an aneurysm. The surrounding tissues may also be damaged as the AVM diverts blood from them.The exact cause of AVMs is unknown. Brain and spinal AVMs are congenital and relatively rare, typically becoming symptomatic between the ages of 20 and 40. Risk factors that increase the likelihood of developing an AVM include smoking.

Common Symptoms of Brain AVMs:

• Seizures
• Sudden onset of severe headaches
• Bruit: a whooshing or ringing sound in the ear caused by blood flow in the AVM
• Muscle weakness
• Unilateral paralysis (loss of movement on one side of the body)
• Difficulty speaking or understanding
• Sensory loss (hearing, taste, or touch)
• Vision problems
• Memory loss
• Cognitive disturbances or confusion
• Hallucinations (sensing things that do not exist)
• Dementia

 

Children under 2 years may exhibit different symptoms, including:

• Hydrocephalus (accumulation of excess fluid in the brain, appearing as an enlarged head)
• Seizures

Common Symptoms of Spinal AVMs:

• Sudden severe back pain
• Weakness in the legs or arms
• Paralysis

The risk of bleeding from an AVM is approximately 2-3% per year, with a mortality rate of 10-30% from the first bleed. If bleeding occurs, the risk of rebleeding from the AVM within the first year is nine times higher.

 

Diagnosis

Diagnosis of AVM is made following a medical history and physical examination, supplemented by imaging tests such as CT (or CAT) scans, MRI (or MRA; angiography), and X-rays using a catheter and contrast material to determine the location, size, type, and involvement with other structures.

 

Treatment of AVM

The goal of treatment is to prevent bleeding that could lead to a stroke. Treatment options for AVM include any of the following methods: surgical intervention, endovascular therapy (treatment from within blood vessels), and radiosurgery (surgery using radiation), either alone or in combination.Endovascular embolization (blocking a blood vessel to prevent blood flow through it) is often performed prior to surgery to reduce the size and risk of bleeding from the AVM during the surgical procedure.Radiosurgery or embolization can be used after surgery to treat any remaining parts of the AVM. The neurosurgeon typically discusses all options with the patient and recommends the most suitable treatment method for the individual.

Monitoring the Patient:
In the absence of any history of bleeding, the physician may decide to monitor the patient, which includes using anticonvulsants to prevent seizures and medications to lower blood pressure.Medication does not eliminate AVMs but can reduce the severity of symptoms such as headaches, back pain, and seizures. Sometimes, the best approach, depending on the size and location of the AVM, is to leave it untreated.

 

Surgical Treatment

Surgery is the primary treatment method, but in some cases, it may not be feasible or should be combined with other methods, such as embolization prior to surgery.

• Radiosurgery: Often used for AVMs that are deeper within the brain or are not surgically accessible. An interventional radiologist inserts a catheter through the patient’s arteries and guides it to the AVM. A blocking agent (coil or acrylic glue) is then introduced through the catheter to close the fistula. This procedure does not eliminate the AVM but reduces blood flow to it, making surgical intervention safer. The duration of the procedure varies; the interventional radiologist places a catheter in the artery and maneuvers it to the feeding arteries of the AVM, positioning it at the abnormal connection between arteries and veins. Then, contrast material is injected through the catheter, followed by a series of X-rays to ensure that the treatment is satisfactory. Typically, the patient is required to rest in bed for 6-8 hours after the procedure and can usually resume normal activities within 24 hours.
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Advantages of Endovascular Embolization:

• Treats AVMs that are initially considered inoperable (those that cannot be surgically removed or pose a significant risk if surgery is attempted).
• Less invasive compared to open surgery, resulting in fewer complications (and less blood loss) and shorter recovery and hospitalization times.
• Does not require a surgical incision; only a small puncture in the skin is made, which does not require stitches.
• An effective method for controlling bleeding, especially in emergency situations.
• Allows for the option of local anesthesia compared to open surgery.
• Prevents bleeding if coils are used to close the fistula and alleviates symptoms.
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Complications of Embolization:

• Pain is the most common side effect of embolization, which can be managed with oral or intravenous medications.
• Any procedure involving skin puncture carries a risk of infection.
• There is a possibility of infection requiring antibiotic treatment.
• Complications may include the risk of embolic stroke from the catheter and rebleeding due to incomplete removal of the AVM, which may require multiple treatments.

 

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Pre-treatment Considerations:

If you choose endovascular treatment/embolization, discuss the following issues with your doctor beforehand:

• Any history of allergies, especially to local anesthetics, general anesthetics, and contrast agents.
• Any medications you are taking, including warfarin, aspirin, non-steroidal anti-inflammatory drugs (NSAIDs), and other blood thinners, as well as herbal supplements.
• Any history of coagulation disorders or other medical conditions.
• Pregnancy in women.
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Preparation for the Procedure:

Before the procedure, blood tests may be performed to assess kidney function and normal blood clotting. The doctor may recommend stopping the use of aspirin, NSAIDs, or blood thinners for a specified period before the procedure. Depending on the type and location of the AVM, you may need to be hospitalized for some time before the procedure, and you may stay overnight or for several days for monitoring after the procedure.Plan for a family member or friend to drive you home after discharge, depending on the doctor's advice. You will receive a gown to wear during the procedure. Any changes to your regular medication schedule will be communicated to you. You should not eat or drink anything for several hours before the procedure.

 

Procedure Steps:

Before the procedure, a CT or MRI may be performed. A nurse or technologist will access a vein in the patient's arm or hand to administer a moderate sedative or general anesthesia through an IV line. The patient will be connected to monitors that continuously display heart rate, blood pressure, and pulse during the procedure.

 

Limitations:

AVMs are well treated with embolization techniques, although regular check-ups are necessary. Complete treatment may not always be achieved, but targeted embolization (PTE) can eliminate at least the dangerous areas of the AVM.

 

Prevention:

There is no known way to prevent AVMs. To help reduce the risk of bleeding, take the following steps:

• Learn ways to avoid increasing blood pressure.
• Do not lift heavy objects.
• Quit smoking.
• Maintain a healthy weight.
• Avoid alcohol.
• Follow a low-sodium diet.
• Use blood thinners (medications like warfarin) as prescribed.
• Periodically visit your doctor for AVM check-ups.