How Doctors Diagnose an Arteriovenous Malformation

Arteriovenous malformations (AVM) occur when the blood vessels that connect your veins and arteries do not form correctly. These abnormal connections prevent adequate blood flow to your tissues. Understanding how the diagnosis of an AVM is made, including the tools and tests that physicians and surgeons use to detect it, can help to guide you on your journey towards treatment. 

Most brain AVMs do not cause any symptoms until they rupture. If symptoms do occur, the most common symptoms include the following:

• Headaches. These can vary in severity, location, and frequency. You can develop a headache on one side of the head or both sides of the head, though it may not necessarily be linked to the location of the AVM. 
• Seizures. Even without a history of seizures, you could develop this symptom.
• Visual problems. These include blurred vision, inability to control eye movement, or partial vision loss/blindness.
• Dizziness or loss of balance
• Confusion
• Muscle weakness, numbness, or tingling
• Difficulty speaking or comprehending words

One of the most distinctive signs of the presence of an AVM is a phenomenon called a bruit, or a rhythmic “whooshing” or “swishing” noise that occurs because of rapid blood flow through an AVM.

A bruit is usually only detectable with equipment. However, when a bruit becomes severe enough, it can become audible to the patient. A severe bruit may interfere with hearing, disturb sleep, and cause general distress. If you develop a bruit in combination with any of the other symptoms, consult with your doctor for testing.

Anyone can develop an AVM. They are typically thought to be congenital, meaning that they are present from birth, though it is extremely rare for an AVM to affect children before they are ten years old. The exact causes of AVM formation are unknown. There are rare forms of AVMs that develop during the lifetime of an individual that are not congenital.

AVMs are not usually hereditary. Cases of AVMs occurring in families have been reported, but whether there is a contributing genetic factor, or the cases were coincidental is unclear. However, some hereditary conditions such as hereditary hemorrhagic telangiectasia (HHT) can increase your risk of developing a vascular malformation (such as an AVM) as an adult.

AVMs are slightly more common in males than females. Risk factors for AVM rupture include:

• Previous AVM hemorrhage
• Presence of aneurysms associated with the AVM
• Deep AVM location and deep venous drainage

There have been conflicting reports on whether increasing age of the patient and smaller AVMs (< 3 cm) are associated with a true increased risk for rupture. Some researchers note that larger AVMs may present with more symptoms and are thus treated before they rupture, whereas smaller AVMs may more often go undetected until they rupture. This may affect the observed relative frequency of rupture.  

After a comprehensive interview of your symptoms, your doctor will perform a physical examination and imaging tests to rule out any other conditions that could be causing your symptoms.

Imaging tests are used to observe the shape and structure of blood vessels, determine the pattern of blood flow, and to look for bleeding. An AVM can be relatively easy to detect on imaging due to its characteristic tangled appearance of blood vessels. Common tests used to detect a brain AVM include:

• Computerized Tomography (CT) Scan: This test uses x-rays to visualize the brain and its bony structures and determine if any acute bleeding has occurred. It can also demonstrate any calcifications if present within the AVM. This test is quicker than an MRI but is less sensitive at finding an AVM especially if it has not bled or is small.  
• Magnetic Resonance Imaging (MRI): This test uses magnetic fields and radio waves to produce more detailed images of the soft tissues of the brain. The lesion and its surroundings can be assessed more closely to differentiate an AVM from other entities such as a brain tumor.
• Cerebral Angiography: This test involves injecting a water-soluble dye (contrast) into an artery then taking x-rays which will highlight the blood vessel structure and pattern of blood flow. This test can identify the exact location of AVM and the blood vessels involved. Angiography is the best imaging modality to truly evaluate AVMs.

The cause of AVMs is unknown and thus there is no way to prevent one. The best course of action is to see your primary physician regularly to monitor for any abnormal symptoms and seek medical attention if you experience potential symptoms of an AVM or AVM rupture.

AVMs are diagnosed primarily through imaging tests such as CT, MRI, and cerebral angiography. These tests will reveal the presence and extent of blood vessel abnormalities and bleeding. AVMs cannot be prevented and unfortunately their early diagnosis is often not possible until rupture occurs.  

• The Aneurysm and AVM Foundation 
• AVM Research Foundation
• Brain Aneurysm Foundation 
• Child Neurology Foundation 
• National Institute of Neurological Disorders and Stroke