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At least 955 records · Page 53Linked to original sources
PubMed1993

Tympanic and transtympanic electrocochleography in acoustic neuroma and vestibular nerve section surgery.

Eighth nerve action potential (AP) amplitudes and latencies and cochlear microphonic (CM) amplitudes were compared using tympanic and transtympanic electrocochleography (ECOG) in two patient groups. Tympanic ECOG was performed with a wick electrode placed on the tympanic membrane (TM). Transtympanic ECOG was performed with a needle electrode placed on the promontory of the anesthetized patient. Eighteen subjects were tested by tympanic ECOG as part of a preoperative assessment for either acoustic neuroma removal or transection of the vestibular portion of the eighth cranial nerve. Surgery occurred within 1 week of the preoperative evaluation. Intraoperative auditory monitoring was performed using transtympanic ECOG. Baseline recordings were compared to the preoperative tympanic ECOG data. Stimuli were condensation and rarefaction clicks and tone bursts, presented by an insert earphone. As expected, the two methods resulted in essentially identical response latencies and large amplitude differences, although the response amplitudes were extremely variable. The AP amplitude and the CM amplitude did not increase by the same factor with the transtympanic (TT) electrode compared to the tympanic electrode. On comparison of preoperative and intraoperative response amplitudes with regard to stimulus polarity, tympanic electrocochleography appears to be a useful method of gathering preliminary information on the status of the patient's auditory system. In this study, tympanic ECOG was found to have some predictive value when trying to ascertain the best intraoperative monitoring situation.

Acoustic Stimulation↗
PubMed1991

[Preservation of hearing and facial nerve function in surgery for acoustic neuroma].

The results concerning the preservation of hearing and facial nerve function in 71 patients with 74 acoustic neuromas operated on from 1979 to 1990 are presented. All patients have been operated on in half-sitting position by one surgeon using the suboccipital-transmeatal approach. Postoperative facial nerve function was good (House degree I or degrees II) in 42/73 patients (58%), moderate (House degrees III or degrees IV) in 13/37 (18%), and poor (House degrees V or degrees VI) in 18/73 (24%). Preservation of useful hearing was achieved in 17%. The smaller the tumour and the easier the preparation the better was the functional result. Beside anatomic integrity of nerves and endolymphatic system the internal auditory artery as the most important vessel for the inner ear blood supply should be respected. The cochlear nerve intact in 47 patients we only found one case with recurrent tumour in a patient with neurofibromatosis 2. Preservation of the cochlear nerve did not have an increased risk of tumour recurrence in our group of patients.

Adolescent↗
PubMed2000

Calculation of cranial nerve complication probability for acoustic neuroma radiosurgery.

PURPOSE: Estimations of complications from stereotactic radiosurgery usually rely simply on dose-volume or dose-diameter isoeffect curves. Due to the sparse clinical data available, these curves have typically not considered the target location in the brain, target histology, or treatment plan conformality as parameters in the calculation. In this study, a predictive model was generated to estimate the probability of cranial neuropathies as a result of acoustic schwannoma radiosurgery. METHODS AND MATERIALS: The dose-volume histogram reduction scheme was used to calculate the normal tissue complication probability (NTCP) from brainstem dose-volume histograms. The model's fitting parameters were optimized to provide the best fit to the observed complication data for acoustic neuroma patients treated with stereotactic radiosurgery at the University of Florida. The calculation was then applied to the remainder of the patients in the database. RESULTS: The best fit to our clinical data was obtained using n = 0.04, m = 0.15, and alpha/beta = 2.1 Gy(-1). Although the fitting parameter m is relatively consistent with ranges found in the literature, both the volume parameter, n, and alpha/beta are much smaller than the values quoted in the literature. The fit to our clinical data indicates that brainstem, or possibly a specific portion of the brainstem, is more radiosensitive than the parameters in the literature indicate, and that there is very little volume effect; in other words, irradiation of a small fraction of the brainstem yields NTCPs that are nearly as high as those calculated for entire volume irradiation. These new fitting parameters are specific to acoustic neuroma radiosurgery, and the small volume effect that we observe may be an artifact of the fixed relationship of acoustic tumors to specific regions of the brainstem. Applying the model to our patient database, we calculate an average NTCP of 7.2% for patients who had no cranial nerve complications, and the average NTCP for was 66% for patients who sustained a cranial neuropathy. For the entire patient population, the actual percentage of patients suffering either facial or trigeminal neuropathy was 14.7%, whereas the calculated average NTCP was 14.8%. DISCUSSION: NTCP calculations using brainstem dose-volume histograms can be used to estimate the rate of cranial neuropathies from acoustic neuroma radiosurgery. More clinical data and further study will lead to refinement of the model with time.

