Introduction
Cerebral arteriovenous malformation (AVM) is a cerebrovasuclar disorder of blood vessels characterized by tangles arteries and veins located in various parts of the brain.
The cause of AVMs remains unknown. Most patients present with either seizures or bleeding due to the fragility of the abnormally structured brain vessels. Some patients may remain asymptomatic or have minor complaints. Interestingly small AVMs are more likely to bleed than larger ones. Additionally, once an AVM bleeds, the probability of re-bleeding increases substantially.
In addition, the AVM may redirect blood flow away from normal brain structures causing a "steal-like" phenomenon that will present with stroke like symptoms.
Symptoms
The most frequently observed symptoms related to AVMs are headaches and seizures. The large tangled mass of blood vessels may irritate the surface of the brain or actually bleed into the brain causing symptoms. Patients will often complain of loss of consciousness, sudden and severe headaches, nausea and vomiting, blurred vision and stiff necks. They may also have focal neurological problems, such as paralysis, numbness, or speech difficulties.
Diagnosis
The diagnosis of an AVM is made using neuroimaging modalities. A CT scan usually is the first study ordered and often shows a tangled mass of blood vessels. This study is often followed up by a CT-angiogram, which is a specialized CT scan looking specifically at blood vessels. A formal angiogram is often ordered as well to look at the cerebral blood vessels. MRI studies can be useful as well.
Figure is an angiogram showing a mass of tangled vessels.
Lumbar punctures are often performed initially to look for evidence of bleeding into the fluid that surrounds the brain. This fluid will often look red and be called "xanthochromic."
AVMs are graded according to a system known as the Spetzler-Martin Grading Classification. This system grades the AVM based on its size, venous drainage, and proximity to important brain areas. The treatment strategy of the AVM is related to the overall grade.
Treatment
The treatment initially involves surgery for any large hemorrhages that may endanger the patients life. Blood pressure has to be aggressively controlled to further prevent any risk of additional bleeding. Anti-seizure medications need to be used to control any irritation to brain caused by the AVM.
Long term treatment of the AVM is geared to preventing any future rebleeding or enlargement of the AVM. Specific treatments depend on its location, size, proximity to critical brain areas and venous drainage patterns. Surgical intervention involves a craniotomy and physical removal of the AVM. Embolization (occlusion of blood vessels) involves passing a catheter through the groin into the cerebral arteries. Special glue is then injected in the AVM to obliterate its blood flow. Stereotactic radiosurgery also is used to destroy AVMs and involves high dose radiation directed to the central part (nidus) of the AVM.
Drawing depiciting endovascular catheterization.
Prognosis
Most patient with AVMs do well since the initial hemorrhage is not neurologically devastating. Once recognized the majority of AVMs are treated successfully and with little morbidity.
Over 100 AVMs are treated each year at the University of Florida by Dr. William Friedman, Dr. Brian Hoh and Dr. Stephen Lewis.
