Head Bleeds

Yesterday we had a discussion about a case involving a significant head injury resulting in death. We ended up talking about different types of head bleeds and I thought it would be good to do a refresher.


Subdural hematoma/hemorrhage (SDH): This is when blood collects within the inner meningeal layer of the dura mater, the outer protective covering of the brain. The picture to the right is a CT scan showing a good sized left SDH, which you can see is also exerting midline shift to the right. (Of note when looking at CT scans, blood shows up white, air is black, brain matter grey, and the image is reversed- like a chest x-ray).



Subarachnoid hemorrhage (SAH): This is bleeding into the subarachnoid space, which is the area between the arachnoid membrane and the pia mater surrounding the brain (meaning the area between the brain and the thin tissues that cover the brain). The SAH image to the left shows blood in bilateral sylvian fissures and down the center interhemispheric fissure. The 2 white spots toward the back are not blood but rather normal calcifications.


Intraparenchymal hemorrhage (IPH): This is where there is bleeding into the tissue of the brain. Pretty obvious, that white blotch on the left.


Epidural hematoma (EDH): This is where blood collects between the dura mater and the skull. This is outside the dura, whereas the SDH was below the dura. It's pretty hard to miss that EDH imaged to the right, which is causing midline shift and compression of the left ventricle.


Question: How can someone status post craniectomy (bone flap NOT replaced) still have elevated ICPs?
Answer: Even with a bone flap missing, neurosurgeons almost always still close the dura, which is that tough outer membrane. The dura is tough enough to still limit significant cerebral edema and impose pressure, therefore raising ICP (intracranial pressures).