The future of Neurosurgery – Image Guided Surgery.

Brain tumors have always been a dreaded diagnosis to give to patients. They have long implied patients with significant post operative deficits and poor quality of life with or without surgery. And, in all fairness are one of the toughest disorders to treat adequately.

Neurosurgery has always been a field at the cutting edge of medical technology with surgeons, engineers and scientists often working in unison to improve patient safety and surgical outcome. One of the more commonly used technologies of the current age is neuronavigation and imageguided surgery.

With these technologies surgeons are able to use the CT and MRI images either preoperative or even intraoperatively, to guide the surgery for more complete tumor removal and preservation of important areas of the brain around the tumor.

Navigation is the ability to know one’s position in real-time and thus the ability to reach one’s destination as per plan. In the early days, sailors and explorers have used stars to estimate their position and today we use a GPS enabled device. It is this concept that led to the development of neuronavigation.

What is NeuroNavigation

The technology involves transferring a high resolution CT or MRI of a patient’s brain or spine into a machine. The machine then registers the patient’s position in space by creating a 3D map and identifying points on the patient and corresponding points on the map. It then can track an instrument in real-time and give information with regard to the position relative to the anatomy. The surgeon is then able to plan precise approaches and trajectories using the data to reach the desired part of the brain, usually a tumor with minimal damage to the surrounding normal brain.

While this seems a complicated explanation, the neuronavigation works like a GPS localization system. The MRI is the map, and the machine has 2 cameras that can localize special instruments in space, quite similar to way GPS satellites can pinpoint the location of our smartphones. This kind of technology has found application in brain and spine surgery making surgery today far safer than it was before.

Why do we need it?

Surgical procedures on the brain are the most intricate and difficult of all interventions since they require a high degree of precision and an excellent knowledge of anatomy. This is componded by the fact that there are very few visibly distinct areas of the brain and most parts look, for all practical purposes the same. In order to therefore identify important structures and plan safe surgical approaches, neurosurgeons relied on a vast knowledge of anatomy. Either the opening of the skull had to be large enough to expose the few anatomical landmarks that could be followed or they would resort to bony landmarks on the surface that would indicate to some extent the exact areas of the underlying brain. This is akin, in someway, to sailors who would hug the coastline and keep it in view while sailing so they wouldn’t get lost in open water.

Tumors on the surface of the brain or close to it do not pose a significant problem and can often be reached following the aforementioned techniques. Deeper tumors, however, are much harder. There is a small but real risk of an incorrect approach and consequent damage to critical brain structures. It is for these tumors that neuronavigation makes a huge difference. The navigation system is made to integrate with the operative microscope and even projects the borders of the tumor as the surgeon proceeds deeper and deeper into the lesion ensuring that the tumor is excised to the maximum extent.

Navigation allows the surgeon to plan the exact approach to any tumor and in reducing the size of the skin incision and skull opening. In deep seated tumors, such as pituitary tumors, tumors of the cavernous sinus, meningiomas, gliomas, it ensures pinpoint accuracy of less than 2mm in guiding the surgical corridor. It lets the surgeon avoid important parts of the brain while getting to a tumor and thus prevents the development of post operative complications. This technology also allows the minimally invasive biopsy of deep lesions without the use of a cumbersome stereotactic frame. The use of navigation is indispensible in functional neurosurgery since it allows the surgeon to localize specific targets for deep brain stimulation for Parkinson’s disease and gives sub-millimetre range accuracy in electrode placement. Navigation can also be used in procedures which are otherwise “blind” that rely entirely on surface landmarks such as ventriculoperitoneal shunt placement to ensure correct placement of the shunt tube within the ventricles of the brain.

Now, this technology can be taken a step further by integrating various intraoperative imaging modalities to the navigation system. These include, ultrasound and 3d ultrasound, CT and MRI images which are performed during the surgery. This gives surgeons an accurate idea of exactly how much tumor has been removed and the relative position of vital fibres and areas of the brain. This becomes important when we look at data for gliomas and astrocytomas where the two major factors that determine progression free survival are the grade of the tumor and the extent of resection. This integration of various surgical tools has made surgery more effective and improved the survival of these patients substantially in the last 5-10 years.

With newer imaging modalities like functional MRI and tractography the areas of the brain responsible for speech and movement and the fibre pathways for the same can be identified. The latest navigation machines can fuse this data to the map and guide the surgeon while performing surgery, thus giving him the information to avoid these areas and make brain surgery safer with better results and outcomes.

Neuronavigation and Image Guided Neurosurgery
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