The leptomeninges of cats were exposed to lidocaine, metrizamide and methiodal sodium and compared with control brains exposed to Ringer's solution. As a sign of blood-brain barrier damage, an increased extravasation of albumin into the cerebral cortex was recorded after exposure to methiodal sodium; lidocaine or metrizamide did not produce such damage. Scanning electron microscopy revealed minor cellular reactions in the mesothelial cells of the leptomeninges after application of metrizamide, lidocaine and Ringer's solution. Methiodal sodium produced an extensive cellular damage of the leptomeningeal cells. The importance of testing the leptomeningeal reactions and the reactions of the blood-brain barrier to all liquid media used on the brain surface is emphasized.

Reactions to contrast material during retrograde pyelography are rare. Two cases are reported, and the literature is reviewed.

The effect of several radiographic contrast media on the complement system in vitro was examined using quantitative crossed immunoelectrophoresis. Diatrizoate, iothalamate, metrizoate, and methiodal did not cause electrophoretic conversion of C3 or properdin factor B. In fact, the small degree of spontaneous conversion occurring when serum is incubated in polypropylene tubes was inhibited by these contrast media or by hypertonic sodium chloride. Metrizamide caused enhanced conversion of C3 and factor B that was only partially inhibited by ethylene glycol tetracetic acid (EGTA) but completely inhibited by ethylenediaminetetraacetic acid (EDTA). Iodipamide caused a unique electrophoretic alteration of C3 that was not affected by EDTA or several other inhibitors and that was not identical with the usual products of C3 activation. Iodipamide in very low concentrations inhibited complement activation through the classical pathway.

Two hundred and fifty-six myelograms in 192 patients were following by repeat myelography using a water-soluble contrast medium. The films of these re-examinations were analysed for signs of meningeal changes. Adhesive arachnoiditis had developed in five of 46 cases after methiodal sodium, in 24 of 96 cases after iothalamate meglumine, in seven of 12 cases after iocarmate meglumine, in seven of ten cases after iodophendylate, but in none of 90 cases after metrizamide. Dose of contrast medium, observation time and protein concentration of the CSF were found to be factors of importance for the development of adhesive arachnoiditis.

Late sequelae (adhesive arachnoiditis) have been reported following myelography with the oily contrast medium (Pantopaque) and with the ionic water-soluble contrast media methiodal sodium (Abrodil, Conturex, Kontrast U) meglumine iothalamate (Conray Meglumine) and meglumine iocarmate (Bis-Conray, Dimer-X). Adhesive arachnoiditis has not yet been reported after the use of the nonionic water-soluble contrast medium metrizamide (Amipaque). Thus, this is considered the contrast medium of choice for lumbar myelography. Using the recommended dose of 10 ml with an iodine concentration of 170 mg/ml for this examination, adhesive arachnoiditis is unlikely to occur. Increased osmolality of spinal fluid after injection of contrast medium is related to increased frequency of arachnoiditis.

The frequency of adhesive arachnoiditis following lumbar radiculography with methiodal sodium (95 patients), methylglucamine iocarmate (20 examinations in 18 patients), and metrizamide (77 examinations in 73 patients) was found to be 29% in patients who were not operated on between methiodal studies and 48% in those who were operated on. With both methylglucamine iocarmate and metrizamide the frequency was very low. No changes indicating adhesive arachnoiditis were seen with these media in patients who were not operated on between radiographic examinations.

A solution of methiodal sodium (20%) and lidocaine HCl (0.20%) was given by intramedullary injection into the lumbar spinal cords of 12 anesthetized dogs (group I). Two control groups of 12 dogs each were subjected to needle placement only or were given 5% dextrose. The results showed that both solutions given by intramedullary injection caused severe spinal cord malacia and cavitation in 2 group I dogs and in 1 group III dog.

Contrast media injected into the subarachnoid space may be eliminated in two different ways, by diffusion through the meningeal membranes or by transport through these CSF pathways. The latter mode of transport may be examined using computer assisted tomography of the head. Diffusion predominants with contrast media of low molecular weight, such as methiodal sodium. The transport through the CSF cihculation increases when contrast media of high molecular weight such as meglumine iocarmate and metrizamide are used.