#med school notes

I write this little series in the hopes that you won’t ever look as bad to your attending doctors as I did back when I was pimped in medical school - which honestly wasn’t that long ago. 

The difference between subdural and epidural hematomas is something I’ve often mixed up, so hopefully by the end of this when your attending doctor points at your patient’s head CT and starts pimping you, you ace the doc’s questions with flying colors. 

The most important thing is to understand the name. Epidural means “above the dura,” and subdural means “below the dura.” Yes, it’s simple, but it means everything.

Now, for the purposes of this talk, we’ll simply state that between the skull and the brain is just the tough fibrous dura. (In reality though, the arachnoid and pia mater exist underneath the dura but they’re pretty much glued to the brain.)

An epidural bleed occurs between the dura and the skull. I colored it bright red because it’s typically an arterial bleed, usually when the middle meningeal artery gets injured. Because it’s a bleed that’s between the dura and the skull, the bleed is literally peeling the dura off the skull as it gets larger. However, there is an area where it’ll stop in its tracks which would be the suture line where the dura and skull are really intertwined. An epidural bleed should not cross suture lines. 

A subdural bleed occurs between the dura and the brain. Because it’s typically venous, I colored the blood a dark red (probably should’ve chosen blue, oh well). Now, unlike an epidural, because the blood doesn’t contact the skull, it doesn’t have to interact with the skull sutures, so you can see it cross through suture lines. However, because it is under the dura, it has to interact with another structure instead - the faux cerebri, which is a fold of dura that separates the left and right hemispheres of the brain. So essentially, the blood hits a wall and it can’t pass. Thus, a subdural bleed should not cross midline.

Of course, all bets are off in the case of severe trauma, and either the suture lines or faux cerebri gets disrupted. 

Lastly, you probably are wondering about why I didn’t mention about how subdurals are concave and epidurals are convex. Well, that’s because it’s not quite reliable a sign as people think. Simply changing your plane of view can quickly change the appearance of the bleed. But as long as you keep that in mind... 

I remember convexity/concavity because an epidural hematoma has to accumulate pressure for it to peel the dura off the skull (hence why it is convex like a balloon). Subdural hematoma exist underneath the dura, and it requires less pressure to peel the dura off the arachnoid mater (which is the layer above the pia  and then the brain), hence why it is concave. 

🍬 Thursday, September 10th 2015 🍬

🍬 9:00 PM 🍬