[Neuronavigation. Methods and prospects]

With the recent developments in computer technology and the improvements in modern neuroimaging, frame-based stereotactic guidance for open microsurgical procedures has been increasingly replaced by neuronavigation, also called frameless stereotaxy. It allows transfer of individual patientís images onto the operative field to assist the neurosurgeon intraoperatively in defining the tumor margins or identifying functionally important brain areas. The different localization techniques employed are articulated position-sensing arms, infrared or ultrasound systems working with the principle of satellite navigation and robotic systems integrated with the operating microscope. In 200 operations performed with different systems (arm-based, robotic and infrared) the method proved to be helpful, enabling fewer invasive procedures to be performed. With a mean deviation of 2.87 +/- 1.9 mm for intraoperative localization, the accuracy was only slightly worse than in frame-based stereotaxy with deviations below 2 mm. Neuronavigation was most helpful for operations on deeply seated lesions, skull-base tumors and lesions in brain areas with high functionality. The major disadvantage is the use of preoperative data for navigation, leading to inaccuracies when anatomical structures are altered during the operation by resection of tumors or shift of intracranial soft tissue. Intraoperative magnetic resonance imaging (MRI) might be a solution for this problem. With the method of intraoperative MRI developed in our department it has already been possible to update neuronavigation with images reflecting intraoperative changes in anatomy. Therefore, neuronavigation is definitely a method with growing importance in operative routine, and it will also spread into other surgical specialties.