Low-Frequency Hearing Loss: Auditory Brainstem Response-Derived Band Analysis

Conventional (0.125-8 kHz) and high-frequency (8-20kHz) audiometry, together with brainstem response audiometry supplemented with derived-band studies have been performed in 6 patients with sensorineural hearing loss: 1 with narrow-band, 3-4 kHz, and 5 with low-frequency threshold elevations. The derived-band results in the latter indicate that the low-frequency audiometric thresholds are spurious, and represent the low-frequency tails of viable high-frequency neurons. Threshold preservation in the 4- to 8-kHz frequency band proved necessary for generation of a normal auditory brainstem response at suprathreshold stimulus levels.

On a étudié sur 6 patients présentant une surdité de perception l'audiogramme conventionnel (0.125-8 kHz) et haute-fréquence (8-20 kHz), ainsi que les potentiels précoces dérivés: l'élévation de seuil était limitée à une bande étroite, 3-4 kHz, chez 1 patient, et intéressait les basses fréquences pour les 5 autres. La technique des potentiels dérivés sur ces derniers sujets montre que les seuils audiométriques sur les graves sont faux et représentent en fait les extrémités basse-frequence de neurones haute-fréquence demeurés sains. La préservation de l'audition au niveau de la bande 4-8 kHz est nécessaire à l'obtention de potentiels précoces normaux aux niveaux supraliminaires.     

Intra-rater variability in low-grade glioma segmentation

Assessment of size and growth are key radiological factors in low-grade gliomas (LGGs), both for prognostication and treatment evaluation, but the reliability of LGG-segmentation is scarcely studied. With a diffuse and invasive growth pattern, usually without contrast enhancement, these tumors can be difficult to delineate. The aim of this study was to investigate the intra-observer variability in LGG-segmentation for a radiologist without prior segmentation experience. Pre-operative 3D FLAIR images of 23 LGGs were segmented three times in the software 3D Slicer. Tumor volumes were calculated, together with the absolute and relative difference between the segmentations. To quantify the intra-rater variability, we used the Jaccard coefficient comparing both two (J2) and three (J3) segmentations as well as the Hausdorff Distance (HD). The variability measured with J2 improved significantly between the two last segmentations compared to the two first, going from 0.87 to 0.90 (p?=?0.04). Between the last two segmentations, larger tumors showed a tendency towards smaller relative volume difference (p?=?0.07), while tumors with well-defined borders had significantly less variability measured with both J2 (p?=?0.04) and HD (p?<?0.01). We found no significant relationship between variability and histological sub-types or Apparent Diffusion Coefficients (ADC). We found that the intra-rater variability can be considerable in serial LGG-segmentation, but the variability seems to decrease with experience and higher grade of border conspicuity. Our findings highlight that some criteria defining tumor borders and progression in 3D volumetric segmentation is needed, if moving from 2D to 3D assessment of size and growth of LGGs.

     

Paediatric auditory brainstem response and pure-tone audiometry: threshold comparisons. A study of 142 difficult-to-test children

Auditory brainstem response (ABR) thresholds have been determined in 142 anaesthetized 'difficult-to-test' children. The stimuli employed were 2-kHz tone bursts. Pneumatic otomicroscopy was carried out prior to the ABR assessment in all cases, and diagnostic myringotomy was performed when there was the slightest suspicion of abnormality. Long-term follow-up pure-tone audiograms were obtained in 56 patients. A comparison was made between ABR and pure-tone thresholds in the 2-4 kHz range both in healthy middle ears and in ears having middle ear effusion (MEE) at the time of ABR measurement. A correction factor for prediction of behavioural threshold from the ABR threshold both in healthy and in MEE ears is proposed.     

Screening for retrocochlear pathology

In 1982, 135 patients were screened for possible retrocochlear pathology, by means of an investigation protocol consisting of caloric test, impedance audiometry and brainstem response audiometry (BRA). A combination of the first two of these procedures had an unacceptably low prognostic accuracy. BRA indicated retrocochlear pathology in 8 and was inconclusive in 4 cases. Enhanced computer tomography revealed an intracranial tumour in 4 of the former, while no space-occupying lesion could be demonstrated in the remainder nor in the 4 patients with inconclusive BRA. BRA is the best single test for screening of this patient category.     

High-frequency audiometry: comparison of electric bone-conduction and air-conduction thresholds

Thresholds have been measured with two commercially available high-frequency (HF) audiometers providing respectively air-conduction (AC) and electric bone-conduction (EBC) stimulation. Normative values for the latter have been obtained, and the reduction of HF sensitivity with both stimulus modes documented in two groups aged 50-59 and 70-79 years. EBC reproducibility is of the same order of magnitude as the AC signal through 14 kHz, while the dynamic range is limited to 50 dB. Lateralization of the EBC signal occurs up to at least 17 kHz. The logarithmic conversion factor of Tonndorf and Kurman [Ann. Otol. Rhinol. Lar. 93: 576-582, 1984] does not result in equivalent AC and EBC thresholds at all frequencies, but does provide similar loudness sensation increases. The 40 log (i) re 1 mA conversion factor must be adjusted with a frequency-dependent additive correction.     

Brain-stem responses of the cat and interaural attenuation.

The early auditory evoked responses have been studied in bilaterally hearing cats, and in animals with hereditary unilateral anacusis. Cross-over stimulation of the hearing ear occurs at an interaural attenuation of 50--50 dB, and all six waves of the responsare present at supra-threshold stimulus levels.     

Hearing in the elderly: a test protocol and preliminary results

Hearing deteriorates with age. ISO 7029 (2000) presents data on hearing threshold as a function of sex and age up to 70 years. There is a need for an extension of these data beyond 70 years. There is also a need for testing the central component of hearing in the elderly. A test protocol was established, and groups of subjects aged 60 to > or = 90 were selected. After a questionnaire and an ear examination, the following tests were performed: air-conduction pure-tone audiometry in the frequency range of 125-16 kHz, tympanometry, speech recognition score in quiet conditions, transient evoked otoacoustic emissions (TEOAE) and cognitive cortical evoked potentials (MMN, P300, N400). Preliminary tests showed the expected age-related reduced hearing sensitivity as seen from the pure-tone audiograms, a lower speech recognition score in the oldest subjects, lack of TEOAE and poor cognitive responses in the elderly. Statistical data will be developed based on the complete material of around 400 subjects.