Arachnoid granulations of the sheep. Structural and ultrastructural changes with varying pressure differences.

Abstract

Sheep arachnoid granulations were examined to determine the morphologic changes induced by varying pressure differences between the subarachnoid space and the superior sagittal sinus. With the superior sagittal sinus pressure maintained at zero, increasing subarachnoid space pressures caused increasing distention of the arachnoid granulations. Granulations fixed in the distended state by combined subarachnoid and arterial perfusion of aldehydes remained distended even when the gradient was reduced to zero. Electron microscopic studies showed that as the pressure difference was increased (1) neighboring endothelial cell overlappings were shorter and the intercellular spaces were irregularly widened, (2) the endothelial-lined tubules became distended, (3) the endothelial cells showed increased pinocytotic activity, and (4) the stromal cellular and extracellular components were more separated.