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Abstract

Introduction: Patients with moderate or severe traumatic brain injury (Glasgow Coma Scale (GCS)≤ 12) have a broad range of functional outcomes, and the ability to predict outcome in the acute period is limited. The amount of tissue above or below certain apparent diffusion coefficient (ADC) thresholds on diffusion weighted magnetic resonance imaging (DWI MRI) has been shown to correlate with patient prognosis, but previous studies conflict regarding particular ADC thresholds. Methods: This retrospective observational study investigated patients with moderate or severe traumatic brain injury (GCS ≤12 on emergency room evaluation). The first MRI obtained for each patient post-injury day 1–13 was analyzed. Thirteen regions of interest (ROI) were manually drawn on T2-weighted images and co-registered with corresponding ADC maps. Mean ADC values within ROI volumes were analyzed and correlated with patient outcome in univariate and multi-variable analyses. The timing of MRI after injury and the correlation with outcome was also analyzed. A good outcome was defined as discharge to home or a rehabilitation facility, a poor outcome was defined as discharge to a long-term care facility or death. Results: 72 patients were included in the analysis. Thirty-eight patients (53%) had a poor outcome. The timing of MRI scans did not differ between groups, but the mean age did (42 yrs vs. 56 yrs, p<0.05, good vs. poor outcome). The mean thalamic ADC value was higher in the poor outcome group (806mm2/sec vs 836mm2/sec, p<0.05, good vs. poor outcome). In the multivariable analysis, higher ADC in the occipital lobe and lower ADC in thalamus adjusted for age were correlated with good outcome. Additionally, the correlation of ADC level in the occipital lobe with outcome diminished in MRIs performed later after injury. Conclusions: Quantitative MRI offers additional information over routine structural analysis. ADC values in specific areas (i.e. thalamus and occipital lobe) may be prognostic biomarkers in the acute setting of TBI. The optimal timing of MRI after brain injury is undetermined.