A cerebral arteriovenous malformation (AVM) is an abnormal connection between the arteries and veins in the brain.
Signs and symptoms
The most frequently observed problems related to an AVM are headaches and seizures while at least 15% of the population at detection have no symptoms at all. Other common symptoms are a pulsing noise in the head, progressive weakness and numbness and vision changes.
In serious cases, the blood vessels rupture and there is bleeding within the brain (intracranial hemorrhage). Nevertheless in more than half of patients with AVM, hemorrhage is the first symptom. Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence, and blurred vision, amongst others. Impairments caused by local brain tissue damage on the bleed site are also possible, including seizure, one-sided weakness (hemiparesis), a loss of touch sensation on one side of the body and deficits in language processing (aphasia). Minor bleeding can occur with no noticeable symptoms.
AVMs in certain critical locations may stop the circulation of the cerebrospinal fluid, causing accumulation of the fluid within the skull and giving rise to a clinical condition called hydrocephalus. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges.
An AVM diagnosis is established by neuroimaging studies after a complete neurological and physical examination. Three main techniques are used to visualize the brain and search for AVM: computed tomography (CT), magnetic resonance imaging (MRI), and cerebral angiography. A CT scan of the head is usually performed first when the subject is symptomatic. It can suggest the approximate site of the bleed. MRI is more sensitive than CT in the diagnosis of AVMs and provides better information about the exact location of the malformation. More detailed pictures of the tangle of blood vessels that compose an AVM can be obtained by using radioactive agents injected into the blood stream. If a CT is used in conjunction of dye this is called a computerized tomography angiogram while if MRI is used it is called magnetic resonance angiogram. The best images of an AVM are obtained through cerebral angiography. This procedure involves using a catheter, threaded through an artery up to the head, to deliver a contrast agent into the AVM. As the contrast agent flows through the AVM structure, a sequence of X-ray images are obtained.
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