Margareta B. Møller

Some forms of tinnitus may involve the extralemniscal auditory pathway

It has previously been shown that the click‐evoked responses recorded from the intracranial portion of the eighth nerve in patients with incapacitating tinnitus are not abnormal, nor is the latency of peak III of the click‐evoked brainstem auditory‐evoked potentials significantly altered; however, the latency of peak V is slightly (but significantly) shortened in comparison to that of patients with the same degree of hearing loss but no tinnitus. In this study the hypothesis that the extralemniscal auditory system is involved in the generation of tinnitus is tested. We made use of the fact that neurons of the extralemniscal auditory system also receive input from the somatosensory system, and that stimulation of the somatosensory system can influence the processing of auditory information in the extralemniscal system. In 4 of 26 patients with mild‐to‐severe tinnitus whose median nerve was stimulated electrically, the tinnitus increased noticeably during stimulation, in 6 the intensity of the tinnitus decreased noticeably, and in the remaining 16 there was no noticeable change in the tinnitus. In some of the patients the character of the tinnitus changed in a complex way. There were no significant differences in hearing thresholds in these three groups of patients. Electrical stimulation of the median nerve in 12 individuals with normal hearing who did not have tinnitus either had no effect on the loudness of sounds or it caused a slight increase in the loudness.

Intracranially recorded responses from the human auditory nerve: New insights into the origin of brain stem evoked potentials (BSEPs)

Auditory evoked potentials were recorded intracranially from the 8th nerve during neurosurgical procedures. The potentials had a large negative peak that occurred 3.0--3.7 msec after the onset of the stimulus (2 000 Hz tone bursts). When these potentials were compared with the scalp recorded brain stem evoked potentials (BSEPs) the intracranial response was found to match the latencies of the P2N3 complex of the BSEP. The results are interpreted as showing that the neural generator of the second peak of the BSEP is the intracranial portion of the auditory nerve and not, as was earlier assumed, the cochlear nucleus.

Disabling positional vertigo

We have identified a group of patients with vestibular disorders whose symptoms are not consistent with the commonly recognized syndromes such as Menieres disease, benign paroxysmal positional vertigo, and vestibular neuronitis. These patients have a constant positional vertigo and are often nauseated to an extent that makes them disabled. Their symptoms do not respond to conventional medical treatment or habituating therapy. We have found specific clinical-pathological signs in these patients that indicate that the vestibular nerve is compressed intracranially by blood vessels. Treatment of nine such patients by microvascular decompression of the eighth nerve brought total relief of symptoms in eight patients and improvement in one. We suggest that this syndrome be named disabling positional vertigo.

Microvascular decompression of the eighth nerve in patients with disabling positional vertigo: Selection criteria and operative results in 207 patients

SummaryTwo-hundred seven patients who were operated on consecutively between January 1983 and December 1990 to relieve disabling positional vertigo (DPV) using the microvascular decompression (MVD) procedure were studied. Selection of the patients for MVD operations was based on both case history and the results of otoneurological tests. Of the 177 patients with unilateral symptoms, 8 were excluded because of previous vestibular nerve section, and 6 did not return for follow-up; of the remaining 163 patients, 129 (79%) were free of symptoms or markedly improved following MVD, and none became worse. Thirty patients had symptoms and signs of bilateral DPV, and of these 1 was excluded because of previous vestibular nerve section and 3 because of multiple operations. Of the remaining 26 patients, 20 (77%) were free of symptoms or markedly improved following MVD. Eleven of these patients had more than 2 operations. The follow-up time was an average of 38 months, ranging from 3 months to 10 years.The cure rate (about 80%) of MVD for DPV is similar to that reported for MVD for trigeminal neuralgia and hemifacial spasm. The cure rate of MVD for DPV was not related to gender or to the duration of the symptoms.Following a total of 254 operations that these 207 patients underwent, 4 patients (1.6%) lost hearing and 4 (1.6%) suffered marked hearing loss. Three patients suffered temporary deficits of other cranial nerves. There were no other complications to these operations.

Technique of hearing preservation in small acoustic neuromas.

The ideal operation for acoustic neurinoma would not only provide total excision without injury to the brain stem and with preservation of facial nerve function, but would also allow retention of useful hearing in those patients who come to operation with intact hearing function. Documented preservation of useful hearing in the rather extensive literature concerning acoustic neurinomas is rare. An operative technique has been developed utilizing a retromastoid approach, brain stem auditory-evoked potentials and direct auditory monitoring, facial nerve electromyography, and microsurgical techniques that have enabled us to preserve useful hearing in three and some hearing in two of six consecutive patients who had preoperative hearing. Rules regarding preservation and criteria regarding documentation of hearing preservation are outlined.

