[Sequential changes of experimental cerebral infarction--CT and histological studies].

Using the canine thalamic infarction model, it was found that hemorrhagic infarction can be produced at a high frequency following recirculation after 6 hours of vascular occlusion. In the current study, sequential changes of histological findings and CT findings in the infarctic foci were investigated. Low absorption areas in the CT scans were apparent already by the 2 hours of recirculation. Thereafter, the boundary with the periphery became more distinct and was visible through the 6th week. Contrast enhancement could be seen 2 hours after recirculation and between 7 and 14 days thereafter. In histological study, leakage of red blood cells from the capillaries and small venules in the focus could be seen 2 hours after recirculation. This finding is thought to indicate that the mechanism of contrast enhancement is extravasation during this period. Macrophages began to infiltrate the focus from the surrounding tissue between the 2nd and 5th day. Between the 7th and 14th day, destruction of nerve cells and capillaries was seen, together with the formation of small cavities, but many small vessels from the peripheral tissue heading toward the focus were regenerated. It is thought likely that the contrast enhancement seen during this period was due to leakage of the contrast medium from these newly regenerated vessels. From around the 3rd week, destruction of the regenerated vessels from the periphery of the focus began and cavity formation progressed. By the 6th week, only a small amount of fibrous neural material remained and the cavity was well-formed.