Academic Frontiers
A brief description of the principles, applications and others of neuronavigation
The term neuronavigation is derived from navigation, which refers to the reliance on a real-time positioning system to select a simple and safe route (approach) to an accurate destination in navigation or land navigation. Similarly, the concept and principle of navigation is applied to neurosurgery, which is called navigated neurosurgery, where computerized image processing and surgical instrument tracking and positioning technology can assist surgeons in optimizing the surgical access and precise operation range. In addition to neurosurgery, navigation technology has been widely used in many fields such as otolaryngology, plastic surgery, urology, and orthopedics, playing an increasingly important and unique role in surgical practice. In neurosurgery, navigation technology has also been applied in major branches such as brain tumor, vascular malformation, spine and functional neurosurgery, becoming one of the irreplaceable tools. This article provides an overview of the history of neuronavigation, its principles and its applications, with an emphasis on its clinical significance in functional neurosurgery.
History of neuronavigation
The concept of navigation was first seen in 1907 in small animals by Horsley and Clark. In 1947, Spiegal and Wycis successfully localized soft tissues with the help of “pneumoencephalography” and pioneered the use of navigation in human surgery. During the same period, Leksell and Riechert in Sweden and Talaiach in France also developed their own methods of localization based on projection imaging techniques, and in the 1950s and 1960s, planar image-based navigation techniques were widely used in thalamotomy. Later, the advent of CT made three-dimensional images a reality and greatly advanced the development of navigation techniques. Between 1986 and 1987, different navigation systems were developed almost simultaneously by Watanabe, Roberts and Basel. In the following two decades, neuronavigation technology has been rapidly developed and widely used, thanks to the emergence of many advanced medical imaging techniques, such as functional MRI, MRI-diffusion tensor imaging (MRI-DTI), MRI-diffusion-weighted imaging (MRI-DWI), MRI-spectral analysis (MRS), MRI-perfusion imaging (PWI), and MRI-perfusion imaging (PWI). imaging (PWI), magnetic source imaging (MSI), magnetoencephalography (MEG), positron emission tomography (PET), intraoperative ultrasound, intraoperative CT/MRI’s, and the development of electrophysiological monitoring techniques. In addition to advances in imaging technology, positioning techniques in navigation systems are becoming increasingly sophisticated (see ‘Principles’ section for details).
Principles of neuronavigation
The core of a surgical navigation system consists of two parts: image and positioning (Figure 1), which are similar to a “map” and “compass” in navigation, respectively. First, medical imaging data is transmitted to the navigator, which can include computed tomography (CT), magnetic resonance imaging (MRI), positron emission computed tomography (PET), digital vascular silhouette (DSA), etc. The two-dimensional data is analyzed and processed by the navigator’s computer to obtain a three-dimensional image that serves as the “map” for navigating the procedure. Next, the actual head position in the operating room is registered with the 3D image of the patient’s head in the navigator by registering the patient’s head marker. It is worth mentioning that the base image of the patient in the neuronavigation system can be integrated with other imaging images (e.g., functional MRI, magnetoencephalography, etc.) and electrophysiological experiments (e.g., cortical mapping by electrical stimulation), so that neuronavigation can not only fully assist in surgical In this way, the neuronavigation not only can fully assist the surgical approach design, but also can reduce or avoid intraoperative damage to functional areas and reduce surgical complications. Figure 1 shows the StealthStation neuronavigation system from Medtronic used in the Department of Functional Neurosurgery at Xuanwu Hospital.
After registration, the relative spatial position of the surgical instrument in the patient’s brain depends on the signal it emits being captured and processed by the Navigator spatial positioning device, which can be displayed in real time on a computer screen to guide the operator in selecting the approach to the target site/target area and the surgical operation in the target site/target area. Signaling between neurosurgical instruments and navigator spatial positioning devices can take many forms, including mechanical, ultrasound, electromagnetic, and infrared positioning. The most widely used in neuronavigation today is optical positioning (including the StealthStation system currently used in our department), where the infrared light-emitting diode on the surgical instrument is used as the measurement target and the CCD camera (charge-coupled device camera) is used as the sensor to calculate the position of the surgical instrument.
Applications of neuronavigation
Since its invention, the neuronavigation technique has become more and more mature and has been widely used in several branches of neurosurgery, such as brain tumors (gliomas, meningiomas, metastases, lymphomas, etc.), cerebrovascular malformations, epilepsy surgery (epileptogenic focus resection, corpus callosotomy), and deep brain electrical stimulator implantation.
The positive significance of neuronavigation in various neurosurgical procedures in terms of precise localization of lesions, optimal surgical approach selection, improvement of total lesion excision rate, and reduction of postoperative complications has been reported in the domestic and international literature. For example, in a paper published in 1999, John Wadley, a British neurosurgeon, used a prospective study design to analyze the use of neuronavigation techniques in 300 neurosurgical procedures over a 2-year period (1998-1999). The 300 neuronavigation procedures covered multiple branches of neurosurgery and multiple types of neurosurgery, including 163 craniotomies, 53 stereotactic biopsies, 7 neuroendoscopies, and 37 complex skull base procedures. The pathological typing analysis included 98 cases of glioma, 64 cases of meningioma, and 23 cases of metastases. In the study, it was found that 99% of the neurosurgeons were able to increase their confidence in the procedure from the use of navigation, and 95% of the neurosurgeons considered the use of neuronavigation techniques to be superior to conventional surgery in these cases. In addition, Dr. Eboli from Sweden reported the successful use of neuronavigation in transsphenoidal pituitary adenomectomy.
