Correlation of MRI, clinical, and electroneuronographic findings in acute facial nerve palsy

Intratemporal enhancement of (Gd-DTPA) was investigated by an interleaved-overlapping magnetic resonance imaging (MRI) technique in 35 cases of acute facial palsy. In a reference group (normal facial function), enhancement was localized from the ganglion geniculi to the stylomastoid foramen. In cases of acute palsy, the facial nerve enhanced in the meatal fundus independent of etiology (idiopathic, herpetic, or traumatic). In 70% of those with Ramsay-Hunt syndrome, the vestibular and cochlear nerves, the labyrinth, and the sheets of the internal and external auditory canal additionally enhanced. No correlation was found between intensity, extension, and duration of the enhancement and the clinical, intraoperative, or electroneuronographic degree of the facial palsy. The pathogenesis of the Gd-DTPA enhancement of the facial nerve appears to be closely connected with the vascular supply of the fallopian canal and the permeability of the neural sheets.

Are papillary adenomas endolymphatic sac tumors?

Papillary adenomas of the temporal bone have been considered as originating from the endolymphatic sac. The radiologic, surgical, and pathologic findings in a patient suffering from von Hippel-Lindau disease with bilateral papillary adenomas of the temporal bone cast some doubt on this site of origin. Radiologically, the center of tumor growth was at the top of the jugular bulb. Intraoperatively, the tumor was found to have reached the lateral wall of the endolymphatic sac, but the lumen was tumor-free. Both ciliated and nonciliated tumor cells were found in the resected tumor, resembling the ultrastructure of normal epithelial lining in the human mastoid. A strong positive immunohistochemical reaction for keratin and negative reactions for vimentin, glial fibrillary acidic protein, and S-100 protein in the tumor tissue of this patient are typical for middle ear mucosa. Therefore, the described papillary adenoma originated from the mucosa of the pneumatic spaces surrounding the jugular bulb, and the theory that the endolymphatic sac is the origin of all papillary-cystic tumors (adenocarcinomas) should be questioned.

[The value of clinical examination methods in diagnosis of acoustic neuroma]

The diagnostic value of routine clinical tests for predicting the presence of an acoustic neuroma (AN) was assessed retrospectively in a group of 391 patients having magnetic resonance imaging (MRI) scans because of a suspected retrolabyrinthine lesion. An AN was found by MRI only in 9% of these patients. The positive predictive value of unilateral sensorineural hearing loss in a pure-tone audiogram (PTA) and unilaterally impaired caloric response was 9% and 12%, respectively. In contrast, AN was found in 36% of patients with pathological brainstem evoked response audiometry (BE-RA). A normal PTA or normal caloric response did not exclude the presence of AN (specificity 90% and 71%, respectively). A normal BERA was found in less than 5% of the patients with AN. According to these results, the following guidelines should be followed for the diagnosis of AN: (1) patients with a high suspicion for AN from history, PTA and caloric responses should be sent directly for MRI; (2) patients with low suspicion for AN from screening tests should have BERA performed to exclude a retrolabyrinthine lesion.

Use of selective tyrosine kinase blockers to monitor growth factor receptor dephosphorylation in intact cells

A novel assay was developed which allows measuring the activity of protein tyrosine phosphatases (PTPases) downregulating the signaling activity of the receptors for platelet-derived growth factor (PDGF) or epidermal growth factor (EGF) in intact Swiss 3T3 cells and nerve growth factor (TrkA) in TrkA-overexpressing PC12 cells. The assay is based on the inhibition of the receptor tyrosine kinases by specific inhibitors which enter the cells rapidly and do not affect the activity of PTPases. Thereafter, the decay of phosphotyrosine in the autophosphorylated receptors is monitored by immunoblotting with anti-phosphotyrosine antibodies. The dephosphorylation kinetics of EGF receptors and PDGF receptors in Swiss 3T3 cells as measured with this assay were found to be strikingly different. EGF receptors are almost completely dephosphorylated after 2 min at room temperature, whereas PDGF receptors are dephosphorylated only by 50% after 5 min. These data agree with previous findings about receptor dephosphorylation kinetics in isolated Swiss 3T3 cell membranes employing conventional dephosphorylation assays. The novel assay will facilitate characterization of the hitherto not identified receptor-directed PTPases for PDGF receptors, EGF receptors, and TrkA. The assay principle is general and should be applicable to any PTPases and their substrates, provided specific inhibitors for the respective kinases are available. Furthermore, it can be applied to screen for regulator molecules of specific PTPases in their physiological environment.

