Computerized Assessment of Superior Semicircular Canal Dehiscence Size Using Advanced Morphological Imaging Operators

Object: Superior semicircular canal dehiscence (SSCD) describes a pathological aperture at the level of the arcuate eminence. Normal fluid dynamics is disrupted by this hole and may produce auditory and vestibular symptoms (SSCD syndrome). Diagnosis is based on clinical exam and identification of the defect on imaging. Techniques for quantifying defect size have been described in the literature with most studies using 2D lengths that inherently underestimate the pathology. The authors of this study describe a novel method of measurement that combines manual segmentation of high-resolution computed tomography (HRCT) images of the temporal bone and a morphological skeletonization transform to calculate dehiscence volume.

Methods: HRCT images of temporal bones of patients with a clinical diagnosis of SSCD were imported into a freely available image segmentation tool; ITK-SNAP (Version 3.4.0) software. Coronal and sagittal planes were used to outline the dehiscence in all slices demonstrating the defect using the paintbrush tool. A morphological skeletonization transform was used to derive a single-pixel thick representation of the original delineation; this “sheet” of voxels overlays the dehiscence. Volume was calculated by counting the number of nonzero image voxels within this “sheet” and multiplying this number by the volume in mm³ of each voxel.

Results: A total of 70 cases of SSCD were identified in 59 patients. Mean age was 50.9 years (SD: 14.4, range: 21–84). Females and males comprised 66.1% (n = 39) and 33.9% (n = 20) of the sample, respectively (approximate female to male ratio, 2 to 1). Overall, mean volume of dehiscence recorded was 0.88 mm³ (SD: 0.57, range: 0.11–2.27). Mean volume for females was 0.89 mm³ (SD: 0.60, range: 0.11–2.27) versus 0.87 mm³ (SD: 0.51, range: 0.20–1.92) for males. Differences in volume by sex did not reach statistical significance.

Conclusion: We present a novel evaluative technique for measurement of SSCD that integrates manual, bi-planar segmentation in all slices of the visualized defect and a morphological skeletonization transform to calculate dehiscence volume. We believe this method not only provides a more accurate representation of the pathology, but also has the potential to standardize measurement of SSCD. Future studies will compare our technique to those described in the literature and seek to validate, as well as, identify new clinical correlates.