Computed Tomography for navigated procedures at the lateral skull base – proof of feasibility on phantom and human temporal bone specimens

Hypothesis: High-resolution imaging as provided by flat-panel based Volume Computed Tomography (fpVCT) could increase navigation accuracy and could therefore be valuable on lateral skull base procedures. O. Majdani S. Bartling Th. Rodt Methods: In the first part of the study we evaluated the accuracy of the image guided surgery (IGS) system using a custommade phantom that H. Eilers was scanned both in a Multislice CT scanner (MSCT, GE Lightspeed C. Dullin 16Pro, GE Healthcare, Milwaukee, WI) and in an experimental fpVCT G. Issa scanner (GE Healtcare). We performed measurements of the Target Th. Rau Registration Error (TRE) with the optoelectronic navigation system VectorVision (BrainLAB, Feldkirchen, Germany). M. Lenarz In the second part of the study four temporal bone specimens were scanned in the fpVCT device. The data were transferred to the VectorViTh. Lenarz 1 M. Leinung sion planning station. The route from the surface of the mastoid to the scala tympani of the cochlea was planned as a direct channel passing the facial recess without injuring the facial nerve and other functionally 1 Klinik und Poliklinik für HalsNasen-Ohrenheilkunde, important anatomical structures of the temporal bone. During surgery the preoperatively defined trajectory was followed from the entry point Medizinische Hochschule to the target point using a navigated and hand-held surgical drill. MSCT Hannover, Hannover, Germany imaging was acquired to document the position of the drilled channel’s position. In addition a routinemastoidectomy and posterior tympanotomy was performed on each specimen to document the drilled route. 2 Abteilung für Neuroradiologie, Medizinische Hochschule Results: The accuracy measurements on the phantom revealed that the average TRE usingMSCT (0.82mm, SD: 0.35mm) was significantly higher than using fpVCT (0.46, SD: 0.22 mm) (p<0.01). Hannover, Hannover, Germany 3 Institut für Robotik, Leibniz Universität Hannover, Hannover, Germany The drilling tests on the cadaver specimens showed that it was possible to preserve all critical structures when performing a navigated, minimally invasive approach to the cochlea. The chorda tympani was damaged 4 Abteilung für Diagnostische Radiologie, in one specimen with an exceptionally narrow facial recess. This collateral damage has been foreseen at the time of preoperative planning. Universitätsklinikum In all four specimens the scala tympani has been opened as intended Göttingen, Göttingen, Germany at the planned location of the cochlea. The surgical procedure itself took about 10 to 15 minutes. Conclusion: Using fpVCT as the basis dataset for the navigation system we were able to perform minimally-invasive cochleostomy defined as a single-channel mastoidotomy with cochleostomy. Current research activities are dealing with the problem of inserting the electrode of a cochlear implant through this narrow approach in order to realize the entire concept of a minimally invasive cochlear implantation.