First stage in predicative measure for transnasal transsphenoidal approach to petrous apex cholesterol granuloma.

OBJECTIVES/HYPOTHESIS This study evaluates the feasibility of the transsphenoidal approach to petrous apex cholesterol granuloma based on the petrous angle. This is the angle centered at the vomer, extending between the medial aspect of the C3 segment of the internal carotid artery and the occipital protuberance. The aim of this study is to determine the average petrous angle in a population of normal computed tomography scans. STUDY DESIGN Retrospective review at the University of Cincinnati Medical Center. METHODS Two of the authors independently reviewed 400 consecutive normal temporal bone computed tomography scans obtained between September and December of 2009. All scans had slice thickness of 1.25 mm at 0.6-mm intervals. Axial images parallel to the orbitomeatal plane were analyzed, and the petrous angle was measured bilaterally. Interrater reliability was tested on 50 of the computed tomography scans. RESULTS A total of 400 temporal bones were reviewed. The mean and median petrous angle was 17.7 and 16.5 degrees, respectively. Eleven (2.8%) had an angle ≤ 10.0, 331 (82.8%) between 10.1 to 20.0, and 58 (14.5%) ≥ 20.1. The interrater variability was highly correlated (r = 0.912, P < .005). CONCLUSIONS Normative data on consistent petrous apex radiographic landmarks are important for assessing the feasibility of the transphenoidal approach to the petrous apex for cholesterol granuloma drainage. Based on a large population of normal computed tomography scans, the majority of temporal bones (82.8%) have a petrous angle ranging between 10.0 and 20.0 degrees.