Does intraoperative monitoring of auditory evoked potentials reduce incidence of hearing loss as a complication of microvascular decompression of cranial nerves

During a 14-month period, 129 individuals underwent 140 operations for microvascular decompression to relieve hemifacial spasm, disabling positional vertigo, tinnitus, or trigeminal neuralgia at our institution. Seven patients were operated upon twice on the same side and 4 were operated upon on both sides at different times. In each case, the brainstem auditory evoked potentials were monitored intraoperatively by the same neurophysiologist. In 75 of these operations, compound action potentials were also recorded from the exposed 8th nerve. Comparison of speech discrimination scores before the operation and at the time of discharge showed that at discharge, discrimination had decreased in 7 patients by 15% or more and increased in 4 patients by 15% or more, in 2 patients by as much as 52%. Essentially similar results were obtained when preoperative speech discrimination scores were compared with results obtained from the 87 patients who returned for a follow-up visit between 3 and 6 months after discharge. Only one patient lost hearing (during a second operation to relieve hemifacial spasm). Another patient (also operated upon to relieve hemifacial spasm) suffered noticeable hearing loss postoperatively, but had recovered nearly normal hearing by 4 months after the operation. Nine patients had an average elevation of the hearing threshold for pure tones in the speech frequency range (500 to 2000 Hz) of 11 dB or more at 4 to 5 days after the operation; 8 of these had fluid in their middle ears that most likely contributed to the hearing loss. Threshold elevations occurred at 4000 Hz and 8000 Hz in 19 and 29 ears, respectively.

Hearing in 70 and 75 year old people: Results from a cross sectional and longitudinal population study***

Audiometric data are presented from a cross sectional and longitudinal population study of 70 and 75 year old people in Gothenburg, Sweden. The population studied included 1148 randomly selected 70 year old men and women. A subsample of 376 was tested with pure tone and speech audiometry. Five years later 261 of those were tested again with the same methods. The mean pure tone thresholds were only 8 to 10 dB. higher than data chosen as representative for presbycusis in selected populations. Between the ages of 70 and 75 there was no detectable change in the pure tone thresholds for men. The hearing threshold in women had deteriorated throughout the entire frequency range and most were at 4 and 8 kHz. Speech discrimination scores were unexpectedly high. Seventy-five per cent of the women and 50 per cent of the men had discrimination scores equal to or better than 92 per cent at the age of 70. At the age of 75 about 65 per cent of the women and 35 per cent of the men had the same excellent speech discrimination

Changes in Pure-Tone Thresholds in Individuals Aged 70-81: Results from a Longitudinal Study

The results of audiometric evaluation of 376 randomly selected men and women, 70 years old and born in 1901, are reported. The investigation is part of a large study on a gerontological population in which the original participants were tested again with pure-tone and speech audiometry at ages 75, 79 and 81. We also report audiometric results obtained at ages 70 and 75 from a second group, consisting of 297 men and women born in 1906. Hearing loss was most pronounced at higher frequencies for both sexes, and men had an average of 10 dB greater hearing loss at 8 kHz than women. The decrease in hearing threshold in men between the ages of 70 and 81 was more pronounced at 2 kHz (27 dB) than at 4 and 8 kHz (15 and 20 dB, respectively). The average hearing loss in women increased at a constant rate between the ages of 70 and 79 (15 dB), while between the ages of 79 and 81 the changes in pure-tone threshold was minimal. There were no significant differences in pure-tone thresholds for women born in 1901 when compared to those born in 1906 at the ages of 70 and 75. However, men born in 1906 had a more pronounced hearing loss at the age of 75 than those born in 1901.

Gamma Knife: An Alternative Treatment for Acoustic Neurinomas

Despite surgical advances and technologic means of better monitoring seventh and eighth nerve function intraoperatively, there remains a group of patients for whom alternative methods of treatment are desirable. These include the elderly, those with bilateral tumors or tumors in only hearing ears, individuals with medical contraindications to major surgery, and those who refuse surgical resection. The University of Pittsburgh became the fifth world center and the first in the United States to install the “gamma knife” for stereotactic radiosurgery. On the basis of the pioneering work done at the Karolinska Institute in Stockholm, acoustic tumor patients who fulfill the above criteria are being treated. A tumoricidal single treatment closed-skull radiation dose is given through 201 sharply focused cobalt 60 sources, minimizing the effects on surrounding brain or other tissues. Our early results are discussed and compared to those from more than 200 cases in Stockholm. Complications and expected long-term results are presented.

Compound action potentials recorded from the exposed eighth nerve in patients with intractable tinnitus

Compound action potentials (CAP) were recorded directly from the exposed intracranial portion of the eighth nerve in 19 patients undergoing microvascular decompression (MVD) of the eighth nerve for intractable tinnitus. The waveform of the CAPs recorded in patients with tinnitus varied from normal to highly abnormal, but only in 1 patient were there distinct abnormalities in the waveform of the CAP that could not be attributed to the patients hearing loss. The mean values of the latencies of the N1 and N2 peaks in the CAPs recorded from the exposed eighth nerve in patients with tinnitus and high‐frequency hearing loss were virtually indistinguishable from the latencies obtained in patients with similar hearing loss but no tinnitus. There was no statistically significant difference between the latency of peak III in the brainstem auditory evoked potentials (BAEPs) in these two groups of patients, but the latency of peak V was slightly shorter (statistically significant) in the patients with tinnitus than it was in the patients without tinnitus.