[Cerebellar infarctions and their mechanisms].

Cerebellar infarcts have been neglected for a long time and are now shown well by CT and especially MRI. Some infarcts involve the full territory supplied by a cerebellar artery. They are frequently complicated by edema with brain stem compression and supratentorial hydrocephalus, requiring at times emergency surgery, and are often accompanied by other medullary, medial pontine, mesencephalic, thalamic and occipital infarcts. On the other hand, partial territory infarcts are usually confined to the cerebellum and have a benign outcome with total recovery or minimal disability. They are more common than full territory infarcts. However, clinical presentations are similar to those full territory infarcts, differing mainly by the lack of drowsiness or unconsciousness. The main symptoms are vertigo, headache, vomiting, unsteadiness of gait and dysarthria. Signs include ipsilateral limb dysmetria, ipsilateral axial lateropulsion, ataxia and dysarthria. Vertigo is more severe and rotary in posterior inferior cerebellar artery territory infarcts, whereas dysarthria and ataxia are prominent in superior cerebellar artery territory infarcts. A few brain stem signs are sometimes added. In these territorial cerebellar infarcts, cardioembolism is the most common cause. Atherosclerotic occlusion comes next, involving the intracranial part of the vertebral artery and, less frequently, the lower basilar artery, both locations inaccessible to surgery. Other causes are artery to artery embolism from a vertebral artery origin stenosis, or the aortic arch, in situ intracranial branch atherosclerotic occlusion, and vertebral artery dissection. Border zone cerebellar infarcts occur in one third of the cases. They are small cortical or deep infarcts. They have the same symptoms and signs as territorial infarcts except for more frequent postural symptoms occurring over days, weeks or months after the ischemic event. The infarcts mainly have a thromboembolic mechanism, and sometimes have a hemodynamic mechanism: 1) focal cerebellar hypoperfusion due to large artery occlusive disease in more than half the cases, 2) small or end (pial) artery disease due to hypercoagulable state (thrombocythemia, polycythemia, hypereosinophilia, disseminated intravascular coagulation), arteritis or intracranial atheroma, and 3) rarely systemic hypotension due to cardiac arrest.