Head injury describes any trauma to the structures and tissues in the head, including the scalp, skull, blood vessels; and when it causes brain damage, it’s called a traumatic brain injury, or TBI for short.
First, let’s review some anatomy and physiology. The skull has two components: the cranium and facial bones. The cranium is the bony casing that houses and protects the brain. It is lined by the meninges, which are three protective membranes that wrap around the brain and spinal cord. These three layers are the innermost pia mater, the arachnoid mater in the middle, and the outermost dura mater. Between the arachnoid and the pia mater lies the subarachnoid space, which is a thin space filled with cerebrospinal fluid that helps to cushion the brain. So within all these structures, you’d think that the brain should be pretty safe from minor trauma or injuries.
Alright now, head injuries can be caused by a variety of mechanisms, including contact head injuries, acceleration-deceleration injuries, and penetrating injuries. Contact head injuries occur when a client hits their head on a hard surface, like when falling down the stairs; or receives a violent blow or jolt to the head, such as when getting hit in boxing, or getting tackled in a football game. On the other hand, acceleration-deceleration injuries happen when the brain bounces around inside the cranium, like when a fast moving car hits a tree and stops suddenly. The bouncing of the brain inside the skull causes damage to the brain on the site of impact, called coup injury. In addition, the recoil force directs the brain the other way to strike the opposite side of the skull, resulting in another contusion called contrecoup injury. Lastly, head injuries can be caused by penetrating injuries, such as a knife or gunshot wounds.
Risk factors for getting a head injury include engaging in high-risk activities like motor racing, rock climbing, sky-diving, or bungee jumping. Additionally, these types of injuries are more common in certain populations, including elderly clients who are more likely to lose balance and fall, clients who are in correctional facilities or who are experiencing homelessness, as well as in clients who use alcohol or illicit drugs.
Okay, so the pathology of head injuries can be widespread, also called diffuse brain injury, or localized, also called focal brain injury. Diffuse brain injuries include concussions and diffuse axonal injury. Concussions are typically associated with blows to the head, which causes a transient disruption of neural activity that may temporarily affect the level of consciousness. On the other hand, diffuse axonal injury happens with traumatic brain injury, which causes a more widespread damage to neuronal axons.
Next is focal brain injury, which includes contusions, brain lacerations, and vascular injuries. Contusions are basically bruises of the brain surface caused by acceleration-deceleration injuries. On the other hand, brain lacerations are caused by a foreign object getting pushed into the skull, which causes a tear in the brain tissue. In addition, head injuries may cause damage to the structures surrounding the brain, like the scalp, skull, meninges, and blood vessels. Scalp and skull injuries include scalp lacerations, which are tears of the scalp, and skull fractures, which may be closed or open. Closed fractures are breaks in skull bones that don’t damage the surrounding tissue, like the scalp for example. On the other hand, open fractures cause damage to the surrounding tissue, like a tear in the scalp, and are also associated with high risk of infection. In both cases, skull fractures may have fragments that push into the brain, causing brain lacerations.
Lastly, vascular injuries include epidural hematoma, which describes bleeding between the dura mater and the inner surface of the skull; subdural hematoma, which describes bleeding between the dura mater and arachnoid mater; and finally, intracerebral hematoma, which describes bleeding within the brain tissue itself.
The clinical manifestations of head injuries vary depending on the degree of severity. Mild head injuries may present with surface wounds, like shallow scalp lacerations and bruises, as well as symptoms like headache, confusion, nausea and vomiting, or dizziness that usually improve within a couple of weeks.
On the other hand, clients with moderate to severe head injuries may present with more severe symptoms, including confusion, seizures, loss of memory, and sometimes loss of consciousness. In severe traumatic brain injuries, there can also be slurred speech, difficulty with walking, weakness in one side of the body, or behavior changes like irritability.
In some cases, head injury can lead to increased intracranial pressure or increased ICP . Early signs and symptoms include altered mental status, nausea and vomiting, headache, sluggish pupillary reaction to light, and even seizures. Additionally, clients with papilledema may experience visual abnormalities, such as double vision or even visual loss.
On the other hand, late signs and symptoms include hypertension, bradycardia, and irregular breathing; these signs are referred to as a Cushing’s triad, which indicate advanced brain stem dysfunction; as well as fixed or dilated pupils. Finally, there could be loss of brainstem reflexes such as the gag reflex, the swallowing reflex or the pupillary and corneal reflexes. There’s also progressive deterioration of the client’s level of consciousness, and if not promptly treated, clients may fall into a deep state of unconsciousness, or coma.
Other worrisome signs include urinary or bowel incontinence; loss of brainstem reflexes, including blinking, gag reflex, and lack of pupillary reaction to light; as well as flaccid paralysis, and abnormal posturing like decorticate or decerebrate posturing. With decorticate posturing, the arms are adducted and flexed on the chest, and the wrists are flexed, with flexed fingers, while the legs are extended and internally rotated, with the feet in plantar flexion. Decerebrate posturing on the other hand, is where the arms are stiffly extended and abducted, and the wrists are pronated, with flexed fingers; while the legs are extended, with the feet in plantar flexion. Finally, severe head injuries may result in an extended period of unconsciousness or coma, from which some clients may not recover.
The diagnosis of head injury starts with the client’s history and physical assessment, which includes a thorough neurological exam. The client’s level of consciousness in response to stimuli is assessed with the Glasgow Coma Scale, or GCS for short, which evaluates verbal, motor, and eye-opening responses. Additional diagnostic tests include imaging like X-rays, which may show skull fractures; CT scans, which detect intracranial hematomas; and MRIs, which may reveal brain tissue damage and herniation. Additionally, urine toxicology, blood alcohol level, and glucose levels should be checked to identify any other potential causes of an altered mental status leading to the head injury.