Characterization of vestibular potentials evoked by linear acceleration pulses in the chinchilla

The objective of this study was to improve vestibular evoked potentials as a qualitative parameter for vestibular function in small laboratory animals. Linear upward acceleration pulses (up to 8 g within 1 ms) were applied to the head of anesthetized chinchillas. Electrophysiologic responses recorded by a chronically implanted electrode within the facial nerve canal consisted of an initial negative potential, labeled N1, within the first millisecond following the onset of acceleration. This potential was followed by a series of positive and negative potentials found to be highly labile to acoustic masking. The initial negative potential was only minimally sensitive to acoustic masking and persisted following surgical cochlear ablation, but completely disappeared following administration of potassium chloride into the inner ear. Recorded from the contralateral ear, N1 was unaffected by these procedures. Amplitudes of N1 decreased with attenuating stimulus intensity (1.45 microV/dB), whereby N1 latencies slightly increased (-0.015 ms/dB). These data, when coupled with the ability to completely abolish N1 with potassium intoxication while the contralateral ear remained intact, indicate that this potential represents electrophysiologic activity resulting from activation of the ipsilateral vestibular labyrinth.

Short latency vestibular evoked responses to linear acceleration stimuli in small mammals: masking effects and experimental applications

Different potential were recorded from a site close to the 8th nerve in chinchillas in response to linear acceleration pulses. Acoustic masking allowed us to distinguish between an early response (within 1 ms after initiation of the acceleration) of probable vestibular origin and later responses of probable cochlear origin. The latter were abolished by intense acoustic masking and by surgical ablation of the cochlea. The early potential was slightly reduced by simultaneous acoustic masking with white noise above 65 dB SPL and was most sensitive to 1 kHz narrow band masking. Vestibular neurons seem to be stimulated by high frequency movements of their hair cell cilia, and vestibular compound action potentials can be recorded as soon as a sufficient number of neurons are brought to a synchronized response. These vestibular evoked potentials may provide a tool for experimental studies on vestibular function in laboratory animals.

The subjective visual vertical as a clinical parameter of vestibular function in peripheral vestibular diseases

The subjective visual vertical, SV, was measured in the upright and side positions in 25 normal subjects and in 73 patients with various peripheral vestibular disorders. Significant deviations of SV (toward the affected ear) were found in 100% of the patients with vestibular nerve section and with Ramsay Hunt syndrome, in 89% of the patients with vestibular neuritis, and in 0% of the patients with benign paroxysmal positional vertigo. The deviation of SV gradually disappeared within a few weeks of the onset of the disease in all patients except in those with total VIIth nerve resection. SV is a parameter of tonic afferent differences between the two labyrinths similar to vestibular spontaneous nystagmus but is mediated by other parts of the inner ear (probably the otolith organs) and thus provides additional information on the labyrinthine function. SV measured in 90 degrees side positions, however, did not reveal asymmetric vestibular sensitivity, which is in contrast to SV tested during eccentric rotation in patients after vestibular neurectomy.

Clinical pathophysiology of vestibular neurectomy

This study attempts to characterize the residual vestibular function remaining after incomplete supralabyrinthine vestibular neurectomy performed for disabling vertigo. Patients with bilateral vestibular neurectomy had preserved horizontal vestibulo-ocular reflexes in response to high angular accelerations with gain enhancement over time. A torsional down-beating spontaneous nystagmus and an important tilt of the subjective vertical were observed when the remaining eighth nerve was sectioned after homolateral incomplete supralabyrinthine vestibular neurectomy. These findings suggest that a reorganization of vestibular reflexes may occur after incomplete supralabyrinthine vestibular neurectomy if afferents of the inferior vestibular branch are partially spared. The vestibular function after incomplete supralabyrinthine vestibular neurectomy does not affect the postoperative control of vertiginous attacks and may have positive effects in case of deterioration of the contralateral inner ear.

Effects of semicircular canal plugging on caloric nystagmus recorded in three dimensions

In Rhesus monkeys, distinct eye movement response components in the planes of the semicircular canals (canal plane vectors, CPV) were identified by 3-dimensional recordings of caloric nystagmus elicited in different head positions relative to gravity. Surgical plugging of single semicircular canals (SCC) was used to identify the generators of these response components. The lateral CPV is a sinusoidal function of head position, compatible with a thermovective mechanisms in this canal. Surgical plugging of the lateral SCC leaves only a small head position independent, lateral CPV, probably due to direct temperature effects on lateral SCC afferents. The posterior and anterior CPVs are complex responses composed of various components of which the present plugging experiments identified two generators: i) effects of thermovection in the lateral SCC, demonstrated by modifications of posterior and anterior CPVs after occlusion of the lateral SCC; and ii) thermovection in the vertical SCCs, demonstrated by effects of plugging a single vertical SCC exclusively on the corresponding CPV. This is the first definite identification of the vertical SCCs as contributors to the generation of nystagmus induced by caloric irrigation of the outer ear canal. It may provide a basis for the development of a modified caloric test measuring more than only lateral canal function in human patients.

