When there is an impact against the skull, the brain continues in motion resulting in forces that cause an intradural herniation and tearing of the bridging vein.
Forces:
- Arachnoid trabeculae pull on arachnoid (suction on inner dural layer)
- As brain moves toward side of impact, subarachnoid pressure is decreased. (suction on arachnoid and inner dural layer)
- Bridging vein is stretched.
- Tear of bridging vein occurs at inter-dural/subdural layer.
After impact:
- Blood accumulates in intradural and subdural locations
- Lower forces required to separate “potential space” between dura and arachnoid so hemorrhage expands between dura and arachnoid
Progression of subdural hematoma:
- Hemorrhage continues along “potential” space between dura and subarachnoid
- Stretches bridging vein (maybe eventually completely tears it).
- Hemorrhage obliterates subarachnoid space and compresses brain.
