Magnetically guided neuronavigation of flexible instruments in shunt placement, transsphenoidal procedures, and craniotomies.

Objective: Magnetically guided neuronavigation of flexible instruments is a new tool that can be used in the frameless navigation of deep-seated lesions or shunt placements. Disadvantages of optical systems such as the line-of-sight problem, the necessity of rigid pin fixation of the head, and missing tracking of the tip of flexible instruments should be solved by the new tracking system. Until now, the accuracy of magnetically guided systems was mostly estimated in laboratory setups.
Methods: In this study, intraoperative accuracy of the system was tested in 60 patients with either hydrocephalus or cranial base tumors. In daily routine use, different operative setups with a variety of metallic instruments were examined. Accuracy of the neuronavigation system was estimated, comparing microscopically or endoscopically identified anatomic landmarks with neuronavigated data and postoperative computed tomographic scans.
Results: The main advantage of the new system is the tracking of a magnetic coil at the tip of a flexible instrument. After an initial learning curve during the developmental phase of the system, the latter showed reliable accuracy values with no operative setups leading to mismatch of more than 2 mm.
Conclusion: Tracking of flexible instruments was easily accomplished as the tip of the instrument was followed within the patient's head. There were no major interferences with other metallic instruments within the surgical field.