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Biomedical subjects

A R Møller

Publications and source records attributed to A R Møller.

At least 91 records · Page 5Linked to original sources
PubMed1987

Avulsion rupture of the internal auditory artery during operations in the cerebellopontine angle: a study in monkeys.

The effect of manipulations in the cerebellopontine (CP) angle on the cochlear nerve was studied in 12 rhesus monkeys to elucidate how surgical procedures in the CP angle may affect the peripheral auditory system. Brain stem auditory evoked potentials and compound action potentials from the cochlear nerve were recorded throughout the experiments and were studied to determine the level of injury to the cochlear nerve. After the manipulations, the animals were perfused with fixatives and their temporal bones were removed and examined histologically. The monkeys showed electrophysiological changes similar to those observed in humans as a result of surgical manipulations in the CP angle. Avulsions of the internal auditory artery and cochlear nerve fibers at the area cribrosa were the most common histological findings. The auditory evoked potentials were suddenly and irreversibly lost during the manipulations in 3 monkeys, and hemorrhagic foci were identified histologically in these animals at the fundus of the internal auditory canal (the area cribrosa). No morphological changes at locations other than the area cribrosa were identified in these 3 monkeys. The results of this study indicate that injury to the internal auditory artery at the area cribrosa may play an important role in the abrupt loss of hearing experienced by some patients while they are undergoing operations in the CP angle. This study also led to speculation regarding the possible existence of collateral circulation to the cochlea as a factor in injury to the internal auditory artery during acoustic neurinoma operations.

Animals↗
PubMed1987

Monitoring facial EMG responses during microvascular decompression operations for hemifacial spasm.

Facial electromyographic (EMG) responses were monitored intraoperatively in 67 patients with hemifacial spasm who were operated on consecutively by microvascular decompression of the facial nerve near its exit from the brain stem. At the beginning of the operation, electrical stimulation of the temporal or the zygomatic branch of the facial nerve gave rise to a burst of EMG activity (autoexcitation) and spontaneous EMG activity (spasm) that could be recorded from the mentalis muscle in all patients. In some patients, the spontaneous activity and the autoexcitation disappeared after the dura was incised or when the arachnoid was opened, but stimulation of the temporal branch of the facial nerve caused electrically recordable activity in the mentalis muscle (lateral spread) with a latency of about 10 msec that lasted until the facial nerve was decompressed in all but one patient, in whom it disappeared when the arachnoidal membrane was opened. When the facial nerve was decompressed, this lateral spread of antidromic activity disappeared totally in 44 cases, in 16 it was much reduced, and in seven it was present at the end of the operation at about the same strength as before craniectomy. In four of these last seven patients there was still very little improvement of the spasm 2 to 6 months after the operation; these four patients underwent reoperation. In two of the remaining three patients, the spasm was absent at the 3- and 7-month follow-up examination, respectively, and one had mild spasm. Of the 16 patients in whom the lateral spread response was decreased as a result of the decompression but was still present at the end of the operation, 14 had no spasm and two underwent reoperation and had mild spasm at the last examination. Of the 44 patients in whom the lateral spread response disappeared totally, 42 were free from spasm and two had occasional mild spasm at 6 and 13 months, respectively, after the operation. Monitoring of facial EMG responses is now used routinely by the authors during operations to relieve hemifacial spasm, and is performed simultaneously with monitoring of auditory function for the purpose of preserving hearing. The usefulness of monitoring both brain-stem auditory evoked potentials recorded from electrodes placed on the scalp and compound action potentials recorded directly from the eighth cranial nerve is evaluated.

Electromyography↗
PubMed1987

Cochlear nerve injuries caused by cerebellopontine angle manipulations. An electrophysiological and morphological study in dogs.

