Head injuries can range in severity, with some being very mild. However, any traumatic injury to your head can be serious because of the potential to affect your brain directly.
Johns Hopkins Medicine describes several common head injuries that, at the very least, have the potential to cause serious damage to your brain. Injuries such as these should receive prompt medical treatment. Even then, brain damage may be permanent.
Diffuse axonal injury
Neural cells in your brain have long tails called axons. Their purpose is to relay messages between different cells in the brain. If an accident, such as a fall or an auto collision, causes your brain to shake violently back and forth, it can damage many axons in the brain at once, causing a diffuse axonal injury. This can be severe enough to send you into a coma. Nevertheless, it can also be hard to diagnose because the damage can occur at a microscopic level, difficult to visualize on imaging studies.
Trauma to the head can cause bleeding inside the skull. When this happens, the blood can collect and start clotting, forming a mass called a hematoma. Intracranial hematoma can range in severity from mild to severe. A severe hematoma may require surgery to remove so that it does not put pressure on the brain.
A skull fracture is any break in the bone of the head. The location of the fracture can determine how serious it is. The most serious type of skull fracture is one that occurs at the base of the head, near where it connects to the neck. Another potentially serious type is a depressed fracture that causes the broken portion of the skull to sink in toward the brain.