J Neurol Surg B Skull Base 2016; 77 - P120
DOI: 10.1055/s-0036-1580065

A Comparison of Cerebellar Retraction Pressures in Posterior Fossa Surgery: Extended Retrosigmoid versus Traditional Retrosigmoid Approach

Brandon D. Liebelt 1, Meng Huang 1, Gavin W. Britz 1
  • 1Houston Methodist Neurological Institute, Houstan, Texas, United States

Introduction: The retrosigmoid approach is a very common and familiar approach utilized to access a wide variety of pathology in the posterior fossa including tumors of the cerebellopontine angle, petroclival region, and proximally within the internal auditory meatus. Some of the major strengths of this approach include that it can be tailored to a wide variety of lesions in the posterior fossa and does not require the assistance of a neurootologist due to its simplistic nature. However, it necessitates cerebellar retraction, which in some cases can be quite significant. The extended retrosigmoid approach minimizes cerebellar retraction by opening the corridor anteriorly by removal of the posterior mastoid portion of temporal bone overlying the sigmoid sinus. This allows anterior mobilization of the sigmoid sinus and thus less retraction of the cerebellum.

Methods: Anatomic dissection of two latex injected cadaver heads was performed for comparison of the surgical approaches. Retrosigmoid craniotomy was first performed on each cadaver. The dura was opened and an intraparenchymal pressure monitor was placed in the cerebellar hemisphere 1cm behind the site of retraction and secured. The cerebellum was then retracted to expose a distance of 1.5cm between the petrous temporal bone and retractor blade. The cerebellar pressure was then recorded after the pressure stabilized for several seconds; this was performed in triplicate by two independent observers. The person retracting was blinded to the pressure values to prevent bias. The sigmoid sinus was then skeletonized, mobilized, and recordings repeated; this was performed bilaterally on both cadavers. Both pre- and post- dissection CT imaging was performed to assess extent of bony removal in the extended retrosigmoid approach.

Results: Cerebellar retraction pressures were greatly reduced to achieve the same 1.5cm exposure with the extended retrosigmoid compared with traditional retrosigmoid approach. Localized cerebellar parenchymal pressure adjacent to the retractor ranged from 14.7 to 25.3 cmH2O in cadaver 1 and 10 to 13.3 cmH2O in cadaver 2 for the traditional retrosigmoid approach. For the extended retrosigmoid approach pressures decreased to 7.3 to 14 cmH2O in cadaver 1 and 3.7 to 5.7 cmH2O for cadaver 2. The mean relative reduction in retraction pressure when utilizing the extended retrosigmoid approach for cadaver 1 ranged from 38.7 to 57.9% depending on side and surgeon. Mean relative reduction in retraction pressures for cadaver 2 ranged from 45.2 to 67.5%.

Conclusion: The extended retrosigmoid approach is an effective modification of a commonly utilized skull base approach, which both increases visualization and decreases retraction during surgery. This leads to markedly reduced localized cerebellar pressure adjacent to the retractor in a cadaver model.