Application of image guidance system in neurosurgery (application of neuronavigation in neurosurgery)
In the middle and late 20th century, image guidance system was gradually introduced into surgical procedures. In the 1990s, along with the development of modern computer technology and positioning and tracking technology, neuronavigation, a bridge between modern imaging technology and microscopic neurosurgery technology, was introduced, and after just a few years of continuous improvement and popularization, neuronavigation was introduced. After a few years of continuous improvement and popularization, combined with the simultaneous emergence of “locked-hole” surgery technology, the concept of neurosurgery has made a qualitative leap and entered the era of minimally invasive surgery. Navigation technology enables the entire surgical process to be monitored in virtual real-time with imaging data, and the accuracy is below 2mm, ensuring that the lesion is removed with the least possible damage.
Neuronavigation-assisted surgery
The neuronavigation system, fully known as frameless stereotactic navigation system, is based on the core of powerful computer technology and image processing software, using the theory of satellite positioning technology, acquiring the position information of the patient’s head and the surgical process during surgery through infrared remote sensing technology, and comparing the high definition image data such as CT and MR to calculate and display the real-time process of surgery, the exact position of the lesion and the relationship of the surrounding structures. According to the physics of navigation devices, they can be classified as infrared navigation and electromagnetic navigation. The neuronavigation system is currently the most ideal neurosurgical aid system. It has the following advantages: (1) the navigation system itself has been highly accurate throughout the surgery; (2) due to continuous improvement, the navigation system has been reduced in size and can be easily placed in the operating room; (3) it is cheaper (compared to intraoperative open MRI systems); (4) it can be used to plan the surgical approach or even simulate resection before surgery; (5) the interface is open. It can be connected to a variety of devices such as endoscopes, bipolar, microscopes, etc.; (6) almost all imaging data can be applied to avoid repeated intraoperative scans; (7) updates of imaging data provided by intraoperative image compensation devices (intraoperative open MRI, intraoperative ultrasound, etc.) are allowed; (8) surgical robots and their corresponding software can be connected to perform fully automated robotic surgery. Although the navigation system is still a virtual real-time image tracking system, it is currently the most ideal system for neurosurgical assistance due to the above advantages.
Indications
The neuronavigation system assisted surgery can be widely used in cerebrovascular disease, cranial tumor, pathological biopsy, foreign body removal, functional neurosurgery, spinal cord and spine lesions, etc.
1.Cerebral vascular disease
(1) cavernous hemangioma: It is the absolute indication for navigation. This kind of disease is mostly located in the deep brain parenchyma, even in the brainstem, thalamus and other fatal parts, with a history of repeated bleeding. Most of the cavernous hemangiomas can be clearly shown on MR and CT plain data. Therefore, the navigation system can precisely guide the surgical procedure and minimize the damage to normal brain tissue and neurological function by combining the “locked hole” craniotomy and sulcus approach. The significance of navigation surgery is: the development of an accurate craniotomy plan; confirmation of the location of the lateral fissures; and ultimately the exact location of the insular cortex; navigation can provide precise localization of the insular cavernous hemangioma and the associated anatomical structures, followed by accurate separation of the lateral fissures and minimally invasive manipulation of the insular cortex with the aid of navigation, allowing safe exposure of the lesion. It is worth noting that some very minute cavernous hemangiomas bleed with only mechanized-like tissue remaining, which, combined with the long time between surgery and bleeding, is difficult to differentiate intraoperatively microscopically from the surrounding brain tissue. Therefore, MR should be used as navigation data, and CT scan must be performed within 3 days before surgery to clarify the absorption of bleeding and to be informed at the time of surgery.
(2) Arteriovenous malformation (AVM): It is a selective indication for navigation. Among them, for AVM with deeper location, smaller volume, located in motor area, sensory area, language area, thalamus and brainstem, navigation can provide three-dimensional image assistance and reduce the damage of functional cortex during surgery. For AVMs with bleeding within 1 month and not yet fully absorbed, CT images should be used as navigation data. For cases without bleeding or where bleeding has been completely absorbed, enhanced MR is recommended as navigation data. A physician experienced in navigation can be of great help in reconstructing the major blood supply and drainage vessels preoperatively.