Selective platelet-derived growth factor receptor kinase blockers reverse sis-transformation

A novel class of tyrosine kinase blockers represented by the tyrphostins AG1295 and AG1296 is described. These compounds inhibit selectively the platelet-derived growth factor (PDGF) receptor kinase and the PDGF-dependent DNA synthesis in Swiss 3T3 cells and in porcine aorta endothelial cells with 50% inhibitory concentrations below 5 and 1 microM, respectively. The PDGF receptor blockers have not effect on epidermal growth factor receptor autophosphorylation; weak effects on DNA synthesis stimulated by insulin, by epidermal growth factor, or by a combination of both; and over an order of magnitude weaker blocking effect on fibroblast growth factor-dependent DNA synthesis. AG1296 potently inhibits signaling of human PDGF alpha- and beta-receptors as well as of the related stem cell factor receptor (c-Kit) but has no effect on autophosphorylation of the vascular endothelial growth factor receptor KDR or on DNA synthesis induced by vascular endothelial growth factor in porcine aortic endothelial cells. Treatment by AG1296 reverses the transformed phenotype of sis-transfected NIH 3T3 cells but has no effect on src-transformed NIH 3T3 cells or on the activity of the kinase p60c-src(F527) immunoprecipitated from these cells. These potent and selective compounds represent leads for the development of novel agents to combat tumors driven by PDGF or to inhibit PDGF action in other diseases in which PDGF plays a key role, such as restenosis.

[Stapotomy with ultrasound? Animal experiment study of possible side effects]

Stapedectomy by ultrasound has been proposed as an alternative method for perforating the stapes footplate in surgery for otosclerosis. Possible functional adverse effects of ultrasound perforation of the otic capsule in guinea pigs were investigated in the present study by means of vestibular evoked potentials (VsEP). VsEP were elicited by pulsed linear accelerations applied to the animal's head following surgical removal of the middle ear, following intense ultrasound drilling around the otic capsule and after drilling a small hole in the anterior bony wall of the vestibule. All manipulations did not affect amplitudes and latencies of the early potential N1 (less than 1 msec after onset of acceleration). Significant alterations of N1 occurred following direct mechanical damage of the otolithic organs, indicating that VsEP can be used to detect lesions of these receptors and therefore may be used as a parameter of vestibular function in experimental animals. Findings indicate that perforation of the otic capsule by ultrasound is possible without inducing functional lesions of the otolithic organs.

Bilateral vestibular neurectomy for treatment of vertigo

The effects of bilateral vestibular neurectomy on equilibrium and vestibular function were clinically evaluated in two patients more than 15 years after surgery. Both patients had bilateral Menière's disease and their vertiginous spells were permanently resolved after the second vestibular neurectomy. Symptoms of disequilibrium were absent in one patient and mild in the other. Reflexive horizontal eye movements on whole body rotation in darkness were absent on low angular accelerations (2 degrees/s2), but could be elicited with angular accelerations of 20 degrees/s2 or higher. Extravestibular cues generating these eye movements seemed to be unlikely because a "control" patient with complete peripheral vestibular ablation after bilateral subtotal petrosectomy did not present reflexive eye movements under the same stimulus paradigms. An incomplete deafferentiation of the vestibular end organ (rather than regeneration of vestibular nerve fibers) and a consecutive impairment of the central velocity storage mechanism may explain the good functional outcome in our bilateral neurectomized patients.

Otoneuroscience and space vestibulo-neuroscience in the new century

From a clinically oriented point of view, efforts of otoneuroscience should be directed toward an improvement of the management of dizzy and vertiginous patients. At present, the main obstacles in this field are: (1) the lack of specific therapies for many of the clinical diagnoses. This reduces the necessity of clinical vestibular diagnosis to a pragmatic exclusion of the few diseases with therapeutic consequences; (2) the lack of feedback to confirm or disprove clinical diagnoses; (3) poor knowledge of the pathophysiology of many of the otoneurological diseases; experiments in animal models may be helpful in this respect; (4) most progress in medicine originates from the results of numerous, poorly controlled 'unscientific' trial and error experiments obtained during treatment of patients; training clinicians in more scientific, critical thinking would help to increase the profits that can be realized from this important source of information; and (5) to date, information obtained during zero-gravity experiments in space have not yet led to important consequences in treatment of patients under 1-g conditions, but are important for a possible evolutionary step of mammals adapting to a new environment.

