J Neurol Surg B Skull Base 2015; 76 - P092
DOI: 10.1055/s-0035-1546719

Comparison of Microscopic and Endoscopic View of the Internal Auditory Canal: A Cadaveric Study

Guilherme R. Montibeller 1, Fabian Fries 1, Ioannis Petrakakis 2, Kurt Becker 3, Joachim Oertel 1
  • 1Department of Neurosurgery, Saarland University, Germany
  • 2Department of Neurosurgery, Hannover Medical School, Germany
  • 3Institute of Anatomy, Saarland University, Germany

Objective: Studies suggest that the endoscope could provide improved exposure of the internal auditory canal after microsurgical resection of intrameatal tumors. The aim of this study is to quantify the difference of the exposure of the internal auditory canal between microscope and endoscope.

Material and Methods: A retrosigmoid approach was performed on 14 cadaver heads. Computed tomography scans were used to plan the size of the craniotomy and perform anatomical measurements. A millimeter gauge was introduced inside the internal auditory canal, and examinations with surgical microscope and 0, 30 and 70-degree rigid endoscopes were performed. The differences between the view of the microscope and different angled endoscopes were analyzed. Other anatomical measurements (length of the internal auditory canal, angle between anterior and posterior wall of the internal auditory canal, relation of sinus sigmoideus, and the fundus, etc.) were performed and also evaluated.

Results: The endoscope allowed for improved exposure of the internal auditory canal in all cases. The more angled was the endoscope, more deeply could the internal auditory canal be investigated. However, also the more intense was the distortion of the image gained. The 0, 30, and 70-degree endoscopes permitted an exposure that was, respectively, 106% (3.75 mm), 215% (5.75 mm), and 320% (7.64 mm) more lateral than the microscopic view (1.82 mm) on average. A decreased necessity of retraction of structures to expose the internal auditory canal could also be noted when using the endoscope. The area inspected by the endoscope was not always accessible using regular microsurgical instruments. The working area was diminished as a result of the additional instrument brought into the operation area while using the endoscope.

Conclusion: The use of the endoscope for inspection of the internal auditory canal can be very useful during intrameatal tumor surgeries. The clear advantage gained by the use of different angled endoscopes in this region could be objectively demonstrated in this anatomical study. The combination of the qualities of both, microscope, and endoscope, provided the best options for intrameatal visualization. Higher resolution, finer instruments, and hands-on experience open the field for new surgical techniques to be thought of and developed.