Head injury

Head injury is a trauma to the head, that may or may not include injury to the brain (see also brain injury).

The incidence (number of new cases) of head injury is 300 per 100,000 per year (0.3% of the population), with a mortality of 25 per 100,000 in North America and 9 per 100,000 in Britain. Head trauma is a common cause of childhood hospitalization.

Causes
Common causes of head injury are traffic accidents, home and occupational accidents, falls, and assaults. Bicycle accidents are also a common cause of head injury-related death and disability, especially among children.

Types of head injury
Head injuries include both injuries to the brain and those to other parts of the head, such as the scalp and skull.

Head injuries may be closed or open. A closed (non-missile) head injury is one in which the skull is not broken. A penetrating head injury occurs when an object pierces the skull and breaches the dura mater. Brain injuries may be diffuse, occurring over a wide area, or focal, located in a small, specific area.

A head injury may cause a skull fracture, which may or may not be associated with injury to the brain. Some patients may have linear or depressed skull fractures.

If intracranial hemorrhage, or bleeding within the brain occurs, a hematoma within the skull can put pressure on the brain. Types of intracranial hematoma include subdural, subarachnoid, extradural, and intraparenchymal hematoma. Craniotomy surgeries are used in these cases to lessen the pressure by draining off blood.

Brain injury can be at the site of impact, but can also be at the opposite side of the skull due to a contrecoup effect (the impact to the head can cause the brain to move within the skull, causing the brain to impact the interior of the skull opposite the head-impact).

If the impact causes the head to move, the injury may be worsened, because the brain may ricochet inside the skull (causing additional impacts), or the brain may stay relatively still (due to inertia) but be hit by the moving skull.

Specific problems after head injury can include:
 * Skull fracture
 * Lacerations to the scalp and resulting hemorrhage of the skin
 * Traumatic subdural hematoma, a bleeding below the dura mater which may develop slowly
 * Traumatic extradural, or epidural hematoma, bleeding between the dura mater and the skull
 * Traumatic subarachnoid hemorrhage
 * Cerebral contusion, a bruise of the brain
 * Concussion, a temporary loss of function due to trauma
 * Dementia pugilistica, or "punch-drunk syndrome", caused by repetitive head injuries, for example in boxing or other contact sports
 * A severe injury may lead to a coma or death

Concussion
Mild concussions are not associated with any sequelae. However, a slightly greater injury can be associated with both anterograde and retrograde amnesia (inability to remember events before or after the injury). The amount of time that the amnesia is present correlates with the severity of the injury. In some cases the patients may develop postconcussion syndrome, which can include memory problems, dizziness, and depression. Cerebral concussion is the most common head injury seen in children.

Epidural hematoma
Epidural hematoma (EDH) is a rapidly accumulating hematoma between the dura mater and the cranium. These patients have a history of head trauma with loss of consciousness, then a lucid period, followed by loss of consciousness. Clinical onset occurs over minutes to hours. Many of these injuries are associated with lacerations of the middle meningeal artery. A "lenticular", or convex, lens-shaped extracerebral hemorrhage will likely be visible on a CT scan of the head. Although death is a potential complication, the prognosis is good when this injury is recognized and treated.

Subdural hematoma
Subdural hematoma occurs when there is tearing of the bridging vein between the cerebral cortex and a draining venous sinus. At times they may be caused by arterial lacerations on the brain surface. Patients may have a history of loss of consciousness but they recover and do not relapse. Clinical onset occurs over hours. A crescent shaped hemorrhage compressing the brain will be noted on CT of the head. Surgical evacuation is the treatment. Complications include uncal herniation, focal neurologic deficits, and death. The prognosis is guarded.

Cerebral contusion
Cerebral contusion is bruising of the brain tissue. The majority of contusions occur in the frontal and temporal lobes. Complications may include cerebral edema and transtentorial herniation. The goal of treatment should be to treat the increased intracranial pressure. The prognosis is guarded.

Diffuse axonal injury
Diffuse axonal injury, or DAI, usually occurs as the result of an acceleration or deceleration motion, not necessarily an impact. Axons are stretched and damaged when parts of the brain of differing density slide over one another. Prognoses vary widely depending on the extent of damage.