(3) Arteriovenous fistula (DAVF): Many scholars believe that endovascular intervention is the best choice for DAVF. However, the feasibility and success of interventional treatment for DAVF depends on many factors, such as the location of the fistula, the drainage method, and the first symptoms; and there are a significant number of DAVFs for which endovascular intervention alone cannot achieve satisfactory results.The key to microneurosurgery for DAVF is the accurate identification of the pathologic vessels, followed by careful removal of the blood supplying arteries and draining veins. Small focal vessels can be electrocautery, while larger focal vessels should be clamped. Recent studies have shown that microsurgery remains a safe and effective option for the treatment of DAVF. With the development of neuroimaging, magnetic resonance arteriography (MRA) can show DAVF very well, especially contrast-enhanced MRA (CEMRA). Applying MRA (TOFMRA) as the scan image data, which can be easily imported into the navigation workstation, can better show the pathological vessels and provide accurate localization. Image navigation is more meaningful for superficial DAVF.
(4) Aneurysm: Since the images of conventional angiography cannot be used in the navigation system. Therefore, the adjunctive role of navigation for aneurysm surgery is limited. In navigated surgery for most aneurysms, preoperative planning is more significant than intraoperative image guidance using the powerful 3D image reconstruction capabilities of the navigation system. By converting CT and MR data into stereoscopic vascular images after drug injection enhancement and opening the simulated resection image window of the navigation system, we can visualize the adjacent relationship between the aneurysm and the surrounding nerves and vessels in the actual surgical field, analyze the angle between the aneurysm and the aneurysm-carrying artery, select an ipsilateral or contralateral craniotomy, and decide on the pterygoid point or supraorbital brow arch approach to reveal and clip the aneurysm at the best and safest angle. For aneurysms located in the proximal segment of the internal carotid artery, ophthalmic artery, vertebral artery, and basilar artery, a detailed preoperative plan with the aid of a navigation system is particularly necessary. Navigation assistance is necessary for complex aneurysms, such as those in the giant aneurysm, distal anterior cerebral artery, posterior inferior cerebellar artery (PICA), and anterior inferior cerebellar artery (AICA). Benvenuti et al. in Italy successfully completed intracranial aneurysm surgery using automatic 3D spiral CT with navigation system.
2.Cranial tumors
(1) Glioma: Glioma, especially astrocytoma of low malignancy, is an absolute indication for navigation. Parenchymal grade I astrocytomas are difficult to distinguish from normal brain parenchyma under the microscope. There are also no obvious abnormalities on the cortical surface, and even experienced surgeons must take tissue for rapid frozen pathology several times during exploration to determine the extent of resection. If the tumor is located near a functional area, it is prone to unnecessary postoperative neurological deficits. Therefore, navigation is important for this type of tumor. In gliomas with higher malignancy, enhanced MR data should be used as navigation information to completely resect the tumor when possible. It should be noted that after opening the dura mater for cystic glioma, navigation should be used to determine the location and extent of the tumor first. Once the cystic fluid is released there will be image drift and the accuracy of navigation is reduced. In recent years, with the popular application of magnetic resonance with high field strength and special scanning functions, navigation has been provided with a richer data source, and the application of navigation has been greatly expanded. Nimsky et al. in Germany applied the spin-echo sequence of 1.5T MRI for diffusion tensor imaging magnetic resonance (DTI-MR) scanning and integrated the data into the navigation workstation, which clearly showed the cone bundle. Performed multiple glioma surgeries and reduced postoperative neurological deficits. In the treatment of glioma in the motor area, Australian physicians used 3T functional MRI to depict the patient’s upper and lower extremity and speech motor areas, and intraoperatively used navigation with motor cortex electrical stimulation to assist in surgical removal of the tumor with good results.
