RESUMO
INTRODUCTION: Many studies have reported on vulnerable areas and neural tracts of the brain after hypoxic-ischemic brain injury (HI-BI). However, little is known about injury of the ascending reticular activating system (ARAS). We attempted to investigate on injury of the lower portion of the ARAS in patients with HI-BI using diffusion tensor tractography (DTT). METHODS: Fourteen consecutive patients with HI-BI and 10 control subjects were recruited for this study. We classified the patients into two subgroups according to the preservation of arousal: subgroup A (eight patients)-intact arousal and subgroup B (six patients)-impaired arousal. The lower portion of the ARAS between the pontine reticular formation and the thalamus was reconstructed using the probabilistic tractography method. Fractional anisotropy (FA), mean diffusivity (MD), and tract volume (TV) were measured. RESULTS: The FA value and TV were decreased in subgroup B compared with those of the control group, although no difference was observed in the MD value (p < 0.05). However, for all DTT parameters, no difference was observed between subgroup A and the control group and between subgroup A and subgroup B (p > 0.05). CONCLUSION: Injury of the lower portion of the ARAS was found between the pontine reticular formation and the thalamus in patients with impaired arousal after HI-BI. We believe that analysis using DTT could be helpful in the evaluation of patients with impaired arousal after HI-BI.