In This Article
- Physicians at Massachusetts General Hospital are minimizing neurologic complications during procedures by monitoring multimodal neurophysiologic potentials during surgery
- Intraoperative neurophysiologic monitoring and mapping (IONM) makes it possible to remove more tumor tissue and improve patient survival and prognosis
- IONM allows physicians to safely incorporate a more aggressive approach to surgeries
- IONM is chosen for procedures that could damage vital functions such as strength and sensation
While monitoring brain and motor function during surgery (and if necessary modifying techniques or approaches on the fly to minimize potential complications) has been around for several decades, the evolution of this approach in recent years has armed neurology and surgical teams with an astounding amount of knowledge on brain function. That knowledge can directly improve the results of a procedure.
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Through providing live functional guidance by analyzing the brain's electrical signals during procedures, the intraoperative neurophysiologic monitoring and mapping (IONM) team at Massachusetts General Hospital has been a driving force behind increased surgical success with reduced neurological complications. Indeed, with IONM, it is now possible to safely remove even more tumor tissue and subsequently improve patient survival and prognosis.
"We work with our surgical team on complex procedures," says Reiner B. See, MD, a neurologist specializing in intraoperative neurophysiology at Mass General. "A patient without neurologic deficit after surgery is one with a much better prognosis and outcomes, and we work hard to achieve that."
For the team, the rewards are palpable.
Dr. See continues: "This provides a feeling of instant gratification for our team's work. By monitoring multimodal neurophysiologic potentials during surgery, we minimize neurologic complications, enhance safety and increase the surgeon's resection of the tumor area. It's very rewarding to be able to improve the patient's quality of life and overall health."
IONM: A Growing Role in Neurosurgery
As one of the fastest-growing fields in neurology, IONM employs the use of electrophysiological technology to see what is happening throughout the body during a neurosurgical procedure as well as to identify nervous structures that need to be protected. Broadly speaking, monitoring and mapping electrical signals in the body through neurologist-led IONM makes use of recordings of electrical potentials coursing through the nervous system during surgery. More simply put, it allows the team to answer the question of what happens, if anything, to the legs, the hands, speech, vision and/or any other areas of the body when the brain is manipulated during surgery.
IONM employs a wide variety of techniques, each of which are chosen for very specific applications. Moreover, multiple modalities can be used in the same surgery, depending on the procedure chosen. Techniques may include motor evoked potentials (MEPs), electroencephalography (EEG), somatosensory evoked potentials (SSEPs), electromyography, visual evoked potentials (VEPs), brainstem auditory evoked potentials (BAEPs) and others. These techniques can be employed for patients undergoing many different types of surgery on the central nervous system, including, but not limited to:
- Cranial neurosurgery
- Epilepsy surgery
- Orthopedic spinal correction
- Interventional radiologic procedures
It is most commonly used with spinal, epilepsy, brain tumor and cerebrovascular surgery, though it can extend into other areas such as vascular and endocrine surgery.
Functions of IONM
Visualizing electrical signals is extremely valuable in neurosurgery. Most importantly, it allows the surgical team to continually assess neurological situations during a given procedure. In this regard, the potential reward is two-fold. First, it allows the team to pinpoint abnormal electrical signals intraoperatively, and if necessary modify surgical management in order to prevent irreversible damage.
Second, it allows the neurosurgeon to pursue a more aggressive approach to the procedure than he or she may have otherwise taken. William T. Curry, MD, neurosurgeon and co-director of Mass General Neuroscience says that in one recent procedure he was able remove roughly 25% more tumor tissue due to the availability of neurophysiologic information through IONM.
"Yes, prevention of disability is a driving factor behind electrophysiologic monitoring." Dr. Curry says. "At the same time, intraoperative monitoring also allows us to remove a much larger area of tumor tissue, knowing we were not harming the patient by doing so."
With IONM, there is a distinct survival advantage: In the past, a lack of comprehensive monitoring would generally lead to a more conservative surgical approach and poorer prognosis as a result.
Another important benefit of IONM is brain mapping. During the surgical procedure, neurophysiologists can identify vital regions of the brain that, for example, control the ability to move or speak, and are located in close proximity to the surgical field itself. The team can then proactively make recommendations to protect these specific areas to limit postoperative impairment. Furthermore, this real-time access to neuro-anatomy and patient neurophysiology allows unique and fundamental discovery of how the human brain actually works.
Collaboration for Higher Patient Success
At Mass General, the neurosurgeon usually takes the first step in deciding which procedures could benefit from the use of IONM. Once the case is identified, s/he discusses the case with the IONM unit and together they determine the best course of action for the procedure. In the operating room, members of the surgical staff collaborate with several members of the IONM team, including multiple neurologists, technologists and neuroanesthesiologists, with constant communication on which electrical signals are firing and which body parts are affected.
This collaboration happens every day at Mass General. Mirela Simon, MD, is a neurologist and medical director of the IONM Unit at Mass General.
"We are a community of neurologists, surgeons, technologists and nurses," says Dr. Simon. "Everyone brings in their unique expertise; through planning and collaboration we work together towards the best possible surgical outcome for the patient. I believe we have an excellent system in place here at Mass General."
Changing the Field of IONM at Mass General
Despite a long history dating back to its early stages in the 1950s, the use of IONM has only recently become mainstream in neurosurgery. This has occurred through the development of commercial IONM technology and the availability of educational programs in the area.
Dr. Simon openly touts the program at Mass General: "It is one of the few institutions that offers comprehensive training in IONM for neurologists. Here, there is a dedicated fellowship program to acquire this expertise."
Intraoperative neurophysiology has a significant beneficial impact on patient care, including safety and survival, and is simultaneously an ideal venue for neuroscience research.
"In neurosurgery, we are constantly trying to further our understanding of the brain and its relationship to the body," Dr. Curry describes. "IONM is becoming more sophisticated and widespread, and it has allowed us to improve and expand our surgical procedures with safer, more predictable results."
Most important with IONM is the end result—the patient.
"We had a young patient who developed neck pain, and who was diagnosed with an intramedullary spinal cord tumor. With this type of tumor, there is a high risk of paraplegia and sensory ataxia," says Dr. Simon. "Intraoperatively, we mapped the dorsal columns of the spinal cord and monitored the motor and sensory functions of the limbs; this allowed safe removal of the tumor. Our team's expertise made a difference in the surgeon's decision on how best to approach this challenging and risky procedure. The patient woke up from surgery neurologically intact—one of our true success stories."
The Way Forward
IONM continues to grow. While not used for every neurosurgical procedure, as many low-risk procedures do not present significant concerns that warrant it, it is chosen mainly for procedures that could damage vital functions such as strength and sensation. However, expansion of the area is evident, with researchers exploring neural networks including those of the brainstem as well as those at the basis of higher cognitive functions such as thought and learning. Dr. Simon is excited about these future directions.
"We are optimistic about the path we are on and proud to be part of this approach to patient care where research and clinical expertise are closely intertwined," says Dr. Simon. "Even though we are consultants, it is great to know that we can contribute to make an existing system better and safer."
Learn more about IONM at Mass General
Learn more about Neuroscience at Mass General