Experimental bacterial meningitis in rats:: Demonstration of hydrocephalus and meningeal enhancement by magnetic resonance imaging

We investigated whether magnetic resonance imaging (MRI) is able to detect intracranial manifestations of advanced bacterial meningitis in rats. Meningitis was induced in nine animals by injecting 150 mul 107 colony forming units per ml of Streptococcus pneumoniae into the cisterna magna. MRI was performed 24 h (n = 5) and 48 h (n = 4) after infection. Controls included (I) animals that were injected intracisternally with 150 mul phosphate-buffered saline or (II) animals without puncture of the cisterna magna. T2-weighted and T1-weighted MR images before and after administration of 0.3 mmol kg(-1) of gadolinium-DTPA were obtained. Hydrocephalus was found in 7 of 9 infected animals, but not in the control group. Abnormal leptomeningeal enhancement was found in all infected animals, but in none of the controls. The animals imaged after 48 h showed a more pronounced hydrocephalus and a more intense leptomeningeal enhancement than animals imaged after 24 h. Even in small animals such as rats, MRI can be used to detect the presence of bacterial meningitis and its associated complications. MRI may be a useful noninvasive method for monitoring the possible effect of adjunctive therapeutic strategies in experimental studies of meningitis.