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PubMed1984

Defense mechanism of the cochlear aqueduct against infection. A morphological study in the guinea pig.

Guinea pigs were used in this study. Physiological saline, india ink, and Staphylococcus aureus were injected into the cisterna magna, and S. aureus was also injected into the scala tympani. Changes in the microstructure of the cochlear aqueduct were observed by light microscopy and also by scanning electron microscopy, mainly by means of fracture preparations. From these experimental results, it could be confirmed that the periotic duct tissue of the cochlear aqueduct reacted especially to bacterial infection.

Animals↗
PubMed1991

Autoregulation of inner ear blood flow in normal and hydropic guinea pigs.

Inner ear and brainstem blood circulation was measured by three different techniques: the laser Doppler (LD), hydrogen clearance (HC) and oxygen tension (PO2) measurements, while systemic blood pressure (BP) was modulated by norepinephrine infusion or removal of whole blood. Results were as follows: (i) The blood flow (BF) change determined by LD correlated well with that measured by HC and PO2 techniques; (ii) BF in the brainstem was maintained constant in the BP range of 35 to 80 mmHg; however, inner ear BF showed a poor autoregulatory function relative to the change of systemic BP; (iii) although the change of BF was similar for cochlea and semicircular canal the amount of PO2 decrease for lowered BP was significantly less in the cochlea than in the canal; (iv) in guinea pigs with unilaterally obliterated endolymphatic sac and duct, the decrease in cochlear BF was larger on the operated side than on the intact side. This suggests that the autoregulatory function for BF is impaired in the hydropic ear.

Animals↗
PubMed2005

Advantages of magnetic resonance imaging over computed tomography in preoperative evaluation of pediatric cochlear implant candidates.

OBJECTIVES: To compare magnetic resonance imaging (MRI) to high-resolution computed tomography (HRCT) in the preoperative evaluation of pediatric cochlear implant candidates. METHODS: The charts of pediatric cochlear implant candidates evaluated between July 1, 2000 and November 30, 2003 with an MRI scan of the inner ear were included in the study. Fifty-six patients were included. Associated HRCT scans were examined. Abnormalities of the cochlea, cochlear nerve, endolymphatic sac, endolymphatic duct, vestibule, and modiolus were noted. A pediatric neuroradiologist gave an opinion as to whether patients with anomalies seen with MRI but without associated HRCT would have been identified by HRCT. RESULTS: Of the 112 temporal bones imaged with MRI, the following abnormalities were encountered: 32% (36/112) had abnormalities of the cochlear turns, 30% (34/112) had abnormal signal in the modiolus, 23% (26/112) had abnormal vestibulae, 16% (18/112) had abnormal endolymphatic ducts, 15% (17/112) had abnormal endolymphatic sacs, 12% (13/112) had abnormalities of the cochlear nerves, 29% (17/56) had abnormalities of the brain. HRCT cannot directly evaluate the cochlear nerve. Available HRCT findings were combined with radiologic opinion and compared with MRI findings. The percentages of abnormalities identifiable by HRCT when compared with those seen with MRI are cochlea 42% (15/36), modiolus 35% (12/34), vestibulae 88% (23/26), endolymphatic duct 100% (18/18), and endolymphatic sac 6% (1/17). CONCLUSION: MRI is more sensitive and specific in diagnosing soft tissue abnormalities in the inner ear than HRCT in cochlear implant candidates (Fig. 4). Moreover, the abnormalities detected with MRI are more likely to influence the implantation process (e.g., asymmetric nerve aplasia, cochlear obstruction). (Figure is included in full-text article).

Child↗
PubMed1997

[A case of hearing loss caused by overdrainage of cerebrospinal fluid after ventriculo-peritoneal shunting procedure].

