The arcuate eminence. Topographic orientation in middle cranial fossa surgery.

The superior semicircular canal (SSC) is an important landmark in the middle cranial fossa approach to the temporal bone. This landmark is frequently located by its topographic association to the arcuate eminence. An anatomic study is reported which examines the relationship of the arcuate eminence to the SSC. Techniques for orientation to the internal auditory canal by the middle cranial fossa approach are reviewed and a technique for localizing the SSC when no arcuate eminence is discernible is presented. 1) In 15% of temporal bone specimens, no arcuate eminence was discernible. 2) Of those specimens with an arcuate eminence, 50% demonstrated that the arcuate eminence was rotated posteriorly from the SSC. 3) Despite displacement of the arcuate eminence, the SSC tended to remain perpendicular to the petrous ridge and 60 degrees from the internal auditory canal. 4) Because of their variable relationship, the arcuate eminence should not be used as a substitute for the SSC in the topographic orientation to the internal auditory canal. 5) A technique for locating the SSC when the arcuate eminence is indiscernible is presented.