Symptoms
Presentation varies according to the injury. Some patients with head trauma stabilize and other patients deteriorate. A patient may present with or without neurologic deficit.

Patients with concussion may have a history of seconds to minutes unconsciousness, then normal arousal. Disturbance of vision and equilibrium may also occur.

Common symptoms of head injury include those indicative of traumatic brain injury:
 * loss of consciousness,
 * confusion,
 * drowsiness,
 * personality change,
 * seizures,
 * nausea and vomiting,
 * headache,
 * a lucid interval, during which a patient appears conscious only to deteriorate later

Symptoms of skull fracture can include:
 * leaking cerebrospinal fluid (a clear fluid drainage from nose, mouth or ear) may be and is strongly indicative of basilar skull fracture and the tearing of sheaths surrounding the brain, which can lead to secondary brain infection.
 * visible deformity or depression in the head or face; for example a sunken eye can indicate a maxillar fracture
 * an eye that cannot move or is deviated to one side can indicate that a broken facial bone is pinching a nerve that innervates eye muscles
 * wounds or bruises on the scalp or face.
 * Basilar skull fractures, those that occur at the base of the skull, are associated with Battle's sign, a subcutaneous bleed over the mastoid, hemotympanum, and cerebrospinal fluid rhinorrhea and otorrhea.

Because brain injuries can be life threatening, even people with apparently slight injuries, with no noticeable signs or complaints, require close observation. The caretakers of those patients with mild trauma who are released from the hospital are frequently advised to rouse the patient several times during the next 12 to 24 hours to assess for worsening symptoms.

The Glasgow Coma Scale is a tool for measuring degree of unconsciousness and is thus a useful tool for determining severity of injury. The Pediatric Glasgow Coma Scale is used in young children.

Diagnosis and prognosis
Head injury may be associated with a neck injury. Bruises on the back or neck, back pain, pain radiating to the arms is a sign of cervical spine injury meriting spinal immobilization and application of a cervical collar. It is common for head trauma patients to have drowsiness but to be easily aroused, headaches, and vomiting after injury. If exam and consciousness are preserved, this is of no concern. But if these symptoms persist > 1 or 2 days, a CT of the head is needed. In some cases transient neurologic disturbance may occur, lasting minutes to hours and causing occipital blindness and a state of confusion. Malignant post traumatic cerebral swelling can develop unexpectedly in stable patients after an injury, as can post traumatic seizures. Recovery in children with neurologic deficits will vary. Children with neurologic deficits who improve daily are more likely to recover. Children who are vegetative for months are less likely to improve. Most patients without deficits have full recovery. However, persons who sustain head trauma resulting in unconsciousness for an hour or more have twice the risk of developing Alzheimer's disease later in life.

Management
Unfortunately, once the brain has been damaged by trauma, there is no quick fix. However, there are some steps that can be taken to prevent secondary damage. If left untreated many patients with head injury will rapidly develop complications which may lead to death or permanent disability. Prompt medical treatment may prevent the worsening of symptoms and lead to a better outcome. Medical treatment should begin at the scene of the trauma. Paramedics will generally immobilize the patient to insure no further damage to the spine or nervous system, insert an airway to insure uninterrupted breathing, and perform endotracheal intubation if indicated. One or more IVs will be inserted to maintain perfusion status. In some cases medications may be administered to sedate or paralyze the patient to prevent additional movement which may worsen the brain injury. The patient should be delivered promptly to a hospital with neurosurgical capabilities. The management of brain injury requires the involvement of subspecialists who are generally available only at larger hospitals. Primary treatment involves controlling elevated intracranial pressure. This can include sedation, paralytics, cerebrospinal fluid diversion. Second line alternatives include decompressive craniectomy (Jagannathan et al. found a net 65% favorable outcomes rate in pediatric patients), barbiturate coma, hypertonic saline and hypothermia. Although all of these methods have potential benefits, there has been no randomized study that has shown unequivocal benefit.