OBJECTIVE: The etiology of symptoms following primary repair of superior canal dehiscence (SCD) may be due to a persistent third window. However, the extent of surgery cannot be seen on postoperative computed tomography (CT) since most repair materials are not radiopaque. We hypothesize that the extent of superior semicircular canal (SSC) occlusion following primary repair can be quantified based on postoperative magnetic resonance imaging (MRI) data. STUDY DESIGN: Retrospective series. SETTING: Tertiary care center. PATIENTS: Adult patients with a history of SCD syndrome who 1) report persistent symptoms following primary SCD repair and 2) underwent heavily T2-weighted MRI postoperatively. INTERVENTIONS: Analysis of SSC using 3D-reconstruction of CT co-registered with MRI data. MAIN OUTCOME MEASURES: Arc length of fluid void on MRI and quantification of persistent SCD based on CT/MRI co-registration. RESULTS: We identified 9 revision cases from a cohort of 145 SCD repairs at our institution (2002-2017) with CT/MRI data. A fluid void on postoperative MRI (indicating occlusion of the SSC) was observed in all cases (anterior limb: 50.1 degrees [±21.8 SD] and posterior limb 48.1 degrees [±28.5 SD]). Co-registration of CT/MRI revealed a residual defect that was most commonly found along the posterior limb in most patients with persistent symptoms. CONCLUSIONS: The extent of SCD repair can be determined using reformatted or direct T2-weighted MRI sequences in the plane of Pöschl. Co-registration of CT/MRI may be useful to determine the location of a residual superior canal defect and when present was found most commonly along the posterior limb.