Traumatic axonal injury on clinical MRI: association with the Glasgow Coma Scale score at scene of injury or at admission and prolonged posttraumatic amnesia

Objective: The aim in this study was to investigate if MRI findings of traumatic axonal injury (TAI) after traumatic brain injury (TBI) are related to the admission Glasgow Coma Scale (GCS) score and prolonged duration of posttraumatic amnesia (PTA).

Methods: A total of 490 patients with mild to severe TBI underwent brain MRI within 6 weeks of injury (mild TBI: median 2 days; moderate to severe TBI: median 8 days). The location of TAI lesions and measures of total TAI lesion burden (number and volume of lesions on FLAIR and diffusion-weighted imaging and number of lesions on T2*-weighted gradient echo or susceptibility-weighted imaging) were quantified in a blinded manner for clinical information. The volume of contusions on FLAIR was likewise recorded. Associations between GCS score and the location and burden of TAI lesions were examined with multiple linear regression, adjusted for age, Marshall CT score (which includes compression of basal cisterns, midline shift, and mass lesions), and alcohol intoxication. The predictive value of TAI lesion location and burden for duration of PTA > 28 days was analyzed with multiple logistic regression, adjusted for age and Marshall CT score. Complete-case analyses of patients with TAI were used for the regression analyses of GCS scores (n = 268) and PTA (n = 252).

Results: TAI lesions were observed in 58% of patients: in 7% of mild, 69% of moderate, and 93% of severe TBI cases. The TAI lesion location associated with the lowest GCS scores were bilateral lesions in the brainstem (mean difference in GCS score -2.5), followed by lesions bilaterally in the thalamus, unilaterally in the brainstem, and lesions in the splenium. The volume of TAI on FLAIR was the measure of total lesion burden most strongly associated with the GCS score. Bilateral TAI lesions in the thalamus had the largest predictive value for PTA > 28 days (OR 16.2, 95% CI 3.9-87.4). Of the measures of total TAI lesion burden, the FLAIR volume of TAI predicted PTA > 28 days the best.

Conclusions: Bilateral TAI lesions in the brainstem and thalamus, as well as the total volume of TAI lesions on FLAIR, had the strongest association with the GCS score and prolonged PTA. The current study proposes a first step toward a modified classification of TAI, with grades ranked according to their relation to these two measures of clinical TBI severity.