Extended Retro/Infralabyrinthine Approach to Cerebellopontine Angle and Internal Auditory Canal, a Radio-Anatomic Study.

Introduction: There is a considerable controversy about approaches that preserve hearing in acoustic neuroma surgery. Transtemporal approaches have the advantage of extradural drilling and minimal cerebellar retraction. We aimed to measure the limits and exposure of extended infra/retrolabyrinthine approach using temporal bone dissection and temporal high resolution computed tomography (HRCT).

Materials And Methods: Hundred temporal bone sides (unpaired) underwent HRCT. The images were used to estimate the limits and exposure of infra/retrolabyrinthine approach. Also, 10 temporal bone sides underwent the same imaging protocol then were dissected to measure actual exposure and limits of dissection. These measures were compared with those retrieved by HRCT to find if they are appropriate to be applied in general population.

Results: Mean posterior fossa angle of vision (24.5 degrees), retrolabyrinthine (internal auditory canal) IAC (58.6%), and infralabyrinthine IAC exposures (73.2%) were documented based on data retrieved from CT scan. After temporal bone dissection, posterior fossa (p = 0.139) and infralabyrinthine exposures (p = 0.674) were not statistically different comparing with measures retrieved from CT scan; however, retrolabyrinthine exposure was overestimated (p = 0.012).

Conclusion: We found that at least 20% more of IAC length can be exposed by extension of retrolabyrinthine to infralabyrinthine dissection. Infralabyrinthine exposure can be estimated preoperatively using temporal bone CT but the same is not true for retrolabyrinthine exposure.