First Stage in Predicative Measure for Transnasal Transsphenoidal Approach to Petrous Apex Cholesterol Granuloma

Objectives: This is the first in a three-stage study, looking at the feasibility of the transsphenoidal approach to the petrous apex (PA) cholesterol granuloma (CG) based on what we refer to as the petrous angle. This is the angle centered at the vomer, extending between the medial aspect of the petrous internal carotid artery (ICA) and the occipital protuberance. The aim of this study is to determine the average petrous angle in a population of normal computed tomography (CT) scans.

Study Design: A retrospective review was conducted.

Setting: The study was conducted at the University of Cincinnati Medical Center.

Subjects and Methods: Two readers independently reviewed 400 consecutive normal temporal bone CT scans performed 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 orbito-meatal plane were analyzed, and the petrous angle measured bilaterally. Inter-rater reliability was tested on 50 of the CT scans.

Results: A total of 400 CT scans were reviewed. The mean and median petrous angles were 17.7 and 16.5 degrees, respectively. Eleven (2.8%) had an angle ≤10.0, 331 (82.8%) between 10.1 and 20.0, and 58 (14.5%) ≥20.1. The inter-rater variability was highly correlated (r = 0.912, P < 0.005).

Conclusion: Normative data on consistent PA radiographic landmarks are important for assessing the feasibility of the transsphenoidal approach to the PA for CG drainage. Based on a large population of normal CT scans, we have found that the majority of temporal bones (82.8%) have a petrous angle ranging between 10.0 and 20.0 degrees.