gms | German Medical Science

Navigation systems are applied increasingly as a matter of routine in cranial base interventions. In the area of the frontal skull base important structures lie functionally in direct neighborhood to the field of operation and are endangered. The routine application of navigation systems with these interventions is desirable, however, because of the long setup time at beginning of every procedure as well as the financial expenditure and the size and complexity of the systems not always realizable. Since the first systems at the beginning of the 90's were conceived for cranial base interventions, the workflow has considerably simplified itself. In the course of the adaptation of the technology to the essential needs of the surgeon slightly servable portable navigation systems have been developed for the head and neck surgery.

We evaluated two portable navigation systems in a 2-branched study:

1.

The precision of the iNAV^® - navigation system of the Medtronic^® company (Colorado, USA, see Figure 1a [Fig. 1]) was evaluated in cadaver instruments. In a second step it was applied in 15 cases of chronic sinusitis via endonasal approach.

2.

The Colibri^® system of the BrainLAB^® company (Heimstetten, Germany, see Figure 1b) [Fig. 1] was used in 8 interventions at the anterior skull base. We performed six endonasal surgeries in chronis sinusitis and two surgeries via bicoronal incision as described by Unterberger in 1953. Furthermore, the extirpation of a vestibular schwannoma was navigated via translabyrinthine approach (see Figure 1f [Fig. 1]; status after removal of the tumor).

We examined the workflow, the necessary setup time, the precision of the navigation (performed via identification of osteosynthesis screws in the cadaver study and anatomical landmarks in the clinical examination) as well as the ease of integration in the clinical routine.

Both electrooptical passive navigation systems are realized as portable systems with a camera unit, which is mounted onto a tripod to survey the surgical site. The transference of the CT-scans took place via intranet or CD-ROM. Headsets or fiducial markers before initiating the imaging were not necessary, because both systems can be registrated via surface matching procedures. Referencing has been done with headbands or headset as well as with a bone anchored reference star (Laterostern^®, BrainLAB).

The installation of the iNAV-system is well-explained step-by-step by use of the short pointer (see Figure 1c and e [Fig. 1]). Unfortunately this instrument is too short to be used in endonasal surgery. For these purposes, a straight suction is available, which is predesigned (other instruments can not be calibrated) and not suitable for left-handed surgeons so far. The endoscope’s or microscope’s view can not be displayed on the touchscreen. The system is a kind of portable laptop with a fold-out screen and a carry handle. Average target registration error (TRE) of the iNAV in cadaver experiments was 1.0 mm ± 0.4 mm standard deviation (SD). In the clinical trial the iNAV delifered an average TRE ± SD of 1.2 ± 0.3 mm.

The colibri-system can be used with the standard equipment of BrainLAB (see Figure 1d [Fig. 1]). The system is equipped with an interface to the surgical microscope. It is small and lightweight but not portable in the truest sense of the word. The average TRE was measured as 1.3 ± 0.4 (SD) mm.

The setup time of both devices took between 5 and 11 minutes.

Both portable systems proofed their portability and an easy use in clinical routine. The cadaver and intraoperative measurements of navigation precision showed accuracies comparable to those of the well-known standard systems. The hardware and software design of Medtronic’s portable device is slightly more pleasing than that of BrainLAB but the equipment is to date limited to a predesigned straight suction for right-handed persons. Furthermore the headset demonstrated the tendency to slip off during surgery which required auxiliary fastening. The colibri offers more features as variable instruments and video integration. Screenshots may be burned to cd in purposes of documentation or later analysis. Installation time for both devices is slightly shorter than that of the established standard systems. Consequently the main advantage of these systems is not a better precision or a shorter installation time but the portability between different operation theatres and the lower cost price. Therefore the portable navigation devices address to small departments or to federations of practicians who share a system.