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PubMed1985

Deterioration of auditory evoked potentials during cerebellopontine angle manipulations. An interpretation based on an experimental model in dogs.

Evoked action potentials from the internal auditory meatus portion of the cochlear nerve (IAM-EAP's) and brain-stem auditory evoked potentials (BAEP's) from the vertex were simultaneously recorded during cerebellopontine angle (CPA) manipulations (retractions of the cerebellar hemisphere and the cochlear nerve) in dogs. The BAEP changes noted in these dogs were the same as those seen in patients. The IAM-EAP's showed graded deterioration related to BAEP changes. The results are as follows: Prolongation of the I-V interpeak latency of BAEP's, the most common finding during CPA manipulations, is the reflection of prolongation of the I-II interpeak latency, which is caused by conduction impairment or block of the nerve impulses between the extracranial portion of the cochlear nerve and the brain stem. The operative manipulations representing stretch or compression injury to the cochlear nerve in the CPA leads to an acute traumatic cranial nerve root lesion--a retrocochlear lesion. The obliteration of all BAEP components including wave I cannot be caused by conduction block. This is caused by occlusion of the internal auditory artery. Wave I of the BAEP's and the P1-N1 complex of the IAM-EAP's are important indicators of cochlear blood flow during surgical intervention. As possible causes of internal auditory artery obstruction, mechanical distortion of the relationship between the anterior inferior cerebellar artery (AICA) and the internal auditory artery at the junctional portion, mechanical vasospasm of the AICA-internal auditory artery complex, and ensuing no-reflow phenomena are discussed. Evoked action potentials are expected to be a useful intraoperative real-time monitor during CPA surgery that can detect rapid changes derived from cochlear artery insufficency. The real-time aspects can overcome some of the disadvantages of BAEP monitoring.

Animals↗

PubMed1988

Damage of the peripheral auditory system after operations in the cerebellopontine angle. A scanning electron-microscopic observation in dogs.

Cochlear nerve injuries caused by manipulations in the cerebellopontine angle were electrophysiologically and morphologically investigated in dogs. Operative procedures similar to those performed in the cerebellopontine angle of humans were applied in dogs. Auditory-evoked potentials were recorded throughout the experiments. Postoperatively, the temporal bones were studied with a scanning electron microscope. The portions of the cochlear nerve fibers and branches of the internal auditory artery that exit from the bony cochlea into the internal auditory canal were susceptible to traction force derived from manipulations in the cerebellopontine angle. The cochlear nerve fibers from the basal turn of the cochlea were most easily pulled out from the fundus of the internal auditory canal. In some cases, massive hemorrhages and exudation of plasma were observed in the entire modiolus; these compressed the cochlear nerve trunk. The Schwann-glial junctions of the cochlear nerves were separated in some dogs, indicating this junction was one of the most vulnerable sites to operative manipulations in the cerebellopontine angle.

Animals↗

PubMed1977

Sudden deafness and facial palsy from metastatic bronchogenic carcinoma.

A 52-year-old man developed sudden total bilateral deafness, and unilateral facial palsy, without other symptoms and findings. He died two months later of of bronchogenic carcinoma metastatic to dura, brainstem, pons, carebellopontine angle, cerebellum and cranial nerves III, VI, VII and VIII. There was bilateral internal auditory canal erosion. Tumour replaced right facial, acoustic and vestibular nerves. Tumour infiltrated spiral ganglion, cochlear nerve, cochlear aqueduct, and destroyed nearly all facial nerve fibres to the level of the stapedius muscle. No tumour cells were found on the left, but few fibres of facial, acoustic and vestibular nerves survived. Both ears showed some cochlear outer hair cell destruction. Metastatic tumour to temporal bone or dura should be considered when loss of peripheral VIIth or VIIIth nerve function occurs.

Brain Neoplasms↗

PubMed1996

Influence of blood supply, thermal and mechanical traumata on hearing function in an animal model.

