This 60-year-old male reports sixth nerve palsy and double vision following a motorcycle accident. You are shown a T2 FLAIR (normal) and a T2* GRE. All other sequences were unremarkable, but the blue arrows on the T2* demonstrate a symmetric deep pattern of hypointensity. Usually, people with siderotic linear signal deep within the brain from trauma are unconscious or in a persistent vegetative state. So why is this patient conscious? Besides motor vehicle accidents, what other life circumstance can sometimes produce similar findings?
When comparing this patient’s case with those of patients in comas who have traumatic axonal injuries, comatose patients usually have a siderotic disposition that is more random, assymetric and deep, as well as peripheral and extensive. While motor vehicle accidents (MVAs) are the most frequent cause of axonal injury, similar findings can be seen in child abuse or shaken baby syndrome cases.
Deceleration (MVA) or shaking injuries (non-accidental trauma in children), known as diffuse axonal injury (DAI), occur in the brainstem, corpus callosum and cerebral hemispheres. Always be suspicious of non-accidental trauma in children when you have any unexplained intracranial hemorrhage, especially with retinal bleed or detachment and/or skull fracture. In the cerebrum of the brain, the frontal and temporal regions are most commonly affected.
Certain portions of the brain which are a bit more dense than the rest of the brain such as the cerebral cortex white matter, superior cerebral peduncles, basal ganglia, thalamus and deep hemispheric nuclei may be at higher risk. It is not uncommon for CT scans to be normal in patients with DAI, so suspect DAI in any patient who is comatose and has had deceleration or acceleration/deceleration trauma with a negative CT. For more neuro case review, visit MRI Online.