(2) Metastatic carcinoma: Most of them are located in the subcortex, which is also an absolute indication for navigation.
(3) Meningioma: Most meningiomas are absolute indications for navigation. Navigation of paranasal and convex meningioma can determine the location and scope of surgical incision, identify the sagittal sinus that is displaced by pressure, maximize the use of skin flap and bone window, and avoid hemorrhage caused by craniotomy mishap. For meningiomas that encircle or are adjacent to important blood vessels or nerve structures, such as meningiomas of the medial pterygoid spine or cerebellopontine angle (CPA), opening the prospective window of navigation can always show the distance from blood vessels, nerves and brainstem to effectively avoid injury.
(4) Pituitary adenoma: Navigation in transsphenoidal pituitary adenoma surgery helps localization. In the past, transsphenoidal surgery had to be performed under the monitoring of a C-type X-ray machine. Due to its inconvenience and radioactive contamination, it has been gradually replaced by a navigation system. Plain CT or MR data can be used as navigation information intraoperatively to clearly indicate the location of the saddle base and avoid fatal injury due to inadvertent slope bone penetration. In recent years, low field strength (0.2T) intraoperative MR has been used in developed countries, combined with navigation systems for transsphenoidal resection of pituitary adenomas. However, low field strength MRI can only show the suprasellar part of the tumor more clearly, and it has little reference significance for the important structures in the parasternal and cavernous sinuses. Therefore, the use of high field strength MRI (3.0T) as the source data of the navigation system is more useful for the surgical treatment of pituitary adenomas, especially invasive pituitary adenomas, which can more clearly show the important structures of the pars anterioris and cavernous sinus and improve the value of the surgical navigation application.
(5) Other: lymphoma, vascular reticulocytoma, nerve sheath tumor, germ cell tumor, inflammatory granuloma, etc. are all selective indications for navigation, especially when the location of the lesion is deep.
3.Biopsy
Puncture biopsy is an absolute indication for navigation. Classical neurosurgical biopsies are performed using a framed stereotactic instrument, which is painful for the patient to install a metal frame preoperatively. Modern navigation systems have an average accuracy of 2 mm or less, do not require the installation of a cranial frame, and provide multi-angle dynamic images of the puncture process, making it safer and more accurate. Therefore, the navigation system will completely replace the framed stereotactic instrument and become the preferred device for puncture biopsy.
4.Functional neurosurgery
After installation of special functional neurosurgery navigation software and related accessories, the navigation system can completely replace the traditional frame stereotactic instrument to complete pallidus destruction, hippocampal resection and other surgeries. For patients with intractable epilepsy for whom drug therapy is ineffective, it is generally accepted that surgical treatment can be used. Most of the surgical methods are subchondral transection, partial hippocampal resection, etc. Navigation-assisted surgery can significantly improve precision and reduce the rate of surgical disability. Rydenhag and Silander in Sweden reported 654 cases of surgery, and the more serious complications were only 3.1%.
5.Spinal cord and spine surgery
In the past five years, a new generation of navigation systems have been installed with spinal and spinal surgery software packages and special accessories, allowing navigation systems to be used in spinal surgery. Some people used this technology earlier, and through the analysis of 41 cases of surgery, it is believed that navigation-assisted technology can be applied to the surgical treatment of common intramedullary astrocytomas, ventricular meningiomas, neurofibromas, cavernous hemangiomas, and other common intramedullary lesions, and can guide the fixation of cone arch nails, which can reduce the probability of surgical injury.