Even with modern neurosurgical techniques preservation of functional hearing in acoustic neurinoma surgery is still impossible in a large number of cases. Due to the necessity of averaging the brainstem auditory evoked potentials (BAEP) this monitoring is not a real time measurement. Therefore the surgeon cannot be sure which manipulation during the tumour dissection has caused the loss of the BAEPs. The direct monitoring of the cochlear nerve (CNAP) may warn the surgeon earlier. But it is not able to explain, which manipulation has caused the worsening of the potentials. A loss of the waves after coagulation of a vessel next to the cochlear nerve may be the result of the heat or of the disturbance of the blood supply. Potentially harmful to cochlear nerve function may be the interruption of inner ear blood supply, thermal or mechanical traumata. Experimental studies are rare to nonexistent. We therefore tested selectively each trauma for its influence on the BAEPs in an animal model. In New Zealand rabbits a lateral craniectomy of the posterior fossa was performed. Care was taken not to retract the cerebellum or to open the inner ear system, because both factors might disturb the BAEPs. Each step of the operation was followed by BAEP recording. After reaching the internal auditory canal, the cerebellopontine angle of 6 animals was exposed to heated water with definitive increasing temperature. The BAEPs did not react significantly until 71 degrees C was reached and protein coagulation started. In the second group, the internal auditory artery of 6 rabbits was compressed with a microdissector for 3 minutes. Subsequently the BAEPs disappeared in all animals. In the last group a constant pressure of 10 g was applied to 6 cochlear nerves for 1 minute consistently causing the loss of the BAEPs. The results are statistically significant (p = 0.03). We therefore concluded that the blood supply of the inner ear is of the upmost importance for cochlear nerve function. Mechanical manipulation should be minimized whereas thermal traumatization of the nerve is only critical when the nerve itself is coagulated.

Animals↗

PubMed2002

Selective retrosigmoid vestibular neurectomy without internal auditory canal drill-out: an anatomic study.

OBJECTIVE: It is well established that selective vestibular nerve section by means of the retrosigmoid or posterior fossa approach can be accomplished with or without drill-out of the internal auditory canal (IAC) by virtue of the presence or absence of a surgically accessible cleavage plane between the vestibular and cochlear nerves. Some reports have indicated that a majority of patients would be amenable to successful separation of the vestibular nerve from the cochlear nerve medial to the IAC, thus obviating the need for IAC drill-out and associated complications. However, other reports have indicated routine difficulty in finding a satisfactory vestibulocochlear cleavage plane within the cerebellopontine angle. This in situ cadaver study was undertaken to determine whether normal anatomic relationships support the hypothesis that selective vestibular nerve section can be accomplished by means of the posterior fossa approach without the need for concomitant IAC drill-out in a majority of circumstances. METHODS: A retrosigmoid approach to the posterior fossa was performed bilaterally on 36 intact human cadavers. After displacement of the cerebellum, an operating surgical microscope was used to visualize the cerebellopontine angle in the surgical position. The ability to develop a satisfactory cleavage plane between the vestibular and cochlear nerves without the need for drill-out of the IAC was established in each case. RESULTS: Seventy-two vestibulocochlear nerve bundles in 36 intact human cadavers were analyzed. A vestibulocochlear nerve cleavage plane within the cerebellopontine angle amenable to neurectomy medial to the porus of the IAC was observed in 81% left and 69% right vestibulocochlear nerve bundles (average, 75%). The facial nerve was found deep or anterior to the vestibulocochlear nerve bilaterally in all cases examined. The anterior inferior cerebellar artery, or a branch of the artery, was found to cross the plane between the facial and vestibulocochlear nerve bundles within the lateral cerebellopontine angle in 47% of the cases on the left and in 50% of cases on the right. CONCLUSIONS: A vestibulocochlear nerve cleavage plane amenable for selective vestibular nerve transection without drilling the IAC was found in 75% of the 72 cerebellopontine angles studied. The facial nerve consistently lies deep or anterior to the vestibulocochlear nerve within the cerebellopontine angle with the retrosigmoid approach. These findings support the rational and feasibility of avoiding drill-out of the IAC in the majority of circumstances when performing selective vestibular neurectomy by means of the posterior fossa approach for Ménière's syndrome and other vestibular disorders.

Aged↗

PubMed1975

The distribution of primary afferents to the cochlear nuclei in the domestic hen (Gallus domesticus).

