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 we ll shown by CT and MRI scans, we can distinguish between territorial i nfarcts - involving the full territory of a cerebellar artery or its b ranches - and borderzone infarcts. This can help to predict the vascul ar mechanisms of the ischemia. Territorial infarcts have a thrombo-emb olic mechanism. Cardiac embolism is the most frequent. Artery-to-arter y embolism, atherosclerotic disease of the vertebral artery (mainly in its intracranial part) or basilar artery, and vertebral artery dissec tion come next. Among them, the importance of intra-arterial embolism from vertebral artery origin disease deserves to be evaluated in the f uture because of the therapeutic implications. Borderzone or endzone i nfarcts may have a hemodynamic mechanism or be due to small emboli. Th e most frequent cause is occlusion of the vertebral or basilar arterie s, either due to atheroma or embolism, small or end (pial) artery dise ase comes next, due to hypercoagulability states (e.g. thrombocythemia , polycythemia, disseminated intravascular coagulation), arteries or i ntracranial atheroma; systemic hypotension is seldom found. The new ne uroimaging methods for the assessment of intracranial hemodynamics (tr anscranial Doppler, magnetic resonance angiography, positron emission tomography and single photon emission computed tomography) provide fut ure 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.