Closed head injury is the most common cause of brain injury. Traumatic brain injuries are closed head injuries, which occur with blunt force or whiplash trauma that does not break the skull and/or the meninges (the membranes around the brain). It occurs when the head is struck or moved violently but the skull and/or membrane lining of the brain is not broken or penetrated.

Such damage often involves “diffuse brain injury,” which involves widespread damage to nerves and blood vessels, twisting and stretching of nerve fibers and bleeding due to the tearing of arteries and veins throughout the brain. The forward motion and rotation of the brain on the relatively fixed brain stem is a common cause of loss of consciousness and coma.

In addition to diffuse brain injury, focal lesions and bruising may occur as the brain collides into the sharp, bony, inner surface of the skull. Focal lesions can occur either where the brain makes contact at the site of impact inside the skull (a coup injury), or at a different site (a contrecoup injury, which most often presents opposite the point of impact).

Blood vessels or brain tissue can tear without impact, simply through the force of violent head movement. Because the skull cannot expand, intracranial bleeding and swelling can’t drain, and any accumulation may eventually press on—and damage—the brain.

Closed head injury injuries are not always easy to spot and may go unnoticed or undiagnosed for several days until symptoms from secondary effects, such as increased pressure inside the skull, become severe enough to cause problems. This may not be obvious to medical staff in an emergency department, and may not receive appropriate treatment until symptoms become worse over several days or months.