The normal anatomy of the three cochlear nuclei in the hen, the nucleus laminaris, the nucleus angularis and the nucleus magnocellularis is described. Following lesions of the cochlear nerve, all three nuclei are shown to receive primary cochlear fibers (silver impregnation methods). The part of nucleus laminaris which consists of a ventral convex sheet of cells is shown to receive cochlear nerve fibers from both ears, the nerve fibers from the ipsilateral ear terminating dorsal to the cell sheet while contralateral nerve fibers terminate ventral to the nerve cells. The cochlear ganglion cells projecting to the nucleus laminaris are apparently situated in other parts of the ganglion that the cells projecting to the nucleus angularis and magnocellularis. The findings are discussed in the light of known data on the organization and function of the cochlear nuclei in birds.

Animals↗

PubMed1982

The absence of substance P from guinea pig auditory structures.

The following auditory structures were examined for Substance-P-Containing cells and fibres using a monoclonal antibody: organ of Corti, spiral ganglion, auditory nerve, cochlear nucleus. No substance P was detected in any of these structures. Giving due consideration to the sensitivity and specificity of this method of detection, it was concluded that Substance P has no function in the lower auditory system of the guinea pig.

Animals↗

PubMed1994

[High resolution magnetic resonance tomography of the temporal bone].

Computed tomography (CT) has long been the method of choice for investigations of the temporal bone. Advances in high resolution magnetic resonance imaging (MRI) enabled MRI of the temporal bone. The purpose of this study was to assess detailed reconstruction of the anatomy of the temporal bone by MRI. Healthy volunteers were examined on a 1T MR whole body scanner (Impact, Siemens, Erlangen, Germany). A Helmholtz-configurated head coil was used. A T1-weighted 2D-FLASH sequence (TR = 400 ms, TE = 10 ms, 90 degrees flip angle, 2 mm slice thickness, 180* 256 matrix, 160 mm FOV) was performed pre- and postcontrast as well as a T2-weighted turbo spin echo sequence (TR = 6300 ms, TE = 112 ms, 3 mm slice thickness, 200 mm matrix, 200 mm FOV). A sagittal and an angulated paraxial projection, parallel to the nasopharyngeal edge of the clivus, were chosen. We suceeded in imaging the facial nerve along its entire course, including the geniculate ganglion and the greater superficial petrosal nerve, the cochlear nerve and the vestibular nerve (superior and inferior part). The facial nerve was visualised continuously from the cerebellopontine angle to the foramen stylomastoideum. The delineation of the different turns of the cochlea, the vestibule and the semicircular canals was excellent. High resolution MRI promises to be of great value in the diagnosis of the temporal bone.

Cochlea↗

PubMed1983

Uptake and release of D-aspartate in the guinea pig cochlear nucleus.

This study attempted to determine if L-glutamate (L-Glu) and/or L-aspartate (L-Asp) might be the transmitters of neurons that provide synaptic endings to the cochlear nucleus of the medulla. The uptake and release of D-[3H]aspartate (D-Asp), a putative marker for L-Glu and L-Asp, were measured in the guinea pig cochlear nucleus before and after destruction of the cochlear afferents by cochlear ablation. The cochlear nucleus was dissected into the anteroventral (AVCN), posteroventral (PVCN), and dorsal (DCN) cochlear nuclei. Subdivisions from unlesioned animals took up D-Asp, achieving concentrations in the tissues that were 13-20 times that in the medium. Subsequently, electrical stimulation evoked a Ca2+-dependent release of part of the D-Asp from each subdivision. Disarticulation of the middle ear ossicles, which attenuates acoustic stimulation, produced a modest inhibition of D-Asp release in each subdivision, but did not alter the uptake of D-Asp. Cochlear ablation strongly depressed both the uptake and the release of D-Asp in each subdivision, presumably as a result of destruction of the cochlear nerve endings in the cochlear nucleus. Nevertheless, after lesions, there was a preservation of the uptake and release of D-Asp in the DCN relative to the AVCN and PVCN. These residual activities in the DCN may be mediated by the axonal endings of the granule cells of the cochlear nucleus. The present findings support the hypothesis that the granule cells of the cochlear nucleus, as well as the cochlear nerve fibers, use L-Glu and/or L-Asp as transmitters.

