This study was performed to determine if the arcuate eminence can be drilled down without opening the semicircular canal to obtain a flatter operative field during an anterior or posterior transpetrosal approach. The depth of the superior semicircular canal from the top of the arcuate eminence was measured in 43 dry temporal bones. We found that the arcuate eminence was situated approximately 20 mm from the petrosigmoid intersection, and the superior semicircular canal was located 2.0 mm deep from the top of the arcuate eminence (range, 0.2 mm to 4.2 mm). The arcuate eminence consists of either (1) the otic capsule and additional overlying bone, (2) the naked otic capsule of normal thickness, or (3) the thinned otic capsule. In cases strictly selected by preoperative computed tomography, it may be possible to drill down the arcuate eminence with meticulous manipulation. The relationship between opening the semicircular canal and hearing preservation is also discussed.
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