VERTEBROBASILAR OCCLUSIVE DISEASE - REVIEW OF SELECTED ASPECTS .3. MECHANISMS OF CEREBELLAR INFARCTIONS

The cerebellum is the largest brain structure in the posterior fossa. However, cerebellar infarcts were understudied up to the 1980s. Now well shown by CT and MRI scans, we can distinguish between territorial infarcts - involving the full territory of a cerebellar artery or its branches - and borderzone infarcts. This can help to predict the vascular mechanisms of the ischemia. Territorial infarcts have a thrombo-embolic mechanism. Cardiac embolism is the most frequent. Artery-to-artery embolism, atherosclerotic disease of the vertebral artery (mainly in its intracranial part) or basilar artery, and vertebral artery dissection come next. Among them, the importance of intra-arterial embolism from vertebral artery origin disease deserves to be evaluated in the future because of the therapeutic implications. Borderzone or endzone infarcts may have a hemodynamic mechanism or be due to small emboli. The most frequent cause is occlusion of the vertebral or basilar arteries, either due to atheroma or embolism, small or end (pial) artery disease comes next, due to hypercoagulability states (e.g. thrombocythemia, polycythemia, disseminated intravascular coagulation), arteries or intracranial atheroma; systemic hypotension is seldom found. The new neuroimaging methods for the assessment of intracranial hemodynamics (transcranial Doppler, magnetic resonance angiography, positron emission tomography and single photon emission computed tomography) provide future opportunities for a better study of these patients and the natural history of these lesions, and for a better definition of the role of various therapies and revascularization procedure.