CT scans answer a specific question: is there bleeding, swelling, or a skull fracture that needs emergency intervention. They answer it well. What they do not do is visualize the microscopic injury to axons and brain cells that characterizes most mild traumatic brain injury.
The evidence for that statement is direct. In the multicenter TRACK-TBI study, researchers took TBI patients whose head CT was normal and performed MRI two weeks later. Twenty-seven percent had visible traumatic abnormalities on MRI that the CT could not see [].
This is why current diagnostic criteria do not require an abnormal scan. Under the American Congress of Rehabilitation Medicine's 2023 criteria, mild TBI is diagnosed clinically, from mechanism, signs, symptoms, and examination findings, with neuroimaging and blood biomarkers as supportive elements []. A normal CT is consistent with mild TBI, not evidence against it.
When imaging is normal, we describe it as normal. A normal result on a test built to detect bleeding says nothing about injury the test was never designed to see. Blood biomarkers exist precisely for this gap: in the same TRACK-TBI cohort, GFAP levels identified which CT-normal patients were likely to have MRI-visible injury [].
If you were told your scan was normal and your symptoms have not resolved, both facts can be true at the same time. That combination is common, it is documented in the largest brain injury studies in the United States [, ], and it is a reason for clinical evaluation, not a reason to dismiss what you are experiencing.