Traumatic Brain Injury (TBI) in the United States
An estimated 1.4 million people experience Traumatic Brain Injury (TBI) each year in the United States, resulting in 1.1 million hospital visits, 235,000 hospitalizations and 50,000 deaths. TBI is a major public health problem among males ages 15 to 24, who account for two-thirds of childhood and adolescent head trauma patients. In addition, TBI is a severe problem among elderly people (age 75 years and older) of both sexes.
Rapid triage, diagnosis and treatment are critical in minimizing the adverse consequences of the more serious TBI cases. Since many TBI cases occur in clusters and are part of complex, extensive trauma to the individual victim (stemming from automobile accidents, war-zone explosions, etc.), the challenges presented to on-site medical personnel are significant. For patients with moderate-to-severe TBI in particular, diagnosis within the first hour (the “golden” hour) of the traumatic event is critical.
Brain Injury Overview
A TBI, one of two subsets of acquired brain injury, can result from a closed head injury (whereby the head suddenly and violently hits an object but the skull remains intact) or a penetrating head injury; the other subset of acquired brain injury is non-traumatic brain injury (e.g., stroke, meningitis). A highly individualized injury, TBI severity depends on the nature of the injury, strength of the force, area of the brain affected as well as physical and genetic variations among patients. The damage from TBI can be localized (focal), confined to one area of the brain, or diffuse (typically a concussion), involving more than one area of the brain.
Types of focal brain injury include bruising of brain tissue (contusion) and rupture of blood vessels inside the skull, thereby resulting in heavy bleeding (intracranial hemorrhage or hematoma). Hemorrhaging can occur inside of the skull but outside of the brain (extra-axial) or within the brain itself (intra-axial). Extra-axial hemorrhages can be further divided into epidural hematoma, subdural hematoma and subarachnoid hemorrhage. Intra-axial bleeding within the brain itself is called an intracerebral hematoma.
Diagnostic and treatment protocols mandate that a patient suffering from head trauma receive immediate medical assessment, including a complete neurological examination. The severity of the head trauma and the responsiveness of the patient in a Glasgow Coma Scale (GCS) evaluation will determine which diagnostic methods will be used for further evaluation. In a GCS evaluation, the patient is scored on his/her ability to open eyes, communicate verbally and demonstrate motor skills. However, the GCS evaluation can be very subjective based upon the individual administering the test and can also be hampered if the patient is under sedation or has restrictions on his/her ability to verbally communicate (i.e., the patient has been intubated).
For patients with mild-to-moderate injuries, further diagnostic tests may be limited to skull and neck X-rays to check for bone fractures. For patients that have demonstrated moderate–to-severe TBIs after undergoing a neurological examination, the gold standard imaging test is a computed tomography (CT) scan, which creates a series of cross-sectional X-ray images of the head and brain and can show bone fractures as well as the presence of hemorrhage, hematomas, contusions, brain tissue swelling, and tumors. Magnetic resonance imaging (MRI), which uses magnetic fields to detect subtle changes in brain tissue content and can show more detail than X-rays or CT, may be used after the initial assessment and treatment of the TBI patient.
TBIs can cause a host of physical, cognitive, emotional, and social effects. And the outcomes for TBIs can be anything from complete recovery to permanent disability or death. An estimated 5.3 million individuals in the United States are living with long-term or life-long disability associated with a TBI that resulted in hospitalization. Unlike most causes of traumatic death, a large percentage of the people killed by brain trauma do not die right away but rather days to weeks after the traumatic event. In addition, rather than improving after being hospitalized, some 40% of TBI patients deteriorate. Primary injury (the damage that occurs at the moment of trauma when tissues and blood vessels are stretched, compressed, and torn) is not adequate to explain this degeneration. Rather, the deterioration is caused by secondary injury resulting from a complex set of biochemical cascades that occur in the minutes to days following the trauma. These biochemical cascades are instigated by brain swelling and inadequate flow of oxygen and blood to the brain resulting from brain compression by the expanding brain hematomas. The aim of the Infrascanner is to catch those hematomas before they are able to do any brain damage and lead to a much earlier intervention to evacuate the expanding brain hemorrhages.
In addition to disability, TBI can lead to increased risks for other debilitating health conditions. Recent studies indicated that in the 1-3-year post-injury period, individuals with TBI are 1.8 times more likely to report binge drinking, 11 times more likely to develop epilepsy and 7.5 times more likely to die. Additionally, the problems in the post-injury period include a 1.5 times higher risk for depression, and 2.3 times and 4.5 times higher risks for Alzheimer’s disease associated with moderate and severe head injuries, respectively.
Types of Intracranial Hematomas after Traumatic Brain Injury (TBI)
Injury to the brain after trauma can be classified as focal or diffuse. Focal mass lesions are less common, but the importance of appropriate and timely surgical treatment is emphasized by the significantly poorer outcome associated with mass lesions. In the Traumatic Coma Data Bank (TCDB) series, the mortality rate after severe closed head injury was 39% with a focal lesion, compared to 24% with a diffuse injury. There are 3 major types of traumatic intracranial hematomas: (1) subdural, (2) epidural, and (3) intracerebral hematomas. Each of these lesions has characteristic clinical and CT scan findings, and can be present on admission to the hospital or can occur in a delayed fashion.