Animals↗

PubMed1989

Characterization of an EPSP-like potential recorded remotely from the round window.

The whole-nerve cochlear action potential (CAP), to tone burst stimulation, was recorded before and after application of tetrodotoxin (TTX) to the intact round window (RW) membrane. TTX abolished the CAP leaving a residual negative potential without altering the summating potential (SP) or the cochlear microphonic (CM). The residual potential retained its polarity when recorded from scala vestibuli. The peak latency, amplitude, and tuning properties of the residual potential showed features similar to the CAP. Application of kainic acid to the RW membrane eliminated the residual potential, leaving the SP and CM unaltered. It is hypothesized that the sources of the residual potential are the excitatory post-synaptic potentials from the peripheral processes of afferent dendrites under the inner hair cells.

Acoustic Stimulation↗

PubMed1975

Auditory fatigue: retrocochlear components.

Changes in auditory sensitivity were measured at the VII nerve, cochlear nucleus, and inferior colliculus after a fatiguing sound exposure. Losses in sensitivity progressively increased from peripheral to central auditory sites. The results suggest that there is a retrocochlear component to auditory fatigue when it is induced by low-level sounds of short duration.

Acoustic Stimulation↗

PubMedDate not supplied

Pediatric and adult cochlear implantation.

The frequency of cochlear implantation has increased tremendously over the past decade. Cochlear implantation is often performed as an outpatient procedure and is considered an acceptable treatment for severe to profound sensorineural hearing loss in patients who are refractory to conventional hearing augmentation. Imaging plays an important part in the work-up of cochlear implant candidates, and an understanding of imaging evaluation procedures is essential. The radiologist must be familiar with imaging findings that contraindicate implantation (absence of the cochlea or cochlear nerve) and with those that could significantly alter surgery (facial nerve dehiscence, cochlear ossification). It is also imperative to be familiar with the growing number of imaging options (particularly magnetic resonance [MR] imaging pulse sequences) to optimize evaluation of cochlear implant candidates. Imaging choices will be substantially influenced by the manufacturer of the computed tomographic scanner or MR imager. Radiologists will assume an expanding role in evaluating affected patients as the frequency of cochlear implantation continues to increase.

Adult↗

PubMed1989

[Attempt of intracranial IC bypass for giant aneurysm in the cavernous portion of the carotid artery].

We report here, a novel method for internal carotid (IC) bypass between C2 and C5, by using the autologous saphenous vein. The patient was a 58 year-old female, complaining of pain and motor disturbance in her right ocular region. She suddenly developed left-sided hemiparesis during her stay in our hospital. The following CT examination demonstrated a high density homogenous round mass, which occupied the right side of the parasellar region with no perifocal edema. The contrast enhancement CT, however, suggested there was still a certain degree of blood flow in the mass. On the other hand, carotid angiography showed an occlusion of blood flow at the C5 level (interosseous portion), which seemed to indicate either giant aneurysm or cavernous angioma. The mass was identified as a giant aneurysm during surgery, and the decompression procedure by removing the intra-aneurysmal blood clot was attempted first. However, this trial failed due to an accidental severe bleeding. Because of this, we then decided to perform the grafting of autologous saphenous for a length of 10 cm between C2 and C5. Intraoperative heavy bleeding mentioned above seemed to have occurred due to release of compression by the aneurysm against the internal carotid artery through which there was restricted blood flow. Postoperative angiography demonstrated that the graft remained patent enough to be approximately equal in size to the original artery. From our experiences in this case, two important points are, we suggest, to be kept in mind while applying this method; (1) to carefully expose the C5 segment, (2) to avoid damage of the surrounding structures such as the Eustachian tube, facial nerve and cochlear nerves, and so forth. In conclusion, we strongly recommend this IC bypass technique for other types of tumors in the cavernous portion as well.

Carotid Artery Diseases↗

PubMed1992

The significance for postoperative hearing of preserving the labyrinth in acoustic neurinoma surgery.

