When we talk about “severe” head injury, as I mentioned Sunday, we’re talking about a classification that’s done CLINICALLY. That means the Glasgow score is assigned without taking into account exactly what the injuries are. Eyes, verbal, motor. That’s it.
We’ve spoken quite a bit about hematomas – collections of blood either outside of the membranes protecting the brain (“extradural” hematoma), within those membranes (“subdural”), under them (“subarachnoid”) or in the brain substance itself (“intracerebral”). Hematomas cause damage by compressing and displacing brain tissue, but also by increasing the intracranial pressure (see earlier posts about this).
When we take a patient to the CT scanner to see what the injuries are, we’re sometimes surprised to see that our (very) comatose patient has a shockingly “normal” looking scan. When the scan shows essentially generalised swelling with no significant focal neurosurgical lesions (i.e., bruises and hematomas), we talk about diffuse axonal injury, or DAI. We HATE when this happens. We have a scan that’s remarkably . . . pristine, with a patient who is seriously comatose.
Let’s look at the terms just a bit:
DIFFUSE: unlike hematomas, which by definition occur at a given location, using conventional imaging, DAI doesn’t show any SPECIFIC location for damage. This obviously isn’t particularly good news, because it precludes systematisation of the patient’s symptoms, makes rehabbing harder, etc.
AXONAL: the axons are the cable part of the nerve cell. They’re insulated cables, to conduct nerve impulses faster, so they’re covered in a fatty membrane, making them whitish. When you group lots of axons together you get white matter. The cell bodies of the nerve cells (neurons) are greyish . . . so when you put a bunch of nerve cell bodies together, yep, there it is, grey matter.
DAI seems to damage the white matter of the brain. The cabling. Once again, this isn’t really great, as the cabling is what allows higher-level information processing by hooking up the various brain areas (e.g., visual and auditory. I SEE you talking, HEAR your words, but actually it’s associative areas of my brain that fuse the information and integrates it into my experience of YOU TALKING. That kind of processing is easily interrupted with DAI.
This will often be associated with brain swelling, at least initially.
I’m totally gutted, sickened, by having to ask you to go back to December and January’s posts for more about ICP if you’re interested. I don’t have the heart to go through this again. Not for another of our guys. Jeez.
DAI is usually associated with a somber prognosis. Jules is young, strong, and is being cared for by a superb team. C’mon Jules. Go for it.