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Relationship between consciousness and injury of ascending reticular activating system in patients with hypoxic ischaemic brain injury

Impaired consciousness is one of the main sequelae of hypoxic ischemic brain injury(HI-BI).1 The ascending reticular activating system (ARAS) comprised arousal pathways and awareness networks, which mainly originates in the reticular formation of the brainstem and projects to the cerebral cortex through synaptic relays in the intralaminar thalamic nucleus, hypothalamus, basal forebrain and several brainstem nuclei.2 Depending on the severity of HI-BI and the timing of imaging, conventional brain MRI usually shows high-signal intensity in the vulnerable areas (eg, basal ganglia, thalamus, hippocampus, cerebellum and cortex). However, it has limitations when demonstrating ARAS injuries. Diffusion tensor tractography (DTT) derived from diffusion tensor imaging (DTI), an imaging technique for evaluation of the integrity of white matter through assessment of water diffusion characteristics, has enabled three-dimensional reconstruction of the three parts of the ARAS: thalamocortical connections, lower dorsal ARAS and lower ventral ARAS. Several studies using DTT have demonstrated injury of the ARAS in patients with HI-BI. However, the relationship between consciousness and the ARAS is unclear.

In this study, we investigated the relationship between injury of the ARAS and consciousness in patients with HI-BI by using DTT.

### Subjects

Twenty-nine patients with HI-BI (from January 2013 to September 2017) and 21 age-matched and sex-matched healthy control subjects were recruited. The Glasgow Coma Scale (GCS) and Coma Recovery Scale-Revised (CRS-R) were used to evaluate the consciousness of the patients at the …