Transhemispheric diaschisis. A review and comment.

126

Summary: Local cerebral hemodynamics and oxygen metabolism were measured by positron emission tomog raphy (PET) with the oxygen-15 C50) steady-state method in baboons, immediately before (TO), 1 (Tl), and 3-4 (T2) h after permanent middle cerebral artery occlu sion (MCAO). At Tl, there was a marked fall in both cerebral blood flow (CBF) and the CBF/cerebral blood volume (CBV) ratio in the occluded territory; these changes were sustained at T2, indicating stable reduction in cerebral perfusion pressure and lack of spontaneous reperfusion within this time range. Compared with pre occlusion conditions, the oxygen extraction fraction (OEF) in the occluded territory was elevated at both Tl and T2, indicative of a persistent oligemia/ischemia for up to 3 h after MCAO. At T2, however, this OEF increase had lessened, concomitantly with a decline in cerebral metabolic rate of oxygen (CMR02). This impairment of Positron emission tomography (PET) studies in humans have provided a unique insight into the metabolic and hemodynamic events which charac terize the evolution of acutely ischemic tissue, es pecially in relation to its function and viability (Baron et aI., 1981(Baron et aI., , 1983 Lenzi et aI., 1982; Wise et aI., 1983;Powers and Raichle, 1985; Hakim et aI.,

Section: Discussionsupporting

confidence: 91%

PET Study of Changes in Local Brain Hemodynamics and Oxygen Metabolism after Unilateral Middle Cerebral Artery Occlusion in Baboons

Pappatà

Fiorelli²,

Rommel³

et al. 1993

126

“…The absence of contralateral cerebral metabolic depression is in agree ment with the reports of Tenjin et al (1992) and Pappata et ai. (1993) infarction, while a lack of delayed metabolic changes las proposed by Andrews (1991)] might be explained by the relatively small infarcts obtained in the present study. Although the early rOEF was maximal in the cortical mantle and significantly higher there than in the deep MCA territory (see Tables 3 and 5), it nevertheless ex hibited an overall trend (significant in one baboon) for a transient increase in the latter region I h after MCAO.…”

Section: Discussionsupporting

confidence: 61%

Relationships between High Oxygen Extraction Fraction in the Acute Stage and Final Infarction in Reversible Middle Cerebral Artery Occlusion: An Investigation in Anesthetized Baboons with Positron Emission Tomography

Young

Sette

Touzani

et al. 1996

Summary: Studies in humans suggest that regions that show maximal increases in brain oxygen extraction fraction (OEF) in the hours following an ischemic episode are those most vul nerable for infarction and are often, although not always, as sociated with the final site of infarction. To clarify this issue, we followed the hemodynamic and metabolic characteristics of regions with an initially maximally increased OEF and com pared them with the ultimately infarcted region in an experi mental stroke model. Positron emission tomography (PET) was used to obtain functional images of the brain prior to and fol lowing reversible unilateral middle cerebral artery occlusion (MCAO) in 11 anesthetized baboons. To model early reperfu sion, the clips were removed 6 h after occlusion. Successive measurements of regional CBF (rCBF), regional CMR02 (rCMR02), regional cerebral blood volume, and regional OEF (rOEF) were performed during the acute (up to 2 days) and chronic (> 15 days) stage. Late magnetic resonance imaging (MRI) scans (coregistered with PET) were obtained to identify infarction. Reversible MCAO produced an MRI-measurable infarction in 6 of II baboons; the others had no evidence of ischemic damage. Histological analysis confirmed the results of the MRI investigation but failed to show any evidence of cor tical ischemic damage. The lesion was restricted to the head of the caudate nucleus, internal capsule, and putamen. The infarct volume obtained was 0.58 ± 0.31 cm 3 . The infarcts were situ ated in the deep MCA territory, while the area of initially

“…Modifications of the electrical activity (Buchkremer-Ratzmann et al, 1996;Meyer et al, 1970;Witte and Stoll, 1997), cerebral blood flow (Andrews, 1991;Dobkin et al, 1989), and/or metabolism (Andrews, 1991;Kuhl et al, 1980) have been reported at the cortical level (diaschisis), mainly within areas mirror to the lesion. In animal models of cerebral ischemia, Izumi et al (2002) recently reported a progressive edema in both hemispheres within the first few hours after MCA occlusion in rats.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal Diffusion Changes in Cerebral Hemispheres after MCA Infarcts

Buffon

Molko

Hervé

et al. 2005

Diffusion tensor imaging can be used in vivo to assess the longitudinal and regional microstructural changes occurring after middle cerebral artery (MCA) infarcts in humans. Nine patients were investigated 1 week (D7), 1 (M1), 3 (M3), and 6 months (M6) after the occurrence of an isolated MCA infarction. First, an overall analysis was performed using histograms of mean diffusivity (MD) and fractional anisotropy (FA) in each hemisphere. Thereafter, the regional pattern of diffusion changes was investigated voxel by voxel with statistical parametric mapping 99. In the hemisphere ipsilateral to the infarction, histogram analysis revealed a significant decrease in FA between D7 and M6 associated with a progressive increase in MD from D7 to M3. Remote from the MCA territory, the voxel by voxel analyses detected a significant increase in MD within the thalamus at M3 and M6 and a reduction in FA along the pyramidal tract at M6. In the contralateral hemisphere, between D7 and M6, a significant hemispheric atrophy was observed in association with a global reduction in anisotropy, in the absence of distinctive regional diffusion changes. These results suggest that micro-and macrostructural tissue modifications can be detected with diffusion tensor imaging in regions remote from the ischemic area in both hemispheres.