Editor’s Note: One obvious way to think about the world of neurosurgery is that it is the culmination of all the care delivered across the subspecialties. Just a few decades ago, subspecialization (and the whole world of CAST, enfolded fellowships, post-residency fellowships, etc.) was the exception, limited to just a small number of academics. Today it plays a much larger role across the neurosurgical spectrum. In a series of pieces, AANS Neurosurgeon explores each of the subspecialties in neurosurgery’s orbit.
The year was 1917. Sergeant Springer had been brought to the hospital tent by his comrades after sustaining a gunshot wound to his head. He had lost consciousness upon impact and was bleeding profusely, so his chances of survival were looking bleak. But Dr. Harvey Cushing was hopeful. With a mortality rate of 28% for the 45 surgeries he had performed, Cushing believed he could succeed, based on his experience and the evolution of the operative technique he used.
Cushing proceeded to remove Springer’s skull en bloc around the site of the cranial penetration, using a soft rubber catheter to detect any in-driven bone fragments. He finished by instilling the antiseptic dichloramine-T dissolved in oils into the wound tract and onto the dura. His technique helped Sergeant Springer and many other injured soldiers survive the perils of war. While Cushing would later pioneer the new surgical specialty of neurosurgery, was his effort the genesis of the subspecialty of neurotrauma or were there earlier attempts?
Earlier Attempts
Archeological evidence exists of neurosurgical procedures predating World War I. Perhaps the oldest neurosurgical procedure known is that of trephination, or creating holes in the skull. It is believed that this may have been performed by prehistoric people for spiritual reasons or as an initiation practice. French physician Paul Broca hypothesized that the first cases of craniotomy were most likely in the prehistoric age for magic or religious rituals, including exorcism.
Later, craniotomy was used to treat traumatic lesions. Without antisepsis and understanding of the brain, survival of these patients would be unexpected. However, at a burial site in France dating to 6500 BCE, 40 of 120 prehistoric skulls discovered had evidence of trephination. Many prehistoric and pre-modern patients had evidence of healed skull trephination sites, suggesting that many of those who underwent surgery survived.
Hippocrates was the first to detail the neurologic consequences of conditions such as skull fracture. He understood the importance of an injury’s location and was aware of the brain’s vulnerability. Hippocrates advised performing a craniotomy without delay, within the first three days post-trauma for severe contusions or simple fractures. In the case of a comminuted fracture or depressed fracture, he suggested removal of bone fragments without violating the meninges.
Nevertheless, neurotrauma must have posed a prognostic dilemma to the doctors of previous eras, as the internal injury cannot be appreciated by the eye. Even today, with advanced imaging technologies such as computed tomography (CT) scanning and MRI, it can be difficult to ascertain the full extent of a brain injury or predict a patient’s outcome.
Imaging Advancements
The advent of CT technology improved neurosurgical planning and care. CT scanning was invented in 1972 by British engineer Godfrey Hounsfield of EMI Laboratories in England and South African-born physicist Allan Cormack of Tufts University in Massachusetts. Hounsfield and Cormack were awarded the Nobel Prize in Physiology or Medicine in 1979 for their contributions. The first clinical CT scanners were installed between 1974 and 1976; the original systems were dedicated to cranial imaging solely.
Advanced CT technology made it possible to visualize intracranial injuries, such as epidural and subdural hematomas. Introduction of and improvements in CT scanning were crucial tools for the field of neurotrauma. By 2014, there were more than 10,000 CT scanners installed in the United States and more than 30,000 scanners installed worldwide. Although the first single-slice CT scan took days to compute, speed and capability of scanners has improved markedly since the 1970s.
Modern Critical Care Practice
At the same time the CT scan became more available, two other developments shaped the neurotrauma care provided today: the development of the U.S. trauma system and the emergence of critical care as a specialty.
Modern critical care began with the development of new technology, specifically, the iron lung and negative pressure ventilation used during the 1952 polio outbreak. The first neurological intensive care unit was created by Dr. Dandy Walker at Johns Hopkins in 1929. Modern neurocritical care began when mechanical ventilation became available in the 1960s; followed shortly by automated vital sign monitoring. For the first time, physicians could keep TBI patients alive, allowing their condition to improve, thanks to the development of the ventilator.
The rise of neurotrauma as a specialty is linked closely with the rise of critical care and, later, neurocritical care. Intracranial pressure (ICP) monitoring facilitated treatment of diffuse TBI and minimization of secondary injury, a mainstay of neurotrauma care today. Neurocritical care was further advanced by the rise of multimodality monitoring. In addition to ICP, physicians could monitor brain tissue oxygen levels, cerebral blood flow, temperature and lactate-pyruvate ratio.
