Superior semicircular canal dehiscence mimicking otosclerotic hearing loss.
(9/67)
A puzzling aspect of middle ear surgery is the presence of an air-bone gap in a small number of cases with no apparent cause. We believe that some of these cases are due to unrecognized superior semicircular canal dehiscence (SSCD). We have now gathered experience from 20 patients with SSCD presenting with apparent conductive hearing loss without vestibular symptoms. All affected ears had SSCD on high-resolution CT scan. The common findings in these patients were: (1) the air-bone gaps occurred in the lower frequencies below 2,000 Hz, and ranged from 10 to 60 dB; (2) bone conduction thresholds below 2,000 Hz were sometimes negative (-5 dB to -15 dB); (3) the acoustic (stapedial) reflex was present; (4) measurement of umbo velocity by laser Doppler vibrometry showed slight hypermobility of umbo motion; (5) the vestibular-evoked myogenic potential response was present, with thresholds that were abnormally low, and (6) the middle ear was normal at exploratory tympanotomy, including normal mobility of the ossicles and a patent round window niche. We have investigated the mechanism of the air-bone gap due to SSCD using a theoretical framework, clinical research data and an animal model (chinchilla). Our research supports the hypothesis that SSCD introduces a 'third' window into the inner ear which produces the airbone gap by (1) shunting air-conducted sound away from the cochlea, thus elevating air conduction thresholds, and (2) increasing the difference in impedance between the scala tympani and scala vestibuli, thus improving thresholds for bone-conducted sound. (+info)
Measurements of human middle- and inner-ear mechanics with dehiscence of the superior semicircular canal.
(10/67)
OBJECTIVES: (1) To develop a cadaveric temporal-bone preparation to study the mechanism of hearing loss resulting from superior semicircular canal dehiscence (SCD) and (2) to assess the potential usefulness of clinical measurements of umbo velocity for the diagnosis of SCD. BACKGROUND: The syndrome of dehiscence of the superior semicircular canal is a clinical condition encompassing a variety of vestibular and auditory symptoms, including an air-bone gap at low frequencies. It has been hypothesized that the dehiscence acts as a "third window" into the inner ear that shunts acoustic energy away from the cochlea at low frequencies, causing hearing loss. METHODS: Sound-induced stapes, umbo, and round-window velocities were measured in prepared temporal bones (n = 8) using laser-Doppler vibrometry (1) with the superior semicircular canal intact, (2) after creation of a dehiscence in the superior canal, and (3) with the dehiscence patched. Clinical measurements of umbo velocity in live SCD ears (n = 29) were compared with similar data from our cadaveric temporal-bone preparations. RESULTS: An SCD caused a significant reduction in sound-induced round-window velocity at low frequencies, small but significant increases in sound-induced stapes and umbo velocities, and a measurable fluid velocity inside the dehiscence. The increase in sound-induced umbo velocity in temporal bones was also found to be similar to that measured in the 29 live ears with SCD. CONCLUSION: Findings from the cadaveric temporal-bone preparation were consistent with the third-window hypothesis. In addition, measurement of umbo velocity in live ears is helpful in distinguishing SCD from other otologic pathologies presenting with an air-bone gap (e.g., otosclerosis). (+info)
Electrophysiologic threshold study in air and bone conduction in children with 2 months or less age.
(11/67)
The differential diagnosis of hearing loss with air and bone Auditory Brainstem Response in small children has not been enough studied in Brazil. AIM: To compare air and bone Auditory Brainstem Response results in children under 2 months of age with normal hearing. STUDY DESIGN: clinical with transversal cohort. MATERIALS AND METHODS: 12 children who passed the hearing screening were evaluated using air and bone Auditory Brainstem Response. No contralateral masking was used in the bone conduction test. The responses were compared and analyzed by the McNemar test and repetitive measurements of the variance test. RESULTS: There were no statistic differences between air and bone conduction Auditory Brainstem Response thresholds (p>0.05). The bone conduction latency for wave V was statistically higher than air conduction latency (p=0.000). CONCLUSION: There was agreement on the results recorded for air and bone conduction Auditory Brainstem Response for threshold intensities; latency for bone conduction wave V was statistically higher than the air conduction latency. (+info)
Keeping an "ear" to the ground: seismic communication in elephants.
(12/67)
This review explores the mechanisms that elephants may use to send and receive seismic signals from a physical, anatomical, behavioral, and physiological perspective. The implications of the use of the vibration sense as a multimodal signal will be discussed in light of the elephant's overall fitness and survival. (+info)
Non-ossicular signal transmission in human middle ears: Experimental assessment of the "acoustic route" with perforated tympanic membranes.
(13/67)
Direct acoustic stimulation of the cochlea by the sound-pressure difference between the oval and round windows (called the "acoustic route") has been thought to contribute to hearing in some pathological conditions, along with the normally dominant "ossicular route." To determine the efficacy of this acoustic route and its constituent mechanisms in human ears, sound pressures were measured at three locations in cadaveric temporal bones [with intact and perforated tympanic membranes (TMs)]: (1) in the external ear canal lateral to the TM, P(TM); (2) in the tympanic cavity lateral to the oval window, P(OW); and (3) near the round window, P(RW). Sound transmission via the acoustic route is described by two concatenated processes: (1) coupling of sound pressure from ear canal to middle-ear cavity, H(P(CAV) ) identical withP(CAV)P(TM), where P(CAV) represents the middle-ear cavity pressure, and (2) sound-pressure difference between the windows, H(WPD) identical with(P(OW)-P(RW))P(CAV). Results show that: H(P(CAV) ) depends on perforation size but not perforation location; H(WPD) depends on neither perforation size nor location. The results (1) provide a description of the window pressures based on measurements, (2) refute the common otological view that TM perforation location affects the "relative phase of the pressures at the oval and round windows," and (3) show with an intact ossicular chain that acoustic-route transmission is substantially below ossicular-route transmission except for low frequencies with large perforations. Thus, hearing loss from TM perforations results primarily from reduction in sound coupling via the ossicular route. Some features of the frequency dependence of H(P(CAV) ) and H(WPD) can be interpreted in terms of a structure-based lumped-element acoustic model of the perforation and middle-ear cavities. (+info)
Differential intracochlear sound pressure measurements in normal human temporal bones.
(14/67)