Starting from the bottom, here are all the areas of subarachnoid hemorrhage (SAH):
Yes, I realize that much of that SAH was fairly noticeable. All that labeling might seem needless since it's all the same SAH. But it's there to highlight the point that many of these areas are all continuous spaces that are normally filled with BLACK CSF.
As you were scrolling through this CT, did you ask yourself if those spaces were filled with black CSF like they are supposed to be?
SAH fills pre-existing spaces. That is one "essence" of SAH. That's what this kind of intracranial bleeding does. And that's what is common to all the SAH on this head CT.
That is how you "see" what you may otherwise miss.
Sometimes you get lucky and the acute, bright blood is obvious. But not always.
Understanding the underlying "essence" of SAH (and realizing you have to check the black CSF spaces to see if they are actually black) helps you see what may otherwise be invisible.
Could you make that into a heuristic?
In the setting of: ______________
Do this: ________________
And look: ________________
And yes, there was some subdural blood here on the tentorium. The tentorium is normally a bright white, but here the left side is thicker than the right, that's because there's a subdural hematoma (SDH). You can see some of it on the axial cuts, slices 43-45. It's just easier to see on the coronal view.
Go back to the website and we'll look at another case.