Is MRI Equal to CT in the Evaluation of Thin and Dehiscent Superior Semicircular Canals?

Can magnetic resonance imaging (MRI) diagnose abnormally thin and dehiscent superior semicircular canals (SSCs) that traditionally rely on evaluation by computed tomography (CT) imaging?

Retrospective clinical study.

Tertiary referral center.

Adults who underwent both MRI and CT of the temporal bones over the past 3 years.

CT and MR images of SSCs were separately reviewed, in a blinded fashion by three neuroradiologists at our institution. CT diagnosis of abnormally thin or dehiscent SSC was used as the "gold" standard.

1) Dehiscent SSC. 2) Abnormally thin SSC. 3) Normal SSC.

One hundred temporal bones with evaluable superior semicircular canals from 51 patients were eligible for review on CT and MR imaging. There were 26 patients of thin SSC and 17 patients of SSC dehiscence on CT imaging, of which 13 and 15 respectively were also found on MRI. There were nine false-positive dehiscent SSC patients and four thin SSC patients observed on MR imaging while not observed on CT. For thin SSCs, MRI sensitivity was 61.9% and specificity of 94.3% with a positive predictive value of 81.3% and a negative predictive value of 86.2%. For dehiscent SSCs, sensitivity was 88.2% and specificity of 89.2% with a positive predictive value of 62.5% and a negative predictive value of 97.4%.

In this series, MRI in the axial and coronal plane had a high negative predicative value for thin SSC (86%) and dehiscent SSC (97%). However, MRI cannot conclusively diagnose thin or dehiscent SSCs.