Heiss W D
Max-Planck-Institute for Neurological Research, and Department of Neurology, University of Cologne, Germany.
J Cereb Blood Flow Metab. 2000 Sep;20(9):1276-93. doi: 10.1097/00004647-200009000-00002.
The ischemic penumbra is defined as tissue with flow within the thresholds for maintenance of function and of morphologic integrity. Penumbra tissue has the potential for recovery and therefore is the target for interventional therapy in acute ischemic stroke. The identification of the penumbra necessitates measuring flow reduced less than the functional threshold and differentiating between morphologic integrity and damage. This can be achieved by multitracer positron emission tomography (PET) and perfusion-weighted (PW) and diffusion-weighted magnetic resonance imaging (DW-MRI) in experimental models, in which the recovery of critically perfused tissue or its conversion to infarction was documented in repeat studies. Neuroimaging modalities applied in patients with acute ischemic stroke--multitracer PET, PW- and DW-MRI, single photon emission computed tomography (SPECT), perfusion, and Xe-enhanced computed tomography (CT)-- often cannot reliably identify penumbra tissue: multitracer studies for the assessment of flow and irreversible metabolic damage usually cannot be performed in the clinical setting; CT and MRI do not reliably detect irreversible damage in the first hours after stroke, and even DW-MRI may be misleading in some cases: determinations of perfusion alone yield a poor estimate of the state of the tissue as long as the time course of changes is not known in individual cases. Therefore, the range of flow values in ischemic tissue found later, either within or outside the infarct, was rather broad. New tracers--for example, receptor ligands or hypoxia markers--might improve the identification of penumbra tissue in the future. Despite these methodologic limitations, the validity of the concept of the penumbra was proven in several therapeutic studies in which thrombolytic treatment reversed critical ischemia and decreased the volume of final infarcts. Such neuroimaging findings might serve as surrogate targets in the selection of other therapeutic strategies for large clinical trials.
缺血半暗带被定义为血流处于维持功能和形态完整性阈值范围内的组织。半暗带组织具有恢复的潜力，因此是急性缺血性卒中介入治疗的靶点。识别半暗带需要测量低于功能阈值的血流减少情况，并区分形态完整性和损伤。这可以通过多示踪剂正电子发射断层扫描（PET）、灌注加权（PW）和扩散加权磁共振成像（DW-MRI）在实验模型中实现，在这些模型中，在重复研究中记录了严重灌注不足组织的恢复或其转化为梗死的情况。应用于急性缺血性卒中患者的神经影像学检查方法——多示踪剂PET、PW-和DW-MRI、单光子发射计算机断层扫描（SPECT）、灌注和氙增强计算机断层扫描（CT）——通常无法可靠地识别半暗带组织：用于评估血流和不可逆代谢损伤的多示踪剂研究通常无法在临床环境中进行；CT和MRI在卒中后的最初几个小时内不能可靠地检测到不可逆损伤，甚至在某些情况下DW-MRI也可能产生误导：只要在个体病例中不知道变化的时间过程，仅灌注测定对组织状态的估计就很差。因此，后来在梗死灶内或梗死灶外发现的缺血组织中的血流值范围相当广泛。新的示踪剂——例如，受体配体或缺氧标志物——可能在未来改善半暗带组织的识别。尽管存在这些方法学上的局限性，但在几项治疗研究中已证明半暗带概念的有效性。在这些研究中，溶栓治疗逆转了严重缺血并减少了最终梗死灶的体积。这种神经影像学发现可能作为大型临床试验中其他治疗策略选择的替代靶点。
