Approach to Imaging in Mild Traumatic Brain Injury and Diffuse Axonal Injury

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Traumatic brain injury is a commonly encountered condition in the emergency department. Mild traumatic brain injury and its squeal of diffuse axonal injury are difficult to diagnose with computed tomography scans as the preferred acute imaging modality. Our current decision on whether or not to scan a patient in the acute setting is best decided upon by the Canadian CT Head Rule. The role for MRI scans in diagnosing diffuse axonal injury is unclear, but current evidence suggests that they are preferred after the initial 48 hour period following head trauma.

While the definition has varied depending on circumstances, Traumatic Brain Injury (TBI) is defined as the result of the application of either external physical force or rapid acceleration/deceleration forces that disrupts brain function as manifested by immediately apparent impairments in cognitive or physical function. This is further classified as mild, moderate, and severe, depending on the patient’s Glasgow Coma Scale Score (GCS). The majority of these cases present to hospital as minor TBI, and previous studies suggest that 40% of these cases are secondary to motor-vehicle-related events.

In terms of neuroimaging following head injury, the decision on whether or not to scan tends to be guided by hospital-specific protocol, or is physician dependent. The general consensus, however, is that patients with new clinical symptoms or a change in GCS following head injury, should undergo a Computed Tomography (CT) scan of the brain. The specific clinical predictors for this are still very much debateable. The Canadian CT Head Rule study, as demonstrated in (Table 1), has developed a highly sensitive clinical decision rule for the use of CT in patients with minor head injuries. These patients are classified into whether or not imaging is required based off five high-risk factors for neurosurgical intervention, and two medium-risk factors for clinically important lesions. The implementation of this guideline in other centres was associated with a modest reduction in CT use and an increased diagnostic yield of head CTs for trauma to the head.