Int J CARS DOI 10.1007/s11548-017-1533-5 ORIGINAL ARTICLE Minimally invasive, multi-port approach to the lateral skull base: a first in vitro evaluation Igor Stenin 1 · Stefan Hansen 2 · M. Nau-Hermes 3 · W. El-Hakimi 4 · M. Becker 4 · J. Bredemann 3 · J. Kristin 1 · T. Klenzner 1 · J. Schipper 1 Received: 26 July 2016 / Accepted: 1 February 2017 © CARS 2017 Abstract Purpose The aim of the study was to validate a minimally invasive, multi-port approach to the internal auditory canal at the lateral skull base on a cadaver specimen. Methods Fiducials and a custom baseplate were fixed on a cadaver skull, and a computed tomography image was acquired. Three trajectories from the mastoid surface to the internal auditory canal were computed with a custom plan- ning tool. A self-developed positioning system with a drill guide was attached to the baseplate. After referencing on a high precision coordinate measuring machine, the drill guide was aligned according to the planned trajectories. Drilling of three trajectories was performed with a medical stainless steel drill bit. Results The process of planning and drilling three trajecto- ries to the internal auditory canal with the presented workflow and tools was successful. The mean drilling error of the sys- tem (Euclidian distance between the planned trajectory and centerline of the actual drilled canal) was 0.53 ± 0.12 mm at the entry point and 1.01 ± 0.39 mm at the target. The inac- curacy of the drill process itself and its physical limitations were identified as the main contributing factors. B Igor Stenin igor.stenin@med.uni-duesseldorf.de 1 Department of Otorhinolaryngology, University Hospital Düsseldorf, 40225 Düsseldorf, Germany 2 Department of Otorhinolaryngology, University Hospital Essen, Essen, Germany 3 Laboratory for Machine Tools and Production Engineering, RWTH Aachen University, Aachen, Germany 4 Interactive Graphics Systems Group, Technical University Darmstadt, Darmstadt, Germany Conclusion The presented system allows the planning and drilling of multiple minimally invasive canals at the lateral skull base. Further studies are required to reduce the drilling error and evaluate the clinical application of the system. Keywords Minimally invasive · Skull base surgery · Computer-assisted surgery · Otology Introduction During recent decades, innovations in medical imaging, endoscopic visualization and instrument miniaturization have facilitated the progress from open to endoscopic approaches in various surgical fields. However, surgery performed near the lateral skull base depends on wide expo- sure and direct visualization of anatomical landmarks and critical structures to avoid complications. In contrast to a laparoscopy, natural manipulation space is not available, and inflation is not possible. The rigid bony texture of the lateral skull base contains critical anatomical structures, such as the facial nerve and the internal carotid artery, in a small con- fined space. The anatomy in this area creates a high demand for a minimally invasive approach to the lateral skull base. Sub-millimetric accuracy, high outcome predictability and consistent results are required to push the transition from explorative surgery to minimally invasive approaches around the lateral skull base. For example, Schipper et al. proposed that accuracy below 0.5mm is necessary to access the scala tympani in minimally invasive cochlear implantation [1]. Compared to currently used approaches at the lateral skull base, e.g., mastoidectomy, minimally invasive approaches reduce iatrogenic tissue damage and yield various benefits such as reduced postoperative pain, quicker recovery, shorter 123