Core infarct volume

Studies using various imaging modalities (Xe-enhanced CT, MRI DWI, CTA source images, and CTP) have demonstrated that pretreatment core infarct size predicts the clinical response to reperfusion, and that core infarct volume less than 70-100 mL may be an effective treatment target... 

Several studies have validated the ability of CTP to distinguish between core and penumbra. In one study, Wintermark et al. found that the volumes of early infarcts in CTP CBV maps were highly correlated with volumes of early DWI lesions, whereas volumes of lesions seen in CTP CBF maps were close to those seen in the corresponding MRP MTT maps. In another study, the volume of the CBF abnormahty in an acute-stage infarct was highly correlated with final infarct volume in patients who did not exhibit recanalization after thrombolysis, consistent with extension of infarction into the penumbra. However, in patients who did exhibit recanalization after thrombolysis, final infarct volume was highly correlated with the initial CBV abnormality, consistent with failure of infarcts to extend into the ischemic penumbra. ... 

The major challenge in using CTP for the assessment of the core infarct is the questionable reliability of dynamic perfusion imaging. CBV measurements are thought to be more robust than CBF and MTT measurements because the calculation of cerebral blood volume is relatively insensitive to bolus delay and dispersion [85, 86]. However, as a calculated parameter, it remains dependent on postprocessing (e.g., partial volume effects) and patient-specific issues (e.g., hematocrit levels) [87-89]. Additionally, as demonstrated in the DIAS-2 study [90], there is poor interrater agreement in assessing the CBV lesion. 

In most cases, the ultimate volume of an infarct is larger than that seen in initial DWI images,encompassing both initially DWI-abnormal tissue and other tissue into which the infarct extends. The ultimate volume of an infarct also is usually larger than that seen in early CBV maps. However, DWI images rather than CBV maps are usually used to identify the infarct core, both because infarcts are usually far more conspicuous in DWI images than in CBV maps, and because the DWI detects lesions that have been irreversibly damaged despite... 

By using a thresholding approach in a 3-D CBF data set, we could show that 54% of the total ischemic lesion volume could be attributed to the penumbra, only 46% to the infarct core at 1.5 h post MCA occlusion (Back et al. 1995). Those areas with pending infarction show potentially reversible changes that can be addressed by therapeutic interventions like recanalizing therapy and/or neuroprotective drugs. 

An early report from our group indicated that, in the absence of early recanalization, CTA-Sl typically defines minimal final infarct size and, hence, like DWI and thresholded CBF maps (Fig.5.5, 5.6), can be used to identify infarct core in the acute setting [34] (Figs. 5.5, 5.6). Coregistration and subtraction of the conventional, unenhanced CT brain images from the axial, post contrast CTA source images should result in quantitative blood volume maps of the entire brain [15, 27, 70]. CTA-SI subtraction maps, obtained by coregistration and subtraction of the unenhanced head CT... 

Fig. 5.10 CT images in a patient with left hemiparesis. Admission CTP images show cerebral blood flow (CBF, upper left), cerebral blood volume (CBV, upper middle), and mean transit time (MTT, upper right). The presence of a matched CBF/CBV perfusion deficit suggests irreversibly ischemic infarct core , likely to correlate with DWI findings, and not a target for reperfusion therapies The admission non-contrast CT...

More recent studies have further refined the impact of core on cUnical outcome. Two studies have demonstrated that in anterior circulation strokes, an acute DWl lesion volume >70 mL has a high specificity for poor outcomes with or without therapy [223, 224], revising the earlier suggestion that 100 mL is the core volume cutoff for poor outcomes. In acute stroke patients treated with lAT between 3 and 6 h of stroke onset, core size was the best predictor of clinical outcome at three months [225]. In particular, any increment of 1 SD (13.2 mL) of the infarct core size increased the mRS score by about one point, whereas any increment of 1 SD (5.8 points) of admission NIHSS score raised the mRS by approximately 0.5 points. 

CT perfusion. Compared to NCCT, dynamic CT perfusion (CTP) has a higher sensitivity for detecting the extent of acute ischemia [78,79]. Evidence indicates that the region of reduced CBV approximates the infarct core [25,73, 80]. One proposed explanation for this finding is that loss of cerebrovascular autoregulation within the infarcted tissue results in the collapse of capillary beds and a decrease in cerebral blood volume [67, 81]. 

As described in the previous chapter on the ischemic penumbra, a patient with significant neurological deficit (NIHSS > 10), the finding of an ICA or proximal MCA occlusion and a small infarct core (<70-100 mL), very likelyhasavolumeofhypoperfused, symptom-producing tissue at risk that is at least 50% greater than the core volume. This concept was initially proposed as the diffusion-clinical mismatch [108, 109], and is based on the fact that the occlusion, core, and penumbra are not independent variables, but are related to each other by the collateral circulation. If one can identify two of the... 

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