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. Methods: In the first part of the study we evaluated the accuracy of the image guided surgery (IGS) system using a custom made phantom that was scanned both in a Multislice CT scanner (MSCT, GE Lightspeed 16Pro, GE Healthcare, Milwaukee, WI) and in an experimental fpVCT scanner (GE Healtcare). We performed measurements of the Target Registration Error (TRE) with the optoelectronic navigation system VectorVision2 (BrainLAB, Feldkirchen, Germany). In the second part of the study four temporal bone specimens were scanned in the fpVCT device. The data were transferred to the VectorVision2 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 important anatomical structures of the temporal bone. During surgery the preoperatively defined trajectory was followed from the entry point to the target point using a navigated and hand-held surgical drill. MSCT imaging was acquired to document the position of the drilled channel's position. In addition a routine mastoidectomy and posterior tympanotomy was performed on each specimen to document the drilled route. Results: The accuracy measurements on the phantom revealed that the average TRE using MSCT (0.82 mm, SD: 0.35 mm) was significantly higher than using fpVCT (0.46, SD: 0.22 mm) (p〈0.01). 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 in one specimen with an exceptionally narrow facial recess. This collateral damage has been foreseen at the time of preoperative planning. In all four specimens the scala tympani has been opened as intended 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.
image guided surgery
Volume Computed Tomography
percutaneus cochlear implant surgery