PubMed · 9042466
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C H Chouard. 1997. Basic surgical techniques.. https://doi.org/10.1159/000058959
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The cochlea is organized tonotopically: each frequency between 20 Hz and 20 kHz has its own location on the basilar membrane. In addition the cochlea has a large dynamic range (sound intensity). Active movements of the outer hair cells of the sensory organ of Corti play a crucial part in determining hearing acuity and frequency selectivity. Long-known properties such as combination tones and more recent observations like spontaneous and evoked otoacoustic emissions (the cochlea as sound source) fit in the same concept of a cochlea acting as a non-linear fine-tuned amplifier. Most sensorineural losses in people with diminished hearing are caused by injury to the hair cells, e.g. by medicines. Damage of outer hair cells impairs the cochlear amplifier, leading to loss of sensitivity to soft sounds and loss of frequency selectivity. Damage to the inner hair cells has much the same effect as conductive hearing loss. Tinnitus is not caused by otoacoustic emissions, but probably by denervation hypersensitivity following loss of cochlear input.
BACKGROUND AND OBJECTIVE: Apart from the ablation properties at the stapes footplate, the degree of thermic loading in the inner ear is important in determining the suitability of pulsed lasers for stapedotomy. The aim of the study is to compare the thermic effects in the vestibule with different pulsed laser systems. STUDY DESIGN/MATERIALS AND METHODS: Temperature increases and heat exchange processes in the fluid (physiological saline) were examined in a calorically and physiologically approximated cochlea model for applying the laser parameters effective in creating footplate perforations. RESULTS: With all systems, increases in the energy density, number of pulses, and thus resultant total energy lead to higher temperatures. In the effective energy density range, the highest temperature increases achieved with the requisite number of pulses at a distance of 2 mm behind the perforation are 26 degrees C with the Ho:YAG laser. The lowest temperature maxima are 5.5 degrees C with the Er:YAG and <5 degrees C with the Er:YSGG laser. The excimer laser, investigated at only one energy density, showed maximal temperatures of 10 degrees C. CONCLUSION: The Er:YSGG and Er:YAG laser can be applied in laser stapedotomy in a relatively broad energy density range without a risk of inner ear damage by thermic loading. On the other hand, the Ho:YAG laser is not recommended for stapedotomy because of the higher energy density and pulse rate required for sufficient perforation and the resultant higher temperature increases in the perilymph. Though likewise achieving perforations with only slight temperature increases in the fluid of the cochlea model, the excimer laser does not seem appropriate for stapedotomy because of the long period of heat exposure (ca. 60 s) due to the lower ablation rate at the stapes necessitating a longer application time.
Pendred syndrome comprises the association of severe congenital sensorineural deafness with thyroid pathology. Although it is the commonest form of syndromic hearing loss, the primary genetic defect remains unknown. The variable clinical presentation allied to the difficulty in securing the diagnosis have resulted in relatively poor documentation of the radiological features of this syndrome. We now present data on 40 patients, all complying with strict diagnostic criteria for the disorder, and describe our experience of the prevalence of specific malformations of the inner ear as well as comparing the relative merits of computed tomography (CT) and magnetic resonance imaging (MRI) in the investigation of this inherited condition. Deficiency of the interscalar septum in the distal coils of the cochlea (Mondini deformity) was found to be a common but probably not a constant feature of Pendred syndrome. However, enlargement of the endolymphatic sac and duct in association with a large vestibular aqueduct was present in all 20 patients examined by MRI. We conclude that thin section high resolution MRI on a T2 protocol in the axial and sagittal planes is the imaging investigation of choice.