Radiographic Assessment of the presigmoid retrolabyrinthine approach

BACKGROUND Lesions of the petroclival fissure are difficult to access surgically. Both retrosigmoid and presigmoid retrolabyrinthine approaches have been described to successfully treat these complex tumors. The retrosigmoid approach offers quick and familiar access, whereas the presigmoid retrolabyrinthine approach reduces the operative distance and the need for cerebellar retraction. The presigmoid retrolabyrinthine approach, however, is constrained by anatomical limits that can be subject to patient variation. We sought to characterize the surgically relevant variation to guide preoperative assessment. METHODS One hundred and seventy-seven high-resolution computed tomography scans of the head (without preexisting pathology) were reviewed. Three hundred and fifty-four temporal bone scans were analyzed for level of aeration, size of Trautmann's triangle dura, and petrous slope. Petrous slope is the angle between the anterior sigmoid sinus and the petroclival fissure at the level of the internal acoustic canal. RESULTS Trautmann's triangle area had a mean of 185.15 mm2 (range 71.4-426.7 mm2). Petrous slope had a mean value of 149° (range 106-178°). Increasing aeration was found to be correlated with decreasing petrous slope and decreasing Trautmann's triangle area. CONCLUSION The presigmoid retrolabyrinthine approach is uniquely confined. Variations in temporal bone anatomy can have dramatic impacts on the operative time, risk profile, and final exposure. Preoperative assessment is critical in guiding the surgeon on the appropriateness of approach. Preoperative measurement of Trautmann's triangle, petrous slope, and aeration can help to reduce surgical morbidity.