Changes in the response from the cochlear nerve in dogs resulting from cerebellopontine angle (CPA) manipulations were correlated with histological changes in the nerve. The aim of this study was to determine the mechanisms underlying hearing deficits incurred as a result of manipulations in the CPA. Compound action potentials (CAP) were recorded from the cochlear nerve in response to click stimulation before, during, and after cerebellar and eighth nerve retractions were performed under anesthesia. The retractions were carried out to elicit different degrees of change in the latency and waveform of the CAP. About 30 minutes after completion of the manipulations, the dogs were perfused with a fixative and their cochlear nerves and brain stems were prepared for histological studies. The results showed that retraction of the eighth nerve caused a disintegration of the myelin sheath, and there were multiple and extensive foci of petechial hemorrhage and thromboses of the vasa nervorum of the cochlear nerve. In two dogs in which retraction was carried to a point at which the N2 peak of the CAP was abruptly obliterated, there was a separation of the central and peripheral myelin junction (Obersteiner-Redlich (OR) zone) and bleeding from the vasa nervorum at the OR zone. In the dogs in which the changes in the CAP had almost recovered before fixative perfusion, there were petechial hemorrhages within the cochlear nerve trunk, thus showing that improvement of electrophysiological responses may not always correlate with the absence of morphological changes.

Animals↗
PubMed1986

Pathophysiological mechanisms of intraoperative and postoperative hearing deficits in cerebellopontine angle surgery: an experimental study.

Pathophysiological mechanisms responsible for intraoperative and postoperative hearing deficits associated with cerebellopontine (CP) angle operations were explored experimentally in dogs. The CP angle operative manipulations performed were the same as those experienced by human patients, and auditory evoked potentials were monitored intraoperatively. As a result of the operative manipulations, petechial or confluent hemorrhages occurred at the compressed portions of the cochlear nerve, and intravascular clots were often observed. Disintegration of the nerve fibers was verified by ultrastructural examination. Moreover, rupture of the microvasculature within the cochlear nerve occurred at locations remote from the operative site, due to stretching of the nerve trunk. The Obersteiner-Redlich zone, the Schwann-glial junction of the cochlear nerve, was a locus minoris resistentiae in CP angle surgery; the vasa nervorum easily bled at this zone and the peripheral and central myelins easily separated at their junctional zones ("central" avulsion injury). Intracochlear hemorrhages were identified as the most probable cause of the sudden loss of all components of the auditory evoked potentials, a frequent predictor of postoperative hearing loss, although rupture, occlusion, or vasospasm of the main trunk of the internal auditory artery have also been implicated as possible causes of such hearing losses. The results of this study show that hearing preservation is highly dependent on preserving not only the nerve at the operative site but also the remote O-R zone and intracochlear structures.

Animals↗
PubMed1986

Physiological abnormalities in hemifacial spasm studied during microvascular decompression operations.

The pathophysiology of hemifacial spasm was studied using electrophysiologic recordings made during neurosurgical operations to relieve it by microvascular decompression of the facial nerve near its entrance into the brain stem. Electrical stimulation of the temporal or the marginal mandibular branch of the facial nerve resulted in a response not only from the muscles that were innervated by the branch of the facial nerve that was stimulated, but also from other muscles, as evidenced by EMG recordings. This "lateral spread" of antidromic activity was facilitated by stimulation at a high rate (50 pps): the response increased five- to tenfold within a few seconds. When the repetition rate was reduced to the initial low stimulus rate (2 to 5 pps), facilitation continued for periods lasting from a few seconds to several minutes. The amplitude of the response of the supraorbital reflex (blink reflex), which can be elicited in patients with hemifacial spasm intraoperatively on the affected side despite the use of inhalation anesthesia, also increased after brief stimulation at a high rate (50 pps). After the facial nerve had been decompressed, both the lateral spread response and the blink reflex response were absent. These results support the hypothesis that hemifacial spasm is the result of hyperexcitability of the facial motor nucleus and facilitation of cross-transmissions between cells in the nucleus that innervate different parts of the face.

Electric Stimulation↗
PubMed1986

Blink reflex in patients with hemifacial spasm. Observations during microvascular decompression operations.

The blink reflex cannot normally be elicited during surgical anesthesia using inhalation anesthetics. However, in patients with hemifacial spasm (HFS) the early component of the reflex response (R1) can be elicited on the affected side but not on the unaffected side during such anesthesia. The electromyographic (EMG) response from the mentalis muscle to stimulation of the supraorbital nerve was recorded during microvascular decompression (MVD) of the facial nerve to relieve HFS and compared to the response from the same muscle to stimulation of the zygomatic branch of the facial nerve in four patients. During the operation before the facial nerve was decompressed, contractions in both the orbicularis oculi and the mentalis muscles could be elicited by stimulation of the supraorbital nerve (mean latencies 12.2 +/- 1.9 and 12.9 +/- 2.0 ms, respectively). When the facial nerve had been decompressed the blink reflex could no longer be elicited, and there was no response from the mentalis muscle to stimulation of the zygomatic branch of the facial nerve. Compound action potentials (CAP) recorded from the 7th cranial nerve in response to stimulation of the supraorbital nerve had latencies of 7.5 ms +/- 1.4 ms to the negative peak.

