Arachnoiditis following myelography with water-soluble agents. The role of contrast medium osmolality.

The role of contrast medium osmolality in postmyelographic arachnoiditis was studied. Monkeys were injected intrathecally with isotonic saline (290 mOs/kg), hypertonic saline (1,449 mOs/kg), metrizamide (456 or 300 mOs/kg), or methylglucamine iocarnate (1,049 mOs/kg). After 12 weeks the animals were examined for evidence of arachnoiditis, with myelography just prior to sacrifice and microscopic examination of the excised dural sac and its contents. Intrathecal injections of methyglucamine iocarmate or metrizamide caused arachnoiditis while saline did not. Only one animal given 170 mg l/ml (300 mOs/kg) exhibited a more severe reaction than the controls. An increase in the cerebrospinal fluid osmolality alone does not cause arachnoiditis.