Comparison of 45 ° Oblique Reformats with Axial Reformats in CT Evaluation of the Vestibular Aqueduct

BACKGROUND AND PURPOSE: Measurement of the vestibular aqueduct on CT scans of the temporal bone is important for the detection of large vestibular aqueduct syndrome; typically this is done in the axial plane. We sought to determine the usefulness of reformats performed in the 45 ° oblique plane for evaluating the vestibular aqueduct. In addition, we provide reference measurements for the vestibular aqueduct in the 45 ° oblique plane. MATERIALS AD METHODS: We selected 15 subjects referred for reasons other than sensorineural hearing loss, and without radiographic evidence of abnormality of the inner ear. Two neuroradiologists independently evaluated both axial and 45 ° oblique images for ease in visualizing the vestibular aqueduct. Then, one of the readers (B.O.) performed reference measurements of the diameter at the mouth and midpoint of the aqueduct. RESULTS: Combining the results of both observers, we judged 82 % of vestibular aqueducts as well-defined or easily traced on 45 ° oblique views, whereas we judged only 55 % as well-defined or easily traced on axial views. The difference in the degrees of visualization between the 45 ° oblique and axial reformats was significant for observer 1 (P .022) and observer 2 (P .001). Intraobserver agreement about the visibility of the aqueduct was higher on the 45 ° oblique than the axial views: