The concept of minimally invasive has been interpreted in different ways: minimal medically induced damage in exchange for maximum therapeutic effect; the least possible operational trauma to achieve the most thorough lesion treatment; anatomical opening and anatomical closing. The need for minimally invasive intracranial surgery is most important due to the specificity of brain function and structure.
To produce minimally invasive results, intracranial surgery cannot be performed without precise positioning, precise observation, delicate operation and careful monitoring. This is because the location of intracranial lesions is quite hidden, the lesions and their surrounding functional brain areas are blurred, and the blood vessels and nerves entering and leaving the cranial cavity are complicated.
1. Precise positioning
The goal of minimally invasive surgery starts from the surgical approach, which is to approach the lesion with small flaps and micro-bone windows, the premise of which is to accurately determine the location of the lesion. Neurological navigation is the technique of preoperative precise positioning and intraoperative real-time judgment of resection range, including orienteering instrument frame navigation, ultrasonic sonographic navigation and magnetic resonance imaging navigation.
Orientator frame navigation was introduced in neurosurgery as early as 1947, but it has many drawbacks and has very few applications.
Currently, in most people’s opinion, magnetic resonance imaging navigation is the mainstay of neurological navigation.
However, its drawbacks are evident.
(1) Structural brain drift is not possible to correct completely and MRI images cannot be accurately navigated;
(2) Navigation based on preoperative imaging data does not reflect the surgical procedure in real time;
(3) The MRI equipment is bulky, cumbersome and time-consuming to operate, which is not convenient for practical application;
(4) Magnetic resonance equipment is expensive, and the cost of shielding the magnetic field in the operating room and demagnetizing surgical instruments is high, which is not easy to promote.
After the invention and widespread use of real-time B-mode ultrasound examination technology, ultrasonic sonographic navigation, which appeared before magnetic resonance imaging navigation, has received renewed attention.
Compared with MRI neurological navigation, ultrasonic sonographic navigation has obvious advantages.
(1) Intraoperative ultrasound has a high probability of detecting lesions, can precisely locate lesions, and accurately determine the edge and extent of lesions;
(2) Intraoperative ultrasound-guided cranial cavity surgery has no brain drift and can be accurately navigated;
(3) Intraoperative ultrasound is easy and rapid to operate, each examination only takes 2-3 minutes, which is a real real-time navigation and can be repeatedly applied to navigate multiple surgeries at the same time;
(4) Intraoperative ultrasound operation protocol is simple, easy to learn and use, and easy to promote;
(5) Intraoperative ultrasound has no special requirements for operating rooms and surgical instruments, and does not increase additional costs;
(6) Ultrasound equipment is simple and inexpensive, and has become a commonly used diagnostic instrument in hospitals at all levels.
Simplification of precise positioning technology: ultrasonic navigation instead of MRI navigation.
2.Precise observation
Only fine operation can produce minimally invasive effect, the premise of which is to see the lesion and its adjacent structures clearly and accurately, which requires extended visual function with the help of optical instruments.
Intracranial surgery can be likened to well operation or pit operation (operation in the pit). Lesions at the base of the skull, in the midline region of the brain, and deep in the brain are difficult to clearly visualize with the eye and its adjacent structures. Optical instruments can magnify and illuminate the surgical field, and optical lenses mounted on a gimbaled stand are like “long-handled eyes” that help the surgeon to reveal the lesion and its adjacent structures clearly from multiple angles.
After the invention and application of digital image acquisition technology, optical lenses can be used in both the lens surgery mode (lens image guided microscopic operation) and the video screen surgery mode (video screen image guided microscopic operation).
The disadvantage of the lens surgery mode is that it binds the surgeon’s hands and eyes, for example, the microscope lens surgery mode has the following disadvantages.
(1) The microscope head and its stand used in the lens surgery mode are large and take up a lot of space, which greatly affects instrument delivery and surgical operation;
(2) In the microscopic lens surgery mode, the surgeon looks at the surgical field through the lens without turning his eyes and performs “close observation and remote operation”, and must bend his neck for a long time and cannot change his posture at any time;
(3) Operators, assistants and instrument nurses have different ways of grasping the surgical process and its effects, making it difficult to cooperate during surgery.
The visual screen surgery mode has many advantages.
