On the pathogenetic mechanism of ring enhancement in subacute intracerebral hematomas on CT

The purpose of the present study was to establish the pathogenetic mechanism of the ring enhancement (RE) on computed tomography in cases of intracerebral bleeding. Cerebral blood flow (CBF) was determined using the Xe-CT method (Shuttle method); rapid sequential scans with an iodinated contrast material (Conray) were also done to document the width as an index of the mean transit time. These procedures made it possible to measure the local CBF (l-CBF) and also the local cerebral blood volume (l-CBV). The results may be summarized as follows: 1) Two patterns of the attitude of cerebral circulation in the area of RE were observed; one had increases in both l-CBF and l-CBV, accompanied by a prolonged transit time, and the other, decreases in both l-CBF and l-CBV. 2) The RE is supposed to be mainly due to the increase in neovascularization in cases of local hyperemia and to the extravasation of the contrast material in cases of a low local perfusion. 3) Although it has been suggested that the main mechanisms of RE are due to newly formed capillaries and extravasation, some dominance of these two mechanisms may exist at various stages of illness. Moreover, we discussed the propriety of using the width as an index of the mean transit time. (author)