Holler, Jon G4; Brandt, Christian T2; Leib, Stephen L5; Rowland, Ian J6; Andersen, Christian Østergaard3
1 Department of Infectious Diseases, Amager and Hvidovre Hospital, The Capital Region of Denmark2 Department of Thoracic Medicine and Infectious Disease, Nordsjællands Hospital, The Capital Region of Denmark3 Department of Clinical Microbiology, Amager and Hvidovre Hospital, The Capital Region of Denmark4 Infektionsmedicinsk Klinik, Finsencentret, Rigshospitalet, The Capital Region of Denmark5 unknown6 Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and research, Amager and Hvidovre Hospital, The Capital Region of Denmark
BACKGROUND: The hippocampus undergoes apoptosis in experimental pneumococcal meningitis leading to neurofunctional deficits in learning and memory function. The aim of the present study was 1) to investigate hippocampal apparent diffusion coefficient (ADC) and volume with MRI during the course of experimental pneumococcal meningitis, 2) to explore the influence of accompanying bacteremia on hippocampal water distribution and volume, 3) and to correlate these findings to the extent of apoptosis in the hippocampus. METHODS: Experimental meningitis in rats was induced by intracisternal injection of live pneumococci. The study comprised of four experimental groups. I. Uninfected controls (n = 8); II. Meningitis (n = 11); III. Meningitis with early onset bacteremia by additional i.v. injection of live pneumococci (n = 10); IV. Meningitis with attenuated bacteremia by treatment with serotype-specific anti-pneumococcal antibodies (n = 14). T2 and diffusion weighted MR images were used to analyze changes in hippocampus volume and water diffusion (ADC). The results were correlated to ADC of the cortex, to ventricular volume, and to the extent of hippocampal apoptosis. RESULTS: Both ADC and the volume of hippocampus were significantly increased in meningitis rats compared to uninfected controls (Kruskal-Wallis test, p = 0.0001, Dunns Post Test, p < 0.05), and were significantly increased in meningitis rats with an early onset bacteremia as compared to meningitis rats with attenuated bacteremia (p < 0.05). Hippocampal ADC and the volume and size of brain ventricles were positively correlated (Spearman Rank, p < 0.05), whereas no association was found between ADC or volume and the extent of apoptosis (p > 0.05). CONCLUSIONS: In experimental meningitis increase in volume and water diffusion of the hippocampus are significantly associated with accompanying bacteremia.