Microcirculation after cerebral venous occlusions as assessed by laser Doppler scanning

Research on cerebral venous circulation disturbances (CVCDs) has been limited partly by the paucity of animal models that produce consistent venous infarction. Occlusion of two adjacent cortical veins in rats by means of a photochemical thrombotic technique provides a minimally invasive, clinically relevant, and reproducible model suited to study the pathophysiology of CVCDs. In this study, the effects of venous occlusion on regional cortical blood flow and the brain damage that ensues were evaluated. Cortical vein occlusion was induced by photoactivation of rose bengal via 100-microm fiberoptic illumination. The cerebral venous flow pattern was examined using fluorescence angiography until 90 minutes after venous occlusion, and regional cerebral blood flow (rCBF) was determined at 48 locations by using laser Doppler scanning. Histological damage was assessed 48 hours after vein occlusion. Occlusion of two cortical veins (Group T; seven animals) was compared with single-vein occlusion and its ensuing brain damage (Group S; five animals) and with sham-operated control (five animals). An rCBF reduction occurred 30 minutes after occlusion in Group T and was more extensive than the decrease in Group S after 60 minutes. Observation frequency histograms based on local CBF data obtained in Group T demonstrated that local CBF at some sites decreased to a level below the ischemic threshold within 90 minutes. Six of the seven rats in Group T had a growing venous thrombus with extravasation of fluorescein. The resulting infarction was significantly larger in Group T (9.8 +/- 4.5% of the hemispheric area) than in Group S (only 3 +/- 1.5% of the hemispheric area). In conclusion, microcirculation perturbations occur early after venous occlusion and result in the formation of a venous thrombus accompanied by local ischemia and severe venous infarction. The extent of vein occlusion determines the resulting brain damage. Based on the results of this study, the authors conclude that CVCDs may be attenuated by prevention of venous thrombus progression together with the use of protective measures against the consequences of ischemia.