Injury of the lower ascending reticular activating system in patients with pontine hemorrhage: Diffusion tensor imaging study.

Many studies have reported about injury of the ascending reticular activating system (ARAS) in patients with various brain pathologies, using diffusion tensor tractography (DTT); however, little is known about injury of the ARAS in patients with pontine hemorrhage. In this study, using DTT, we attempted to investigate injury of the lower ventral and dorsal ARAS in patients with pontine hemorrhage. Twenty-three consecutive patients with pontine hemorrhage and 14 control subjects were recruited into this study. The patients were classified into 2 subgroups on the basis of the preservation of arousal: subgroup A (14 patients)-intact arousal, subgroup B (9 patients)-impaired arousal. The lower ventral and dorsal ARAS between the pontine reticular formation with hypothalamus and thalamic intralaminar nucleus were reconstructed. Fractional anisotropy (FA), mean diffusivity (MD), and tract volume (TV) values were measured. The TVs of the lower ventral and dorsal ARAS were significantly lower in subgroup B than in the subgroup A and control group (P < 0.05). In terms of FA value, the lower dorsal ARAS were significantly lower in subgroup A and subgroup B than in the control group (P < 0.05). In conclusion, injury of the lower ventral and dorsal ARAS was demonstrated in patients with impaired arousal following pontine hemorrhage. We believe that analysis of the ARAS using DTT would be helpful in evaluation of patients with impaired consciousness after pontine hemorrhage.