Hypoperfused tissue compartments after acute MCA occlusion and the consequences of decreasing cerebral perfusion pressure. (a) The three hypoperfused tissue compartments (the core, the penumbra and the oligaemia) after acute middle cerebral artery occlusion. A further compartment with normal perfusion but partially exhausted vascular reserve (denoted autoregulated) surrounds the oligaemic compartment (see text). (b) Consequences of decreasing cerebral perfusion pressure, as a result of, for example, a fall in systemic blood pressure or an increase in intracranial pressure from vasogenic oedema, on the four tissue compartments illustrated in (a), showing an enlargement of the core at the expense of the penumbra, and of the latter into the oligaemia and autoregulated compartments, with attending clinical deterioration. The final infarction potentially involves all four compartments entirely.