The embolus is usually derived from the heart or sometimes from atheromatous plaques in the carotid or vertebrobasilar systems. Emboli commonly consist of thrombi, atheromatous plaques, Cardiac vegetations and calcareous particles, but rarely fat, air and tumor tissue may be seen. The clinical setting in which embolism occurs often provides the clue to the nature of the embolus. When an embolus lodges in an artery, it leads to distal thrombosis along the ramifying vessels or it may fragment and get impacted in smaller vessels. Infarcts caused by emboli are often hemorrhagic since the blood flowing into damaged vessels escapes into ischemic or necrotic brain tissue. The middle cerebral artery territory is most frequently involved in embolism. The commonest cause is chronic artrial fibrillation occurring in either rheumatic or atherosclerotic heart disease. The other causes include mural thrombi from myocardial infarction, vegetations on prosthetic valves, bacterial endocarditis and mitral valve prolapses in rare cases. Iatrogenic causes include complications during arteriography or surgery of the neck and thorax.
The clinical picture depends on the artery involved. Usually the embolus lodges in one of the branches rather than the mainstem of an artery. Thus it is more common to produce a focal disorder like monoplegia or motor aphasia rather than a complete hemiplegia. Often the deficit is transitory since the embolus passes distally into smaller vessels.
Diagnosis: This is confirmed by a CT Scan. Examination of the CSF may exclude a hemorrhagic lesion. In septic embolus CSF may show pleocytosis.
Management: Prevention of cerebral embolism is more important than its treatment. Restoring atrial fibrillation to normal sinus rhythm and long-term anticoagulant therapy in patients with myocardial infarction and cardiac valve prosthesis prevent embolic complications. However, once the embolism is complete, it is necessary to exclude a hemorrhagic infarct before anticoagulant therapy is started. In cerebral embolism complicating bacterial endocarditis, it is advisable to withhold anticoagulants because of the danger of intracranial bleeding.