Anesthesia, General↗
PubMed1986

Neural generators of the somatosensory evoked potentials: recording from the cuneate nucleus in man and monkeys.

The neural generators of the somatosensory evoked potentials (SEPs) elicited by electrical stimulation of the median nerve were studied in man and in rhesus monkeys. Recordings from the cuneate nucleus were compared to the far-field potentials recorded from electrodes placed on the scalp. It was found that the shape of the response from the surface of the human cuneate nucleus to stimulation of the median nerve is similar to that of the response recorded more caudally in the dorsal column, i.e., an initially small positivity followed by a negative wave that is in turn followed by a slow positive wave. The beginning of the negative wave coincides in time with the N14 peak in the SEP recorded from the scalp, and its latency is 13 msec. The response from the cuneate nucleus in the rhesus monkey has a similar shape and its negative peak appears with the same latency as the positive peak in the vertex response that has a latency of 4.5 msec; the peak negativity has a latency of about 6 msec and thus coincides with P6.2 in the vertex recording. Depth recordings from the cuneate nucleus and antidromic stimulation of the dorsal column fibers in the monkey provide evidence that the early components of the response from the surface of the cuneate nucleus are generated by the dorsal column fibers that terminate in the nucleus. The results support the hypothesis that the P14 peak in the human SEP is generated by the termination of the dorsal column fibers and that the cuneate nucleus itself contributes little to the far-field potentials.

Animals↗
PubMed1986

Neural generators of the brain-stem auditory evoked potentials (BAEPs) in the rhesus monkey.

Brain-stem auditory evoked potentials (BAEPs) were recorded from rhesus monkeys in response to click stimuli. The BAEPs in the monkey have only 4 major peaks, while 5 major peaks can be identified in the human BAEP. The responses from electrodes placed at the vertex and the mastoid recorded either differentially or separately using non-cephalic references were compared to concomitant recordings from the auditory nerve, the cochlear nucleus, and the inferior colliculus, including the lateral lemniscus and the brachium of the inferior colliculus. It was found that the response from the intracranial portion of the auditory nerve lags behind the far-field response recorded from the mastoid by about 0.2 msec. The major component of the potentials recorded from the lateral lemniscus appeared with a latency that was close to that of the fourth peak in the BAEP. Deafferentation of the inferior colliculus resulted in only small changes in the BAEP, indicating that the contributions to the BAEP from the inferior colliculus and more central structures of the ascending auditory pathway are insignificant. It is concluded that the main reason for the difference between the human BAEP and the BAEP in the rhesus monkey is the smaller size of the monkey's head and the resulting shorter auditory nerve. The result is that the auditory nerve in the monkey only generates one peak in the far-field response, while in man the auditory nerve gives rise to both of the two earliest peaks in the BAEP; thus, the BAEP in man has 5 peaks while that in the monkey has only 4 peaks.

Animals↗
PubMed1986

Dynamic properties of the responses of single neurons in the inferior colliculus of the rat.

The responses of single cells in the central nucleus of the inferior colliculus of the rat were studied with characteristic frequency tones amplitude modulated by pseudorandom noise or sinusoidal waveforms, in order to investigate the degree to which these responses can be described by a linear model. When pseudorandom noise was used as the modulating waveform, period histograms of the response locked to the periodicity of the noise were cross-correlated with a single period of the noise. The response of a model, having this cross-correlogram as its impulse response and the pseudorandom noise sequence as the input waveform, differed in appearance from the corresponding period histogram of the neural discharges, indicating that the latter contained a non-negligible, nonlinear component. Further manipulation of the data showed that the most significant nonlinearities were of even order, which indicates that the changes in neural discharge rate to increments and decrements in stimulus intensity are asymmetrical. In some units, particularly at low mean stimulus intensities, this was clearly evident as a halfwave rectification of the period histogram. The magnitude of the modulation of the period histograms increased as a function of the sound intensity for some units, while in others it decreased; in still other units the magnitude of the modulation of the neural discharges was relatively constant over a large range of stimulus intensities. When the modulation transfer functions were estimated from the responses to noise-modulated sounds they were found to be very similar to those obtained using sinusoidally modulated sound, despite large degrees of nonlinearity being present in the responses to both types of sound.

