A model of intracerebral hematoma that closely resembles the state in humans after spontaneous intracerebral hematoma was developed. Sequential changes in experimental intracerebral hematomas were compared with the in vivo findings in spontaneous intracerebral hemorrhage. The clinical series consisted of 28 patients with spontaneous intracerebral hemorrhage observed by CT during their natural course from 1976 through 1978. The experimental series consisted of 26 adult mongrel dogs with intracerebral hematoma near the basal ganglia studied by CT and histological examinations. In neither the clinical nor the experimental series was the time of decrease in density beginning in the periphery of the hematoma or the first appearance of ring enhancement and its concentric concentration toward the center of the hematoma affected by the size of the hematoma. In the experimental series, the tissue reaction near the periphery of the intracerebral hematoma showed constant processes: First, a necrotic layer appeared; this was then replaced by immature connective tissue with newly formed vessels and argentophilic fibers, and finally the immature layer was gradually transformed into mature connective tissue with collagenous fibers. Ring enhancement was accompanied by the appearance of immature connective tissue and capillaries. This process of change was also unrelated to the size of the hematoma. The following correlations were suggested from the chronological observation of CT images and the histological appearance: 1) acute stage - homogeneous high density extending to the periphery, appearance of the necrotic layer; 2) subacute stage - decreased density spreading from the periphery and formation of ring enhancement, appearance of immature connective tissue with argentophilic fibers; 3) chronic stage - concentric concentration of ring enhancement and development of mature connective tissue with collagenous fibers.

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SummaryAs models of clinical hypertensive intracerebral hematomas, intracerebral hematomas were induced experimentally in 26 mongrel dogs. The CT images of the hematomas during healing were compared with histological findings to determine the cause of ring enhancement in contrast enhanced CT.The ring enhancement appeared at almost the same time in all dogs, 9 days after formation of the hematomas.Formation of many new capillaries in the peripheral region of the hematomas was seen from day 9 and the ring enhancement was found to be closely associated with these new capillaries. Electron microscopy showed that these newly formed capillary vessels had a similar ultrastructure to those of the muscle. These vessels seemed to have no blood brain barrier. Thus the ring enhance ment was attributed to the accumulation of contrast medium in these newly formed vessels and its leakage from the vessels owing to their increased permeability.

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