Endoscope-assisted Anatomic Study Of The Presigmoid Retrolabyrinthine Approach.

OBJECTIVE:To determine anatomic parameters that influences the manipulation of endoscope in presigmoid approach for the excision of lesions in cerebellopontine angle and petroclival area. METHODS:Microscopic dissections were performed in 15 preserved and silicone-injected cadaver heads using 3 to 40x magnification microscope and endoscope. Morphometric data from measurements of the relationships of the surface landmarks in the petroclival region were provided. To determine anatomic parameters that influence the manipulation of endoscope, cerebellopontine angle and petroclival area were observed via endoscope. Brain tissues were removed after the observation, and structures correlated with the presigmoid approach and retrosigmoid approach were investigated. Differences between these approaches were discussed. RESULTS:Manipulation of endoscope can be influenced by the highly placed jugular bulb, dominant sigmoid sinus and vital neurovascular structures. With minimal cerebellar and temporal lobe retraction, the endoscope arrived at the cerebellopontine angle and petroclival area through the space created by the drilled bone. Structures and the ventral aspects of brain stem that not visible in microscope were clear in endoscope via presigmoid approach. The operative distance to the clivus is shortened than that provided by retrosigmoid approach.CONCLUSION:The presigmoid approach has the advantages of minimal cerebellar and brain stem retraction, Anterior and lateral aspects of the brain stem can be observed with few cerebellar retractions in retrolabyrinthine approach. The operative distance to the cerebellopontine is shorter than that provided by the retrosigmoid approach. Manipulation of the endoscope in the complex approach is affected by the anatomic structure. The results and the observations could be useful to understand the anatomy better, and to estimate the degree and direction of a safe bony removal for the transpetrosal surgery. The cerebellopontine structures can be fully...