Toshihiro Tsuzuku

Auditory Nerve Disease of Both Ears Revealed by Auditory Brainstem Responses, Electrocochleography and Otoacoustic Emissions

We report on two patients who showed absence of auditory brainstem response (ABR) but broad compound action potentials on electrocochleograms and almost normal otoacoustic emissions, together with absence of caloric response and preservation of per rotatory nystagmus for both ears. Patient 1, a 53-year-old woman, had noted auditory and vestibular problems since the age of 15 years, and Patient 2, a 68-year-old woman, had noted problems of the same age of 30 years. They could hear words and understand sentences if spoken slowly, but they could not discriminate monosyllables very well. Their auditory examinations disclosed mild threshold elevation in pure-tone audiometry and markedly poor scores in speech audiometry and good scores in auditory comprehension test. They were diagnosed as having auditory nerve disease of unknown cause.

Delayed motor function and results of vestibular function tests in children with inner ear anomalies

The relation between the results of vestibular function tests and gross motor development was examined in 4 children with inner ear anomalies. CT scans demonstrated the absence of lateral semicircular canals in both ears in all 4 cases. None responded to caloric stimulation using 40 ml of icewater. In contrast, the damped rotation test elicited per-rotatory nystagmus in all cases. Per-rotatory nystagmus was provoked in only two cases by the Bárány rotation test. Development of gross motor function, especially independent walking, was more delayed in the two children in whom the Bárány rotation test failed to elicit per-rotatory nystagmus.

P300 response to tones and speech sounds after cochlear implant: A case report

P300 potentials evoked by tones and spoken words were recorded from a 20‐year‐old man with a House‐3M® single‐channel cochlear implant. Three months after cochlear implantation, there was a slight appearance of P300 response to both pure‐tone stimuli and spoken‐word stimuli; 6 months later, clearly identifiable P300 response to both pure‐tone stimuli and spoken‐word stimuli were obtained. These results are consistent with an encoding improvement for re‐establishment of information processing after auditory rehabilitation.

Girl with accelerated growth, hearing loss, inner ear anomalies, delayed myelination of the brain, and del(22)(q13.1q13.2).

We report on an 18-month-old Japanese girl with 46,XX,del(22)(q13.1q13.2). To our knowledge, this is the first report of a case of interstitial deletion of a 22q13.1-q13.2 segment. Clinical features included hearing loss accompanied by inner ear anomalies, hypotonia and minor anomalies, such as a long philtrum, full eyelids, epicanthus, left transverse palmar crease and psychomotor developmental delay. Despite the chromosomal deletion, her physical growth was accelerated: her height was between the 75th and 90th percentiles for her age. Her brain MRI showed signs of delayed myelination. The three-dimensional MRI of the inner ear showed abnormalities of the cochlea and vestibule in both ears. Clinical features of the patient are similar to those of a patient with a del(22)(q13.1q13.33) karyotype previously reported by Romain et al.

Temporal Bone Findings in Keratitis, Ichthyosis, and Deafness Syndrome Case Report

In 1981, the term KID syndrome was suggested for patients with congenital ichthyosis associated with deafness and keratitis. We had a chance to examine the temporal bone of an infant with this syndrome. This patient showed no auditory brain stem response in either ear. Temporal bone studies revealed cochleosaccular abnormality. These findings are offered as a possible explanation for the patients deafness. The pathologic inner ear findings of congenital deafness syndromes associated with ichthyosis have been heretofore reported in Refsums syndrome and in a case with universal alopecia. In these cases, the temporal bone pathologic findings were a result of cochleosaccular abnormality. From our case and previous reports, it is suggested that the deafness associated with congenital ichthyosis might be the result of cochleosaccular abnormality.

