Background: The use of Image Guided Surgery (IGS) systems at lateral skull base surgery is controversial due to the limitation of
the accuracy of the systems. The intraoperative accuracy of the IGS is dependent on deferent parameters, mainly the precision of
the system, resolution of utilized imaging, rigidity of the reference frame/adaptor, registration method, calibration of the utilized
instruments, and intraoperative movement of the reference markers.
Objectives: In this study the researchers examined the target registration error of an electromagnetic IGS system on different important structures of lateral skull base through different approaches. This study compared two registration methods and two scanning systems.
Methods: In 10 formaldehyde-fixed human cadaver heads, 69 target points were marked with titanium screws for determining
target registration errors. The target points were facial nerve, lateral semi-circular canal, geniculate ganglion, superior semi-circular
canal, internal auditory canal, and the foramen rotundum. Seven heads were scanned using a Cone Beam CT Scanner (CBCT) and
three heads were scanned using a CT scanner. Three screws were implanted around the mastoidectomy cavity as Fiducial Markers
(FM). Two different registration methods were applied, including point based registration using the FM versus surface registration.
All samples were dissected via the middle cranial fossa approach, retrosigmoid approach, and transmastoid approaches.
Results: The overall accuracy of the IGS-system was 1.2mmand plusmn; 0.15 mm. Optimum accuracy was reached with CBCT-scan
and the FM registration marker. Navigation using CT scans with the surface registration method, using CT scans with FM registration
method, and using CBCT-scans with surface registration method had lower accuracy, respectively, yet their difference was not
statistically significant (P > 0.5). The best accuracy was noted on the facial nerve in the mastoid approach (mean 0.8 mm).
Conclusions: The feasibility of the use of an electromagnetic IGS system in lateral skull base, surgery using Cone Beam CT as well as
conventional CT scanner with fiducial marker registration as well as surface registration were evaluated. The accuracywasbest at the
lateral region of the temporal bone and decreased on further medial targets, such as lower cranial nerve and trigeminal ganglion.
Keywords: Image Guided Surgery, Navigation System, Lateral Skull Base