We describe a case of intracranial hypotension syndrome due to overdrainage of cerebrospinal fluid presented with hearing loss after ventriculoperitoneal shunting procedure. A 69-year-old man suffering from subarachnoid hemorrhage presented with an angiogram showing two aneurysms, one of the right internal carotid and one of the middle cerebral artery. Neck clipping was performed. One month later, he developed normal pressure hydrocephalus (NPH), which was treated by ventriculoperitoneal (NPH), which was treated by ventriculoperitoneal shunting procedure using low pressure Pudenz system. Trias of NPH were improved by insertion of shunt system. However, he complained of hearing loss which was worsened by upright position and improved by lying down. Such kinds of phenomenon were demonstrated by audiogram showing that the transitory decrease of hearing and electrocochleography showing the elongation of N1 latency at upright position. These data suggested that his hearing loss was caused by inner ear or auditory nerve lesion. After the shunt system was replaced into the antisiphon device, his hearing disturbance improved. Axial computed tomography of bone window at the level of orbitomeatal line demonstrated widely perilymphatic duct on both sides. This finding suggested that the fluctuation of intracranial pressure was easily transmitted into the cochlear through the widened perilymphatic duct, resulting in hearing disturbance.

Aged↗
PubMedDate not supplied

Functional and morphological changes in experimental endolymphatic hydrops.

Electrocochleograms (ECochG) in response to tone bursts and electronystagmograms (ENG) during sinusoidal rotational stimulation were monitored in guinea pigs equipped with chronically implanted round-window and periocular electrodes before and for as long as 90 days after uni- or bilateral surgical obliteration of the endolymphatic duct. The presence of cochlear and saccular endolymphatic hydrops was verified during microdissection of the inner ear, and cochlear hair cell counts were performed in some of the animals. The results indicate that in surgically-induced endolymphatic hydrops, cochlear and vestibular changes occur similar to those observed clinically in Menière's disease: fluctuant threshold shifts, threshold elevation at low frequencies, sensorineural loss at all frequencies with recruitment, increase in the ratio of summating potential to compound action potential (SP/CAP), asymmetry and recruitment in the ENG, and increased vestibular excitability, with occasional post-rotational and spontaneous nystagmus. Functional changes could not be clearly correlated with those seen by light microscopy, since hair cell loss was confined mainly to the apical coil. The observations indicate that the guinea pig with surgically-induced endolymphatic hydrops can be a useful model of Menière's disease, not only on morphological grounds, but also on the basis of functional changes, which over the relatively short term of observation represent a dysfunction rather than a loss of sensorineural structures.

Animals↗
PubMed1991

Computer-aided three-dimensional reconstruction of guinea pig cochlear aqueduct.

A computer-aided method of three-dimensional reconstruction was applied to the determination of the overall spatial configuration of the guinea pig cochlear aqueduct. The rotation function of the reconstructed images was useful in showing the individual small parts of the duct. A semi-translucent display of the segmental reconstruction of the duct demonstrated a difference in the density of the cellular components between the opening to the perilymphatic space and the duct portion. We propose that the cochlear aqueduct serves as a protective mechanism against a sudden change in CSF pressure in the subarachnoid space.

Animals↗
PubMed1989

[Cochlear aqueduct].

The morphology and structure within the cochlear aqueduct have been investigated on the basis of a histological analysis of 234 temporal bones ranging from 12-week old to adult. Barrier membrane was found in 28.6% of the temporal bones examined, and fibrous reticular tissues of the inner opening of the cochlear aqueduct in 38.1% of the temporal bones. No any tissue in the inner opening of the cochlear aqueduct was seen in 33.3%. Periotic duct was filled with loose reticular tissue. The clinical significance of contents in the cochlear aqueduct was discussed.

Adult↗
PubMed1975

Trisomy 18. A temporal bone report.

Since Edwards first described the trisomy 17-18 syndrome in 1960, the findings in the temporal bones of only four patients with this condition have been reported. They varied widely, ranging from a normal temporal bone, to severe malformations of both the middle and inner ear structures. This study describes the temporal bone findings in a patient with this syndrome. Many of the abnormalities described previously were present as well as the following unreported findings: complete bony atresia of the external canal, an aberrant tensor tympani muscle that did not insert into the malleus but rather attached to a dehiscent area in the Fallopian canal, wide short utricular and saccular ducts, and a widely patent cochlear aqueduct. There was also a developmental arrest of the membranous structures within the cochlea that probably occurred during the 12th week of fetal life.