Among 186 patients with preoperative hearing, a total of 189 acoustic neurinomas were removed through a lateral suboccipital approach with anatomical preservation of the cochlear nerve. Functional hearing was preserved in 92 (49%) of these patients; despite anatomical preservation of the cochlear nerve, deafness was the result in 51% of the series. Many factors have been considered to cause hearing loss in patients whose cochlear nerve was intact after surgery; these include nerve retraction, nerve or cochlear ischemia, overheating and vibration damage to the nerve, and opening of the labyrinth. To evaluate the significance of injury to the labyrinth in postoperative hearing loss, a prospective study was undertaken. High-resolution computerized tomography studies through the inner ear with bone algorithm were performed pre- and postoperatively. The postoperative status of the labyrinth was classified into three patterns: intact, fenestrated, and widely opened. Injury to the labyrinth occurred in 30% of the cases. The most frequently injured labyrinth structures were the crus commune of the posterior and superior semicircular canals (52%), the posterior semicircular canal (23%), the vestibule (21%), and the superior semicircular canal (4%). A statistically significant relationship was found between injury to the labyrinth and deafness, elevated thresholds, and lower discrimination values at pure-tone audiograms and speech audiometry (p < 0.0001). The degree of the injury (comparison between fenestration and wide opening of the labyrinth) was also significantly related to postoperative deafness (p < 0.0001). Disturbance of the inner-ear fluids was considered to be the cause of the hearing loss. In 12 patients labyrinth injury was not associated with deafness. This finding may support the existence of mechanisms of cochlear protection. The homeostatic function of the endolymphatic sac was considered to play an important role in recovery of damaged hearing in these 12 cases.

Adolescent↗

PubMed1997

Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections.

OBJECTIVE: The realistic chances of hearing preservation and the comparability of international results on hearing preservation in complete microsurgical vestibular schwannoma resections were the focus of this study in a large patient population treated by uniform principles. METHODS: One thousand vestibular schwannomas were operated on at Nordstadt Neurosurgical Department, from 1978 to 1993, by the senior surgeon (MS). There were 1000 tumors in 962 patients, i.e., 880 patients with unilateral tumors and 82 patients operated on for bilateral tumors in neurofibromatosis-2 (120 cases). Preservation of the cochlear nerve was attempted whenever possible. The audiometric data were analyzed by the Nordstadt classification system and graded in steps of 30 dB by audiometry and in steps of 10 to 30% by speech discrimination; for comparability, the data were also evaluated by the criteria of Gardner, Shelton, and House, and they were assessed in relation to the Hannover tumor extension grading system. RESULTS: Anatomic cochlear nerve preservation was achieved in 682 of 1000 cases (68%), as well as in some preoperatively deaf patients, a very few of whom regained some hearing. Of a total of 732 cases with some preoperative hearing, anatomic cochlear nerve preservation was achieved in 580 cases (79%) and functional cochlear nerve preservation in 289 (39.5%); analysis over time revealed an actual preservation rate of 47% in the most recent 200 cases. Specific factors, such as gender, tumor extension, preoperative hearing quality, and symptom duration, were investigated for their predictive value for hearing preservation. Male gender, small to medium tumor size (mainly extending within the cerebellopontine cistern; Classes T2 and T3), good to moderate hearing (up to 40-dB loss), and short duration of hypoacusis (< 1.5 yr) or of vestibular disturbances (< 0.7 yr) were advantageous factors, with chances of hearing preservation between 47 and 88%. CONCLUSION: Functional cochlear nerve preservation in complete microsurgical resection should belong to the contemporary standard of treatment goals.

Audiometry, Pure-Tone↗

PubMed1995

Time course of axonal myelination in the human brainstem auditory pathway.

Structures in the human brainstem auditory pathway, from the proximal end of the cochlear nerve to the inferior colliculus, undergo myelination between the 26th and 29th fetal weeks. By the 26th week of gestation, axons in the cochlear nerve and brainstem pathways have acquired linear arrays of oligodendrocytes, and faint myelin sheaths can be distinguished. By the 29th week, definitive myelination is present in all auditory pathways, including the proximal end of the cochlear nerve, trapezoid body, lateral lemniscus, dorsal commissure of the lemniscus, commissure of the inferior colliculus and brachium of the inferior colliculus. Subsequent to the 29th gestational week, density of myelination increases in all pathways until at least 1 year postnatal age. The time of onset of myelination coincides with the onset of acousticomotor reflexes and brainstem auditory evoked responses, processes which depend on rapid, synchronized conduction of auditory impulses in the cochlear nerve and brainstem. The cotemporality in appearance of myelin, reflex responses, and evoked responses supports the idea that the 26th to 28th gestational weeks are a critical period in the onset of human central auditory function. The subsequent increase in myelin density is likely to be a factor in the steady decrease in ABR wave III-V latencies observed during the perinatal period.