(1) It does not bind the operation of the hand and the observation of the eye, and the posture can be changed at will during the operation, which makes the operation comfortable;
(2) The operator, assistant and nurse get the same visual information, so it is easy to cooperate intraoperatively;
(3) Simultaneous observation of the surgical process is possible, which facilitates real-time discussion of surgical difficulties and visual teaching;
(4) The film data of the surgery can be saved, which is convenient for retrospective analysis and teaching research;
(5) It can simplify the intraoperative observation system, and the equipment is light and low cost;
(6) can optimize the combination of a variety of optical lenses to obtain the best observation effect.
Simplification of precision observation technology: replacing the lens surgery mode with the video screen surgery mode.
3.Fine operation
Fine operation can be called microsurgery. Do not equate microsurgery with surgery under a microscope. In addition to microscope, optical instruments include magnifying glass, telephoto, endoscope and exophthalmoscope. The visualization mode of surgery breaks the limitation of focal length, and the fine operation can be performed under any optical lens. The choice of optical lens is whatever one prefers. Accordingly, the concept of microsurgery should also be extended to fine operations performed under any optical lens.
The instruments for microsurgery are necessarily delicate and lightweight. Using microsurgery to deal with parenchymal lesions, a working channel of 2×3 cm is sufficient, and the recommended mode of video-screen surgery has the advantage that a microscope, telescope, external or endoscope can be chosen at will, and fine surgical instruments can be used universally; using microsurgery to deal with cystic fluid lesions, the working channel need not be more than 1 cm, and trauma can be minimized, only non-endoscopic, and surgical instruments should be more delicate.
By the way, microsurgery and minimally invasive surgery should be distinguished. Microsurgery is the means, the way to produce minimally invasive effect; minimally invasive surgery is the effect, the result of microsurgery.
4.Careful monitoring
Monitoring is for protection. The neurological function monitoring during the process of cranial cavity surgery should cover the brain, spinal cord, cranial nerve and spinal nerve. To monitor the function of brain, EEG or magnetoencephalography can be used; to monitor the function of spinal cord, spinal cord electrogram or spinal evoked potential can be used; to monitor the function of cranial nerve and spinal nerve, sensory evoked potential, auditory evoked potential, visual evoked potential, motor evoked potential, etc.
Among them, EEG monitors the function of cerebral cortex, sensory evoked potential monitors the function of sensory nerves, auditory evoked potential monitors the function of auditory nerves, visual evoked potential monitors the function of optic nerves, and motor evoked potential monitors the function of pyramidal bundles. In addition, facial nerve function can be monitored by direct stimulation of the facial nerve, and trigeminal nerve function can be monitored by both direct stimulation and evoked potentials. As for magnetoencephalography, monitoring brain function is expensive and time-consuming.
Minimally invasive neurosurgery likewise follows the principles of necessity and simplicity, and what can be done simply, should not be done in a complex and cumbersome manner. “We have MRI neuronavigation, you don’t” is bragging; “They have magnetoencephalography, we have to have it too” is climbing. The use of tiny flap and bone window access must ensure that the lesion is reached by a shortcut, provided that the localization is accurate. If accurate localization is possible based on CT, MRI and other imaging data, do not think about navigation. If you have to navigate, you don’t always have to give up MRI navigation, and ultrasound navigation is fine.
The profession should not believe that “the vast majority of surgeries are done under a microscope”. Microscopes and endoscopes are all observation tools. If a lesion is clearly visible to the eye and has to be observed under a microscope, it is like walking smoothly with a cane, just like pretending. If you really need an optical lens, you don’t have to be obsessed with the lens surgery model. The visual screen surgery model is easy to learn and use, low cost, lightweight, and you can choose from a variety of optical lenses, so why reject it out of hand!
”There is no minimally invasive neurosurgery without neurological function monitoring” is not so absolute. Operating within the lesion, even if it is a functional area, the procedure does not result in severe loss of function. If the lesion is so large that no lesion visible to the naked eye can be removed, neurological function monitoring is nothing more than a staged procedure and is not worth the excessive time and effort. Neurological monitoring is only relevant when operating between the lesion and normal tissue where function is important. Neurological monitoring is most important in surgery at the base of the skull, especially in the pontocerebellar horn region.