In 1998 some patients with hyperglycemia-related hemichorea-hemiballism have been reported with a hyperintense putamen on T1-weighted MR images, presumably resulting from petechial hemorrhage. I questioned this explanation from my experience because (1) the areas of hyperintense lesions and their time evolutions did not match with those of the high density lesions on CT, (2) these hyperintense lesions persisted for years, and (3) the hyperintense lesions extended inferiorly to the midbrain. Therefore, a biopsy was performed in one patient and disclosed a fragment of gliotic brain tissue with abundant gemistocytes, which I proposed was sufficient to explain the shortening of T1 relaxation time. In addition, because two of our patients were associated with cortical infarcts and without hyperglycemia, I have suggested that cerebral ischemia might be a more important cause. In 1999 Fujioka et al reproduced the MR finding in animals 7 days after 15-minute occlusion of the middle cerebral artery. Therefore, both studies have suggested that the MRI finding resulted from a progressive pathological reaction in an incomplete infarction. In 2003 Fujioka et al further reported that the hyperintensity on T1-weighted MR images after mild ischemia may involve a paramagnetic effect resulting from tissue manganese accumulation in reactive astrocytes.