Association of cause of injury and traumatic axonal injury: a clinical MRI study of moderate and severe traumatic brain injury.

Objective: The authors investigated the association between the cause of injury and the occurrence and grade of traumatic axonal injury (TAI) on clinical MRI in patients with moderate or severe traumatic brain injury (TBI).

Methods: Data for a total of 396 consecutive patients, aged 7-70 years, with moderate or severe TBI admitted to a level 1 trauma center were prospectively registered. Data were included for analysis from the 219 patients who had MRI performed within 35 days (median 8, IQR 4-17 days) and for whom cause of injury was known. Cause of injury was registered as road traffic accident (RTA) or fall (both with respective subcategories), alpine skiing or snowboarding accident, or violence. The MRI protocol consisted of T2*-weighted gradient echo, FLAIR, and diffusion-weighted imaging scans. TAI lesions were evaluated in a blinded manner and categorized into 3 grades, hemispheric/cerebellar white matter (grade 1), corpus callosum (grade 2), and brainstem (grade 3). The absence of TAI was analyzed as grade 0. Contusions and mass lesions on CT were also registered.

Results: Cause of injury did not differ between included and nonincluded patients. TAI was found in 83% of patients in the included group after RTAs and 62% after falls (p < 0.001). Observed TAI grades differed between the subcategories of both RTAs (p = 0.004) and falls (p = 0.006). Pedestrians in RTAs, car drivers/passengers in RTAs, and alpine skiers had the highest prevalence of TAI (89%-100%) and the highest TAI grades (70%-82% TAI grades 2-3). TAI was found in 76% of patients after falls from > own height (45% TAI grade 2-3), 63% after falls down the stairs (26% TAI grade 2-3), and 31% after falls from ≤ own height (12% TAI grade 2-3). Moreover, 53% of patients with TAI after RTAs and 68% with TAI after falls had cortical contusions or mass lesions on CT.

Conclusions: This prospective study of moderate and severe TBI is to the authors' knowledge the first clinical MRI study to demonstrate both the high prevalence and grade of TAI after most of the different types of RTAs, alpine skiing accidents, and falls from a height. Importantly, TAI was also common following more low-energy trauma such as falls down the stairs or from own height. Physicians managing TBI patients in the acute phase should be aware of the possibility of TAI no matter the cause of injury and also when the CT scan shows cortical contusions or mass lesions.