Neuro navigation

A path-breaking technology it helps high resolution CT or MRI

What is Neuro Navigation?

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 tumour with minimal damage to the surrounding normal brain. The ability to relate the position of a real surgical instrument in the surgeon's hand or the microscope's focal point to the location of the imaged pathology, updated in "real time" in an "integrated operating room", highlights the modern version of this set of technologies.

What does it consist of?

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 the way GPS satellites can pinpoint the location of our smart phones. This kind of technology has found application in brain and spine surgery making surgery today far safer than it was before.

It basically consists of a computer which processes the scans (CT/ MRI) done before surgery and reconstructs the scan to give a multi-planar and three dimensional view of the brain along with the tumour, so that the exact location and extent of the tumour can be made with utmost precision. The other important component is an infra red dual camera system which tracks the surgeon’s instruments during surgery and displays their position in relation to the tumour on a monitor.

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. Therefore, in order to 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 some way, to sailors who would hug the coastline and keep it in view while sailing so they wouldn't get lost in open water.

Tumours 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 tumours, 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 tumours that neuro navigation makes a huge difference. Navigation allows the surgeon to plan the exact approach to any tumour and in reducing the size of the skin incision and skull opening.

In deep seated tumours, such as pituitary tumours, tumours 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 tumour 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-millimeter range accuracy in electrode placement. Navigation can also be used in procedures which are otherwise “blind” that rely entirely on surface landmarks such as ventriculo peritoneal shunt placement to ensure correct placement of the shunt tube within the ventricles of the brain.

On a similar note in spine surgery, the placement of screws into vertebral bodies involves the accurate knowledge of anatomy and placement of the screws in predetermined angles based on the imaging of the patient. With minimally invasive spine surgery, where screws are placed into the vertebra through small skin incisions, the chances of mal-position rises as does the amount of intra-operative x-ray use, which increases the radiation exposure.

Navigation technology can be used to exactly localize the vertebral body and show the passage of screws and other implants in real-time to completely avoid the possibility of screw mal-position and reduces the radiation exposure to a bare minimum. 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.

How is it useful to a patient?

The advantages are numerous:

Even before starting surgery the surgeon can locate the exact location of tumour from outside and can plan the best possible approach to the tumour. The surgeon will be using the smallest possible incision to get into the tumour, resulting in lesser pain and faster recovery for the patient. The exposure of the normal brain during surgery is reduced, so that less damage to healthy tissues and lesser complications from surgery. The surgeon can estimate the amount of excision of tumour so that maximal safe resection is achieved with minimal complications.

In what type of surgeries can Neuronavigation be used?

Neuronavigation is useful in all brain surgeries including VP shunt insertion, biopsy and excision of a variety of tumours in the brain, excision of AV malformations and evacuation of hematomas, drainage of abscesses, epilepsy surgeries as well as movement disorder surgeries. Apart from these, Neuronavigation is also useful in various spinal surgeries including fixation of spine with screws, rods and plates.

(The doctor is Senior Neuro Surgeon at Yashoda Hospitals, Secunderabad)