Ischemic core

Studies in animals have shown, that rrCBV within the ischemic core decreases immediately after occlusion and is likely to raise to values above the baseline, if early reperfusion is achieved (Hamberg et al. 1994). Studies in patients have shown, however, that rrCBV does not depict the ischemic lesion reliably (Tong et al. 1998). Particularly in very small ischemic lesions (< 1 cm3) the map of rrCBV does not show distinct signal changes (Flacke et al. 1998). In tissue with increased rMTT or TTP, particularly within the penumbra, rrCBV is likely to increase due to compensatory vasodilatation as a response to the decreased perfusion pressure (Tsuchida et al. 1997) (Figs. 6.7,6.8). 

One of the intensely debated issues during the past few years was the issue of potential DWI lesion reversibility. Initially, it was believed that DWI abnormalities depict irreversibly damaged tissue in humans, i.e the ischemic core. Only few convincing cases had been reported in the literature with resolution of DWI lesions (mostly small lesions, often located in white matter). There is still no doubt that... 

This suggests that after 120 min of MCAO, neuronal metabolism in the ischemic core is not rescued by 120 min of reperfiision whereas neuronal integrity is preserved in the penumbral zone. 

The proinflammatory effects of HMGBl were studied in the postischemic brain of rats. Ischemia injury in the brain proceeds with excitotoxicity-induced acute neuronal cell death in the ischemic core, followed by delayed damage to the penumbra (Lee et al., 2000b). It was observed that HMGBl was immediately released into... 

Jovin TG, Yonas H, Gebel JM, Kanal E, Chang YE, Grahovac SZ, Goldstein S, Wechsler LR. The cortical ischemic core and not the consistently present penumbra is a determinant of clinical outcome in acute middle cerebral artery occlusion. Stroke. 2003 34 2426-2433... 

Inadequate z-direction coverage resulting in incomplete evaluation of ischemic core and penumbra... 

Table 8.2 highlights some of the difficulties entailed in using PWl to identify the ischemic core and penumbra. One such difficulty is the use of PWl in delineating the infarct core. It has been suggested that the quantitative analysis of CBF maps could be used to identify the core, because only blood flow below a certain level would be expected to result in infarction. However, this cannot be done reliably for several reasons. First, non-viable core tissue may exhibit postischemic hyperperfusion, in which case, obviously, no threshold of hypoperfusion would identify the tissue as part of the core. Second, perfusion imaging techniques that rely on... 

Because perfusion measuranents cannot reliably identify infarct core, and lesions in PWl maps are far less conspicuous than those in DWI images, DWI is generally used to identify the putative ischemic core in acute stroke patients, rather than PWl. PWl s chief role in acute stroke is a different one, to identify any additional hypoperfused tissue that lies outside of the DWI lesion. This tissue that is underperfused but DWI-normal, often called the diffli-sion-perfusion mismatch, either constitutes the ischanic... 

These modalities and how they are used to define the ischemic core and penumbra are summarized in Table 9.2. For these more widely available methods to be useful, it is important that careful correlative studies be performed. To date, most correlative studies have involved PET and MRl, which we summarize here. 

Table 9.2 Imaging modalities used to approximate the ischemic core and penumbra in patients...

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