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Head injuries may be categorized in several ways. Injuries are classified by mechanism (closed vs. penetrating injury), morphology (fractures, focal intracranial injury and diffuse intracranial injury), and severity (mild, moderate and severe).

Mechanisms of Injury

Classifying head injuries according to the mechanism is useful when planning treatment of the injury. Open head injuries, also referred to as penetrating injuries, occur when both the skin and the dura (a tough, leather-like substance that invests the brain) is penetrated either by a foreign object (e.g., a bullet or rod) or a bone fragment of a fractured skull. Closed head injuries are injuries in which the skin remains intact and there is no penetration of the dura by a foreign object. The severity of these injuries varies according to the velocity of impact and the vector (linear vs. rotational) of forces applied. History of the accident is utilized to determine the velocity of the injury. This is also useful in determining which diagnostic test to order as well as whether an admission to the hospital is warranted. Low-velocity injuries include a child falling a short distance, an accidental blow to the head as with a baseball bat, or an aggressive tackle in a football game. These injuries are usually mild and usually require observation only. Examples of a high-velocity injury include a fall from an upper-story window, a pedestrian being struck by a moving car, or automobile accidents. Even in the absence of neurological dysfunction, children who have had this type of injury are usually observed in the hospital.

Morphology of Injury

Skull fractures may be in the cranial vault or skull base and may be linear or stellate, depressed or nondepressed. Most skull fractures are obvious on plain skull X-rays. The main significance of finding a fracture is that it is an indication of the "force" of the injury. Infants or toddlers who sustain a fracture often develop a subgaleal hematoma (a blood clot between the scalp and skull bone). Inasmuch as there is a common association of subgaleal hematoma and skull fracture, a skull X-ray is indicated for a child with a subgaleal hematoma. If a fracture is present but the child is neurologically well, there is no need for a CT scan, but the skull X-ray should be repeated in three to four months for infants with fractures to be sure that the fracture has healed. "Ping-Pong" fractures (an indentation of the skull resembling an indentation of an indented Ping-Pong ball) in the newborn may be associated with difficult forceps delivery or, rarely, a prolonged labor. This is also a common fracture in infants who have fallen from a height. In most cases they do not require elevation because the brain pulsation will push the bone out and reestablish a normal skull contour within a few weeks.

Depressed fractures are almost invariably associated with high-velocity injury and may result in brain injury. Therefore a computerized axial tomography (CAT) scan is mandatory, even in the absence of neurological dysfunction. Many depressed fractures (usually less than 10 mm) heal without surgery. Basal skull fractures may involve the floor of the skull's brain cavity and are occasionally associated with cerebrospinal fluid (CSF) rhinorrhea or otorrhea (leakage of spinal fluid into the nose and ears). Basal skull fracture may be suspected in the presence of significant drainage from the nose or ears (in the absence of local trauma to the respective area). The presence of bilateral bruising around the eyes ("raccoon eyes") or unilateral bruising behind the ear, extending down the neck ("battle sign") is also an indicator of a basal skull fracture (again in the absence of local trauma).

A concussion is a head injury associated with a transient loss of consciousness. Although a concussion is not in itself associated with structural brain injury, if it occurs as a result of a high-velocity injury, a CT scan should be considered. In some cases there is no loss of consciousness, but there is a transient impairment in higher cortical function (e.g., confusion, disorientation).

Hematomas (blood clots) occur epidurally (outside the dura), subdurally (between the dura and brain) or intraparenchymally (within the brain). "Classical" clinical evolution of an epidural hematoma includes a blow to the head with or without transient loss of consciousness, followed by a lucid interval, then increasing headache and a subsequent clinical deterioration as the mass lesion increases in size (remember, "classical" is uncommon). Typically, an artery has been torn as a result of a fracture of the temporal bone when an epidural hematoma exists. Therefore, there is a history of transient loss of consciousness associated with an epidural hematoma due to the force that caused the fracture with a resulting "concussion." After regaining consciousness, the child experiences a very severe headache from the bleeding between the dura and the skull (the dura is exquisitely pain sensitive). The rapidly expanding mass of blood from the torn artery causes neurological deterioration. An acute subdural hematoma results from torn veins bridging the space between the brain and dura. It is usually associated with a high-velocity injury with immediate and severe neurological dysfunction. This is because a blow that is of sufficient magnitude to "tear" bridging veins is usually of such a magnitude to cause primary brain injury. In other words, the subdural hematoma is first an "epiphenomena" that may subsequently evolve into a huge life-threatening mass as bleeding from the torn veins continues.

A contusion is a focal injury to the brain, classically having a "salt-and-pepper" appearance on CAT scan. It is most often at the poles of the frontal and temporal lobes and is the result of an impact of the brain against the skull during an acceleration/deceleration injury. Although a contusion may appear relatively "innocent" on the initial CAT scan, it may coalesce into a life-threatening intraparenchymal hematoma over hours or a few days.

Severity of Injury

The severity of the injury to the central nervous system (e.g., mild, moderate, severe) is scored using a tool widely accepted, the Glasgow Coma Scale (GCS). The Glasgow Coma Scale was developed in 1974 as an assessment tool for patients with altered levels of consciousness. It is easy to use and has proven to be reproducible when used in the field by emergency technicians. It can also be used to follow a child in the hospital for signs of progressive deterioration. Patients who open their eyes spontaneously, obey commands and are oriented score a total of 15 points. Those who are flaccid and do not open their eyes or talk score a minimum of 3 points. A GCS of 8 or less is the accepted definition of the comatose patient. Thus, severe head injury is associated with a GCS less than or equal to 8, moderate head injury a GCS of 9 to 12, and a mild head injury a GCS of 13 to 15. The scale has been adapted for infants and young children, the Pediatric Coma Scale.