The successful use of microdialysis to quantify metabolites in neural tissue by Ungerstedt and colleagues during the late 1970s and early 1980s contributed significantly to the understanding of TBI and secondary brain injury. Brain oxygen first was measured in the early 2000s and became an integral part of severe TBI management in the first decade of the 21st century. A randomized, controlled trial currently underway compares outcomes of brain oxygen-targeted therapy versus those obtained via ICP-targeted therapy. Understanding of the pressure reactivity index and cortical spreading depression also has shaped neurocritical care over the past decade.
Trauma Response
The American trauma response system as we know it today has its roots in the creation of the national emergency telephone number, 9-1-1, in 1968. Although hospital-based ambulance systems had existed in this country for more than a century at that time, access was limited. Today, 98.9% of people in the United States can call 9-1-1, connect to a public safety answering system and receive a dispatched ambulance. The use of a standardized trauma assessment and management form ensures that patients are taken to a center with the appropriate level of trauma care. This has helped expedite the type of high-level care that patients with severe TBI need through transport to the most appropriate hospital. Improved trauma response has greatly reduced interhospital transfer of these patients, thus saving valuable time between injury and receipt of the neurosurgery care needed.
With a new trauma response and triage system and development of critical care, health care providers needed a standardized and reliable way to communicate a patient’s level of consciousness among providers and hospitals. This led to the widespread adoption of the Glasgow Coma Scale (GCS).
Assessing Injury Severity
In the early 1970s, Bryan Jennett and Graham Teasdale in Glasgow, U.K., drew attention to the importance of secondary ischemic brain damage, which occurs in the hours and days following the initial TBI. Their team established assessment of the severity of damage using the GCS and CT scanning to form the basis of management in the acute stage of TBI, and in comparing early severity with outcome. The scale uses unambiguous terms that are readily understood by a wide range of observers. Assigning numbers to responses makes communication and display of responsiveness easy and the overall score leads to classification of brain injury severity for use in triage. The GCS also facilitates monitoring in the early stages after injury for rapid detection of complications.
Although the GCS has been shown to be effective, many authors have cited weaknesses in the scale, including a nonlinear relationship of the scale with outcome. In addition, the verbal score is often unavailable in the setting of trauma or in the ICU. One of the biggest drawbacks, however, is that the GCS is relied on so heavily to classify TBI that very different diseases might be included in a single category. An EDH and a diffuse axonal injury both can present as patients with a GCS of 5, but have different pathoanatomic and pathophysiologic features and outcomes. This especially matters when GCS is used to enroll patients in clinical trials. Nonetheless, the scale is a widely used tool today.
Recent Research
Research questions that have consumed neurotrauma specialists over the past 50 years involve hypothermia, steroid use and decompressive craniotomy. With various unsuccessful, and even harmful, clinical trials, the direction to use hypothermia and steroids in TBI has been laid to rest. This is not so with decompressive craniectomy, and recent trials have demonstrated lower mortality rates in the decompressive craniotomy groups without improved functional survival. Proponents of decompressive craniotomy blame the relatively short primary outcome time frame of six months for this outcome. One-year follow-up of participants in the decompressive craniotomy group has shown improved functional outcomes. Hence, the question of decompressive craniotomy effectiveness has not been definitively answered.
Although the implementation of the trauma response system and critical care, especially neurocritical care, have decreased TBI mortality since the 1960s, over the past two decades, a slight increase in TBI-related mortality has been noted. The increase has been attributed to the aging population, since TBI-related deaths are highest among older adults (aged 75 years and over).
The Future
Where do we go from here? Hopefully, advancements will improve the ability to diagnose and categorize TBI based more on pathophysiological parameters. The hope is that easily accessible biomarkers will do just that. Physicians do not look at a CT scan of the heart to see whether a patient has had a heart attack and to determine their ejection fraction, but this is exactly what we do with the brain after TBI. Biomarkers might provide the type of quantitative information we need to determine the pathophysiologic mechanisms that underlie the traumatic brain injury.
In addition, artificial intelligence can help neurosurgeons prognosticate better and treat ICP proactively, rather than retroactively. Further, the rehabilitation community has taught us that patients with TBI often require one to two years of rehabilitation to reach their full recovery potential. Together, these endeavors will help move the field of neurotrauma forward.