Development and problems of neuronavigation
1.Image drift
The displacement of tissue structures in navigation-assisted surgery often causes a large error between the image of the navigation system and the real position, i.e. image drift, also known as brain shift, which is the biggest drawback of the navigation system and affects the accuracy of navigation to a certain extent. The current navigation system uses a virtual real-time image tracking technology. It mainly relies on optical digital sensing technology, co-registration technology and dynamic positioning technology to achieve. Its virtual real-time image is not the real intraoperative image. Therefore, despite the relatively fixed connection method and high speed and accurate computer computation, deviation of the navigation image from the real structure is inevitable. The incidence of image drift of the StealthStation navigation system in microneurosurgery was found to be 66%, with a drift of 3-24 mm. Therefore, minor image drift or image drift after the discovery of the lesion has limited impact on the surgery and can be overcome by the rich clinical experience of the surgeon.
2.Image drift classification
(1) Systemic image drift: that is, image drift caused by the loosening of the reference ring connecting bracket, head frame or displacement of the positioning marker.
(2) Structural image drift: that is, image drift caused by the release of cerebrospinal fluid or lesion capsule fluid, lesion or brain tissue removal resulting in the displacement of intracranial structures during surgery, image drift error is caused by the structure. For systemic image drift, the main cause is the reduced stability of navigation and surgical equipment. Therefore it can be completely avoided or corrected by the following methods Strictly follow the surgical navigation operation specification for each step of the operation, especially after exposing the skull, make sure to first drill 4 marks outside the bone window range with a microdrill and register the precise positioning points. The re-registration of these 4 points has proven to correct most of the systematic image drift. It is important not to use excessive force when drilling the bone holes, as this may result in displacement of the head frame from the patient’s head or even loosening of the head frame. Here, we recommend using a high-speed pneumatic drill to drill a hole and then open the bone flap with a milling cutter. Practice has shown that there has been no case of systematic image drift due to drilling in any of the procedures using this method. When installing the cephalic frame, the bone nail should not be too close to the positioning marker, the distance between them should be >2cm, otherwise the bone nail will be screwed in, which will pull the scalp and marker to shift, causing image drift. Once this happens, the markers near the bone nail should be removed, and the tip of the nose and the inner and outer canthus of the eye should be used as additional marker points for re-registration and co-registration. To ensure the success of this method, the scalp model should be made as smooth and clear as possible when building the 3D model. Foreign scholars have explored more about structural image drift and believe that its occurrence is related to the patient’s position, the opening of the ventricular system, the release of lesioned cystic fluid, and the volume of tumor or brain tissue removed. The main focus for such image drift lies in prevention. It is therefore recommended to.
① Avoid preoperative lumbar puncture or intraoperative ventricular puncture for drainage of cerebrospinal fluid; excessive cerebrospinal fluid release can cause significant image drift. Some scholars believe that avoiding the use of dehydrating drugs can prevent image drift. However, the author found that the appropriate use of dehydrating drugs and the administration of 250 ml of mannitol in a rapid sedative drip after exposure of the skull did not result in image drift that significantly affected continued navigation.
② For tumors with cystic changes, puncture to release cystic fluid should be avoided until the location of the tumor is clear. (ii) Try to find or remove the solid part of the tumor under navigation.
(iii) For tumors with deep location, try not to remove normal brain tissue.
During cortical fistula, try to select the natural cerebral sulcus of brain tissue as the fistula site to reduce the volume of tissue resected, thus minimizing image drift. Structural image drift can only be corrected by doing image compensation with real-time image scanning. There are 3 main methods for this.
① 3D ultrasound system can detect the image of the localization marker well, which is beneficial to detect image drift. However, it has poor visualization of substantial structures. Therefore, sometimes the drift cannot be completely corrected.
② Intraoperative CT scan, which can provide more satisfactory image compensation information to the navigation system, but cannot provide accurate data of smaller lesions. And because of radioactive contamination, surgical medical staff must wear protective clothing, which is not conducive to operation.
Intraoperative open MRI, which has developed rapidly in recent years in developed countries, can provide very accurate real-time image compensation and is the most ideal method to solve image drift, but is expensive. The navigation system has become an indispensable auxiliary device for modern neurosurgery.