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At least 1,099 records · Page 61Linked to original sources
PubMed1985

Loss of auditory function in microvascular decompression for hemifacial spasm. Results in 143 consecutive cases.

Auditory function was studied before and after surgery in 143 consecutive patients who were operated on for hemifacial spasm by microvascular decompression of the intracranial portion of the facial nerve. The acoustic middle ear reflex was abnormal preoperatively in 41% of the patients, indicating that the vascular abnormalities that caused the hemifacial spasm also affected the auditory nerve. Three patients suffered a profound hearing loss in the ear on the operated side, and one lost hearing function totally. In addition, 24 patients had a moderate elevation in the pure-tone threshold at one or more octave frequencies. Of these, 16 patients experienced a hearing loss at only one frequency (8000 Hz), while eight had a threshold evaluation of no more than 20 dB in the speech frequency range (500, 1000, and 2000 Hz). Two patients were deaf on the side of the spasm before the operation. Three patients were not tested postoperatively, and one patient was tested only after surgery. Thus, in this series of 143 patients, only 2.8% suffered a significant hearing loss as a complication of facial nerve decompression to relieve hemifacial spasm.

Adult↗
PubMed1995

Microsurgery versus radiosurgery in the treatment of small acoustic neurinomas.

Microsurgical preservation of the facial nerve during removal of acoustic neurinomas can hardly be compared with microsurgery of the eighth cranial nerve. Many more anatomical and pathogenetic factors are involved that need careful consideration. In small neurinomas, of grades I and II, total extirpation of the tumour with preservation of both the facial nerve and segments of the vestibulocochlear nerve not directly involved by the tumour has become a safe and practical technique. In small acoustic neurinomas immediate facial nerve function could be preserved in 88% and "useful hearing" could be preserved in 78%. A number of different types of tumour-cranial nerve relationships could be established in small acoustic neurinomas, showing also the effects of adjusted surgical techniques on the preservation of hearing. Optimal selective separation of cranial nerves from the tumour is only possible through open surgical intervention, while radiosurgery requires the irradiation of the entire tumour/nerve complex.

Adult↗
PubMed1995

Recordings from slices indicate that octopus cells of the cochlear nucleus detect coincident firing of auditory nerve fibers with temporal precision.

Acoustic information in auditory nerve discharges is integrated in the cochlear nuclei, and ascends through several parallel pathways to higher centers. Octopus cells of the posteroventral cochlear nucleus form a pathway known to carry information in the timing of action potentials. Octopus cells have dendrites oriented to receive converging input from many auditory nerve fibers. In all 34 intracellular recordings from anatomically identified octopus cells in slices, shocks to the auditory nerve evoked brief, consistent, graded EPSPs. EPSPs were about 1 msec in duration. At all but the lowest shock strengths, the delays between shocks and the peaks of resultant EPSPs had SDs of 0.02 msec. Polysynaptic excitation, perhaps arising from the axon collaterals of octopus cells, was observed. No detectable glycinergic or GABAergic inhibition was evoked with shocks. The input resistances were low, around 10 M omega, voltage changes were rapid, with time constants of about 1 msec, and action potentials were small. The low input resistance resulted in part from a Cs(+)-sensitive conductance. In the presence of 10 or 15 mM extracellular Cs+ the time constants increased 20-fold in the hyperpolarizing voltage range. As several subthreshold inputs were required to produce suprathreshold responses, octopus cells detect the coincident firing of auditory nerve fibers. Under physiological conditions the low input resistance and resulting short time constant limit the time over which temporal summation of excitation from auditory nerve fibers can occur and thus provide temporal precision to electrical signaling.

Action Potentials↗
PubMed2003

Acoustic response properties of lagenar nerve fibers in the sleeper goby, Dormitator latifrons.

