Selective Alteration of the Blood-Brain Barrier

'HILE most neurosurgeons have been uneasy at the prospect of possible cerebral or blood-brain barrier damage induced by various arteriographic media and have attempted to decrease this effect, these harmful aspects suggested a potential usefulness. It is well documented that every currently used radiopaque substance may, at certain dosage levels, induce damage to normal brain through alteration of the blood-brain barrier, red blood cell aggregation or toxic effects upon the intima of blood vessels. 1,~,1~ Minor arguments exist as to which agent is better or worse; and, using a variety of test situations, investigators have championed one agent or another. There may be a wide differential in the existing blood-brain barrier in various parts of the brain with significant variations in susceptibility to damage. In this discussion, the expression blood-brain barrier refers to the failure of most substances passing through blood vessels to enter normal brain tissues. Certain areas may not have a bloodbrain barrier. 6 The choroid plexus, area postrema, intercolumnar tubercle and the pituitary and pineal glands may be examples; moreover, there is normally a moderate blood-brain barrier difference between white and gray matter, s The most important factor is the substance being used to test the barrier; there are differing beliefs in the superiority of one test compound over another. For instance, trypan blue was for many years a favorite tool to differentiate "normal" from impaired blood-brain barrier. Since the advent of radioisotopes, trypan blue has fallen into