Arteriovenous Malformation (cont.)
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Where Do Neurological AVMs Tend to Form?
AVMs can form virtually anywhere in the brain or spinal cord -- wherever arteries and veins exist. Some are formed from blood vessels located in the dura mater or in the pia mater, the outermost and innermost, respectively, of the three membranes surrounding the brain and spinal cord. (The third membrane, called the arachnoid, lacks blood vessels.) AVMs affecting the spinal cord are of two types, AVMs of the dura mater, which affect the function of the spinal cord by transmitting excess pressure to the venous system of the spinal cord, and AVMs of the spinal cord itself, which affect the function of the spinal cord by hemorrhage, by reducing blood flow to the spinal cord, or by causing excess venous pressure. Spinal AVMs frequently cause attacks of sudden, severe back pain, often concentrated at the roots of nerve fibers where they exit the vertebrae; the pain is similar to that caused by a slipped disk. These lesions also can cause sensory disturbances, muscle weakness, or paralysis in the parts of the body served by the spinal cord or the damaged nerve fibers. Spinal cord injury by the AVM by either of the mechanisms described above can lead to degeneration of the nerve fibers within the spinal cord below the level of the lesion, causing widespread paralysis in parts of the body controlled by those nerve fibers.
Dural and pial AVMs can appear anywhere on the surface of the brain. Those located on the surface of the cerebral hemispheres -- the uppermost portions of the brain—exert pressure on the cerebral cortex, the brain's "gray matter." Depending on their location, these AVMs may damage portions of the cerebral cortex involved with thinking, speaking, understanding language, hearing, taste, touch, or initiating and controlling voluntary movements. AVMs located on the frontal lobe close to the optic nerve or on the occipital lobe, the rear portion of the cerebrum where images are processed, may cause a variety of visual disturbances.
AVMs also can form from blood vessels located deep inside the interior of the cerebrum. These AVMs may compromise the functions of three vital structures: the thalamus, which transmits nerve signals between the spinal cord and upper regions of the brain; the basal ganglia surrounding the thalamus, which coordinate complex movements; and the hippocampus, which plays a major role in memory.
AVMs can affect other parts of the brain besides the cerebrum. The hindbrain is formed from two major structures: the cerebellum, which is nestled under the rear portion of the cerebrum, and the brainstem, which serves as the bridge linking the upper portions of the brain with the spinal cord. These structures control finely coordinated movements, maintain balance, and regulate some functions of internal organs, including those of the heart and lungs. AVM damage to these parts of the hindbrain can result in dizziness, giddiness, vomiting, a loss of the ability to coordinate complex movements such as walking, or uncontrollable muscle tremors.
Medically Reviewed by a Doctor on 3/26/2014
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