American Journal of Neuroradiology 2008;29:30.
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American Journal of Neuroradiology
DOI 10.3174/ajnr.A0735
HEAD & NECK
Comparison of 45° Oblique Reformats with Axial Reformats in CT Evaluation of the Vestibular Aqueduct
From the Department of Radiology (B.O.), Faculty of Medicine, Hacettepe University, Ankara, Turkey; and the Massachusetts Eye and Ear Infirmary (M.E.C., P.A.C., H.D.C.), Boston, Mass.
Please address correspondence to Mary E. Cunnane, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114; e-mail: mary_beth_cunnane{at}meei.harvard.edu
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: (
= 0.682, SE = 0.171) for 45° oblique reformats; ( = 0.480, SE = 0.145) for axial reformats. On the 45° oblique reformats, the mean external aperture dimension of the vestibular aqueduct was measured as 0.616 ± 0.133 mm, and the postisthmic segment had a mean width of 0.482 ± 0.099 mm.
CONCLUSIONS: The 45° oblique plane gives a more reliable depiction of the vestibular aqueduct than the axial plane in CT evaluation of the temporal bone. This technique can be useful in cases of borderline enlargement of the vestibular aqueduct.