Second-side surgery in superior canal dehiscence syndrome

Dehiscence of the superior semicircular canal is associated with a distinct set of vestibular and auditory phenomena, including sound- and pressure-evoked nystagmus, conductive hyperacusis, and autophony (1–6). Characteristic deficits observed on physiologic testing include an air-bone gap on pure-tone audiometry and heightened responses on vestibular-evoked myogenic potential (VEMP) testing (2,7). Varying combinations of these symptoms and signs along with computed tomographic confirmation of superior canal (SC) dehiscence constitute SC dehiscence (SCD) syndrome. Dehiscence of the bone overlying the involved SC can be confirmed at the time of surgery, and repair of that dehiscence resolves the symptoms in most cases (8). Dehiscence of the SC is thought to cause the associated symptoms and signs by creating a “third mobile window,” allowing abnormal flow of endolymph in the canal after provocative stimuli (9–11). Temporal bone histopathologic studies as well as radiographic investigations demonstrate a 20% to 50% occurrence of bilateral dehiscences of the superior semi-circular canals, possibly owing to a congenital or developmental process (12, 13). We demonstrated in previous work that SC plugging surgery for SCD syndrome (SCDS) does not typically produce permanent global dysfunction of the operated labyrinth. Rather, it leads to an isolated deficit in the involved canal (14, 15). However, plugging both SCs would be expected to not only cause loss of the vestibuloocular reflex (VOR) for rapid downward head movements in the respective planes of the affected canals but throughout the entire range of approximately 90 degrees spanned by these canals. This would include higher frequency pitch downward head movements that occur during routine ambulation and running (16). Thus, bilateral SC plugging might be expected to cause vertical oscillopsia with associated visual impairment and gait instability and potentially more significant disability compared with the preoperative state (17). We report here a series of 5 patients with bilateral SCDS who elected to pursue sequential plugging of both SC dehiscences. We evaluated which symptoms prompted patients with bilateral SCDS to seek second-side surgery and the degree of disability associated with those symptoms. We also determined the frequency of disabling imbalance and oscillopsia after bilateral SC plugging in this small cohort.