CTs and MRIs Miss Most Traumatic Brain Injuries
The most common brain imaging used in hospital emergency rooms after a person sustains head trauma is a CT scan. CT stands for Computed Tomography, which is a radiology imaging technique that combines X-rays with computer processing to allow physicians to see “slices” of the brain. CT scans are helpful in identifying skull fractures and brain bleeds, which may be extremely important if prompt neurosurgical help is needed.
Unfortunately, CT scans do not do a good job of determining if a person has sustained a mTBI, (a so-called “mild” traumatic brain injury). According to a leading standard medical textbook in the field1, CT scans catch only 6-7% of mTBIs. In other words, in the great majority of cases, the injured person’s brain CT looks “normal” when the person in fact has a brain injury.
MRI, or Magnetic Resonance Imaging, is another tool used by physicians to help evaluate brains after head trauma. MRIs use magnetic fields and computer-generated radio waves to help create more detailed images of the brain. A 2013 medical study looked at people who had mTBI and whose CT brain scans had been read as normal; of these people, 27% had abnormal brain MRIs.2 While MRIs identified some of the mTBIs that the CT scans missed, roughly 3 out of 4 people with a traumatic brain injury still had a normal MRI.
This is not to minimize the importance of imaging for physicians who are trying to help people after head trauma. But there are limitations on what imaging can reveal. Neither CT scans nor MRIs indicate whether the brain is working normally; a person who has just died from a heart attack, for example, should have a normal brain MRI shortly after death. Even for people who are alive, MRIs are simply not sensitive enough to pick up typical mTBIs because an MRI is not powerful to see individual neurons, much less the axons of neurons (the part of the brain cells that extend from one neuron to another, allowing the brain cells to communicate). Many mTBIs involve what is called diffuse axonal injury, in which axons are sheared as the brain rapidly accelerates and decelerates inside the skull. Such injury to the axons is simply not visible on an MRI, because the technology is not sensitive enough. A “normal” MRI does not mean that a person has not sustained a traumatic brain injury.
The term “mild” traumatic brain injury has more to do with neurosurgery than it does with how the person does after brain damage. Recent medical literature documents that more than half of people with mTBI had impairments more than a year after the injury,3 and did not have a full recovery.4 People with so-called “mild” traumatic brain injuries have more than double the risk of dementia later on as compared to people who did not suffer a mTBI.5 As one expert neurologist put it in one of our recent trials, a “mild” traumatic brain injury might be anything but mild to the brain-injured person and their family.
1Osborn’s Brain, 2017
2Yuh, Mukherjee, et al., 2013
3McInnes, Friesen, et al., 2017
4Nelson, Temkin, et al., 2019
5Barnes, Byers, et al., 2018