Dural Landmark to Locate the Internal Auditory Canal in Large and Giant Vestibular Schwannomas: The Tubingen Line

BACKGROUND: In cases of large and giant vestibular schwannomas (VS), the visualization of the internal auditory canal (IAC) opening is difficult or impossible. OBJECTIVE: To describe the Tubingen line and explore its relationships with the IAC as a landmark to help locate the IAC. METHODS: Ten cadaveric heads were used in this study. Between 2004 and 2009, the senior author (M. T.) used the Tubingen line as a landmark to recognize the IAC in 300 consecutive patients with VS. To locate the Tubingen line, the initial step was to identify several vertical foldings of dura located around the area of the vestibular aqueduct. After this, foldings upward consistently reached a linear level where all of the foldings ended and the dura tightly adhered to the bony surface in a smooth, foldless shape. RESULTS: The Tubingen line was identified in all temporal bones studied and in all 300 patients operated on, with the exception of 2 cases (<1%). Removal of the bone just above the Tubingen line located the IAC in all temporal bone specimens studied. Similarly, the surgical cases showed that the Tubingen line helped locate the IAC in all patients. CONCLUSION: The Tubingen line is an easy, consistent, and safe method to locate the projection of the IAC along the posterior surface of the temporal bone.