Longitudinal tracing of white matter integrity on diffusion tensor imaging in the chronic cerebral ischemia and acute cerebral ischemia

Abstract

Brain ischemia leads to insufficient oxygen supply or hypoxia and thus to ischemic stroke or chronic hypoperfusion, which results in neuronal death and white matter damage is irreversible or partially recoverable under the interruption of blood flow more than a few minutes. The present study investigated the abnormal characteristics of white matter integrity after the chronic cerebral ischemia in a mouse model of bilateral carotid artery stenosis and the acute cerebral ischemia in a mouse model of middle cerebral artery occlusion via longitudinal diffusion tensor imaging, which revealed that the mean diffusivity of corpus callosum (cc) was decreased as early as the 1 st day after chronic cerebral ischemia, and then the damage gradually aggravated and lasted to the 28th day. Moreover, the brain regions, including cingulum (cg), dorsal hippocampal commissure (dhc), forceps major of the corpus callosum (fmj), alveus of the hippocampus (alv) and medial lemniscus (ml), were damaged in duration of 7∼28 days after chronic cerebral ischemia. Oppositely, white matter signals in the contralateral hemisphere appeared compensatory increase in the internal capsule (ic) at the 1 st day after acute cerebral ischemia, simultaneously the ipsilateral hemisphere signals were decreased in alv, cerebral peduncle (cp), external capsule (ec), ml, fimbria of the hippocampus (fi), ic, forceps minor of the corpus callosum (fmi) and dhc. While these regional white matter signals were decreased in the bilateral hemisphere at the 7th day after acute cerebral ischemia. In addition, the motor function was impaired after acute cerebral ischemia, and cognitive function were impaired after chronic and acute cerebral ischemia. Furthermore, voxel-wise analysis revealed the obvious differences of white matter integrity in these two models of ischemia. The chronic cerebral ischemia showed better white matter integrity in the ipsilateral hemisphere of acute cerebral ischemic model at the 1 st day after surgery, but worse in the contralateral hemisphere. Subsequently, these differences were reduced significantly and just only the ipsilateral cp and bilateral ml signals were higher in chronic cerebral ischemia. Taken together, the present study demonstrates that the chronic and acute cerebral ischemia cause progressive damages of white matter that are irreversible in a relatively long time, of which the contralateral white matter present transient compensation in acute cerebral ischemia but not in chronic cerebral ischemia. These might be helpful to better diagnosis of clinical different cerebral ischemia.

Keywords: Cerebral ischemia; Diffusion tensor imaging; Longitudinal; Mean diffusivity; White matter.