For the most part, bleeding in the brain (intracranial hemorrhage) is a pretty bad thing. Though like most things in medicine, there are varying degrees of badness, all with different mechanisms that help us sort of why we really wouldn’t want something to happen.
Intracranial hemorrhages are categorized into 5 subtypes, and are given obvious sounding names depending on where the bleed is in the brain and in relation to the layers of the meninges.
- Epidural (above the dura, right under the skull)
- Subdural (below the dura, above the arachnoid)
- Subarachnoid (below the arachnoid, above the brain)
- Intraventricular (in the ventricles)
- Intraparenchymal (in the meat* of brain)
* The brain is not meaty, “parenchyma” means the functional part of the organ
The poor pia mater did not get any hemorrhage named after it, but if you want you can think of intraparenchymal as “subpial” just so it doesn’t feel left out.
Telling them apart
The most confusing thing, and thing that likes to get asked the most on exams, is the difference between epidural and subdural hematomas.
| Epidural | Subdural | Subarachnoid |
| Above the dura | Below the dura | Below the arachnoid |
| Respects suture lines | Doesn’t respect suture lines | No respect for anything |
| High force trauma | Low force trauma | Aneurysm rupture or high force trauma |
| Arterial blood (commonly the middle meningeal artery) | Venous (from venous plexus) | Arterial from the circle of Willis |
| Lentiform (lens-shaped) or biconcave on CT | Cresent (banana-shaped) on CT | Lining surface, going into fissures and sulci and sella (death-star) |
| Acute presentation | May be insidious (worsening headache over days) | Acute presentation (thunderclap headache) |
The reason intraventricular and intraparenchymal aren’t included in the table as they each have a bunch of causes, but for both of them trauma is a potential cause as well as hypertension and stroke. It’s good to remember that premature infants are at a much higher risk of intraventricular hemorrhages.
Blood on CTs
- New blood: bright white
- 1-2 weeks: isodense
- Old blood (2-3 weeks): dark grey