My last post discussed subdural hematomas, so it’s a good time to talk about epidural hematomas. As previously mentioned, the Dura is a fibrous membrane attached to the inner surface of the skull. Like all tissue, it needs a blood supply. The artery feeding it (the Middle Meningeal artery) runs just in front of the ear where the skull is quite thin and easily fractured. When fractured, the bone edge can be quit sharp and cut this artery. Unlike veins that transmit blood at low pressure, arteries carry blood at high pressure. So when the meningeal artery is cut a blood clot forms between the skull and dura; hence the name of epidural hematoma. Because the bleeding is under arterial pressure, the clot can grow large quickly.
As the clot enlarges it pushes brain aside. But since the skull can’t expand the compressed brain becomes squeezed. And just like a tube of toothpaste, the squeezed brain seeks the path of least resistance, which is out the base of the skull – a phenomenon termed herniation. This is considered a surgical emergency.
Epidural hematomas seldom occur in isolation and are usually accompanied by additional forms of traumatic brain injury. For this reason, even with prompt removal, a patient may remain in coma depending upon any other injuries.