A 78-year-old woman was referred to our clinic with bilateral hearing loss with sound distortion, tinnitus and auditory hypersensitivity, recurrent vertigo/dizziness induced by loud noises (Tullio phenomenon), and a diagnosis of bilateral SSCD at the temporal bone HRCT performed in the emergency room (Figures 2a-c).
Preoperative audiometry indicated severe mixed hearing loss in the right ear, with moderate conductive hearing impairment in the left ear (Figure 1). A pure tone sound of 110 dB at 500 and 1,000 Hz in the right ear, and pneumatically increasing external auditory canal pressure induced dizziness without detectable nystagmus on video-oculographic (or Frenzel goggles) examination. Her tympanogram was bilaterally normal. A stapedial reflex could not be performed due to patient intolerance (dizziness). Mastoid vibration elicited dizziness without detectable nystagmus on video-oculographic (or Frenzel goggles) examination. A temporal bone 1.5-T MRI with 3D reconstruction performed two months before did not show the bilateral dehiscence (Figures 2d-h). Air conduction cervical VEMPs (cVEMPs) demonstrated a threshold of 85 dB HL on the right side and 100 dB HL on the left side. The cVEMPs were recorded from both ears using 500 Hz short tone-bursts (STBs). A video head impulse test for horizontal and vertical canals, including both dehiscent SSC, showed normal vestibulo-ocular reflex gain bilaterally (Table 1).
Possible surgical procedures (superior canal plugging or resurfacing either through a middle fossa approach or via a transmastoid route, or RW niche plugging) were discussed with the patient. Comorbid cardiopulmonary conditions represented major contraindications for general anesthesia, so the latter procedure was the only possible option to pursue.
Since the patient did not show bilaterally any benefit from an air conduction hearing aid but rather had deteriorating auditory and vestibular symptoms on the right, we decided to perform the surgical procedure in the right ear as it had worse vestibular and auditory symptoms, a poorer hearing threshold, and greatly altered HRCT and VEMPs findings.
With local-assisted anesthesia, we performed a transcanal approach with elevation of the tympanomeatal flap and preservation of the chorda tympani nerve with a minimally invasive retroauricular incision. Ossicular mobility and continuity were assessed, we excluded the stapedial fixation, and no cerebrospinal fluid (CSF) leak was observed during the surgical procedure. After identification and reshaping of the RW niche, a vibroplasty was performed paying particular attention to correctly plugging the round window and coupling it with the floating mass transducer (FMT) of the VSB (Figure 3). We opted to couple the FMT with the RW because concomitant RW plugging was performed and from previous studies it seemed to provide a more stable coupling over time than incus. No ossicular chain abnormalities or perilymphatic fistula were observed intraoperatively.
The plugging of the round window was achieved using cartilage and perichondrium (tragus). This autologous tissue also helped to seal off the FMT in the round window niche. Furthermore, VSB hearing outcomes were monitored with electrocochleography using a cotton-wick recording electrode placed on the hypotympanum (Figure 4).
The wire of the VSB was housed in a canal tunnel drilled up to the tympanic attic. Minimal drilling of the cortical temporal bone posterosuperior to the external auditory meatus was necessary to house the implant receiver and extra wire (Figure 4). The ear canal tunnel was covered with autologous cartilage and external auditory meatus packing was performed.
This study received an exemption from the ethics committee of the University Hospital of Siena (Comitato Etico Regione Toscana, area vasta Sud Est-AOU Senese, Usl Toscana Sud Est) on 10/21/2019 for publication.
Surgery was uncomplicated, the patient did not complain of any post-operative vestibular symptoms. Sutures and external meatus packing were removed on the 10th postoperative day. At the 1-month follow-up, the patient underwent VSB activation and hearing and vestibular examination. She reported a significant improvement in auditory hypersensitivity and reduced sound distortion although tinnitus remained unchanged. No disabling vestibular symptoms were reported. Neither dizziness nor nystagmus could be observed in response to loud sounds or increased external ear pressure on the right side. The postoperative pure tone audiogram revealed a mild increase at 500, 1,000, and 2,000 Hz and a mild decrease at 250 and 4,000 Hz for bone conduction thresholds (Figure 1). An improvement to moderate hearing loss in the VSB-aided hearing threshold was confirmed at 3 months (Figure 1). The maximum speech recognition score of bysillabic words at 65 dB HL improved from 10% preoperatively to 70% at the last follow-up. The improvement of hearing and vestibular symptoms was confirmed subjectively by the patient on the right side. Discomfort and mild dizziness associated with loud sounds on the left side remained unchanged. Using a visual analog scale (0-10), the patient reported an improvement in symptoms from 10 to 4 and from 9 to 2, respectively, for hearing and vestibular complaints (3-month follow-up). Left side mild symptoms related to dehiscence remained unchanged. No short-term surgical complications such as device extrusion or external or middle ear canal infection/inflammation were identified at the 3-month follow-up (Table 1). Control HRCT was not performed since correct positioning of the FMT and plugging of the RW were confirmed by improvements in symptoms and stability of VSB-aided hearing. Air conduction VEMPs were not performed for safety reasons due to the risk of mobilizing the plugging or FMT from the RW.