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PubMedDate not supplied

Histopathological study of the cochlea with altered perilymph metabolism.

In 41 guinea pigs an experiment was conducted to determine the effect of kanamycin on ears with or without blockage of the cochlear aqueduct. In 24 animals the cochlear aqueduct was blocked on one side, and after 1 to 21 days, kanamycin (300 mg/kg) was given daily and subcutaneously until the pinna reflex began to decrease. The remaining animals were used for controls: exposure of and trauma to the aperture of the cochlear aqueduct and kanamycin administration (8), blockage of the cochlear aqueduct only (3 plus 17 previous cases), and kanamycin administration to normal animals (6). The survival time of all these animals was four months. The results showed that ears with blockage of the cochlear aqueduct and kanamycin administration consistently demonstrated a more severe and extensive atrophy of the cochlear sensory cells. The lesions occurred primarily at the basal end and spread toward the apical turn, although the lesions in some specimens jumped from the basal to apical turn. The outer hair cells were more extensively affected than the inner hair cells. Proteinaceous precipitates were often found to be slightly greater in the perilymph of cochleae with blocked cochlear aqueducts. From these observations, it is concluded that the decrease in patency of the cochlear aqueduct will impair perilymph metabolism, causing the cochlear sensory cells at the basal turn to become more vulnerable to noxious substances.

Animals↗
PubMed1980

Later stages of development of the periotic duct and its adjacent area in the human fetus.

The later stages of development (16-40 weeks in utero) of the periotic duct and its adjacent areas in the human fetus indicate that the critical stages of development occur in four specific time related stages over a six-week period (20-26 weeks). First, the petrous apex ossifies to separate th inferior cochlear vein into the canal of Cotugno and forms the medial wall of the cochlear aqueduct (22 weeks); second, the canalicular otic capsule fuses with the cochlear otic capsule to obliterate Hyrtl fissure and forms of the lateral wall of the cochlear aqueduct (24 weeks); third, progressive bone deposition to the medial surface of the membranous labyrinth and cochlea at the petrous apex elongates the periotic duct and cochlear aqueduct (32 weeks in utero); and fourth, active arachnoid tissue ingrowth into the periotic duct occurs at 20-24 weeks and 34-40 weeks in utero. The terminal event is widening of the CNS opening of the periotic duct at 32 weeks in utero. The periotic duct and cochlear aqueduct length increase with gestation from 25 weeks until term. The periotic duct width remains the same throughout the gestation. The cochlear aqueduct width diminishes with gestational age. The periotic duct remains patent throughout 16-40 weeks in utero.

Cochlea↗
PubMed2002

A new classification for cochleovestibular malformations.

OBJECTIVE: The report proposes a new classification system for inner ear malformations, based on radiological features of inner ear malformations reviewed in 23 patients. STUDY DESIGN: The investigation took the form of a retrospective review of computerized tomography findings relating to the temporal bone in 23 patients (13 male and 10 female patients) with inner ear malformations. The subjects were patients with profound bilateral sensorineural hearing loss who had all had high-resolution computed tomography (CT) with contiguous 1-mm-thick images obtained through the petrous bone in axial sections. METHODS: The CT results were reviewed for malformations of bony otic capsule under the following subgroups: cochlear, vestibular, semicircular canal, internal auditory canal (IAC), and vestibular and cochlear aqueduct malformations. Cochlear malformations were classified as Michel deformity, common cavity deformity, cochlear aplasia, hypoplastic cochlea, incomplete partition types I (IP-I) and II (IP-II) (Mondini deformity). Incomplete partition type I (cystic cochleovestibular malformation) is defined as a malformation in which the cochlea lacks the entire modiolus and cribriform area, resulting in a cystic appearance, and there is an accompanying large cystic vestibule. In IP-II (the Mondini deformity), there is a cochlea consisting of 1.5 turns (in which the middle and apical turns coalesce to form a cystic apex) accompanied by a dilated vestibule and enlarged vestibular aqueduct. RESULTS: Four patients demonstrated anomalies involving only one inner ear component. All the remaining patients had diseases or conditions affecting more than one inner ear component. Eight ears had IP-I, and 10 patients had IP-II. Ears with IP-I had large cystic vestibules, whereas the amount of dilation was minimal in patients with IP-II. The majority of the semicircular canals (67%) were normal. Semicircular canal aplasia accompanied cases of Michel deformity, cochlear hypoplasia, and common cavity. In 14 ears, the IAC had a defective fundus at the lateral end. In two ears the IAC was absent. In all seven cases of common cavity malformations, there was a bony defect at the lateral end of the IAC. In five of them the IAC was enlarged, whereas in two the IAC was narrow. All patients with IP-I had an enlarged IAC, whereas in patients with type II disease, four had a normal IAC and 10 had an enlarged IAC. All cases of IP-II had an enlarged vestibular aqueduct, whereas this finding was not present in any of the cases of IP-I. In all cases, the vestibular aqueduct findings were symmetrical on both sides (simultaneously normal or enlarged). No patient demonstrated enlargement or any other abnormalities involving the cochlear aqueduct. CONCLUSIONS: Radiological findings of congenital malformations in the present study suggested two different types of incomplete partition. Cystic cochleovestibular malformation (IP-I) and the classic Mondini deformity (IP-II). The type I malformation is less differentiated than the type II malformation. Classic Mondini deformity has three components (a cystic apex, dilated vestibule, and large vestibular aqueduct), whereas type I malformation has an empty, cystic cochlea and vestibule without an enlarged vestibular aqueduct. Mondini deformity represents a later malformation, so the amount of dysplasia is much less than in type II. Therefore, it is more accurate and useful for clinical purposes to classify these malformations (in descending order of severity) as follows: Michel deformity, cochlear aplasia, common cavity, IP-I (cystic cochleovestibular malformation), cochlear hypoplasia, and IP-II (Mondini deformity). Only in this way can these complex malformations be grouped precisely and the results of cochlear implantation compared.

