PMC5461570_01
Preoperative audiometry and ocular VEMP data (a and b) demonstrated a low-frequency air-bone gap for the symptomatic left ear, as well as elevated ocular VEMP amplitudes in the contralateral eye in response to 500 Hz tone bursts in the symptomatic ear. Three months after surgery (c and d) the low-frequency air-bone gap decreases, without any sensorineural hearing loss, and the ocular VEMP amplitudes normalize, both consistent with the patient's resolution of symptoms
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F1
An audiogram showed normal hearing bilaterally, with a 20 dB gap between air conduction and bone conduction thresholds at 250 Hz in the left ear and a bone-conduction threshold of -10 dB HL indicating bone-conduction hyperacusis [Figure 1a]. Ocular VEMPs were performed and showed abnormally large amplitudes in response to 500 Hz tone bursts applied to the left ear (70.9 muV, Figure 1b), suggesting a diagnosis of SCDS. Follow-up audiogram 3 months after surgery demonstrated resolution of the air-bone gap and bone conduction hyperacusis, with no sensorineural hearing loss [Figure 1c]. Similarly, the elevated ocular VEMP amplitude was normal after surgery [Figure 1d].
High-resolution computed tomography (CT) demonstrated a thin but intact covering of bone over the right superior semicircular canal on reformation in the plane of the affected canal (a) and orthogonal to that plane (b). A dehiscence was seen affecting the superior semicircular canal on the left side (c and d)
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F2
CT scan of the temporal bone was performed and demonstrated a dehiscence of the left superior semicircular canal [Figure 2].
Intraoperative ECochG revealed significantly elevated SP/AP ratio that did not decrease after plugging of the affected superior semicircular canal. In fact, the elevated SP/AP ratio further increased during surgery. (a) Baseline ECochG prior to plugging, followed by (b) ECochG immediately after plugging the canal and (c) at the completion of surgery (each window is labeled with time of day). (d) Contralateral ear demonstrates a normal (<0.4) SP/AP ratio. (e) ECochG tracings stacked over an approximately 2-hour intraoperative time interval. Time of day and notable intraoperative events are labeled
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F3
ABR were simultaneously recorded, and are shown in Figures 3 and 4. A large elevation of SP resulted in an SP/AP ratio >1 [Figure 3a], which persisted throughout the case as shown by the stacked traces and the post-plugging result [Figures 3b, c and e]. This is in contrast to the conventional SP/AP ratio on the contralateral side [Figure 3d].
Intraoperative ABR is normal for the contralateral ear (a) and shows the appearance of a separate wave prior to wave I, and corresponding to the ECochG summating potential in the affected ear (b). Similar to the SP on ECochG, the new wave becomes elevated during the case and remains elevated at the conclusion of surgery (c and d, each window is labeled with time of day)
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F4
ABR were simultaneously recorded, and are shown in Figures 3 and 4. A large elevation of SP resulted in an SP/AP ratio >1 [Figure 3a], which persisted throughout the case as shown by the stacked traces and the post-plugging result [Figures 3b, c and e]. Note the typical wave I of the ABR for the contralateral side [Figure 4a] but the appearance of a separate wave preceding wave I on the affected side, which appears to represent the large SP.