Superior Semicircular Canal Dehiscence by Superior Petrosal Sinus: Proposal for Classification.

Objectives: This study aimed to present 3 different clinical stages in patients presenting with superior semicircular canal dehiscence (SSCD) by the superior petrosal sinus (SPS). A specific 3-class classification based on clinical, radiological, and audio-vestibular arguments is proposed.

Materials And Methods: We retrospectively compared clinical and radiological findings in 3 patients with different degrees of audio-vestibular dysfunction in whom the imagery evocated the diagnosis of SSCD by SPS. Imaging sensitivity was improved by combining inner ear high-resolution computed tomography (HRCT) scan and magnetic resonance imaging in fusion, allowing us to compare and corroborate clinical and audio-vestibular findings in each case with the imagery.

Results: HRCT and 3T inner ear fusion imaging highlighted a direct contact and/or compression between SPS and the membranous superior semicircular canal (SSC). We propose a new classification of SSCD by SPS. Class "A" corresponds to an HRCT image with a "cookie bite" and thin bone still covering the SSC. Class "B" corresponds to a "cookie bite" image with confirmed contact between the SPS wall and the membranous SSC in MRI labyrinthine sequences. Class "C" type corresponds to a "cookie bite" image, contact, and obvious compression of the membranous SSC by SPS on MRI sequences.

Conclusion: Anatomical systematization is needed for daily practice. This classification of SSCD by SPS would contribute to a better understanding of the wide variety and variability in the occurrence and onset of symptoms.