A brain arteriovenous malformation (AVM) is a rare, abnormal tangle of blood vessels found in the brain. These malformations create irregular connections between arteries and veins, disrupting the normal pattern of blood flow within the brain. While often present from birth, many brain AVMs go undetected until symptoms appear, sometimes much later in life.
Understanding Brain Arteriovenous Malformation
In a healthy brain, oxygen-rich blood flows from arteries to smaller vessels called arterioles, then into a network of tiny capillaries. These capillaries are where oxygen and nutrients are delivered to brain tissue, and waste products are collected. From the capillaries, oxygen-depleted blood moves into venules and then into veins, which carry it back to the heart and lungs.
With a brain AVM, this normal circulatory pathway is bypassed. Arteries connect directly to veins without the intervening capillary network. This direct connection forms a central core of tangled vessels known as the “nidus.” The absence of capillaries means that high-pressure arterial blood flows directly into the lower-pressure veins, which are not designed to withstand such force.
This abnormal shunting of blood can cause several problems. High pressure can stretch and enlarge veins, making them susceptible to rupture. The rapid bypass of blood through the AVM can also deprive surrounding brain tissue of oxygen and nutrients, potentially leading to damage. Brain AVMs are believed to form during fetal development, though their exact cause is not fully understood.
Recognizing the Signs
Brain AVMs can present with a variety of symptoms, though some individuals may remain asymptomatic until a significant event occurs. Headaches are a common symptom, often described as severe or localized, and they may sometimes resemble migraines. Seizures, which can be focal (affecting a specific part of the body) or generalized, are another frequent manifestation of a brain AVM.
Neurological deficits can also develop, reflecting the AVM’s impact on specific brain regions. These may include muscle weakness or numbness in a limb or part of the face, changes in vision, or difficulties with speech and understanding. Some people might experience a pulsating noise in their head, known as pulsatile tinnitus. These symptoms often lead individuals to seek medical attention.
The most serious complication of a brain AVM is hemorrhage, or bleeding in the brain. This medical emergency can cause sudden, severe headache, confusion, nausea, vomiting, neck stiffness, or loss of consciousness. A brain hemorrhage can lead to brain damage or a stroke, and in some cases, it can be life-threatening. Approximately half of all individuals with a brain AVM discover their condition only after experiencing such a bleeding event.
Diagnosing Brain AVM
The diagnostic process for a brain AVM begins with a thorough neurological examination, assessing symptoms and medical history. Sometimes, a physical exam may reveal a “bruit,” a whooshing sound caused by turbulent blood flow through the AVM. Imaging techniques are then employed to visualize the AVM and assess its characteristics.
A computerized tomography (CT) scan is often a first imaging test, especially in cases of acute hemorrhage, to quickly detect bleeding in the brain. Magnetic resonance imaging (MRI) provides more detailed images of brain structures and can visualize the AVM as a tangle of vessels, appearing as “flow voids” from rapid blood movement. Magnetic resonance angiography (MRA) is a specialized MRI that highlights blood vessels and shows blood flow patterns.
Cerebral angiography is the most detailed test for diagnosing a brain AVM. During this procedure, a thin catheter is inserted into an artery and guided to the brain using X-ray imaging. A dye is then injected, making the blood vessels visible for detailed mapping of the AVM, including its feeding arteries and draining veins. This comprehensive mapping is valuable for treatment planning.
Treatment Options for Brain AVM
Treatment for a brain AVM is individualized, based on the AVM’s size, location, symptoms, and patient health. The primary goal is to prevent hemorrhage and manage existing symptoms like seizures or headaches. For some asymptomatic or low-risk AVMs, especially in older individuals, observation with regular imaging may be recommended. This involves monitoring the AVM for any changes over time.
Surgical resection involves the removal of the AVM. This is often the preferred method when the AVM is in an accessible location and has bled, providing immediate protection from future bleeding. The procedure is performed under general anesthesia and can last several hours, with neurosurgeons removing the abnormal tangle of vessels.
Endovascular embolization is a minimally invasive procedure where a catheter is threaded to the AVM through blood vessels. Through the catheter, embolic agents (e.g., small particles or a glue-like substance) are injected to block the arteries feeding the AVM, reducing blood flow to the malformation. This technique can be used alone for smaller AVMs or, more commonly, as a pre-surgical step to shrink the AVM or reduce bleeding risk during subsequent open surgery.
Stereotactic radiosurgery (SRS) uses focused radiation beams to target and damage the blood vessels within the AVM. This non-invasive procedure causes the AVM vessels to scar and gradually close off over one to three years. SRS is suitable for smaller AVMs located deep within the brain or in areas difficult to reach surgically.
Life After Brain AVM Diagnosis
Following a brain AVM diagnosis, whether treated or under observation, ongoing medical follow-up is necessary. Regular imaging tests, such as MRI, MRA, or angiography, are performed to monitor the AVM’s status, assess treatment effectiveness, or detect changes. This is especially relevant for children and young adults, as AVMs can recur even years after successful treatment.
While most individuals experience good outcomes, some may have residual symptoms depending on the AVM’s location and any prior complications, such as a hemorrhage. For instance, if epilepsy developed due to the AVM, anti-seizure medication may be prescribed to manage seizures.
Adhering to medical advice and maintaining a healthy lifestyle contribute to long-term well-being. The goal is to allow individuals to resume normal activities and live full lives. Ongoing research continues to improve understanding of AVMs and refine treatment approaches, with innovations in imaging and surgical techniques aiming to enhance precision and safety.