gms | German Medical Science

ESBS 2005: Skull Base Surgery: An Interdisciplinary Challenge
7. Kongress der Europäischen Schädelbasisgesellschaft & 13. Jahrestagung der Deutschen Gesellschaft für Schädelbasischirurgie

18. - 21.05.2005, Fulda

Application of bone anchored referencing with an electromagnetic navigation system to the lateral skull base?

Meeting Contribution

  • O. Majdani - Medical University Hannover, Department for Otolaryngology, Hannover, Germany
  • R. Heermann - St. Franziskus Hospital Münster, Department for Otolaryngology, Münster, Germany
  • S. Bartling - Medical University Hannover, Department for Neuroradiology, Hannover, Germany
  • T. Lenarz - Medical University Hannover, Department for Otolaryngology, Hannover, Germany
  • M. Leinung - Medical University Hannover, Department for Otolaryngology, Hannover, Germany

ESBS 2005: Skull Base Surgery: An Interdisciplinary Challenge. 7th Congress of the European Skull Base Society held in association with the 13th Congress of the German Society of Skull Base Surgery. Fulda, 18.-21.05.2005. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc05esbs53

doi: 10.3205/05esbs53, urn:nbn:de:0183-05esbs533

Veröffentlicht: 27. Januar 2009

© 2009 Majdani et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen ( Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.




Currently, electromagnetic navigation systems are well-established in procedures at the frontal skull base. Problems arise if a surgeon intends to perform lateral skull base surgery by use of these systems. For example the heaset of the InstaTrak3500 (GE Medical®) is optimized for endonasal surgery but hinders sterically surgical approach to the lateral skull base. Furthermore the flexible headset reduces long-time navigation precision due to intraoperative shift of the electromagnetic transponder. The manufacturer actually provides a bone-anchored fixation for a modified transponder.

Materials and methods

We prepared 10 cadavers with 9 miniosteosynthesis screws each. After acquiring a computed tomography imaging following standard protocols the 3D-datasets were transferred to the navigation systems. Five of the screw served as artificial landmarks for registration. The other four osteosynthesis screws exemplified the surgical site and were used to measure the Target Registration Error (TRE): The head of each screw was located within the dataset and marked via a straight pointer. The resulting distance (signifying the misalignment of the registration procedure) was measured by means of screenshots in high magnification.

After a small incision of the skin nearby the intended surgical site a 4 mm hole was drilled into the calotte and an adapter (lateropin®, see Figure 1a [Fig. 1] and Figure 1b [Fig. 1]) was fixed by a central screw and three peripheral thornes. The electromagnetic transponder was then fixed to the lateropin (see Figure 1d [Fig. 1]). The time involved of the preparation was noted.


The preparation time varied between 15 and 28 minutes, while the fixation of the bone anchored referencing pin (9 to 22 minutes) was the biggest part of it. The pointer was mainly use for navigation. Other utilizable instruments (curved suction, Blakesley) are optimized for interventions in the area of the frontal skull base and therefore their use was limited in the much tinier anatomy of the lateral skull base. Average TRE was 2.0 mm (min.0.7 mm, max. 3.6 mm). A source of error was the electromagnetic interference that occurred when the microscope was too close to the transponder (less than 10 cm). Electromagnetic interferences decrease intraoperative navigation accuracy. However, the navigation system recognizes such a condition and sends a warning signal to the surgeon.


All together the application of the electromagnetic navigation system is possible in the lateral skull base surgery. It is keenly important to position the lateropin in an area, with a calotte thickness of more than 4 mm to prevent an opening of the intracranial space (see Figure 1c [Fig. 1]).

Ideally, surgery of the lateral skull base requires navigation accuracy of less than 1 mm. So far our results are not satisfying in this respect. Mostly bad navigation quality resulted from involuntary mechanical stress on the lateropin which caused a tipping of the adapter. Modifications of the reference pin as well as the development of adjusted instruments for the lateral skull base procedures are work in progress.