Changes in the cerebrocortical capillary network following venous sinus occlusion in cats

Although the important protective effect of venous collateral pathways in sinus occlusion on parenchymal injury has been demonstrated in previous works, the vascular response in the capillary microcirculation itself after cerebral venous occlusion has not been fully elucidated. We examined the morphology of the capillary network after venous occlusion by relating stereologic morphometric parameters to changes in local cerebral blood flow and the development of brain edema.

Experimental venous sinus occlusion was induced by injection of 0.5 mL of cyanoacrylate into the superior sagittal sinus and by immediate ligation of both external jugular veins in chloralose-urethane anesthetized cats (n = 24). Capillaries in the adjacent cortex (marginal and suprasylvian cortex) and remote cortex (piriform cortex) were injected with Evans blue dye 2 minutes before sacrifice at 15-minute and 120-minute postsinus occlusion. The stereologic morphometric parameters including volume density, minimum intercapillary distance, capillary diameter, and number of perfused capillaries were computed on a fluorescence microscopic photograph using an image analysis system. Cerebral blood flow (CBF) was measured by hydrogen clearance method, and brain tissue water content was measured using the dry-wet method.

In the cortex adjacent to the superior sagittal sinus, the volume density and the number of perfused capillaries were increased significantly (p < 0.02, and p < 0.05, respectively) and the minimum intercapillary distance was decreased significantly (p < 0.02) at 15 minutes after venous occlusion (n = 10). Cerebral blood flow (CBF) was also decreased to 53% of that in the control group (p < 0.01). Although the morphologic parameters returned to the control level by 120 minutes after venous occlusion, the CBF remained decreased after venous occlusion. No change was observed in the water content of the adjacent gray matter at 15 minutes after venous occlusion; however, it was increased (p < 0.05) at 120 minutes.

These results indicate that the recruitment of reserve capillaries occurs during the early phase of venous occlusion. While CBF decreased to half of the control after venous occlusion, capillary perfusion remained above or near the control level until 120 minutes postocclusion, suggesting that venous recruitment would be potentially beneficial in clinical patients in the early stage of venous occlusion.