Video Head Impulse Test Demonstrates a Residual Function after Plugging of Dehiscent Superior Semicircular Canal

Abstract

ObjectivePlugging a symptomatic dehiscent superior semicircular canal (SSCC) often leads to a nonfunctional postoperative canal. However, in some instances, a residual function has been described. This study attempts to describe what factors may lead to such residual function.Study designRetrospective study.SettingTertiary referral center.PatientsThirty-five patients with confirmed SSCC dehiscence.InterventionVideo head impulse test was conducted pre- and postoperatively to assess any difference in the function of the SSCC.Main Outcome measuresMean gain and pathological saccades were recorded according to well-established thresholds along with dehiscence length and location to evaluate any associations to residual canal function.ResultsWhen comparing preoperative to postoperative SSCC abnormal gains, a significant increase was observed after plugging (p = 0.023). This also held true when abnormal gain and pathologic saccades were taken together (p < 0.001). Interestingly, 55.3% of patients were observed to remain with a residual SSCC function 4 months postoperatively even with a clinical improvement. Of these, 47.6% had normal gain with pathologic saccades, 38.1% had an abnormal gain without pathologic saccades, and 14.3% had normal gain without pathologic saccades (normal function). Preoperatively, SSCC abnormal gain was associated with a larger dehiscence length mean (p = 0.002). Anterosuperior located dehiscences were also associated with a larger dehiscence length mean (p = 0.037). A residual SSCC function after plugging was associated with a shorter dehiscence length regardless of location (p = 0.058).ConclusionDehiscence length and location may be useful in predicting disease symptomatology preoperatively and canals function recovery after plugging. These factors could be used as indicators for preoperative counseling and long-term management.

Posterior Semicircular Canal Dehiscence with Vestibulo-Ocular Reflex Reduction for the Affected Canal at the Video-Head Impulse Test: Considerations to Pathomechanisms

“…Accordingly, both patients reported an improvement in both auditory and vestibular symptoms after surgery. The lady who underwent canal plugging developed a transient global vestibular hypofunction overlapping the postoperative findings in patients after SSC occlusion in SSCD [48,50,51]. On the other hand, the man who underwent RW reinforcement developed symptoms due to a contralateral HSCD with the FN after surgery, similar to what has been described in patients with multiple third window disorders, highlighting the importance of an extensive preoperative clinical, instrumental and radiological assessment [13].…”

“…Recently, alternative mechanisms have been offered to explain how some SSCD patients with SSC hypofunction on vHIT still exhibit symptoms and signs consistent with a TMWM. In fact, a TMWM is expected to fade after a spontaneous canal occlusion, similarly to what it is expected from a surgical canal plugging [48][49][50][51]. An incomplete canal occlusion or a membranous canal indentation at the dehiscence leading to an endolymphatic flow dissipation during impulsive tests have been recently hypothesized [47,49].…”

“…Thanks to its easy accessibility, in recent years, the vHIT has become the key office procedure to test SC activity in both acute and chronic vestibular disorders, allowing clinicians to detect peculiar lesion patterns depending on the underlying pathomechanisms and etiologies by matching vHIT data with audiometric and VEMPs results [34][35][36][37][38][39][40][41]. Nevertheless, few studies have investigated vHIT data in SCD so far [42][43][44][45][46][47][48]. Most of them have focused on the modification of the VOR gain of the affected SC in SSCD, where a hypothetical spontaneous prolapse of the middle cranial fossa into the canal through the bony dehiscence is assumed, resulting in a natural occlusion of the membranous duct and in an impaired SSC activity.…”

Manual neuronavigation for superior semicircular canal dehiscence surgery

“…Through MCFA plugging, there may be a lower risk of sensorineural hearing loss to the SSC and/or vestibular function impairment in the other canals ( 3 , 8 ). In addition, a recently published study by Renteria et al demonstrated residual SSC function 3 months postoperatively in 55.3% of patients operated on for SSC dehiscence through the MCFA ( 9 ). On the other hand, the TMA avoids craniotomy and temporal lobe retraction and remains the preferable approach for cases of medial and purely posterior dehiscence ( 3 ).…”

Transmastoid Surgery for Superior Canal Dehiscence: Prospective Longitudinal Objective and Patient-Reported Audiovestibular Outcomes

“…We found pathological vHIT function in four of six superior semicircular canals preoperatively, of which some normalized after surgery. The previously proposed auto-plugging hypothesis suggests that dural herniation and compression of the membranous labyrinth imped normal endolymphatic flow and normal VOR response (5,16,36–38). However, the dural compression must create insufficient occlusion as the four patients with abnormal VOR response were both symptomatic and showed objective measures of a third window by VEMP and audiometric testing.…”