Cerebral Arteriovenous Shunts Re-examined

Cerebral arteriovenous (A-V) shunts have been described in some histological studies, but their existence has been denied in others. Previous attempts to detect the presence and amount of A-V shunting using radioactive microspheres have suggested that large amounts of blood could bypass cerebral capillaries in this fashion. A reappraisal seemed indicated. The present study, using the radioactive microsphere technique, confined the injected spheres specifically to the cerebral circulation of a nonhuman primate. The conclusion of this study is that structural, noncapillary A-V shunting definitely occurs, but is very small and variable in amount. The implications of this finding in relation to previous studies and to the clinical phenomena of red cerebral veins and early venous filling are discussed.