After the development of microsurgery, the introduction of neuronavigation contributed significantly to the improvement and facilitation of modern brain tumour surgery. The method has become established since its introduction in our department (the first surgery took place on 5.7.1996), with well over 1000 interventions as a standard procedure, and has been continuously developed scientifically ever since. Neuronavigation supports the surgeon in planning and carrying out surgery on the brain or vertebrae, by providing him exact anatomical orientation during the intervention.
It is particularly important in:
- location of small tumours (< 2 cm³) deep in the brain (avoiding access requiring damage on the way to the tumour)
- exact location of superficial tumours on the brain surface (minimizing the access from shaving through skin incision up to skull opening)
- support for radical as possible removal of tumour (indicates the resection borders)
Before the actual surgery the surgeon plans the intervention on the computer. He determines, based on the available data sets (Neuronavigation-MRI, 88 slices, 2 mm thick), the target point and the access point (opening of the skull).
Fig. 1: Tumour segmentation (red) and determination of trajectories (determined by target point and access point, more plans possible).
Neuronavigation does not strain the patient. The principle of the procedure is based on as accurate as possible conformity of the two independent data sets of the patient. The first extensive data set is generated by computed tomography (CT) or magnetic resonance imaging (MRI). The second data set is generated in the operating theatre, where the patient is already laid in a fixed position.
Only a few mutual points from both data sets are required today, in order to match the changed situation (matching). The points of the new data set are wirelessly transmitted, e.g. by a laser scan of the patient to the navigation PC. The software installed there adjusts the existing CT or MRI data set to the specific surgical requirements so that now the appropriate surgical instruments, such as the movement of the pointer in correspondence to a patient, can be realistically followed on the monitor. The pointer is recognized by an infrared camera (tracking), if it is equipped with special markers.
Because the surgery plan has already been elaborated with the first data set (determination of an access point and target point), the surgeon can find again, only in sterile conditions, the planned access point on the patient’s skull. He can also see on the monitor the target outlined in the plan in surgical conditions and can orientate himself at any time. Despite all of this, 3D neuronavigation is only an additional tool in the hands of an experienced neurosurgeon, who will never entirely trust this technique.
Recently not only can one use anatomical data when planning an operation, but also the extremely important nerve pathways can be displayed. During this procedure the diverse mobility of water molecules in the nerve pathways is used. In grain direction the mobility around dimensions is higher than for instance in crosswise directions. The special MRI sequences are able to capture these mobility differences of molecules and with the help of special software at the end e.g. a very important pyramidal tract in the brain can also be visualized. This procedure is called fibre tracking and the method is called diffusion tensor imaging (DTI). We also successfully use this new procedure in our clinic.
The use of neuronavigation for necessary operations on vertebrae has also become established. With higher precision e.g. pedicle screws, as here in the image in the example of a dense fracture (cervical spine), can be shown, implanted and their position can be immediately checked.