What is the arcuate eminence?

A study was made of 100 homogeneous CT scans of the petrous part of the temporal bone to determine whether or not the arcuate eminence (AE) is a good landmark for the superior semicircular canal (SSCC) in the suprapetrous approach to the internal acoustic meatus which is used in the extirpation of acoustic neuromas. Direct measurements were made on consecutive coronal sections, 1 mm thick. The AE was absent from the petrous surface in 15% of cases. It corresponded to the relief of the SSCC in 37% of cases; laterally, however, it was separated from the petrous cortex by bone whose thickness varied from 0.5 to 5 mm. Finally, in 48% of cases, the AE was not a good landmark for the canal although nonetheless it participated in the development of this bulge in 46% of cases, always lying towards the medial border of the pneumatized eminence. In addition, study of the coronal sections with MRI allowed us to confirm that the AE does not routinely correspond to the imprint of a temporal sulcus. The AE, whose presence on the petrous surface is due to the combined effects of the SSCC, the air cells of the petrous part of the temporal bone and the temporal sulci, is only a good guide to the SSCC in 37% of cases and should not be considered as a reliable surgical landmark.