The duration of a coma caused by a car accident is determined by the severity of the cranial brain injury. Most cranial brain injuries caused by car accidents are more severe and the coma lasts for a longer period of time, from as little as a month to as many as a few months, or even for a prolonged period of time. The mildest cranial brain injuries caused by car accidents fall into the category of concussions, with a coma lasting from a few minutes to no more than 30 minutes. More serious brain injuries, such as cerebral contusions, epidural hematomas, subdural hematomas, and after surgery for craniocerebral injuries, are usually comatose for 1-2 months. Very serious craniocerebral injuries, such as extensive cerebral contusions, diffuse axonal injuries, and primary brainstem injuries, will result in a very long coma, usually more than half a year, or even a prolonged coma with a vegetative state of survival.