Superior Semicircular Canal Dehiscence: A Series of 13 Cases

Abstract

Increasingly more detailed imaging techniques have recently highlighted the frequent occurrence of bony labyrinthine dehiscence. Among them, superior canal dehiscence (SCD) has been described in a number of cases presenting different features. Here, we report a series of 13 cases, in which the detection of vestibular evoked myogenic potentials (VEMPs) in response to stimuli of abnormally low intensity as compared to normal responses led us to suspect the presence of a ‘third window effect’. An accurate HRCT investigation allowed the diagnosis of SCD. Anamnestic and symptomatologic differences seem difficult to explain, although in our opinion a dural rupture could be at the basis of the onset of pathologic manifestations after many years of silence of a probably malformative condition.

Conductive Hearing Loss Caused by Third-Window Lesions of the Inner Ear

“…1). Therefore, supranormal thresholds for bone conduction may be evident, as in many patients with SCD (11,(13)(14)(15)(16). Such improvements of bone-conducted thresholds produced by the third window may be masked by an accompanying true sensorineural hearing loss.…”

“…Low-frequency (<2,000 Hz) bone conduction thresholds are sometimes at supranormal levels, 0 to −20 dB, or better. The lack of middle ear pathologic findings as a cause for the CHL in SCD has been well documented by a variety of diagnostic tests such as tympanometry, acoustic reflexes, laser Doppler vibrometry, air-conducted VEMP testing, otoacoustic emission (OAE) testing, and by exploration of the middle ear (9)(10)(11)(12)(13)(14)(15)(16). Definitive evidence that the SCD can cause a CHL is demonstrated by resolution of the air-bone gap upon patching or plugging the dehiscence, as has been reported by various investigators (9,12,20,21).…”

“…A low-frequency air-bone gap with bone conduction thresholds that are better than 0 dB (−5 to −20 dB) can be a clue especially in dehiscence of the semicircular canals (11,(13)(14)(15)(16)32). Therefore, it is important to accurately assess audiometric bone conduction thresholds to levels less than 0 dB hearing level.…”

“…Therefore, it is important to accurately assess audiometric bone conduction thresholds to levels less than 0 dB hearing level. Acoustic reflexes are typically absent in true middle ear disease but are generally present in third-window lesions (9)(10)(11)13). Vestibular evoked myogenic potential testing with air-conducted sound and measurement of OAEs is also helpful.…”

“…The report of Minor et al is noteworthy because these patients did not have any features of genetic deafness or apparent malformations of the inner ear, and their clinical presentation was similar to patients with middle ear disease such as otosclerosis. Several authors have now reported CHL as a manifestation of SCD (9)(10)(11)(12)(13)(14)(15)(16). Our research group has conducted a series of studies to investigate the mechanisms by which an SCD results in a CHL (11,(17)(18)(19)(20)(21)(22).…”