Arcuate eminence: Is it due to semicircular canal?

Abstract

Background: Arcuate eminence (AE) is an arc-like elevation seen on the anterior surface of petrous part of temporal bone in the middle cranial fossa (MCF). It has been believed and conventionally taught that AE is a protrusion caused because of the superior semicircular canal (SSC) present in the petrous bone. AE is an useful anatomical landmark in the MCF during surgical approaches to acoustic neuroma through suprapetrosal approach. However, the relevance of relation to AE and SSC has been questioned in recent times. Presence of AE of various shapes and dimensions supports this view. Aim: To study and to establish the relation between shape of AE and inferior surface of cerebral hemispheres. Classify various types and subtypes in case of variation in shape based on its appearance. AE could be a negative impression of either gyrus or a sulcus. Material and Methods: The study was conducted in two parts. In the first part, the shape of AE and the impression on cerebral surface were correlated while removing brain from cranial cavity in 8 cadavers (16 wet temporal bones). In second part of the study, 100 dry temporal bones were examined. Relevant photographs were taken. A total of 116 temporal bones were studied. AE was classified as linear, globular, generalized swelling, and flat based on the appearance. Results and Conclusion: 10 AE of 16 wet temporal bones were linear type and did correspond with a sulcus, whilein 1 cadaver no relation was seen. In dry bones, maximum linear variety was seen. There was no relation to shape of AE and cerebral surface in two cadavers. Diversity in shapes, (linear type 47%) and correlation with sulci on cerebral surface contests the earlier understanding that AE is due to SSC. Thickness of bone over SSC was not measured in this study. Having seen so many shapes of AE in this study, authors are of the opinion that there is a need to revisit this bony landmark in MCF and rethink if it can be used as a guide in middle canial fossa surgeries. This study, however, did not look into the bony thickness overlying SSC, which could have added the knowledge of depth of SSC from bony surface of petrous apex.