Very small (border zone) cerebellar infarcts. Distribution, causes, mechanisms and clinical features.

Computerized tomography (CT) and magnetic resonance imaging (MRI) allow accurate anatomical localization of large thromboembolic cerebellar infarcts in the territories of the cerebellar arteries and their branches. In addition, MRI and CT show very small cerebellar infarcts as discrete foci of signal change that are not easily localizable within well-defined arterial territories. They could be border zone infarcts. Their anatomy, mechanism and clinical features have not been studied. By reviewing our CT and MRI files over a 2-year period, we found 47 patients with very small cerebellar infarcts; 23 patients had angiography. Infarcts were cortical (32 patients), deep (10 patients) and both (five patients). Most lesions corresponded to border zone cerebellar infarcts. The mechanisms of infarction were (i) global hypoperfusion due to cardiac arrest (two patients); (ii) small or end (pial) artery disease due to intracranial atheroma or hypercoagulable states (nine patients); (iii) focal cerebellar hypoperfusion due to large artery (vertebral or basilar) occlusive disease (16 patients) or brain embolism (11 patients) resulting in infarcts in the watershed areas (27 patients total); (iv) unknown mechanism (nine patients, 19%). Large artery occlusive disease was more frequently observed in deep than in cortical infarcts (9 out of 15 versus 11 out of 37; P < 0.0001). The most frequent symptoms were dizziness, lightheadedness, unsteadiness with axial lateropulsion, dysarthria and limb clumsiness. These symptoms were either transient or recurrent, at times related to positional changes of the head or trunk. Position-related symptoms often persisted for weeks or months after the ischaemic event, and occurred mainly in patients with combined carotid and vertebrobasilar occlusive disease. Physical findings were either absent or included wide-based gait, lateropulsion, mild ipsilateral dysmetria, dysarthria or dysdiadochokinesia. We conclude that very small cerebellar infarcts are often found on CT and MRI. Their border zone distribution and frequent posturally related symptoms most often result from large or pial artery disease rather than from systemic hypotension.