Arteriovenous malformation (AVMs) are issues in the vascular system. An AVM is a tangle of abnormal blood vessels. The feeding arteries are connected directly to a venous drainage network without interposition of a capillary bed. Arteries carry blood away from the heart and to the rest of the body. They carry oxygen rich blood. Oxygen poor blood is carried back to the heart by veins. Arteries and veins are connected by capillaries. An AVM makes this process defective and leads to tangled arteries and veins that are connected without capillaries.
An AVM in the brain and spine are very risky when they bleed. AVMs can happen at any location in the body. Abnormal brain tissue is usually connected with abnormal blood vessels and the brain and blood vessels form during embryonic development. AVMs are thought to be caused partially due to genetic manipulation and angiogenic stimulation. AVMs can form in the utero after a cerebral ischemic or hemorrhage incident.
The cause of AVMs are not known but it may be related to genetics
Half of AVM patients usually have a bleed. Most patients will not have symptoms and the condition is accidentally discovered. Patients that are diagnosed with unruptured AVMs have nearly doubled in proportion over the last thirty years due to better imaging. Around 12% of AVM patients will experience symptoms. An AVM can irritate brain tissue and lead to headaches or seizures. Here are some symptoms of an AVM:
- Muscle weakness
- Coordination loss
- Difficulty with organizing
- Disturbance visually
- Language issues
- Numbness or tingling
- Random pain
- Memory deficits
There is a 4% rupture rate from brain AVMs. A trail of unruptured brain AVMs shows a low random rupture rate of 2.2% every year. There is a lower bleeding rate of 2% per year of unruptured AVMs. After there is a rupture, the bleeding risk can increase to around 6 or 8% during the first year. AVMs related to a high risk of a hemorrhage include:
- When the brain AVM shows up with a hemorrhage
- Deep venous drainage is present
- Related to an aneurysm
- Located deep
If intense headaches, seizure, arm or leg weakness, vision issues, balance issues, memory issues, or attention issues present, seek medical care. If there is an AVM, a neurosurgeon should be consulted.
Angiography and an MRI are often used to diagnose an AVM. These tests may need to be done multiple times as an AVM is dynamic. If an AVM is not treated, they can grow and rupture and lead to a brain hemorrhage or subarachnoid hemorrhage. There can be permanent brain damage done. Intracerebral or intraparenchymal hemorrhages are deep bleeding. A subdural hemorrhage is bleeding on the brain surface.
The location of the AVM will be related to the damage done and symptoms present. Deep brain AVMs usually lead to an increase in neurological damages than brain surface AVMs. Nonsurgical treatment of an AVM as early as possible is recommended to decrease the risk of a rupture.
The Spetzler-Martin Grade scale is often used to predict how severe a brain AVM is. The score is a composite of nidus size, important of adjacent brain structures, appearance of deep venous drainage. A higher score means the AVM is more severe.
Treatment is done to prevent rupture. Other goals of treatment are to reduce symptoms, especially symptoms related to seizures and neurological deficits. Interventional treatment of ruptured brain AVMs is usually recommended as there is a higher hemorrhage risk (4.5-34%) than an unruptured one.
Microsurgical techniques, endovascular embolization, and stereotactic radiotherapy may be used in treating an AVM.
Sometimes an AVM can be removed but it may be better to have multiple treatments instead, this depends on the case though. ARUBA did a study on 223 patients with unruptured brain AVMs. They found that the risk of death was much lower in the group that received medical treatment compared to an interventional therapy group.