Child↗
PubMed1993

[Deafness caused by malformation of the inner ear. Current contribution of x-ray computed tomography].

Hearing loss due to malformations of the auditory system may involve morphologic abnormalities of the external canal, the middle ear, or the inner ear. Various combined malformations are possible. Audiologic assessment and computed tomography make it possible to perform a precise diagnostic evaluation of inner ear malformations. In a series of 71 children with congenital sensorineural hearing loss, 31 had computed tomographic evidence of malformations. Since 19 children had bilateral lesions, a total of 50 ears were studied. The cochleovestibular abnormalities were typed and correlated to the severity and progression of hearing impairment. The 3 most frequently encountered malformations were: 1) isolated large cochlear aqueduct (n = 12), 2) large vestibular aqueduct (n = 8) and 3) the Mondini malformation (n = 7). The most severe hearing losses were associated with cochlear hypoplasia and incomplete cochlear segmentation. The severity of hearing impairment decreased with the following abnormalities in the order given: 1) large cochlear aqueduct, 2) Mondini malformation and 3) large vestibular aqueduct. Among the 15 patients with progressive hearing loss, 13 had large cochlear aqueducts either isolated or concomitant with other lesions. While certain evident abnormalities, such as cochlear aplasia or Mondini malformation, are relatively easy to diagnose, other more subtle morphologic changes, such as large cochlear aqueduct, still need to be better defined according to precise criteria for radiographic evaluation.

Child↗
PubMed1990

The influence of acute venous congestion on the guinea pig cochlea.

The effects of sudden occlusion of the vein of the cochlear aqueduct (VCAQ) on the cochlear blood flow, endocochlear potential (EP), endolymphatic and perilymphatic fluid pressures (PE and PP) were studied in the guinea pig. Cochlear blood flow showed a sudden decrease, and EP began to drop within 90 s, ranging from 50 to 70 mV in 5 of 11 animals studied, recovering to normal levels when the animals were placed on a continuous inhalation of carbogen. The PE and PP increased simultaneously (max. PE = 3.4 +/- 1.4 mm Hg; max. PP = 2.5 +/- 1.0 mm Hg) and returned to their initial values after 5 min. The EP was sustained within the normal range, even when there was an apparent decrease in cochlear blood flow (61.4 +/- 8.4%). We believe that variations in EP following VCAQ occlusion were due to anatomical differences in collateral venous communications among the animals studied. Carbogen inhalation produced uniform recovery patterns, indicating that individual collateral vessel responses were eliminated.

Animals↗
PubMed2003

Isolated vestibular ossification after meningitis associated with sensorineural hearing loss.

OBJECTIVE: Sensorineural hearing loss after bacterial meningitis is common. It is thought to be secondary to cochlear inflammation from direct bacterial seeding through the cochlear aqueduct. Although cochlear ossification with or without vestibular involvement is common, isolated vestibular ossification is rare. We review our recent experience with isolated vestibular ossification associated with profound sensorineural hearing loss and the implication for cochlear implantation in this population. STUDY DESIGN: Retrospective case review. SETTING: Academic tertiary referral center. PATIENTS: Patients referred with profound sensorineural hearing loss after bacterial meningitis with evidence of ossified vestibular labyrinth but normal cochleae on computed tomographic scanning were included in the study. INTERVENTIONS We review the history, imaging findings, operative intervention, and operative findings in this series of patients. MAIN OUTCOME MEASURES Clinical history, imaging findings, operative intervention, and operative findings. RESULTS: Three patients with isolated vestibular ossification without computed tomographic evidence of cochlear osteoneogenesis were identified. Two of these patients subsequently underwent cochlear implantation with the Clarion device with complete insertion of the electrode array. Intraoperatively, one patient had isolated scala tympani ossification and the implant electrode array was placed within the scala vestibuli. CONCLUSION: A pattern of sensorineural hearing loss and isolated ossification of the vestibular system without radiographic evidence of cochlear involvement may be seen after bacterial meningitis. In these patients, magnetic resonance imaging scanning should be performed, because computed tomographic scanning may not always detect cochlear ossification. Cochlear implantation is feasible in these patients.

