Novel Brain Ischemic Change on MRI

Abstract

Background and Purpose-Specific change of persistent hyperintensity/hypointensity on T1-weighted (T1W) and T2-weighted (T2W) MRI, respectively, has been reported to develop in the human basal ganglia after brief hemispheric ischemia. We investigated whether this ischemic change observed in humans could be reproduced experimentally in rats after brief middle cerebral artery (MCA) occlusion (MCAO), and if so, what the neuroradiological change represented histologically. Methods-The origin of the right MCA of male Wistar rats (nϭ25) was occluded for 15 minutes by inserting a silicon-coated nylon thread from the external carotid artery into the internal carotid artery. After 15 minutes' MCAO, coronal MR images (T1W, T2W, and T1W with fat saturation pulse) were obtained once at 3-day reperfusion (nϭ5) and twice at 3-and 7-day reperfusion (nϭ20). Brain specimens were examined histologically immediately after the last MRI study in all rats. Results-Neither T1W nor T2W MRI showed marked signal changes 3 days after reperfusion following 15-minute MCAO. However, the ischemic change of hyperintensity and hypointensity on T1W and T2W MRI, respectively, appeared in the striatum following 7-day reperfusion after 15-minute MCAO (nϭ19/20). Histological examination revealed that the specific lesion in the rat striatum on MRI corresponded to selective neuronal death and proliferation of reactive astrocytes and microglia without infarct, hemorrhage, lipid accumulation, or calcification. Conclusions-Brief MCAO with reperfusion induces the delayed ischemic changes of hyperintensity and hypointensity on T1W and T2W MRI, respectively, in the rat striatum with high reproducibility. This specific ischemic change on MRI histologically corresponded to selective neuronal death and gliosis with preservation of the macroscopic structure of the brain. A similar MRI pattern reported in patients who have sustained brief ischemia may represent similar histology. We speculate that the ischemic change reflects some biochemical changes affecting the magnetic field as the brain tissue undergoes subtle structural changes.

How Healthy Is the Acutely Reperfused Ischemic Penumbra?

“…Similarly intriguing following temporary MCA occlusion in the rat is the observation of delayed hyperintensity on T1-weighted with hypointensity on T2-weighted MRI affecting the striatum, with histopathological evidence of SNL and reactive microglia [32, 33]. Interestingly, similar MRI findings have been observed in stroke patients with spectacular shrinking deficit, involving both the basal ganglia and cortex, despite normal CT scans and complete clinical recovery [34].…”

Safety Validation of Repeated Blood–Brain Barrier Disruption Using Focused Ultrasound

“…It has been reported that calcium deposits reduce both T1 and T2 relaxation times, leading to hyper-intensities on T1-WI and hypo-intensities on T2-WI (Dell et al 1988). Selective neuronal necrosis and gliosis have the same MRI pattern (Fujioka et al 1999). In three of five animals with mineralization spots, hyper-intensities on T1-WI have been observed.…”

Susceptibility Weighted Imaging as a Useful Imaging Adjunct in Hemichorea Hyperglycaemia

“…Some authors suggest microhaemorrhage as a cause [7], while other studies failed to demonstrate microhaemorrhage histopathologically, suggesting calcium deposition as the favoured aetiology [3]. Others consider cerebral ischemia as the most appropriate explanation of the T1 signal alteration [8, 9]. …”