PA Anatomy: Brain: Summary

Summary:

1. Brain tissue is slightly less dense on CT than blood in vessels, and grey matter is more dense than white matter on CT.

2. Fresh hemorrhage is whiter than brain tissue on CT, but not as white as calcification-when looking for blood, NON-CONTRAST CT is often used so that white areas will not be confused for vessels.

3. Flowing blood on MR is usually dark, but can be white on special sequences; hemorrhage on MR has complex signal features, depending on how old it is.

4. It is important to know the meningeal layers that cover the brain, and their relationship to adjacent vessels in order to identify different types of hemorrhage.

5. Subdural hemorrhage (between dura and arachnoid) is typically crescent-shaped, and is often caused by tearing of the bridging veins between the cortex and dural sinuses.

6. Epidural hemorrhage (between skull and dura) is typically lens-shaped, and is usually caused by injury to middle meningeal vessels, often with associated skull fracture.

7. Subarachnoid hemorrhage (between pia and arachnoid) typically extends down into the sulci and cisterns and may be caused by injury to cerebral vessels, or rupture of aneurysms.

8. It is important to know the vascular territories of the brain to characterize strokes, which can be seen on CT, but MR is more sensitive.