How and Why Do Doctors Determine the Severity of Traumatic Brain Injuries?

Dr. Thomas Swirsky-Sacchetti: When people hear the term “mild,” they assume it’s not serious. And that’s one of the things I don’t like about the classification system — mild, moderate, and severe — because “mild” can actually be broken down further into complicated and uncomplicated.

A mild, uncomplicated head injury would be one in which there are no physiological markers — no skull fracture, no bleeding on the brain, no hematoma. A mild, complicated head injury — you can still have a skull fracture and bleeding on the brain, and it can still be technically classified as a mild head injury.

I saw one person — an older patient — who fell and didn’t even really lose consciousness. They had just a brief alteration of awareness, a little fuzzy for a few minutes. Their Glasgow Coma Scale score was near-perfect. They were classified as a mild head injury.

Six months later, they showed up in the emergency room because they had a slow bleed from that fall — a bleed that wasn’t picked up by the CT scan at the time because it had just started. But over six months, it grew to the size of a lemon. Their life was threatened. They wound up in emergency surgery with a neurosurgeon.
And that’s classified as a mild head injury.

Stewart Cohen: In your experience, and based on your testing — do MRIs and CT scans always show the damage to the brain?|

Dr. Thomas Swirsky-Sacchetti: No. The rule of thumb is that an MRI — something has to be at least the size of your pinky fingernail in order for an MRI to pick it up. And sometimes, because they’re taking slices, if the lesion falls in between a slice, it can be missed. It’s less likely to be missed with repeated MRI.
But the problem with brain injuries is that the injury is on a microscopic level — it’s on a cellular level. So if you think about brain cells — they’re called neurons. There’s the cell body, and the axon, and then there are dendrites that come out. They don’t totally connect with the next neuron. There’s a space in between, and that’s where neurotransmitters come in.
Neurotransmitters are chemical bridges that allow electrical stimulation to travel down one neuron and jump that gap to stimulate the next neuron. So when you’re doing something like remembering a phone number, probably 50,000 of these neurons are firing in a second.
What happens in a head injury is that these neurons get twisted and pulled apart. So now the gap — the synapse — between the neurons is too big for those chemical bridges to work. And that’s why you have slower information processing. That’s why you have people who can’t find the right word to express themselves — it’s sort of reaching a dead end.

The other thing that an MRI or CT scan may not pick up is micro-hemorrhages — when tiny blood vessels, the capillaries, get broken. The skull is not a smooth surface on the inside — there are small bony protrusions, and when the brain gets shaken back and forth, it rubs against those protrusions, causing capillaries to break.
If it’s a major blood vessel, you’re going to find a collection of blood that’s visible on an MRI. But if it’s minor, as it often is, it won’t be. That’s why I tell people all the time to think about it in terms of structure and function — they’re not the same things.

Conversely, I’ve had people with huge, slow growing brain tumors that would basically wipe out their left frontal lobe – the size of a lemon. And on my testing I couldn’t find any functional impairment because the guy was really bright and this brain tumor was a slow-growing type. It might have been growing for 15 years. And it allowed him, because it was slow-growing, to begin to use his left frontal lobe to do things that the left frontal lobe would normally do. So yes, structure and function are two different things.