It seems that after the tragic deaths of both Natasha Richardson and Billy Mays, head injuries have been getting a lot of play time in the media. Richardson died of an epidural bleed after a helmetless fall on skis. Mays was found to have an enlarged heart, but the minor head injury he received the night before his death launched speculation that he had died from intracranial bleeding as well.
Both of these incidents bring to light an important element of head injury response and evaluation. Patients with critical, life threatening brain injuries don’t always present as sick. Often they report feeling just fine. The emergency responder needs to approach head injuries with a high index of suspicion.
Today were going to begin a three part series on head injuries. In part one we’ll take a look at the different ways the skull and brain get injured. In part two we’ll talk about how the brain bleeds and how that can change the patients presentation. In part three we’ll look at treatment considerations for the head injured patient.
The brain occupies about 80% of of the space inside your skull and it is divided into four areas. They are:
- The brainstem (This includes the medulla, the pons and the midbrain)
- The diencephalon (Primarily the thalamus and hypothalamus)
- The cerebrum
- The cerebellum
If we emptied the human skull into a blender, liquefied the contents and let them separate, we would find that 58% of the stuff in your head is water, 25% is brain solids, 7% is cerebrospinal fluid and 10% of it is blood. I would also recommend disposing of the blender. (And perhaps the skull as well.)
Your brain contents are wrapped-up and encased within the meninges. We’ll discuss the layers of the meninges more in part two.
The ways that trauma can be inflicted upon the skull are infinite. If you disagree, make sure you catch the next episode of Nitro Circus. (God bless and watch over Travis Pastrana – Amen.) Continuing … In light of the many ways you can exert force upon your nugget, injuries to the skull tend to fall into one of these categories:
Concussions (mild diffuse injury)
Think of it as a brain bruise. Concussions are fully reversible brain injuries that do not result in structural damage to the brain. As you would imagine, they are caused by mild to moderate forces impacting the skull.
Concussive forces can cause enough movement of the brain within the cranial vault to interrupt brainstem function and produce short (less than five minute) loss of consciousness (LOC). Patients with positive LOC may experience retrograde or antegrade amnesia. (They won’t remember what happened just before or just after the loss of consciousness.)
Moderate diffuse injury
Moderate injury involves minute petechial hemorrhaging(see arrows in the photo at left) as well as bruising to the surrounding brain tissue. Moderate injuries usually involve an accompanying loss of consciousness. This degree of injury is commonly associated with basilar skull fractures and significant coup-contra-coup type mechanisms.
Moderate brain injury classifications account for approximately 20% of all reported brain injuries. Most patients with this degree of brain injury will survive but many will have some form of permanent neurological impairment.
Diffuse axonal injury
When the brain moves significantly within the skull during a traumatic mechanism, we get our most severe form of close head injury, diffuse axonal injury. With this degree of injury, forces on the brain cause shearing, stretching and tearing of vasculature and nerve fibers within the brain. Depending on the severity of diffuse injury (Yes, there are also three levels of diffuse injury severity.) unconsciousness can last from 6 hours multiple days. Mortality increases with the length of coma. Patients with DAI tend to exhibit posturing and more severe signs of significant brain injury.
Management of DAI patients will commonly focus on adequate airway management and proper sedation. Over 90% of patients with diffuse axonal injuries will never regain consciousness. Those who do wake up tend to experience significant neurological impairment.
Focal Injury (Impact Phenomenon)
When traumatic lesions, contusions and hemorrhage are obvious on brain scans and localized to a specific area we consider those injuries focal brain injuries. Deficits secondary to focal injury are primarily dependant on the area of brain involved. Larger focal injuries portend greater deficits and more significant long term neurological implications and vice-versa.
Skull fractures come in many shapes and sizes but they also have predictable patterns. Brain injuries are commonly associated with fractures of the skull. Knowing these common patterns is helpful when discussing the potential mechanisms, insults and physical findings in head injury. Here a few of them to keep in mind.
- Linear fractures – These account for 80% of all skull fractures. These fractures appear as lines on x-ray films. They are usually not depressed and carry a low rate of complication. Linear fractures can be present without any other external signs of trauma.
- Basilar skull fractures – Are usually associated with significant impact trauma. While they can be caused by the mandibular condyles perforating the base of the skull, they are more commonly extensions of linear fractures out across the floor of the skull. Basilar fractures are difficult to diagnose on an x-ray and are more commonly inferred based on other findings such as battle signs, raccoon eyes or blood behind the tympanic membrane.
- Depressed fractures – Are most commonly caused by small objects striking the skull at high velocity. Most depressed fractures are signaled by obvious external soft tissue injury. 30% will also have significant cerebral contusions.
- Open vault fractures – Among the most devastating of fractures, these are defined by open communication between the external soft tissue trauma and the cerebral substance within the cranial vault. Due to the forces required to open the cranial vault these fractures carry a high mortality rate.