Superior canal dehiscence and ‘near-dehiscence’ syndrome: clinical and instrumental aspects.

Even though superior canal dehiscence syndrome (SCDS) has already been widely studied from a clinical, etiopathogenetic and therapeutic point of view, some diagnostic aspects have yet to be clarified. It is well-known that highresolution CT (HRCT) scan tends to overestimate the prevalence of the bony defect requiring the detection of lowered thresholds of air-conducted (AC) VEMPs to confirm the diagnostic suspect. The most recent definition of the so-called near-dehiscence syndrome (NDS), in which an extremely thinned bony roof of the superior canal results in the onset of a symptomatological scenario overlapping SCDS, has allowed to explain most cases of incongruence between imaging analyses and electrophysiological data. Moreover, no univocal explanation to the wide symptomatological and semeiological variability of SCDS has been offered yet. The aim of this paper is to face the diagnostic dilemma offered by the complexity of this two-fold syndrome (SCDS vs NDS) reviewing the clinical and instrumental data and submitting to statistical analyses a subsample of 100 patients (193 ears) selected from a group of 242 patients (114 M, 128 F, mean age 56.8 y, range 8-88 y) showing a dehiscence or a an extreme thinning of the superior canal at least from one side at HRCT scans. Firstly, we verified the effectiveness and the diagnostic accuracy of imaging in confirming electrophysiological data, considering the threshold lowering of AC cervical VEMPs as the gold standard in diagnosing an increased inner-ear admittance due to SCD and we offered physiopathogenetic explanation for those cases of incongruence between results. Secondly, we sought among instrumental set (AC and BC cervical and ocular VEMPs, video head impulse test) the test allowing the best diagnostic criteria for ‘near dehiscence’ and the parameter correlating most significantly with the size of dehiscence in case of SCDS. While mostly all data collected can reliably differentiate SCDS from NDS, from this study emerges that ocular VEMPs represent an effective method to detect the ‘neardehiscent’ condition among the normal cases.