A 49-year-old woman presented with the chief complaint of "I can hear my eyes move." Her symptoms included chronic dizziness, sensitivity to loud sounds, and autophony. Approximately 10 years prior to presentation, she began noticing that she would feel vertigo when near sirens, during applause in stadiums, or when the radio volume was high while driving in the car. She would experience momentary dizziness with coughing or straining, and could hear her heartbeat constantly in her left ear. In addition to hearing her eyes move, she heard her back cracking in her left ear and each swallow transmitted loudly to that ear. On physical examination, her ears appeared normal by otoscopy. She had normal vestibulo-ocular reflex function to rapid head impulses in the planes of each semicircular canal. Dix-Hallpike positioning maneuvers did not elicit any positional nystagmus or vertigo. Using infrared goggles, however, vertical nystagmus was seen in the plane of the left superior semicircular canal when 500 Hz and 750 Hz tones were applied to the left ear at 110 dB hearing level (HL). Simultaneous head movements in the plane of the left superior semicircular canal were also observed with application of these tones.
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. Cervical VEMPs in response to click stimuli revealed a reduced threshold of 70 dB nHL in the left ear and a normal threshold in the right ear (90 dB nHL). CT scan of the temporal bone was performed and demonstrated a dehiscence of the left superior semicircular canal [Figure 2]. She elected to proceed with surgical plugging and resurfacing of the affected canal by the middle cranial fossa approach.
During surgery, ECochG and 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]. 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. The elevated baseline SP and wave I of the ABR increased further in amplitude during the case, and remained elevated at the conclusion of surgery.
She recovered well from surgery, with complete resolution of her symptoms of autophony and sound or pressure-induced vertigo. As expected, she transiently had oscillopsia with head movements in the plane of the superior semicircular canal that symptomatically improved after vestibular physical therapy. 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].