21/54. Pure word deafness. Two cases of pure word deafness, both with bilateral temporal lobe lesions due to cerebrovascular disease, are presented. This rare disorder is briefly discussed. ( info) |
22/54. Cortical auditory disorders: clinical and psychoacoustic features. The symptoms of two patients with bilateral cortical auditory lesions evolved from cortical deafness to other auditory syndromes: generalised auditory agnosia, amusia and/or pure word deafness, and a residual impairment of temporal sequencing. On investigation, both had dysacusis, absent middle latency evoked responses, acoustic errors in sound recognition and matching, inconsistent auditory behaviours, and similarly disturbed psychoacoustic discrimination tasks. These findings indicate that the different clinical syndromes caused by cortical auditory lesions form a spectrum of related auditory processing disorders. Differences between syndromes may depend on the degree of involvement of a primary cortical processing system, the more diffuse accessory system, and possibly the efferent auditory system. ( info) |
23/54. Audiological rehabilitation of patients with brainstem disorders. A brief account is given of the course of rehabilitation of three patients with severe brainstem injuries. Particular use has been made of synthetic speech pattern assessment procedures which have been integrated into the management model of Goldstein and Stephens (1981). The use of speech stimuli of controllable simplicity has two main clinical benefits: the early course of re-acquisition can be examined analytically, second, aspects of speech receptive and productive rehabilitation can be facilitated. Re-acquisition of perceptive ability in some of these patients may follow a progression from simple to complex acoustic pattern contrasts and this may provide an effective basis for future techniques of rehabilitation. ( info) |
24/54. Is preservation of hearing in acoustic neuroma worthwhile? In a series of 300 translabyrinthine removals of acoustic neuromas, comprising almost all tumours operated on in denmark during a period of 10 years, the preoperative hearing in the tumour ear and in the contralateral ear was analysed in 72 patients with tumours smaller than 2 cm in extrameatal diameter. These patients constitute likely candidates for a hearing preserving operation via the suboccipital approach. In the tumour ear in 4 patients there was a pure-tone average (PTA) of 0-20 dB and a discrimination score (DS) of 81-100%. Applying this criterion to the whole series, 1% of the patients would be candidates for a hearing preserving procedure. Changing the criterion to a PTA of 0-40 dB and a DS of 61-100%, the number of candidates would increase to 8 patients (3%), and with a PTA of 0-50 dB and a DS of 51-100% 14 candidates (5%) would have been found. In all of these patients, contralateral hearing was normal (SRT 0-20 dB, DS 95-100%). Since preservation of hearing would be achieved in only half of those subjected to suboccipital removal and since the hearing retained in patients with successful operations is generally poorer than the preoperative level, the number of patients obtaining serviceable hearing is so modest that preservation of hearing cannot be considered an argument in favour of suboccipital tumour removal. It should be borne in mind that contralateral hearing is normal in these patients and that, according to most reports, the mortality rate is higher and paralysis of the facial nerve more frequent with the suboccipital approach than with the translabyrinthine procedure. ( info) |
25/54. Psychoacoustic and electrophysiologic correlates of central hearing disorders in man. Evaluation of central hearing disorders in neuropsychologic patients is handicapped by their insufficient ability to describe auditory deficits and by the lack of easily applicable audiological tests. A novel psychoacoustic discrimination test (PDT) was developed to determine ear asymmetries in the discrimination of changes in intensity, frequency, or temporal structure of regularly presented dichotic stimuli. In 19 of 21 patients with lesions of the auditory cortex or the acoustic radiation according to CT scan evaluation a higher error score was observed for target stimuli presented at the ear contralateral to the side of brain infarction (6 right, 15 left). In the remaining 2 and in 3 other patients with lesions sparing auditory structures no significant ear asymmetries were seen. This may indicate that auditory perception is reduced in patients with only one intact auditory cortex or one intact acoustic radiation, possibly because of a limitation in information processing capacity. Auditory evoked potential results are presented for a normal subject and two patients to illustrate electrophysiologic correlates of central hearing disorders. Using a transformation of scalp into dipole source activity (Scherg and von Cramon 1986), a unilateral loss of middle latency activity was found in case A, who had a lesion of the left acoustic radiation. The extended lesion of the right auditory cortex in case B resulted in a loss of both middle and late latency dipole source potentials of the right temporal lobe. In both cases a corresponding increase in the PDT error score on the contralateral ear was found. ( info) |