Autopsy↗
PubMed1997

Inhibition of experimentally induced endolymphatic hydrops by middle ear ventilation.

The tympanic membrane was perforated (n = 19) or a tube was inserted into the middle ear through the wall of the tympanic bulla (n = 6) immediately after blockage of the endolymphatic duct in guinea pigs. Total cochlear endolymph volume and volumes in each cochlear turn were determined from serial sections of the temporal bones and volume changes were analyzed statistically by comparison with hydropic controls without treatment (n = 12). Results showed that both middle ear ventilation procedures significantly reduced the subsequent development of endolymphatic hydrops. This inhibition of hydrops was presumed to be due to pressure release into the middle ear and/or improved oxygenation of the middle and inner ears. Findings suggest the possible merit of a tympanostomy as a treatment for Meniere's disease in carefully selected patients refractory to medical management.

Animals↗
PubMed2000

A macro-mechanical model of the guinea pig cochlea with realistic parameters.

The post-mortem transfer function of the cochlea of the guinea pig was compared to the transfer function generated by a model with parameters derived from physical measurements of the guinea pig cochlea. Both the formulation and parameters of the model were carefully chosen to be realistic using evidence from published measurements. The fit between the transfer function of the model and recent mechanical measurements of the passive guinea pig cochlear response was good, with a root mean square ratio of 6.3 dB in amplitude and 0.33 pi rad in phase. The model was used to explore the effect of cochlear partition mode factor and duct geometry upon the mechanical response of the cochlea. Possible inadequacies of the model which could explain the remaining differences between the output of the model and measurements are discussed.

Animals↗
PubMed1995

Advanced techniques in magnetic resonance imaging in the evaluation of the large endolymphatic duct and sac syndrome.

The purpose of this report is to compare temporal bone computed tomography (CT) to high-resolution magnetic resonance (MR) imaging using a novel thin-section fast spin echo (FSE) pulse sequence in identifying and characterizing patients with large vestibular aqueduct syndrome. Sixteen patients with sensorineural hearing loss and a CT diagnosis of large vestibular aqueduct(s) underwent high-resolution fast spin echo magnetic resonance imaging with dual, 3-in phased array receiver coils centered over the external auditory canals. Magnetic resonance imaging parameters included axial and oblique sagittal fast spin echo with an effective slice thickness of 1 mm contiguous. Thirty-eight patients with 76 normal inner ears who underwent MR imaging using this technique had their endolymphatic duct measured. MR alone identified the enlarged endolymphatic sac seen along with the large endolymphatic duct in all cases. Three cases (five inner ears) with enlarged bony vestibular aqueducts on CT showed no evidence of endolymphatic duct or sac enlargement on MR. MR alone identified a single case of mild cochlear anomaly in conjunction with an enlarged endolymphatic duct and sac. In the normal population the size of the normal endolymphatic duct at its midpoint measured from 0.1 to 1.4 mm. Thin-section, high-resolution fast spin echo MR imaging of the inner ear may be superior to CT in the evaluation of patients with the large vestibular aqueduct syndrome.

Adolescent↗
PubMedDate not supplied

Cochlear blood flow in endolymphatic hydrops.

There is no animal model for Meniere's disease but by obliteration of the endolymphatic duct, endolymphatic hydrops may be achieved in several animal species. In order to measure the cochlear blood flow in ears with endolymphatic hydrops the endolymphatic duct was obliterated in 9 guinea pigs. The blood flow was measured with the microsphere method and the cochlear histology was studied. The regional and total blood flow was determined in the serially sectioned cochleas 2, 4 and 8 months after obliteration of the endolymphatic duct. No change in regional or total cochlear blood flow was observed in the hydropic ears.

Animals↗
PubMed2000

Congenital sensorineural hearing loss and enlarged endolymphatic sac and duct: role of magnetic resonance imaging and computed tomography.

