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PubMed1992

[Intraoperative monitoring of early auditory evoked potentials in hearing acoustic neuroma patients complemented by cochlear nerve action potentials].

Hearing preservation was attempted in eight cases of acoustic neurinomas with good preoperative hearing. This was successful in 3 cases. Brain-stem auditory evoked potentials (BAEP0 were monitored in all cases, and compound nerve action potentials (CNAP) were recorded from the cochlear nerve in the last 3 cases. The BAEP was extremely sensitive to intraoperative manipulation. Intraoperative loss of wave V in BAEP was observed not only in all 5 cases with postoperative hearing loss, but also in 2 out of 3 cases with successful hearing preservation. CNAP correlated better with the hearing outcome than BAEP. In the cases where hearing was preserved, intact CNAP responses were demonstrated at the end of the operation. Conversely, deterioration of CNAP was seen in a case of postoperative hearing loss. CNAP was 10-15 times larger in amplitude than BAEP, so that the new responses were obtainable in shorter intervals. This capability of frequent examination seemed to increase the possibility of avoiding irreversible damage to the hearing by changing surgical tactics. The addition of CNAP monitoring is a good supplement to conventional BAEP monitoring in acoustic neurinoma surgery.

Adult↗
PubMed1993

[Intraoperative monitoring of the facial nerve in transtemporal surgery of acoustic neurinoma].

Acoustic neuroma ablation by the enlarged middle cranial fossa approach results in a low incidence of postoperative facial nerve dysfunction. In 25 consecutive patients with tumors in the cerebellopontine angle with a diameter up to 2.3 cm, intraoperative monitoring of the facial nerve was evaluated. The facial nerve was monitored electrophysiologically with recordings of the spontaneous EMG and electrically evoked potentials (CMAP) from at least three groups of facial muscles. In 4 cases monitoring was helpful for identification and delineation of the facial nerve. The mechanically elicited potentials during tumor preparation and CMAP after electrical stimulation close to the brain stem were compared with the postoperative facial nerve function and the time course of recovery. If the ongoing EMG recordings resulted in potentials below 0.5 mV and the CMAP at the end of tumor preparation was higher than 0.5 mV, facial nerve function was normal in 9 of 10 cases on the first postoperative day. One patient had mild facial palsy. Poor results could be predicted if numerous discharges with amplitudes higher than 0.5 mV and affected CMAP after stimulation near the brain stem were found at the end of surgery. All 3 patients with these findings had facial paralysis at hospital discharge (an average of 9 days after the operation). Recovery from the palsies was found to be prolonged. Intraoperative monitoring of the facial nerve is now used routinely in surgery of the cerebellopontine angle and the internal auditory canal.

Adult↗
PubMed1985

Intraoperative facial nerve monitoring: a comparison of stimulating electrodes.

Preservation of the facial nerve during acoustic neuroma resection may be enhanced by the use of intraoperative electrical stimulation. Although stimulation of the extratemporal facial nerve is an effective and established procedure, anatomic differences of the intradural facial nerve and its microenvironment demand more exacting stimulus protocols. The absence of epineurium may make the intradural nerve more susceptible to mechanical or electrical trauma while intermittent pooling of cerebrospinal fluid (CSF) at the cerebellopontine angle may shunt current away from nerve. Four stimulus configurations were examined under varying conditions simulating CSF pooling. The results indicated that: 1. insulation of stimulating electrodes prevents CSF current shunting and allows utilization of a constant current source, and 2. monopolar and bipolar configurations demonstrate significantly different electrical characteristics which may be employed selectively based upon specific clinical goals.

Adult↗
PubMed1965

BACKGROUND AND EVOKED ACTIVITY IN THE AUDITORY PATHWAY: EFFECTS OF NOISE-SHOCK PAIRING.

Unanesthetized cats with electrodes permanently implanted along the auditory pathway were presented first with suistained " white" noise stimuli and then with the same noise paired with subcutaneous electric shocks. Pairing noise with shock decreased both background and noise-evoked activity inthe inferior colliculus, and, in some cats, also in the cochlear nucleus, trapezoid body, and at the round window. No changes occurred in medial geniculate or auditory cortex recordings. The effects in the inferior colliculusdo not depend on changes in the degree of arousal of the animal, on change in the medullary auditory areas, or on the actions of the middle-ear muscle.

Animals↗
PubMed1999

Acoustic neuroma: outcome of surgical resection and study on the anatomy of facial and cochlear nerves.

The treatment of acoustic neuroma (vestibular schwannoma) has evolved greatly. In this report, we studied the history of acoustic tumour surgery, and documented the value of technical advances in benefiting patients. We also present our outcome of surgery for this benign tumour in support of its use as the treatment of choice. In 611 patients undergoing initial surgery at Johns Hopkins from 1973-1994, complete resection was obtained in all but one case (intentional), and permanent morbidity and mortality rate was 0.3%. Including temporary morbidity, the rate was 3.8%. Tumour recurrence was seen in only 0.8% of cases. The facial nerve was preserved in 97.6% and function at one-year was House-Brackmann grade 1 or 2 in 89.7%. Lastly, we present results of an anatomical study localizing the nerves and vessels, and the frequency of involvement by tumour, associated with acoustic neuromas in 1006 surgical cases. We continue to offer surgery as the best treatment option for the majority of our patients, and prefer the suboccipital route because of its unrestricted access to all posterior fossa structures, and ability to preserve hearing.

Adolescent↗
PubMed1995

Preservation of cranial nerve function after treatment of acoustic neurinomas with fractionated stereotactic radiotherapy. Preliminary observations in 26 patients.

Twenty-seven acoustic tumors in 26 patients were treated with multiple fractionated linear-accelerator-based stereotactic radiotherapy (SRT). All patients with intact pretreatment facial nerve function with either small or large tumor volumes have thus far experienced no treatment-related facial neuropathy, including 9 patients with a mean follow-up of 22.4 +/- 1.6 months. The incidence of evaluable trigeminal neuropathy was 13%, and in 5 of 7 patients with serviceable pretreatment hearing, audiometry was unchanged in the immediate posttreatment period. Longer follow-up will be necessary to evaluate hearing preservation after SRT. Tumor response with central necrosis was seen in all assessable patients. SRT can be performed for cerebellopontine angle tumors with accuracy and reproducibility. It achieves a biological response similar to single fraction radiosurgery and may lower the incidence of facial and trigeminal neuropathies.

Adult↗