The internal carotid artery provides blood supply to most of the brain's cortex on one side, including the frontal, parietal and temporal lobes. Only the posterior parts of the brain are supplied by different arteries. The internal carotid divides into two large branches, the middle and anterior cerebral arteries, and symptoms arise from disruption of blood flow to the areas they supply.
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Occlusion Without Symptoms
Though occlusion of this major artery can have devastating effects, no part of the brain is dependent solely on the internal carotid from one side. As shown in "Sobotta - Atlas of Human Anatomy," blood flows to the same areas from communicating arteries that come from the posterior circulation, and from the internal carotid on the other side.
Each person is born with a different degree of communication between the large blood vessels. Symptoms, therefore, vary widely between different people. In addition, if occlusion develops gradually, the communicating arteries have more time to grow and to provide more blood to the other side, should it become occluded. According to "Adams and Victor's Principles of Neurology," 30 to 40 percent of occlusions of the internal carotid artery occur without symptoms.
Occlusion of the internal carotid can lead to paralysis of the entire opposite half to the face and body. This is mainly due to disruption of blood flow in the middle cerebral artery, one of its two main branches, which leads to a stroke in the main motor area of the cortex. The other large branch, the anterior cerebral artery, supplies blood to the areas that control the feet and lower limbs. Paralysis may be complete or partial, may affect only an leg, or the leg and arm on the opposite side.
Vision and Sensation
Occlusion of the carotid is often preceded by temporary blindness in one eye, a condition known as amaurosis fugax. As described in "Harrison's Principles of Internal Medicine," a completed stroke can cause loss of half of the visual field or a smaller portion of it. Sensation may be lost on the other side of the body, since the sensory part of the cortex is also supplied by the middle cerebral artery. As with motor symptoms, sensory disturbances can vary from mild to severe. The patient can also lose the sense of spatial location, and may be unable to perform complex integrated movements, even if the muscles are fully functional.
Speech and Language
The patient might become completely mute. He might be able to produce speech but it will be unintelligible. His understanding of language might be intact or might be completely lost. Symptoms of stroke can often improve with time, especially if the patient undergoes rehabilitation with specific exercises designed to restore the lost function.
Personality changes, including passivity and inability to plan ahead, may occur. According to "Harrison's Principles of Internal Medicine," seizures are common symptoms of stroke. Gaze disorders may occur even if the nerves supplying the eye muscles are nto affected—the patient has difficulty moving the eyes toward the direction she chooses. Memory may be impaired. Urinary Incontinence is another possible symptom.