Adult↗
PubMedDate not supplied

Fluid pathways in temporal bones.

Five temporal bones were serially sectioned and studied concerning spread of erythrocytes and blood-derived precipitate in patients who died from subarachnoid hemorrhage. Erythrocytes followed the natural pathways--the cochlear aqueduct, the cochlear, vestibular, facial and glossopharyngeal nerves, and were demonstrable in the inner ear fluid spaces. The temporal bone marrow spaces were also filled with erythrocytes, particularly in the hypotympanal area. In the microimmunoelectrophoresis, no specific precipitation lines formed between the anti-CSF serum from rabbits and middle ear exudate from human ears with acute otitis media. Although, in animals, middle ear spaces have been shown to be connected to the middle ear space this does not seem to apply to human ears, and CSF fluid components are not involved in the formation of middle ear exudate.

Adult↗
PubMed1998

[Progressive sensorineural hearing loss in childhood].

Prevalence of progressive sensorineural hearing loss in childhood seems to be extremely variable, as percentages reported range from 4 to 30%. Differences in the criteria employed for identifying the deterioration, in the groups of patients, and the age range, could explain this wide range of reported figures. The etiology of the progressive sensorineural hearing loss in infants can be hereditary or acquired. Hereditary causes are divided into syndromic and non-syndromic, whereas the acquired causes include congenital or acquired infection (syphilis, cytomegalovirus, rubella virus and toxoplasma infections, bacterial meningitis and acquired viral infections) and congenital inner ear anomalies (Mondini's dysplasia, large vestibular aqueduct, large cochlear aqueduct). Other acquired causes such as disorders of the metabolism, chronic use of ototoxic drugs, autoimmune diseases, perilymphatic fistula and head or acoustic trauma are less common. The age of onset of deterioration shows a great variability because even the congenital hearing losses may occur late after birth. The progressive evolution seems to be binaural in most patients, but more commonly it presents interaural differences, and when the hearing deficit is initially asymmetrical the deterioration is usually greater in the ear which appeared least affected in the first audiogram. Furthermore, at the different frequencies, there is a tendency to a greater deterioration at the frequencies initially least affected, but some authors are not in agreement because they report a uniform pattern of progression in the range of 0.5 to 4 kHz with no modification of the audiometric shape in most of the examined patients.

Child↗
PubMed2002

Inner ear pressure changes following square wave intracranial or ear canal pressure manipulation in the same guinea pig.

Inner ear pressure was measured in scala tympani with a micropipette during square wave pressure manipulation of the intracranial compartment and, subsequently, of the external ear canal (EEC) in the same guinea pig. As expected, the combination of the cochlear aqueduct and the inner ear behaves as a low-pass filtering system for intracranial pressure manipulation and as a complementary high-pass system for ear canal pressure manipulation. Time constants for pressure equalization were in the order of seconds and depended on the direction of flow through the cochlear aqueduct. Pressure equalization curves could not be fitted to a single exponential function; more complicated functions were needed for good fits, showing that the pressure equalization process is nonlinear. This means that the flow resistance of the cochlear aqueduct and/or the compliance of the cochlear windows is not constant, which is in accordance with a flow-direction dependent resistance of the cochlear aqueduct. An explanation for this can be found in the special structure of the periotic duct inside the aqueduct.

Animals↗
PubMedDate not supplied

Transmission of complex pressure waves through the perilymphatic fluid in cats.

The response of the perilymphatic fluid to complex pressure waves, composed of low-frequency sine waves superimposed on square-wave pressure pulses of varying amplitude was studied. In cats with a patent cochlear aqueduct a pronounced positive pressure change could be induced in the perilymphatic fluid when complex pressure waves were used. The time constants associated with the stabilization of the perilymphatic pressure after the application of pressure complexes were longer than those associated with square-wave pulses alone. The results indicate that the functional patency of the cochlear aqueduct could be influenced by the transmission of complex pressure waves. The results also indicate that when trying to influence the inner ear hydrodynamic balance in patients with Meniere's disease, the effect of complex pressure waves is far superior to the effect of square-wave pressure pulses in patients with an open cochlear aqueduct.

Animals↗