CT techniques for detecting acute stroke and collateral circulation: in search of the Holy Grail.

The management of acute “brain attack” is in evolution. A proliferation of new treatment approaches directed at lysing thrombus, normalizing cerebral perfusion, and reversing or minimizing neuronal ischemic damage are recently approved or currently under investigation. Preservation of “tissue at risk” within the ischemic penumbra is the goal of many of these newer therapies. The ischemic penumbra is a volume of metabolically unstable brain at the margins of the ischemic core that undergoes a reduction of cerebral blood flow in the range of 20% to 40% of normal (1–3). Experimental and clinical studies have shown that a narrow window of opportunity, probably no longer than 3 to 4 hours after the onset of acute ischemic symptoms, exists before complete and irreversible ischemic infarction extends throughout the ischemic penumbra (1). The promotional slogans “brain attack” and “time is brain” are a response to the new interest in timely interventions directed at salvaging as much of the penumbra as possible.