Overview of Head Injuries: Head Injuries: Merck Manual …

The thick, hard bones of the skull help protect the brain from injury. Also, the brain is surrounded by layers of tissue (meninges) containing cerebrospinal fluid, which cushions the brain. Consequently, most bumps and knocks on the head do not injure the brain. Head injuries that do not affect the brain are considered minor.

Head injuries may cause brain injury (traumatic brain injury, or TBI). In the United States, about 13 in 10,000 people sustain minor head injury, and about 3 in 10,000 sustain severe head injury each year. In the United States, from 2002 to 2006, about 1.7 million civilians had TBI each year. About 1.4 million were treated and released from emergency departments. About 275,000 were hospitalized and discharged alive, and 52,000 died. TBI is responsible for about 33% of all deaths caused by injuries of any kind. About 5.3 million people have permanent disabilities due to head injury. About 25 to 33% of people in the United States who have a severe head injury die.

About half of head injuries result from motor vehicle crashes, and head injuries occur in more than 70% of severe motor vehicle crashes. Other common causes are falls (especially in older adults and young children), assaults, and mishaps during sports or recreational activities. Mishaps in the workplace (for example, while operating machinery) and firearms also cause head injuries. Often, injury is caused by direct impact. However, the brain can be damaged even if the head has not been hit. For example, violent shaking or sudden deceleration can damage the soft brain as it collides with the rigid skull. In such cases there may be no visible injuries to the head.

Head injuries include injury to the scalp, skull fractures, concussions, bruises (contusions) and tears (lacerations) of the brain, accumulation of blood within the brain or between the brain and skull (intracranial hematoma), and damage to nerve cells throughout the brain (diffuse axonal injury). Bleeding can also develop between the layers that cover the brain (subarachnoid hemorrhage). Alternatively, the brain may not be damaged even when external injuries are severe.

A bump may appear on the head. If the scalp is cut, bleeding may be profuse because the scalp has many blood vessels close to the skin surface. Consequently, a scalp injury may appear to be more serious than it is.

Common symptoms may include headache and the sensation of spinning or light-headedness. Some people also may have mild confusion, nausea, and, more commonly in children, vomiting. Young children may simply become irritable.

A concussion (see Concussion) is a temporary, brief change in mental function without damage to the structure of the brain. Often, people lose consciousness briefly (usually a few minutes or less), but they may simply become confused or be unable to recall events and experiences (amnesia) that occurred shortly before or soon after the injury.

For some time after a concussion, people may experience headache, dizziness, fatigue, poor memory, inability to concentrate, trouble sleeping, difficulty thinking, irritability, depression, and anxiety. These symptoms are called the postconcussion syndrome.

People may have some of the same symptoms as occur with minor head injury. Some, such as headache, may be more severe. Also, symptoms often start with a period of unconsciousness that begins at the time of impact. How long people remain unconscious varies. Some people awaken in seconds, while others do not awaken for hours or even days. On awakening, people often are drowsy, confused, restless, or agitated. They may also vomit, have seizures, or both. Balance and coordination may be impaired. Depending on which area of the brain is damaged, the ability to think, control emotions, move, feel, speak, see, hear, and remember may be impairedsometimes permanently.

Clear fluid or blood may drain from the nose, ears, or both if a person has a fracture of the base of the skull (see Skull Fracture).

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Overview of Head Injuries: Head Injuries: Merck Manual ...