You probably noticed the hyperdensity in the right cerebellum. The concern is that it's a contusion (blood) in the setting of trauma.
Remember, CSF should normally be a dark grey. Sometimes it's almost black depending on how you set the brightness/contrast.
In this case, there is visible CSF in front of and around the brainstem. Plenty of CSF. All of these contiguous CSF spaces around the brainstem are the basal cisterns. Here too there is CSF in front of and around the brainstem.
That's odd...
The basal cisterns are NOT effaced, but instead they are OPEN (technical term).
Something doesn't add up here: That hyperdensity, if it is in fact acute blood, SHOULD be causing mass effect and effacing some of the basal cisterns (similar to the prior patient), BUT IT'S NOT.
Open Basal cisterns = NORMAL = you can take a moment to breath.
It turned out that hyperdense lesion was a cavernoma (type of vascular malformation) that he already had. The appearance on this scan was the same as on a prior scan done months ago.
You don't need to know what a cavernoma is or what it looks like. What's important here is that the lesion was less likely to be an acute bleed because it had no local mass effect.
Let's be honest, you probably still have to assume it's a bleed and you would still get neurosurgery involved. But you don't need to act immediately to lower ICP like in the prior case where the basal cisterns were effaced.
In the setting of: Trauma or altered mental status
Do this: Stop scrolling at the level of the brainstem
And look: at the basal cisterns, decide if they are open or effaced
Thank you for completing this head CT curriculum!
Hopefully, these teaching cases and their associated heuristics have provided a structure for interpreting a head CT in a way that's useful for EM docs. We don't need to interpret them as a radiologist would, we just need to know things that affect our ED management & dispo (e.g., is there blood, are the basal cisterns open).