Acoustic Stimulation↗
PubMed1986

Diagnosis and surgical treatment of disabling positional vertigo.

This report reviews the characteristic symptoms of disabling positional vertigo (DPV), and the tests used to reach a differential diagnosis of this disorder. Twenty-one patients were operated on consecutively for management of DPV between March, 1983, and September, 1984. In all patients one or more arteries or veins was found to be compressing the eighth cranial nerve when the nerve was exposed for microvascular decompression to relieve the symptoms of DPV. After the operation, 16 of the 21 patients were free of symptoms, or symptoms were so much improved that the patients returned to normal work or social life. Two patients had no improvement and three had limited relief of symptoms postoperatively. None of the patients experienced hearing loss as a result of the operation to relieve DPV, but one patient suffered a cerebellar contusion during the operation.

Adolescent↗
PubMed1986

Operative management of tumors involving the cavernous sinus.

In the past, neurosurgeons have been reluctant to operate on tumors involving the cavernous sinus because of the possibility of bleeding from the venous plexus or injury to the internal carotid artery (ICA) or the third, fourth, or sixth cranial nerves. The authors describe techniques for a more aggressive surgical approach to neoplasms in this area that are either benign or locally confined malignant lesions. During the last 2 years, seven tumors involving the cavernous sinus have been resected: six totally and one subtotally. The preoperative evaluation included axial and coronal computerized tomography, cerebral angiography, and a balloon-occlusion test of the ICA. Intraoperative monitoring of the third, fourth, sixth, and seventh cranial nerves was used to assist in locating the nerves and in avoiding injury to them. The first major step in the operative procedure was to obtain proximal control of the ICA at the petrous apex and distal control in the supraclinoid segment. The cavernous sinus was then opened by a lateral, superior, or inferior approach for tumor resection. Temporary clipping and suture of the ICA was necessary in one patient. None of the patients died or suffered a stroke postoperatively. Permanent trigeminal nerve injury occurred in three patients; in two, this was the result of tumor invasion. One patient suffered temporary paralysis of the third, fourth, and sixth cranial nerves, and in another the sixth cranial nerve was temporarily paralyzed. Preoperative cranial nerve deficits were improved postoperatively in three patients. Radiation therapy was administered postoperatively to four patients. These seven patients have been followed for 6 to 18 months to date and none has shown evidence of recurrence of the intracavernous tumor.

Adenoma↗
PubMed1986

Effect of click spectrum and polarity on round window N1N2 response in the rat.

The effect of the duration of click stimuli on the compound action potential recorded from the round window in the rat and the effect of low-pass filtering of short click sounds were studied. Thus the intensity functions of the round window N1 potential have a two-segment course and there is a difference in the response to rarefaction and condensation clicks, depending upon the content of low-frequency components in the click stimulus. The intensity function of the rat's response to broadband clicks does not show the same two-segment course as has been reported in experiments in other animals, and there is little difference between the response to condensation clicks and that to rarefaction clicks in this animal. However, when the duration of the click is increased or when broadband clicks are subjected to low-pass filtering, the intensity functions in response to condensation clicks do show a change in course, while the response to rarefaction clicks remains essentially unchanged. A similar change in the response to a broadband click can be induced by adding a low-pass-filtered click to the broadband click. The response to such a combination is not only a linear summation of the neural response to the individual components of the stimuli and the cochlear microphonics, but the low-frequency components that are added also affect the response to the broadband click, mainly by reducing the amplitude of the response.

Acoustic Stimulation↗
PubMed1985

Synkinesis in hemifacial spasm: results of recording intracranially from the facial nerve.

We show evidence that the motonucleus of the facial nerve is involved in producing the synkinesis in patients with hemifacial spasm. These results were obtained by recording from the intracranial portion of the facial nerve and from the orbicularis oculi muscle in patients operated upon for hemifacial spasm during electrical stimulation of the mandibular branch of the facial nerve. Also, the electromyographic response from the same muscle was recorded when the facial nerve was electrically stimulated at a location near the brainstem. The results show that it is unlikely that the symptoms of patients with hemifacial spasm can be explained on the basis of ephaptic transmission at the site of lesion of the facial nerve.

Action Potentials↗