The Ischemic Penumbra PDF

Preface

In the world of acute ischemic stroke, nothing is more important than an understanding of the ischemic penumbra. The whole concept of the existence of salvageable tissue, that is, the penumbra, is based on the daily clinical observation of almost immediate and early recovery from an episode of hemiparesis or other clinical expression of occlusion of a blood vessel within any of the arterial territories of the brain. Indeed, even before there was an appreciation of the complexities of the ischemic cascade, many clinicians dealing with stroke understood that something akin to the ischemic penumbra was likely to exist. These ideas, which fueled pivotal experimental studies to document the penumbra, clashed with the then prevailing dogma that the ischemic brain was doomed to die within minutes of onset of the clinical event. It is because of this central positioning of the penumbra in stroke outcome and therapy that we felt that a volume dedicated to its existence was timely.

The editors are all clinical scientists working in the field of stroke, but coming from different perspectives. In particular, we have backgrounds in imaging and therapies for stroke, as well as its pathophysiology and neurochemistry. Hence, we have tried to draw together an overview of the ischemic penumbra viewed predominantly from the clinical perspective, but providing the reader with a solid component of the more basic experimental and neurochemical aspects. Also, we are of an opinion that this should also be put in historical context. Here we have been particularly fortunate in having an enthusiastic contribution from Professor Lindsay Symon, who had such a pivotal role in defining the ischemic penumbra during the 1970s by means of a series of rigorous animal experiments. We have also included chapters that summarize aspects of the penumbra in a way that has not been done before, such as providing an overall view of species differences in thresholds for the penumbra and its duration. The duration of the penumbra is particularly relevant if we are to extend the time window for treatment so more patients can benefit from modern therapies.

In bringing together ideas about the definition, criteria, and the various penumbral imaging modalities now available, one message becomes quite clear. Although already clearly useful in the clinical setting, the concept of the ischemic penumbra is still evolving as there is still no entirely satisfactory definition, and the operational criteria for its existence need refining. Perhaps even more obviously, there is no ideal imaging technique to confirm its presence. Each of the penumbral imaging techniques described in this volume have their advantages and disadvantages, and none really directly and precisely images the penumbra as originally defined. One conclusion that can be drawn from this is that the penumbra is still a fertile area of research with many new discoveries of importance still to be made.

Hence, we hope that this volume is a useful resource for clinicians, researchers, and students alike who have an interest in the ischemic penumbra. While we have attempted to include a broad range of elements of the penumbra together, there are, of course, always areas that could have been strengthened and others that may have been overemphasized. As the first major attempt to paint a scientific picture of the penumbra on one canvas, we hope that this has been a reasonable start. If the benefit achieved is to enhance penumbral research even to a small extent, we will have realized our aim of helping those who, unfortunately, have been the victims of stroke.