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At least 199 records · Page 11Linked to original sources
PubMedDate not supplied

Neuroimaging of acoustic nerve sheath tumors after stereotaxic radiosurgery.

Using a strict method for measuring tumor size, we evaluated tumor response to radiosurgery in 88 patients with 89 acoustic tumors treated over 3 years with a 201-source cobalt-60 gamma unit. Overall, tumor size was unchanged in 73% of patients and increased in 4%. In 22% of patients, tumor diameter decreased an average of 4.9 mm 3-33 months after treatment. Tumor shrinkage occurred in 36% of 50 patients who were followed for at least 1 year after treatment. Loss of tumor contrast enhancement was seen in 79% of patients 1-18 months after treatment. Delayed communicating hydrocephalus developed in four patients. In eight patients, increased signal on T2-weighted MR images developed in the adjacent cerebellar peduncle (n = 5) or the peduncle and dorsolateral pons (n = 3) 5-15 months after treatment. T1-weighted MR imaging and CT were insensitive to these adjacent brain changes. Stereotaxic radiosurgery is an important alternative treatment for selected patients with acoustic tumors. There is no mortality or major perioperative morbidity, hospitalization time and costs are smaller than for microsurgery, patient employment or functional level is maintained, and hearing preservation and facial neuropathy rates are comparable to those in published microsurgical series. Although the rate of occurrence of trigeminal neuropathy is greater than those reported in published microsurgical series, the majority of cases are mild, transient, and nondebilitating. MR imaging before and after radiosurgery is the most sensitive imaging tool to evaluate tumor response, the presence of adjacent parenchymal signal changes, and ventricular size. With a mean follow-up time of 14.6 months, the rate of complications detected by neuroimaging is low and the tumor control rate is 96%.

Adolescent↗
PubMed2001

Cochlear nerve acoustic envelope response detection is improved by the addition of random-phased tonal stimuli.

We test Lowenstein's dc bias hypothesis as an alternative mechanism for the phenomenon sometimes called 'stochastic resonance'. Probe stimuli consisting of paired phase-locked tones at frequencies f(1) and f(2) (where f(2)-f(1)=800 Hz, f(1)>4.5 kHz) and at equal intensity were used to generate synchronous 800 Hz cochlear nerve activity (envelope responses). When a background tone of the same intensity, with a frequency halfway between f(1) and f(2), is presented simultaneously with the probe stimulus, the envelope response amplitude typically decreases. Consistent with Lowenstein's hypothesis, however, when the intensities of the probe and background tone are near the detection threshold of the envelope response (approximately 0-20 dB sound pressure level), the simultaneous presence of the background tone often increases the amplitude of the envelope response. At these same intensity levels, when the background tone precedes the probe stimulus, it decreases the amplitude of the response to the probe stimulus. The effects of simultaneous presentation of the probe and the background tone are frequency-dependent, becoming less pronounced or reversing as the frequency of the background tone departs from those of the probe stimuli.

Acoustic Stimulation↗
PubMedDate not supplied

[Stimulating effect of focused ultrasound on auditory fibers of the acoustic nerve in the frog Rana temporaria].

After mechanical destruction of the receptor apparatus, application of focused ultrasound (frequency 2.34 mHz) to the auditory fibers of the frog elicited the electrical activity in the auditory midbrain centers (torus semicircularis). Action potentials evoked by focused ultrasound were similar to those evoked by activation of the intact contralateral labyrinth. After introduction of horseradish peroxidase into the destroyed auditory capsule, fibers activated by ultrasound were detected. Therefore electrophysiological and histochemical experiments reveal stimulating effect of focused ultrasound on the auditory fibers of the VIIIth nerve.

Acoustic Stimulation↗
PubMed1978

[Electrode model for multiaxonal stimulation of the acoustic nerve (author's transl)].

An electrode arrangement is described, which allows an isolated stimulation of 25--50 singular axons: By laser beams a small ceramic plate got 25--50 perforations through which glass isolated platin wires were so fixed that they end like a brush. Only the tips of the "hairs" are not isolated. The diameter of the electrodes is approximately 10 micrometer, the length ranges between 0,5 and 1,5 mm. This electrode system is enough stabile to be pressed into a hard boiled egg without being damaged.

Acoustic Stimulation↗