#lyco's notes

So our team has a patient, 64 years old and admitted to the hospital for alcoholic pancreatitis. He also has Wernicke’s encephalopathy - in short, he drank enough alcohol to give himself thiamine deficiency which eventually fried his brain, so he has confusion, memory problems, unusual eye movements (lateral nystagmus, if you care), and trouble coordinating his movements at baseline.

So this morning, we hear a Rapid Response ring through the intercoms with this patient’s room number being called while we’re rounding. After the entire team had a nice jog up several flights of stairs, we find him back in the bed with the nurses explaining that he got out of bed and fell.

When asked about why he got out of bed and fell, he just told us “What are you talking about? I’ve been in bed the whole time.” Given his chronic memory problems from alcohol, this was sadly a normal response from him. He didn’t seem any different and resisted a quick physical examination from my fellow intern taking care of him, saying his stomach still hurts (remember he’s here for an angry pancreas). But everyone in the room can see the bump on the side of his head. 

Naturally, we get a stat head CT to make sure he didn’t have a brain bleed or fractured his skull.  

When the head CT was finished, the whole team was taking a look at it. The scalp hematoma was obvious, this nasty blood-filled bump outside of the skull, but it was clear there wasn’t any blood within the brain nor any fractures.

At this point, the attending looks at the team - me, my fellow intern, the senior, and the two medical students - and begins pointing at structures in the brain and asks us what they are - a good old pimping session. 

But as the attending was going up and down through the image, my eyes kept getting drawn to this subtle asymmetry in the mid brain. Right next to the right putamen, there was this blurriness where the gray and white matter met that didn’t quite match to the nice distinction of gray and white on the left. I must’ve looked really focused or confused or something, because the attending asks me what’s going on, and I just pointed at the spot that caught my attention and blurted my thoughts.

“I think this guy just had a stroke. I'm seeing loss of the insular ribbon.”

My attending does a double take at the image, squints his eyes, and dials the number for the Radiology department. 

“Hey. Can you take a look at the recent CT for this patient, medical record number xxxxxxx? My intern found something lateral to the right putamen. I want to know: is this a stroke?”

I wait nervously for the verdict as the radiologist downstairs brought up the image, regretting a bit for sticking my head out there - but knowing that I’d regret it more if I didn’t say anything and this guy did have a stroke. 

After a minute or two, my attending hangs up the phone, looks at me with something akin to pride and amazement, and then nods his head with a smile.

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.