CAS-system MKM (TM): Use and results in lateral skull base surgery.

Background: Computer assisted surgery has reached an advanced stage of deve lopment and offers new possibilities in daily surgical procedures. Methods: The MKM(TM)-is a navigation system fitted with a laser-guided, autofocus-m icroscope for referencing purposes. The coordinates can be set using variou s marker systems and a special workstation is used for preoperative plannin g. It is possible to add landmarks and display them in the surgeon's eyepie ce. The clinical integration, the time required for the use of the navigati on system and the intraoperative accuracy of the system were evaluated on t he basis of 136 lateral skull base procedures. Results: The degree of accur acy is determined by the type, amount and positioning of markers. The adjus tment of reference points should be carried out following macrosurgery in o rder to avoid shifting factors. For an additional increase in accuracy, an improvement in the spatial resolution of the CT scans is required, with a s ection thickness of 1 mm and a pixel size of 0.5mm. The bone-anchored struc tures of the temporal bone do not underlie shifting or extensive intraopera tive swelling. Skull base surgery is, therefore, ideally suited for the app lication of CAS. We found that registration was accurate to less than 1 mm (0.68 mm +/-0.17 mm) and that the MKM(TM) System made an additional contrib ution to surgical safety by identifying important structures. Conclusions: A practical accuracy found to be approximately one millimetre suggests that the non-invasive referencing system may be effective, accurate and useful for computer assisted identification of vital structures. We expect navigat ion systems to improve the quality and reduce the risks of surgical intrave ntions.