40-Hz Steady State Response in Awake Cats After Bilateral Chronic Lesions in Auditory Cortices or Inferior Colliculi

To reveal the generators of 40-Hz steady state response, the following investigations in awake cat were performed: (i) analyses of 40-Hz SSR without any lesions, and study of stimulus rate; (ii) effect of chronic lesions in the bilateral auditory cortex; (iii) effect of chronic lesions in the bilateral inferior colliculus. The maximum amplitudes were obtained at stimulus rates of 40-50 Hz. In cat with lesions in the bilateral auditory cortex, the wave configurations and the phase were retained but the amplitude was reduced to 90%. In cat with lesions in the inferior colliculus, the wave configurations and the phase were retained but the amplitude was reduced to 60%. These data suggest the following conclusions: (i) cat was a suitable animal model for humans 40-Hz SSR; (ii) the auditory cortex could be one of the generators of 40-Hz SSR; (iii) the inferior colliculus could be an important generator of 40-Hz SSR; (iv) 40-Hz SSR seems to be generated through not only primary auditory pathways, but also nonspecific auditory pathways, which receive auditory information in parallel from the brainstem, thalamus, and cerebrum.

Tuberculous meningitis-induced unilateral sensorineural hearing loss: a temporal bone study

The relationship between meningitis and sensorineural hearing loss (SNHL) has long been studied. Many histopathological studies of animal models and human temporal bones with respect to bacterial meningitis have been carried out. However, the relationship between SNHL and tuberculous meningitis was seldom addressed and the pathophysiology remains unclear. We carried out temporal bone studies on material from a 22-year-old patient who developed a right unilateral SNHL before dying from tuberculous meningitis. The histopathological findings for the right temporal bone were as follows: (1) inflammation mainly appeared in the internal auditory canal, modiolus and Rosenthals canal and extended to the osseous spiral ligament, whereas the perilymphatic spaces were less involved; (2) the organ of Corti, cochlear nerve fibres and spiral ganglion cells were severely degenerated, particularly in the basal and middle turns; (3) the contralateral side (for which the patient had no complaints) showed an inner space free from inflammation, but some granulomatous formations were observed in the middle ear cavity. We conclude that the modiolus and cochlear aqueduct are the main routes for the spread of infection from the meninges to the inner ear. The progression of hearing loss resembles that of bacterial meningitis and shares attributes of retrocochlear SNHL.

Analysis of auditory brain stem response with lidocaine injection into the cerebrospinal fluid in rats.

Auditory brain stem response (ABR) was recorded in 10 rats with total spinal anesthesia induced by injection of 2% lidocaine hydrochloride into the subarachnoid space through the skull. The ABR disappeared immediately (within 4 minutes) after the injection of 13.3 to 40.0 mg/kg lidocaine. The disappearance started with the later waves of the ABR. After cessation of the injection, the ABR reappeared and recovered progressively from wave I to wave IV. The effect of lidocaine on the ABR was reversible and extended in the acoustic nerve to the midbrain.

Effects of primary auditory cortex lesions on middle latency responses in awake cats.

In order to clarify the role of the primary auditory cortex (AI) on middle latency responses (MLRs), we recorded the auditory evoked potentials (AEPs) from the vertex and the right and left AI areas of the skull simultaneously before and after creating serial lesions of the AIs contralateral and ipsilateral to the stimulated ear in 7 awake cats. The auditory brainstem responses (ABRs) and MLRs recorded from the vertex in normal awake cats revealed the presence of peaks 1-8, NA and PA within the analysis time of 50 msec. After there were serial AI lesions, (1) all the peaks remained at nearly the same latencies, (2) the amplitude of the NA was decreased significantly, that of the PA was slightly decreased and those of peaks 6, 7 and 8 were variable, and (3) the difference between the effects of the first operation (contralateral AI) and the second operation (ipsilateral AI) was not statistically significant. These findings indicated that the main, prominent effect of bilateral AI lesions on MLRs in the awake cat is a significant decrease in the NA amplitude.

Comparison of duration of deafness and tumour invasion to the inner ear from metastatic tumours of the internal auditory canal: human temporal bone pathology.

Four cases (seven ears) of metastatic tumour of the internal auditory canal were studied. The histopathological findings confirmed that the inner ear invasion of the tumour follows a unique course, as reported in the literature. Relationship between duration of deafness and extent of tumour invasion in the inner ear is discussed. It is suggested that the deafness could occur via neural invasion or compression near the ductus spiralis foraminosus.