Auditory and vestibular functions of otolithic organs vary among vertebrate taxa. The saccule has been considered a major hearing organ in many fishes. However, little is known about the auditory role of the lagena in fishes. In this study we analyzed directional and frequency responses from single lagenar fibers of Dormitator latifrons to linear accelerations that simulate underwater acoustic particle motion. Characteristic frequencies of the lagenar fibers fell into two groups: </=50 Hz and 80-125 Hz. We observed various temporal response patterns: strong phase-locking, double phase-locking, phase-locked bursting, and non-phase-locked bursting. Some bursting responses have not been previously observed in vertebrate otolithic nerve fibers. Lagenar fibers could respond to accelerations as small as 1.1 mm s(-2). Like saccular fibers, lagenar fibers were directionally responsive and decreased directional selectivity with stimulus level. Best response axes of the lagenar fibers clustered around the lagenar longitudinal axis in the horizontal plane, but distributed in a diversity of axes in the mid-sagittal plane, which generally reflect morphological polarizations of hair cells in the lagena. We conclude that the lagena of D. latifrons plays a role in sound localization in elevation, particularly at high stimulus intensities where responses of most saccular fibers are saturated.

Acoustic Stimulation↗
PubMedDate not supplied

[A reliable symptom in differential diagnosis of cochlear and retrocochlear neurosensory hypoacusis (study of sound lateralization in Weber's test and ultrasound)].

Sound laterality in Weber test occurs mainly in peripheral defects of the acoustic analyzer (lateral conduction or reception acoustic defects of the cochlea). In retrocochlear unilateral hypoacusis or loss of hearing, laterality in this test is absent in 80-90% of the cases (affection of the VIII nerve root, acoustic nuclei, stem and midbrain conductors). This symptom is most reliable in differentiation of cochlear with retrocochlear unilateral hypoacusis and deafness. In combination of retrocochlear hypoacusis of deafness with impaired sound conduction in the same ear, the sound in Weber test can show a paradoxical laterality in an absolutely deaf ear. This indicates that Weber test sound laterality definitely reflects changes in sound conduction. Ultrasound laterality occurs in the better hearing ear in any unilateral cochlear or retrocochlear lesions, thus complicating recognition of cochlear from retrocochlear affections. Laterality of ultrasound is a sensitive indicator of neurosensory abnormalities. Major trepanation bone defects of the parietotemporal skull did not influence sound laterality in Weber test.

Cochlea↗
PubMed1994

Sciatic nerve palsy as a complication after acoustic neurinoma resection in the sitting position.

We present a case of sciatic neuropathy after operation in the sitting position. Sciatic nerve palsy as a complication of the sitting position appears to be extremely rare. The patient we describe was a short, plump woman. To attain optimal surgical exposure, a greater flexion of the hips than usual was utilized. That may explain the possible stretch injury of the sciatic nerve.

Adolescent↗
PubMed2005

Intraoperative electrophysiologic identification of the nervus intermedius.

OBJECTIVE: Although enormous attention has been directed to the localization and preservation of the facial nerve in acoustic neuroma surgery, the nervus intermedius has largely been ignored. In this article, we describe a method for intraoperative electrophysiologic identification of the nervus intermedius. STUDY DESIGN: Retrospective case review. SETTING: University hospital (tertiary care center). PATIENTS: Thirty-three patients who underwent intraoperative facial nerve monitoring for various cerebellopontine angle procedures. Recording electrodes were placed in the orbicularis oculi and orbicularis oris muscles. A constant-voltage stimulator was used to stimulate both the facial nerve and the nervus intermedius. INTERVENTIONS: None. MAIN OUTCOME MEASURE: Electrophysiologic response after stimulation of the nervus intermedius. RESULTS: Stimulation of the nervus intermedius produced long-latency, low-amplitude response recorded only on the orbicularis oris channel. The response had a mean threshold 0.4 V, a mean latency of 11.1 ms, and a mean amplitude of 11.1 microV, all significantly different from responses to stimulation the facial nerve. CONCLUSION: Knowledge of electrophysiologic features of nervus intermedius stimulation can help protect the facial nerve during cerebellopontine angle surgery. The surgeon must recognize that stimulation of the nervus intermedius can cause electromyographic activity in the facial nerve monitoring channels, but the main trunk of the facial nerve may lie in entirely different location in the cerebellopontine angle.

Adolescent↗
PubMed1988

Ipsilateral acoustic-reflex adaptation testing for detection of facial-nerve pathology: three case studies.

Abnormal acoustic-reflex adaptation monitored in the same ear for both contralaterally and ipsilaterally presented tonal activators is reported in three cases. One case had Bell's palsy, whereas the other two cases had no clinically observable evidence of seventh-nerve involvement. These cases show that the existence of abnormal acoustic-reflex adaptation in the absence of Bell's palsy does not necessarily implicate the presence of eighth-nerve pathology.

Acoustic Impedance Tests↗