Brain Stem↗
PubMed2005

Effects of acoustic noise on the auditory nerve compound action potentials evoked by electric pulse trains.

This study investigated the effects of acoustic noise on the auditory nerve compound action potentials in response to electric pulse trains. Subjects were adult guinea pigs, implanted with a minimally invasive electrode to preserve acoustic sensitivity. Electrically evoked compound action potentials (ECAP) were recorded from the auditory nerve trunk in response to electric pulse trains both during and after the presentation of acoustic white noise. Simultaneously presented acoustic noise produced a decrease in ECAP amplitude. The effect of the acoustic masker on the electric probe was greatest at the onset of the acoustic stimulus and it was followed by a partial recovery of the ECAP amplitude. Following cessation of the acoustic noise, ECAP amplitude recovered over a period of approximately 100-200 ms. The effects of the acoustic noise were more prominent at lower electric pulse rates (interpulse intervals of 3 ms and higher). At higher pulse rates, the ECAP adaptation to the electric pulse train alone was larger and the acoustic noise, when presented, produced little additional effect. The observed effects of noise on ECAP were the greatest at high electric stimulus levels and, for a particular electric stimulus level, at high acoustic noise levels.

Action Potentials↗
PubMed1987

[Complete excision of acoustic neurinoma. Preservation of the facial nerve and hearing].

Using microtechniques, total removal of acoustic neuromas with facial nerve preservation is possible today in most cases. The next barrier of operative treatment is hearing preservation which is routinely attempted, with the help of intraoperative brainstem auditory evoked responses monitoring. The present series deals with 176 operations performed sub-occipitally in 159 patients from 1970 up to 1985. Twelve patients were operated upon 29 times. According to the W.T. Koos classification, there were 16 type II, 39 type III and 121 type IV neuromas. Ten patients died postoperatively. In seven of these, death was related to surgery, in two it was caused by respiratory failure. In the last patient unexplained sudden death occurred. 169 patients had no facial weakness preoperatively, in 158 of these the facial nerve was anatomically preserved (93.5%). Facial nerve function was judged by evaluation of function of face at least 12 months after operation. Up to 36 months after surgery, a good facial result may be expected in cases where the facial nerve was macroscopically spared at completion of removal. Functional results have been reviewed in 151 patients according to the J.W. House's International Evaluation System, with an excellent or good result in 66 (44%), fair in 65 (43%), bad or poor in 20 (13%). The anatomical preservation of the cochlear nerve could be achieved in 80 patients of the group of 169 in whom the auditory function had not been damaged by a previous operation. In fact, the auditory function preservation could be reasonably attempted in 79 patients: showing a hearing loss below 70 dB on tone audiometry, whatever may be the result of speech discrimination score. 59 patients (75%) of this later group had their auditory nerve preserved, 14 (18%) showed preserved hearing function postoperatively, 10 of these with a speech discrimination score over 50%. Two of these showed an improvement of preoperative hearing, two others showed a total recovery of hearing function after removal.

Adolescent↗
PubMed1995

Facial nerve involvement in patients with acoustic neurinomas. Examination with magnetic single- and bi-stimulation.

The diagnosis of acoustic neurinomas is usually made by auditory and vestibular testing and magnetic resonance imaging. As clinical involvement of the facial nerve is infrequent, occurring only in large tumours, only little is known about the subclinical involvement of the facial nerve. Transcranial magnetic stimulation of the VIIth cranial nerve in the temporal bone, adjacent to acoustic neurinoma growth, seems to be an adequate instrument for electrophysiological measurements of minimal nerve lesions without clinically obvious facial palsy. In 70% out of 97 patients with surgically and histologically confirmed acoustic neurinomas, obvious elongation of the intratemporal conduction time of the facial nerve was found. This affection was dependent on tumour size. No correlation was found to preoperative or postoperative facial nerve function and hearing function. The latencies of the conduction time showed a tendential increase in patients with a more difficult grade of surgery and of facial nerve preparation due to fibrous adhesions and nerve spreading on the tumour capsule. A completely new stimulation modality, the application of two magnetic stimuli in quick succession, was applied for the first time in acoustic neurinoma patients, and revealed facial nerve involvement by acoustic neurinoma growth. Facial nerve involvement in acoustic neurinoma can be detected by transcranial magnetic stimulation even in patients with small and medium sized tumours but with clinically normal facial function.

Cranial Nerve Neoplasms↗