Chronic infarct in brain meaning
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Understanding Chronic Infarct in the Brain
Definition and Pathophysiology of Chronic Brain Infarct
A chronic brain infarct refers to a region of the brain that has undergone permanent damage due to a prolonged lack of blood supply, typically following a stroke. This condition results in the death of brain tissue, which can be identified through various imaging techniques.
Viability of Brain Tissue Post-Stroke
Research has shown that even after a stroke, some brain tissue may remain potentially viable for a period before it eventually becomes necrotic. This tissue, often referred to as the "penumbra," is at risk but not yet irreversibly damaged. Studies using positron emission tomography (PET) have demonstrated that within the first 18 hours after a stroke, there can be substantial volumes of brain tissue with a cerebral metabolic rate of oxygen (CMRO2) above the threshold for irreversible damage. However, this tissue can still evolve towards necrosis if not treated appropriately.
Imaging and Identification of Chronic Infarcts
Advanced imaging techniques such as PET and single photon emission computerized tomography (SPECT) have been instrumental in studying chronic infarcts. For instance, PET studies have shown that the mean CMRO2 in infarcted voxels significantly decreases from the acute to the chronic stage, indicating the progression from potentially viable to necrotic tissue. Similarly, SPECT imaging using 123I-isopropyl iodoamphetamine (IMP) has identified two distinct zones within chronic infarcts: a central area with severe decreases in IMP uptake and regional cerebral blood flow (rCBF), and a peripheral area with moderate decreases in these parameters.
Importance of the Periinfarct Area
The periinfarct or peripheral area surrounding the central infarct zone plays a crucial role in the overall impact of the stroke. This area, characterized by moderate decreases in blood flow and IMP uptake, may represent regions of the brain that are not directly affected by the ischemic insult but suffer from secondary effects such as deafferentation or selective neuronal loss. The volume of this peripheral area can be quite large and is often correlated with the patient's neurological status, making it a significant factor in prognosis and therapeutic evaluation.
Conclusion
Chronic brain infarcts result from prolonged ischemia leading to permanent brain tissue damage. Advanced imaging techniques have revealed that some brain tissue remains potentially viable for a period post-stroke, highlighting the importance of timely intervention. The identification of central and peripheral areas within chronic infarcts provides valuable insights into the pathophysiology of stroke and aids in the assessment of patient prognosis and treatment efficacy.
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