Brain parenchyma penetration by intrathecal ionic and nonionic contrast media

Area of Science:

• Neuroradiology
• Neuroscience
• Pharmacology

Background:

• Intrathecal metrizamide, a nonionic contrast medium, penetrates the normal brain.
• Complications from intrathecal metrizamide may correlate with cerebral concentration.
• Metrizamide is considered less neurotoxic than ionic contrast media at equivalent iodine concentrations.

Purpose of the Study:

• To compare the brain penetration of intrathecal metrizamide and methylglucamine iothalamate.
• To investigate if reduced cerebral concentration explains the lower neurotoxicity of metrizamide.
• To assess blood-brain barrier integrity following intrathecal contrast administration.

Main Methods:

• Adult greyhound dogs received intrathecal injections of metrizamide and methylglucamine iothalamate at a similar iodine concentration (280 mg I/ml).
• Brain penetration depth and cortical gray matter concentration were evaluated 1 hour post-injection using computed tomographic scanning.
• The integrity of the blood-brain barrier was assessed qualitatively using Evans blue.

Main Results:

• No significant difference in brain penetration depth or concentration was observed between metrizamide and methylglucamine iothalamate.
• The rate of diffusion across the cerebrospinal fluid-brain interface appears similar for both contrast media.
• No gross disruption of the blood-brain barrier was evident with either contrast agent.

Conclusions:

• The comparable brain penetration of metrizamide and methylglucamine iothalamate does not support the hypothesis that metrizamide's lower neurotoxicity is due to reduced cerebral concentration.
• The observed differences in neurotoxicity are likely attributable to factors other than contrast medium concentration at the brain interface.
• Both nonionic and ionic contrast media, at the tested concentrations, did not appear to compromise the blood-brain barrier integrity significantly.