Three-dimensional Fourier transformation constructive interference in steady state magnetic resonance imaging of the inner ear in patients with unilateral and bilateral Menière's disease.

OBJECTIVE: In this study, three-dimensional Fourier transformation constructive interference in steady state (3DFT-CISS) magnetic resonance imaging was used to quantify the distance between the vertical part of the posterior semicircular canal and the posterior fossa as a measure of the endolymphatic sac and duct in patients with Menière's disease. Differences in this distance between affected and unaffected ears, as well as differences between unilaterally and bilaterally affected patients, were studied and compared with a control group. Also, possible correlations between the measured distance and the duration and severity of symptoms, patient age, and average hearing loss were investigated in the group of patients with Menière's disease. STUDY DESIGN: Retrospective clinical study. SETTING: Tertiary referral center (University Hospital) as part of a large, diagnostic research project on Menière's disease. PATIENTS: Of the 111 patients with Menière's disease initially included, 90 patients underwent 3DFT-CISS MRI. Eighty-six of these patients were analyzed in this MRI study. Fifty-six patients had unilateral Menière's disease, and 30 patients had bilateral Menière's disease (116 affected and 56 unaffected ears). Sixty-two ears in patients without Menière's disease were studied as controls. INTERVENTION: The distance between the vertical part of the posterior semicircular canal and the posterior fossa was determined by 3DFT-CISS MRI. MAIN OUTCOME MEASURES: Contiguous axial 3DFT-CISS MRI slices of 0.7 to 1.0 mm were made by a radiologist according to a strict protocol. Measurements of the distance between the vertical part of the posterior semicircular canal and the posterior fossa were taken by two professionals-a radiologist and an otolaryngologist-using a ruler and the original scan. RESULTS: A significantly smaller distance (2.9 mm) between the vertical part of the posterior semicircular canal and the posterior fossa as visualized on MRI scans was found in the ears of patients with Menière's disease than in the ears of patients in the control group (3.8 mm, p < 0.001). In both uni- and bilaterally affected patients (n = 56 and n = 30, respectively), no significant difference between ears was found (p = 0.44 and p = 0.19, respectively). In bilaterally affected patients, however, this distance (3.2 mm) was significantly greater than the distance in unilaterally affected patients (2.7 mm, p = 0.004). There was no relationship between the MRI-visualized distance between the vertical part of the posterior semicircular canal and the posterior fossa and the duration of disease, average hearing loss, or severity of symptoms in uni- and bilaterally affected patients. CONCLUSION: The difference in MRI-visualized distances between the vertical part of the posterior semicircular canal and the posterior fossa of uni- and bilaterally affected patients strongly suggests that unilateral and bilateral hearing loss are two different entities in patients with Menière's disease. The size of the endolymphatic sac seems not to be the only factor in the pathogenesis of Menière's disease. That the MRI-visualized distance between the vertical part of the posterior semicircular canal and the posterior fossa does not have any relationship to the duration of the disease or to patient age indicates that this distance is a congenital feature.

Pure-tone and speech audiometry in patients with Menière's disease.

The aim of this study was to reinvestigate many of the claims in the literature about hearing loss in patients with Menière's disease. We carried this out on a well-defined group of patients under well-controlled circumstances. Thus, we were able to find support for some claims and none for many others. As part of a diagnostic protocol, pure-tone and speech audiometry was performed on 111 patients with Menière's disease according to the 'Definition Menière Groningen'. This was a prospective clinical cohort study. Affected ears of patients suffering from Menière's disease show reduced hearing, both in pure-tone and in speech audiometry. A classification method was devised to determine audiogram shape in an objective manner. The results of this method indicate that affected ears more frequently show 'low' or 'low + high' hearing losses (P = 0.006). The shape of the hearing loss does not depend on the duration of the affection of the disease. In combination with the fact that the average hearing loss does not correlate with the duration of the disease, this leads to the conclusion that, if a classification of the hearing loss in Menière's disease is possible, such a classification cannot be connected to the duration. This conclusion is further supported by the fact that no relationship is found between the duration of the disease and the classification of the hearing loss over the 3 months before hospital admission, as given by the patients in a questionnaire. A relationship between the (objective) audiometric data and the (subjective) classification of the hearing loss by the patient seems to be present, but is not very strong. Correlations between pure-tone and speech audiometry are present as in non-Menière ears (r = 0.899, P < 0.001), and no indications are found of reduced speech discrimination relative to the expectation based on pure-tone loss. The audiogram shape does not appear to play any additional role in speech discrimination (in addition to the influence of the average pure-tone loss).

