Endoscopy-Assisted Drilling and Exposure of the Entire Length of the Internal Auditory Canal through a Presigmoid Retrolabyrinthine Approach: A Cadaveric Study

Objectives: The presigmoid retrolabyrinthine approach to the cerebellopontine angle is traditionally described to not provide access to the internal auditory canal (IAC). This study aimed first to evaluate the extent of the IAC that could be exposed with endoscopic drilling by the presigmoid retrolabyrinthine approach and second to measure the percentage of the IAC that could be visualized with the microscope and various endoscopes after drilling had been completed.

Methods: Presigmoid retrolabyrinthine approaches including decompression of 2 to 3 cm of retrosigmoid dura were performed bilaterally on 4 whole fresh cadaveric heads. After identification of the porus and exposure of the medial IAC with microscopic guidance we transitioned to endoscopic guided drilling to expose the lateral extent of the IAC to the fundus. We then measured the length of the IAC and the length of IAC that could be visualized with the microscope, 0-degree endoscope, 30-degree endoscope, 45-degree endoscope, and the 70-degree endoscope.

Results: Drilling the lateral 50% of the IAC under endoscopic guidance allowed for exposure of the entire IAC in 100% (8/8) temporal bone specimens. The microscope afforded mean view of 83% (n = 8) of the IAC. The 0-degree endoscope, 30-degree endoscope, 45-degree endoscope, and the 70-degree endoscope all afforded a view of 100% (8/8) of the IAC.

Conclusions: Endoscopic drilling of the IAC of can provide an extradural, extracranial means of exposing the entire length of the IAC while preserving the labyrinth. Here we describe the first cadaveric study of endoscopy-assisted presigmoid retrolabyrinthine approach.