The subdural hematoma is the most common focal intracranial lesion, occurring as the primary initial lesion in 24% of patients with severe closed head injuries in the TCDB, and occasionally as a delayed lesion. The hematoma is between the dura and the brain, usually resulting from a torn bridging vein between the cortex and the draining sinuses. An acute subdural hematoma typically appears on a CT scan as a high-density, homogenous crescent-shaped mass paralleling the inner surface of the skull.
Most acute subdural hematomas require surgery. Despite surgical evacuation, the mortality rate in patients with subdural hematomas was 50% in the TCDB series. The rapidity of surgical evacuation and the degree of associated brain damage are major determinants of outcome. Several studies report a decrease in the early mortality or morbidity in patients who underwent an early evacuation of subdural hematoma.
Epidural hematomas, or collections of blood between the skull and dura, are less common, occurring as the primary initial lesion in 6% of patients with severe closed head injuries in the TCDB series. Epidural hematomas can be present on the admission CT scan or less commonly may develop at some later time. In a consecutive series of 161 patients with epidural hematoma, 8% had delayed formation of the hematoma. The delayed epidural hematoma can develop after evacuation of a hematoma on the opposite side or after a hypotensive patient has been resuscitated. In addition, epidural hematomas can recur after surgical evacuation. In a study of 88 patients with post-operative hematomas, 47 patients with an epidural hematoma developed a post-craniotomy hematoma requiring a second surgical procedure.
Although patients with subdural hematomas are usually immediately comatose, only a third of patients with an epidural hematoma are unconscious from the time of the injury, one third have a lucid interval, and one third are never unconscious. An epidural hematoma is almost always associated with a skull fracture (91% in adults, and 75% in children). The blood comes from torn dural vessels, usually arterial, from the fractured skull bone, or occasionally from torn venous sinuses. On CT scan, an epidural hematoma is characterized by a biconvex, uniformly hyperdense lesion. Associated brain lesions are less common than with subdural hematomas.
Most epidural hematomas require surgery, and mortality and morbidity of surgical evacuation is low if the patient is operated upon early. The outcome of the patient with an epidural hematoma depends on the neurological status at the time of surgery. The mortality rate varies from 0% for patients who are not in coma, to 9% of obtunded patients, to 20% for patient in deep coma.
Intracerebral blood can take the form of a hematoma or a contusion. Intracerebral hematomas are more common, occurring as the primary lesion in 10% of the severe closed head injuries in the TCDB series. Most intracerebral hematomas are visualized on CT scan as hyperdense mass lesions. They are typically located in the frontal and temporal lobes and can be detected on a CT scan immediately after the trauma. However, delayed intracerebral hematomas may also be manifest during the hospital course. A delayed hematoma is one that is seen on a repeat CT scan within 24 to 48 hours of the injury or operation but is not present on the initial CT scan. Commonly, a delayed hematoma is associated with clinical deterioration.
Hemorrhagic contusions were present as the primary lesion in 3% of severe closed head injuries in the TCDB series. Single contusions are located either below the region of the impact or opposite the region of impact. Contusions appear as heterogeneous areas of brain necrosis, hemorrhage, and infarct representing mixed-density lesions on CT scan. Multiple focal contusions have a “salt and pepper” appearance on CT scan.
The decision to operate on an intracerebral hematoma is based on the patient's general condition, associated brain injuries, site and size of the hematoma, the ICP, and the magnitude of the mass effect. Generally accepted indications for surgery include (1) a hematoma associated with mass effect or in the anterior temporal lobe or in the cerebellum, (2) progressive neurological deterioration, or (3) refractory intracranial hypertension.
Delayed Intracranial Hematomas
Delayed intracranial hematomas are a treatable cause of secondary injury if identified early, but can cause significant disability or death if not promptly recognized and treated. CT scanning has revealed that delayed hematomas after head trauma are more common than had been previously suspected. Recurrent hematomas, postoperative epidural hematomas, and delayed traumatic intracerebral hematomas occur in up to 23% of patients with severe head injury. Mortality rates and the incidence of a poor neurological recovery are significantly increased in patients who develop delayed traumatic intracranial hematomas. Early identification, prior to neurological deterioration, is the key to successful surgical treatment.
Serial CT scans are the most reliable method for detecting a delayed hematoma. However, CT scans require that patients, many of whom are critically ill, be taken out of the intensive care unit, and the yield is relatively low if serial scans are obtained in all patients. Some clinical monitoring technique for accurate selection of patients requiring follow-up CT scanning would improve the yield. Nevertheless, current clinical monitoring techniques are not ideal for detecting delayed hematomas. Patients with delayed hematomas may appear to be relatively normal only to undergo sudden neurological deterioration, or may not exhibit a change in their neurological examination. Intracranial pressure (ICP) may be normal in up to 20% of patients harboring delayed hematomas that require surgery.
The ideal clinical monitor would be capable of making on-line continuous measurements in the intensive care unit, and would identify the development of a hematoma prior to the onset of clinical neurological deterioration. The technique of near-infrared spectroscopy (NIRS) may have these characteristics.