Evidence for the distortion product frequency place as a source of distortion product otoacoustic emission (DPOAE) fine structure in humans. I. Fine structure and higher-order DPOAE as a function of the frequency ratio f2/f1.

Critical experiments were performed in order to validate the two-source hypothesis of distortion product otoacoustic emissions (DPOAE) generation. Measurements of the spectral fine structure of DPOAE in response to stimulation with two sinusoids have been performed with normal-hearing subjects. The dependence of fine-structure patterns on the frequency ratio f2/f1 was investigated by changing f1 or f2 only (fixed f2 or fixed f1 paradigm, respectively), and by changing both primaries at a fixed ratio and looking at different order DPOAE. When f2/f1 is varied in the fixed ratio paradigm, the patterns of 2 f1-f2 fine structure vary considerably more if plotted as a function of f2 than as a function of fDP. Different order distortion products located at the same characteristic place on the basilar membrane (BM) show similar patterns for both, the fixed-f2 and fDP paradigms. Fluctuations in DPOAE level up to 20 dB can be observed. In contrast, the results from a fixed-fDP paradigm do not show any fine structure but only an overall dependence of DP level on the frequency ratio, with a maximum for 2f1-f2 at f2/f1 close to 1.2. Similar stimulus configurations used in the experiments have also been used for computer simulations of DPOAE in a nonlinear and active model of the cochlea. Experimental results and model simulations give strong evidence for a two-source model of DPOAE generation: The first source is the initial nonlinear interaction of the primaries close to the f2 place. The second source is caused by coherent reflection from a re-emission site at the characteristic place of the distortion product frequency. The spectral fine structure of DPOAE observed in the ear canal reflects the interaction of both these sources.

Evidence for the distortion product frequency place as a source of distortion product otoacoustic emission (DPOAE) fine structure in humans. II. Fine structure for different shapes of cochlear hearing loss.

Distortion product otoacoustic emissions (DPOAE) were recorded from eight human subjects with mild to moderate cochlear hearing loss, using a frequency spacing of 48 primary pairs per octave and at a level L1 = L2 = 60 dBSPL and with a fixed ratio f2/f1. Subjects with different shapes of hearing thresholds were selected. They included subjects with near-normal hearing within only a limited frequency range, subjects with a notch in the audiogram, and subjects with a mild to moderate high-frequency loss. If the primaries were located in a region of normal or near-normal hearing, but DP frequencies were located in a region of raised thresholds, the distortion product 2 f1-f2 was still observable, but the DP fine structure disappeared. If the DP frequencies fell into a region of normal thresholds, fine structure was preserved as long as DPOAE were generated, even in cases of mild hearing loss in the region of the primaries. These experimental results give further strong evidence that, in addition to the initial source in the primary region, there is a second source at the characteristic place of fDP. Simulations in a nonlinear and active computer model for DPOAE generation indicate different generation mechanisms for the two components. The disappearance of DPOAE fine structure might serve as a more sensitive indicator of hearing impairment than the consideration of DP level alone.

Spatial periodicity in the cochlea: the result of interaction of spontaneous emissions?

In this study the results of simulations with a nonlinear macromechanical model of the human cochlea are presented. In this model it is possible to investigate the interactions between large numbers of spontaneous emissions. The focus of this study is on the effect of a local maximum in emission strength on its direct surroundings. The suppression that such an emitter causes depends on the distance between suppressor and suppressee in a strongly nonmonotonic manner. This nonmonotonicity leads to natural minimal distances between emission frequencies, without additional assumptions about the mechanics of the cochlea. The origin of this nonmonotonicity in the suppression lies in reflection of the generated energy at the stapes. The fact that these minimum distances correspond to distances observed between measured SOAE frequencies in adults, but not in newborns, suggests that the nonmonotonicity may play a role in the development of the cochlea in the early years of childhood.