The development of ischaemic damage of the brain depends on the severity and duration of the impaired cerebral supply. If the blood flow declines, loss of function in this area of the brain occurs while the integrity of the cerebral tissue is preserved, and thus the ischaemic changes are potentially reversible (= functional threshold). If there is a further decline of the blood flow (or the ischaemia persists), irreversible failure of the membranous functions and permanent morphological changes occur (= morphological threshold). Cerebral tissue with perfusion values between the two thresholds is called „ischaemic penumbra“. With regard to the potential reversibility of the functional affection in case of rapid and adequate reperfusion, saving of the cerebral tissue in the area of the ischaemic penumbra is the objective of therapeutic efforts. The time interval between the development of ischaemia during the period of reversibility of cerebral tissue is called „therapeutic window“ which lasts 3 - 6 hours but in some instances (and for minor areas) even 48 hours. A decline of the regional blood flow 55 ml/100 g/min leads to the proteosynthesis inhibitation below 35 ml to stimulation of anerobic glycolysis, below 20 ml to loss of electric function, below 10 - 12 ml to ischaemic necrosis. Particularly sensitive are the neurons of the hippocampus, basal ganglia and of some cortical areas. The basic factor of ischaemia of cerebral tissue in the ischaemic penumbra is loss of ATP, other manifestations are waves of spreading depolarization, release of excitatory amino acids (and their penetration into neighbouring tissue with possible spread of the ischaemia), activation of calcium channels, release of free radicals and other mechanisms. Evidence of ischaemic penumbra is obtained best by means of PET but also modern methods of MR (perfusion and diffusion) are used, MR-spectroscopy and SPECT. In the acute therapeutic stage there is the possibility of acute thrombolysis and in particular treatment by neuro- protective agents.

        Key words: ischaemic penumbra, electric and morphological threshold, excitatory amino acids, reper- fusion, thrombolysis, neuroprotective agents