Application of neuronavigation in functional neurosurgery
Compared to other branches of neurosurgery, the use of neuronavigation in functional neurosurgery is relatively late, but it has shown the same important value and positive significance, becoming one of the important tools of modern functional neurosurgery. Epilepsy surgery is an important branch of functional neurosurgery. As with tumor resection, epilepsy focal resection not only allows for the design of optimal surgical access with the aid of neuronavigation techniques, minimizing surgical trauma and finding the lesion accurately, but also, and more importantly, allows for the integration of functional imaging and electrophysiological data to adequately remove the epileptogenic focus while protecting motor, sensory, or speech areas, reducing postoperative complications and improving the patient’s quality of life. In 2001, Roux published an article in Neurosurgery specifically on the fusion of functional imaging and cortical electrical stimulation results in neuronavigation procedures. Another example is temporal lobe epilepsy surgery: in 2000, Wurm proposed the application of neuronavigation to selectively resect the hippocampal amygdala (selective amygdolohippocampectomy), a technique that ensures precise selectivity of surgical resection while adequately reducing damage to other cerebral cortex and blood vessels.
In addition, corpus callosotomy is a palliative procedure to consider in generalized refractory epilepsy, especially in the form of atonic (nervous) seizures. Pediatric neurosurgeon Jea, writing in Neruosurgery Focus 2008, suggests that the application of a neuronavigation system can help the surgeon determine the extent of the dissection (total or partial) during corpus callosotomy, as well as the lateralization of the cerebral hemisphere for the surgical operation (in order to protect the superior sagittal sinus pars plana). In conclusion, neuronavigation, together with neuromonitoring, has been recognized as one of the essential tools in modern epilepsy surgery and is of irreplaceable value in improving surgical success and reducing postoperative complications.
Deep brain stimulation (DBS) is a microinvasive neurosurgical approach. It uses a stereotactic approach for precise localization and high-frequency electrical stimulation by implanting electrodes at specific targets in the brain. This changes the excitability of the corresponding nuclei to improve symptoms. The effectiveness of deep brain electrical stimulation in movement disorders depends on multiple factors such as good patient selection and precise electrode implantation, the latter traditionally achieved by framed stereotactic surgery (stereotaxy).
If neuronavigation is applied to deep brain electrical stimulation, the surgeon can confirm the surgical path on a computer screen in real time, without relying on the head frame, but only through wireless infrared positioning. The patient only needs to fix a number of markers on the head, which is less uncomfortable and stressful, and facilitates movement and cooperation during the intraoperative electrical stimulation test, which is called frameless DBS. Compared with frameless stereotactic surgery, frameless DBS has obvious advantages in terms of patient comfort and shorter operative time. More foreign researchers have concluded that the two are comparable in terms of accuracy, i.e., the new frameless DBS also has satisfactory accuracy of electrode implantation. At present, domestic DBS mainly adopts the traditional framed stereotactic method, and no comparative study with frameless type has been reported. Considering the obvious advantages of frameless DBS (application of neuronavigation technology) in terms of patient comfort and shortened operation time, it is worthwhile to carry out more clinical applications and related studies in the future.
In addition to epilepsy surgery and deep brain electrical stimulation, neuronavigation technology has also been applied to other functional neurosurgical diseases such as motor cortex electrical stimulation for neuropathic pain and coil placement for transcranial magnetic stimulation for patients with chronic pain and depression, showing a wide range of application prospects and important clinical and scientific research values. For example, in the application of spinal cord stimulation for the treatment of intractable pain, neuronavigation can assist in the localization of spinal segments. In radiofrequency thermal coagulation for trigeminal neuralgia, neuronavigation can indicate the surgical site in a timely and dynamic manner to ensure precise positioning and minimal damage.
Limitations of neuronavigation
During neuronavigation, brain tissue structures may be displaced for various reasons, so that the position of the surgical instruments determined by the navigation based on preoperative scanning and registration may differ from the real position, which is called image drift (also known as brain shift), and the incidence of which is as high as 66% in foreign countries. To solve this problem, intraoperative or real-time MRI can be performed to correct the deviation. In addition, practical experience in minimizing the loss of cerebrospinal fluid or cystic fluid before reaching the target site can significantly reduce the occurrence of drift and decrease the impact on surgical accuracy, which depends on adequate technical training and clinical exploration.
Conclusion
With the popularity of microneurosurgery and the concept of minimally invasive treatment, the adjunctive role of neuronavigation systems in neurosurgery has become increasingly prominent in order to better protect patients’ neurological function and improve their postoperative quality of life. Nowadays, neurosurgery in many foreign hospitals has adopted neuronavigation technology as a routine adjunct, and the application of neuronavigation in China has been expanding, especially its application and research value in the field of functional neurosurgery has shown great value. As with any technical tool, neuronavigation has unique advantages as well as limitations. Adequate study, practice, research, and development of neuronavigation technology will promote greater progress in neurosurgery, including functional neurosurgery.