During the past 20 years, there have been significant advances in cochlear implants as the treatment of choice for profoundly hearing-impaired children. The increasing application of cochlear implant has brought with it an increase in the investigational use of computed tomography and magnetic resonance imaging. In this article, the author reviews (a) the anatomy and embryology of the inner ear, (b) the pathological changes associated with congenital sensorineural hearing loss (SNHL), and (c) the spectrum of imaging findings in patients with SNHL.

Child↗
PubMed1979

The effects of vascular occlusion on the human inner ear.

Occlusion of the anterior vestibular artery has resulted in severe degeneration and new bone formation limited to the utricle, saccule, and superior and lateral semicircular canals. Depriving the inner ear of its main blood supply, i.e. the internal auditory artery, has resulted in severe degeneration and ossification of the entire membranous labyrinth, except the endolymphatic duct and sac. A more severe cochlear sclerosis was seen when both arterial and venous blood supplies to the cochlea were occluded. The implications of these findings on the etiology and management of inner ear disorders are emphasized.

Adult↗
PubMed1979

Effects of local application of ototoxic antibiotics on cochlear potentials in guinea pigs.

The effects of neomycin, kanamycin and dihydrostreptomycin on the cochlear microphonic, the action potential of the auditory nerve and the endocochlear potential were studied in guinea pigs in which these drugs were locally administered by perfusion. These drugs suppressed the cochlear responses markedly when applied to the endolymph but were less effective when applied to the perilymph. The mechanisms of action of antibiotics on the hair cells of the organ of Corti are discussed.

Action Potentials↗
PubMed1984

Electrophysiological measures of cochlear function in guinea pigs with long-term endolymphatic hydrops.

Experimental endolymphatic hydrops was induced in guinea pigs by obliteration of the endolymphatic sac and duct. From 3 to 24 months after this operation, cochlear action potential (AP) audiograms and AP tuning curves were measured. The purpose of this study was to establish parallels, if any, between this supposed animal model of Menière's disease and the auditory symptoms of the disease in man. In some animals, low and middle frequency AP threshold elevations were observed whilst higher frequency regions maintained normal sensitivity. Other animals developed flat or very gradually sloping AP audiograms. These patterns are qualitatively similar to those found clinically in Menière's disease. AP tuning curves measured in frequency regions of threshold elevation indicated a deterioration of cochlear frequency selectivity; psychophysical and electrocochleographic studies demonstrate related changes in Menière's patients. One animal exhibited modifications in AP thresholds and tuning as a result of glycerol administration. These observations improve our confidence in the validity of this animal model for further studies of the pathophysiology of Menière's disease.

Action Potentials↗
PubMedDate not supplied

Endolymphatic sac obstruction. Biochemical studies.

Inner ear fluids were studied biochemically in guinea pigs from 1 to 16 weeks after producing endolymphatic hydrops by obstructing the endolymphatic duct. Fluid collected from beneath the footplate showed changes of 50% of the animals indicating distension of the saccule. There was an increase in potassium concentration and decrease in sodium concentration of the collected fluid, indicating a traumatic mixing of endolymph and perilymph produced by rupture of the saccule during collection of the fluid. The smallest changes occurred at one week, and the greatest changes were found four months after endolymphatic sac obstruction. Similar findings were observed in studying inner ear fluids obtained from patients with Ménière's disease. Cochlear endolymph showed biochemical alterations after endolymphatic duct blockage. There was a two- to three-fold increase in sodium concentration and a decrease in potassium concentration with the total ionic concentration remaining approximately the same. Some guinea pigs showed similar changes in vestibular endolymph. This study indicates that in the guinea pig, endolymph obtained in the distended endolymph compartment has a slightly different sodium-potassium ratio as compared to the normal ear. In patients with Ménière's disease there may also be an elevation of endolymph sodium concentration. The significance of this change and hearing loss observed in experimental endolymphatic hydrops and Ménière's disease is open to speculation at the present time.

Animals↗