26/54. Neurological aspects of infant hearing assessment. The relationship between the results of an infant hearing screening program and neurological impairment may be considered in two ways: 1) Is there a correlation between incidence of neurological dysfunction and the incidence of sensorineural hearing loss in the target population? In our target population, the incidence of sensorineural hearing impairment was 3.13% for the group with a positive neurological history vs. 1.3% in those with a negative neurological history. 2) Do auditory evoked potentials used for hearing screening and follow-up provide any additional information on the neurological status of the target population, or, are certain neurological conditions associated with certain typical auditory evoked potential configurations? In our experience auditory evoked responses do provide additional information especially if for diagnostic purposes both the brainstem and the later components are considered. Often, specific neurological problems may be associated with typical auditory evoked response configurations. ( info) |
27/54. Neuroradiologic evaluation of patients with central auditory lesions. CT and MR imaging have revolutionized diagnostic medical imaging. MR scanning in particular is the method of choice to evaluate the CP angle lesion or other posterior fossa lesion. With CT pneumocisternography, neurovascular structures of the internal auditory canal and lesions can be visualized. Experience indicates that MR scanning will replace CT. ( info) |
28/54. A neurologist's approach to a patient with hearing impairment. This article is a review of the central auditory pathways from an anatomic and clinical perspective. An approach to the assessment of patients with hearing impairment of central origin is provided. The review of the patient's history, physical examination, and laboratory assessment are dealt with in detail. ( info) |
29/54. The use of subjective and objective audiologic test procedures in the diagnosis of multiple sclerosis. The necessity of using a test battery approach in the diagnosis of the MS patient is described. The objective and subjective audiologic test procedures complement each other by implicating different CNS sites influenced by the demyelinating process. Since two or more central lesions must be demonstrated to confirm a diagnosis of MS, different audiometric test procedures, sensitive to dysfunction at various CNS levels, are vital. The multi-sensory evoked-response procedures have been particularly helpful in revealing subclinical abnormalities. Researchers do advocate, however, inclusion of other neuro-otologic test procedures, such as detailed auditory and vestibular testing, interaural time discrimination, and localization testing as part of the diagnostician's test battery. ( info) |
30/54. Auditory Brainstem Response audiometry. Applications in central disorders. ABR is the most sensitive and specific test in the audiology battery for detecting disorders that affect the brainstem. When combined with central speech audiometry, ABR can detect most intra- and extra-axial tumors, demyelinating lesions, and polyneuropathies that affect brainstem auditory structures. Alone, it is a promising tool for monitoring neural maturation, tumor growth, coma, and neurologic or vascular therapies. The test can be severely compromised by peripheral hearing loss and knowledge of the audiogram is a prerequisite for any central testing application of ABR. Six cases of intra- or extra-axial brainstem pathology are described here. ABR results were abnormal in all but one case, based on response latency measurements. In two cases, ABR was the only audiologic test that detected the abnormality. In general, ABR was sensitive to and conventional tests were insensitive to central lesions involving the eighth nerve. ABR abnormalities were not in themselves sufficient to define the precise site of the lesion, nor could they determine the kind of lesion present. However, they were indicative of the level and extent of direct involvement by the disease process or of the pressure and distortion effects of the lesion on the brainstem. In one case where ABR failed to detect the lesion, central speech testing was abnormal. The potential usefulness of ABR to monitor brainstem status is emphasized. A case is described where ABR provided valuable information on the effects of an experimental embolic therapy for AVM. Special precautions are described for monitoring ABR in neonates. ABR is an important screening test for the detection of brainstem disorders, especially those that cannot be detected radiographically. Its greatest use, however, may prove to be as inexpensive and noninvasive monitor of brainstem status in patients with confirmed or suspected brainstem disorders. ( info) |