Objective: The retrolabyrinthine approach is a hearing preservation approach that can be applied to internal auditory canal (IAC) pathology with endoscopic assistance. Information regarding the surgical advantages and anatomic constraints of this approach is lacking. This study aims to define the minimum amount of retrosigmoid dural decompression necessary for exposure of the entire IAC and the degree of surgical freedom afforded by this approach.
Methods: Presigmoid retrolabyrinthine approaches were performed on fresh cadaveric heads. The IAC was exposed under endoscopic guidance. The retrosigmoid posterior fossa dura was decompressed in a step-wise fashion until the fundus of the IAC was exposed and successive measurements were made. Degree of surgical freedom at the fundus of the IAC was calculated for each specimen after both the retrolabyrinthine approach and translabyrinthine approach.
Results: The IAC was entirely exposed in 9 specimens with a median length of 12 mm (range 10 to 13 mm). Complete IAC exposure could be achieved with 1 cm of retrosigmoid dural decompression in 8 of 9 mastoids. One mastoid required 2 cm of dural decompression to expose the entire IAC. For the retrolabyrinthine approach, the median anterior-posterior surgical freedom was 13° (range 6° to 23°) compared with 46° (range 36° to 53°) for the translabyrinthine approach (P=0.014). For the retrolabyrinthine approach, the median superior-inferior surgical freedom was 40° (range 33° to 46°) compared 47° (range 42° to 51°) for the translabyrinthine approach (P=0.022).
Conclusions: Using endoscopic assistance, the retrolabyrinthine approach can expose the entire length of the IAC. We recommend that at least 1.5 cm of posterior fossa dura is exposed for this approach. Compared with the translabryinthine approach, this strategy provides significantly less instrument freedom in both the horizontal and vertical axes. This approach may be appropriate for carefully-selected patients with intact hearing and small- to medium-sized tumors involving the IAC.
