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Global Positioning System (GPS) is the embodiment of modern, satellite-based navigation today. Originally developed for military purposes, navigation – guidance based on the determination of current positioning and accurate map information – is now a key tool in many civil areas also. In cars, navigation systems are practically standard these days. Surgical navigation solutions have also been developed since the 1990s. These are now utilized in various disciplines, such as in brain surgery, where they make procedures gentler and safer, and minimize damage to healthy tissue.

Some preparation is necessary, however. With the help of imaging systems such as CT/MRT, a sort of 3D digital map of the patient's brain and of the diseased area (e.g. a tumor or vascular anomaly) can be created before the planned procedure. Based on this 3D patient information, the neurosurgeon then draws up a plan for the operation on the navigation computer, marking important anatomical structures such as the tumor or certain areas of the brain which must be avoided, and pinpointing entry and target points in the brain. This information is then transferred to the navigation system.

During the operation, various markers on the patient and on defined navigated surgical instruments are used for orientation purposes. The positions of the navigated instrument, e.g. an aspirator or a probe, and of the patient are measured and displayed on the monitor using an infrared camera system. This provides the surgeon with important extra information about the current position of the instruments and the distance to the tumor and, for instance, its size. At the same time, the navigation system shows the structures on the way to the tumor which must not be damaged.

Modern surgical microscopes like the Carl Zeiss OPMI PENTERO 900 are already equipped for neurosurgical navigation applications and can be linked to these navigation systems. A small monitor in the microscope – the data injection system – enables doctors to see the navigation information in their field of view directly, without needing to take their eyes off the microscope to look at the navigation system monitor.

But, similar to road transport, these navigation solutions are not 100 per cent perfect. Monitoring by surgeons is essential. They must thoroughly check if the information given for navigation to the tumor is correct. During the operation, the surgeon is regularly required to verify the current navigational accuracy. The navigation system can be turned off at any time during the operation, in the event of an error. Navigation systems offer a valuable contribution, providing important assistance for a successful procedure, but they cannot replace years of surgical experience or make up for deficient anatomical knowledge.

September 21, 2011