~' q-he electron microscope examination of arachnoid villi from dogs after the subarachnoid injection of blood reveals that erythrocytes accumulate and degenerate in the villi. A continuous layer of endothelium separates the villus from the lumen of the sagittal sinus. No evidence for pores through the endothelium or for the passage of intact erythrocytes from CSF to blood through arachnoid villi has been found.
KEY WORDS electron microscopy arachnoid villi subarachnoid hemmorrhage erythrocytesFro. 2. Electron micrograph of arachnoid villus fixed 24 hours after blood injection. The endothelium (E) with its basement membrane (B) separates the red blood cells in the CSF space from the lumen of the sagittal sinus. A tight junction (J) between two endothelial cells is present. Lead citrate and uranyl acetate, • 38,250.] 94
A primary malignant melanoma of the central nervous system is studied by light and electron microscopy. There were numerous endothelial fenestrae and basement membrane abnormalities in intrinsic tumor capillaries. It is felt that these vascular abnormalities may play a role in explaining why these tumors have an increased incidence of bleeding. No characteristic findings were encountered which would help distinguish this tumor from one of peripheral origin.
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