*Address correspondence to:

Hiraga et al. Objective: Ataxic hemiparesis (AH) is a well-recognized lacunar syndrome involving homolateral ataxia with accompanying corticospinal tract impairment. Most previous studies of lesion location in AH did not use diffusion-weighted magnetic resonance imaging (DW MRI). The purpose of this study was to use DW MRI to evaluate the radiological correlation in patients presenting AH. Methods: Retrospectively we studied 29 patients with AH using DW MRI. Results: All patients were scanned within 4 days of onset. Acute infarction was identified in 28 of 29 of them (97%). A single lesion was identified in 26 patients; location pons 8, internal capsule 6, corona radiata 2, distended internal capsule from corona radiate 7, frontal subcortical area 1, and precentral with or without post central gysrus 2. Two lesions were found in 2 patients; in the pons and corpus callosum of 1 patient, and in the corona radiata and subcortical white matter of the other. Conclusions: AH mainly is caused by pontine or internal capsule/corona radiata lesions. It also occurs in the precentral gyrus, including the precentral knob, with or without postcentral gyrus lesions. Fibres of the fronto-ponto-cerebellar system may originate from the frontal cortex, including the precentral gyrus, probably nearby the pyramidal tract. Damage at this location may cause AH