Diffusion of contrast media in cerebrospinal fluid: comparison of iohexol, iopamidol and iotrolan in vitro.

Diffusion of iohexol (300 and 240 mgI/ml), iopamidol (300 and 200 mgI/ml), and iotrolan (300 and 240 mgI/ml) in the cerebrospinal fluid (CSF) of 16 patients was studied in vitro. Test tubes containing CSF were kept in a waterbath at 37 degrees C. Contrast medium was injected along the wall into the tubes, and diffusion of contrast media in the tubes was followed with repeated computed tomography for 5 h. The contents of the tubes were then mixed by shaking, and the tubes were scanned immediately and 8 h later. The contrast media first settled in the bottom of the tubes and then diffused upwards. Iotrolan diffused more slowly than the other media, but the difference was only significant at a concentration of 300 mgI/ml. The difference between iohexol and iopamidol was minimal. In general, diffusion was slower in CSF samples with an elevated protein content, but the difference in the diffusion of contrast medium in normal and pathological CSF was seldom statistically significant, perhaps owing to the small number of samples (5) with an elevated protein content. All contrast medium-CSF mixtures remained homogeneous after mixing. These experiments showed measurable differences in the diffusion of contrast media in CSF, but it does not seem very likely that these would be significant in clinical practice.