Axons↗

PubMed2001

Is cochlear implantation possible after acoustic tumor removal?

HYPOTHESIS: This study aimed to assess the possibility of hearing restoration after acoustic tumor removal. BACKGROUND: Hearing restoration surgery may be indicated after surgery of bilateral acoustic tumors or surgery of acoustic tumor in the only hearing ear. The choice is between cochlear implantation and brainstem implantation. METHODS: From the temporal bone collection at the House Ear Institute, Los Angeles, the author histologically examined eight temporal bones from seven patients who had undergone acoustic tumor removal during their lifetime. Special emphasis was put on examining the patency of the cochlear turns and on survival of the spiral ganglion cells and cochlear nerve. RESULTS: This study showed that after translabyrinthine acoustic tumor removal, there is progressive osteoneogenesis of the cochlea associated with almost complete degeneration of the spiral ganglion cells and cochlear nerve. Similar findings were noticed after middle fossa removal of acoustic tumor with unsuccessful hearing preservation. CONCLUSIONS: The histologic changes described in the cochlea and cochlear nerve represent the effects of ischemia resulting from inadvertent cutting of the blood supply during acoustic tumor removal. It is possible to do cochlear implantation after acoustic tumor removal provided that the result of promontory electrical stimulation test is positive (the cochlear nerve is intact) and that implantation is done at the time of acoustic tumor removal or shortly thereafter, before cochlear ossification is complete.

Cochlea↗

PubMed2006

[Observation of auditory brainstem response and distortion product otoacoustic emission on the animal model of autoimmune auditory neuropathy].

OBJECTIVE: To set up an animal model of autoimmune auditory neuropathy and to observe the auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) in guinea pigs. METHODS: The spiral ganglion and the cochlear nerve were obtained and purified by electrophoresis from 250 normal guinea pigs. The purified cochlear nerve antigen was mixed with an equal volume of complete Freunds adjuvant for immunization. Seventy guinea pigs were divided into three groups: experiment group (50 guinea pigs), control group (10 guinea pigs), normal group (10 guinea pigs). ABR, DPOAE, serum IgG levels, and morphological changes of spiral ganglion cells and the cochlear nucleus were observed. The protein expressions of the antigen were examined by immunohistochemistry and the super-structure of the auditory nerve were observed. RESULTS: The threshold of ABR response increased ranged from 10 to 25 dB in 32% (32/100 ears) of the guinea pigs. The peak latencies of waves I , III and the interpeak latency I approximately III were prolonged in the hearing loss group of guinea pigs. Prolonged peak latency of wave III was noted in hearing loss group at 2 and 3 weeks post immunization and slowly decreased to normal peak latency. The amplitude of DPOAE was no difference in the guinea pigs. The levels of serum IgG increased significantly compared with those of the control group. Inflammatory cell infiltration was observed in the cochlear nerve and the number of spiral ganglion cells detected. On the contrary, inflammatory cell infiltration was not observed in the cochlear nucleus. The cell densities and the across-sectional areas of neurons in anteroventral cochlear nucleus and posteroventral cochlear nucleus were no difference in the guinea pigs. The antigen protein distributed strictly in cochlear nerve and the spiral ganglion. Some demyelinated areas in cochlear nerve was observed in this group. The threshold of ABR response in 68% guinea pigs (68/100 ears) did not increase. The data of DPOAE and the serum IgG levels show no difference compared with the control group. There were not pathological observation in spiral ganglion cells, cochlear nucleus and cochlear nerve. CONCLUSION: An animal model of autoimmune auditory neuropathy has been set up successfully and the character of the ABR and DPOAE was observed.

Animals↗