Three-dimensional analysis of caloric nystagmus in the rhesus monkey

The aim of this study was to investigate whether caloric nystagmus contains response components that can be attributed to a stimulation of the vertical semicircular canals. Three dimensional eye movement recordings with a dual search coil technique revealed important horizontal, vertical and torsional nystagmus components following irrigation of the external ear canal with cold water in various head positions relative to gravity. Horizontal nystagmus components, i.e. lateral semicircular canal vectors, followed a cosine function of both the pitch and yaw angle of the head relative to gravity, confirming a mainly thermovective mechanism for stimulation of the horizontal canals. Vertical and torsional nystagmus components behaved differently following left and right ear irrigations. Right-left symmetrical vectors emerged only when the vertical and torsional components were transposed into vectors of single semicircular canal directions. The intensity of these vertical semicircular canal vectors as a function of the position of the corresponding canal relative to gravity, however, excludes important thermovective mechanisms acting at the vertical canals. It remains an open question whether these vertical canal vectors represent a non-thermovective caloric stimulation of vertical canal afferents.

On the pathomechanism of cochlear dysfunction in experimental perilymph fistulas

The mechanism leading to hearing impairment in perilymph fistulas was investigated in guinea pigs with perforated round window membranes (RWM) by analyzing alterations of inner ear fluid pressure, changes of auditory function following manipulations to get presumed air bubbles out of the cochlea ("positional audiometry"), and temporal bone sections. The instantaneous loss of normal positive inner ear fluid pressure after RWM perforation had no immediate effect on auditory function. Inner ear pressure was restored 4 days following RWM perforation. "Positional audiometry" was negative in guinea pigs with perforated RWM. All ears in which auditory thresholds had increased had additional iatrogenic lesions at the spiral lamina. Fistulas in the RWM per se do not affect auditory thresholds. The question of the surgical repair of fistulas was not directly addressed; it only can be concluded that there are no direct sequelae of an isolated fistula which induce auditory impairment and which could be prevented by surgical repair of the fistula.

The measurement and manipulation of intralabyrinthine pressure in experimental endolymphatic hydrops

Three to four months after unilateral surgical ablation of the endolymphatic duct and sac, endolymphatic and perilymphatic pressures were measured in both the normal and hydropic ears of 11 guinea pigs. In normal ears, endolymphatic pressure always approximated perilymphatic pressure. Endolymphatic pressure exceeded perilymphatic pressure in all ears with hydrops, except one in which these pressures were equal. The effect of postural inversion on inner ear pressures were studied in both normal and hydropic inner ears. Normal ears showed endolymphatic and perilymphatic pressure to rise equally during this maneuver. In hydropic ears, the difference between endolymphatic and perilymphatic pressure was notably reduced from measurements obtained in the prone position. This study indicates that an alteration in pressure regulation within the inner ear may be important in the pathogenesis and manifestation of experimental endolymphatic hydrops in the guinea pig. Physiologic mechanisms and clinical implications of these results are described.

Vertical Optokinetic Nystagmus and Optokinetic Afternystagmus in Humans

Vertical optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN) were recorded in 6 normal subjects using the magnetic scleral search coil technique in order to reevaluate the up-down symmetry of these responses. The effects of body position relative to gravity were investigated by comparing OKN and OKAN elicited with the subjects in an erect and in a lateral side position. No consistent up-down asymmetry in vertical OKN was found but OKAN was asymmetric (up slow phase velocity > down slow phase velocity). Most subjects had an immediate reversal in OKAN slow phase velocity after downward stimuli. No significant effects of static head position (upright versus lateral position) on vertical OKN and OKAN were found. These features of human OKAN can be explained by the summation of two oppositely directed velocity storage mechanisms.

Experimental endolymphatic hydrops: are cochlear and vestibular symptoms caused by increased endolymphatic pressure?

The correlation between inner ear pressure and cochlear function was investigated in guinea pigs with unilaterally obliterated endolymphatic sacs and ducts. In 11 animals that developed endolymphatic hydrops, auditory thresholds as monitored by auditory evoked action potentials had increased with recruitment. Most of these animals also experienced episodes of spontaneous nystagmus. In control ears endolymphatic pressure did not differ more than 0.5 cm H2O from perilymphatic pressure. In six of 11 hydropic ears, endolymphatic pressure was more than 0.5 cm H2O higher than perilympathic pressure; auditory thresholds in all these ears had deteriorated within 2 weeks before pressure recording. No further hearing deterioration within this period was noted in five hydropic ears with endolymphatic pressure equal to or lower than perilymphatic pressure. Endolympathic-perilymphatic pressure gradients may contribute to auditory threshold increase in endolymphatic hydrops, but are not its only cause.

Endoneurial fluid pressure in the facial nerve of guinea pigs and rabbits

Endoneurial fluid pressure (EFP) was measured in the facial nerve in rabbits and guinea pigs using a servo-controlled micropipette system. EFP in the tympanic segment was 5.3 +/- 1.2 cm H2O in rabbits and 4.1 +/- 0.9 and 4.2 +/- 0.9 cm H2O in the tympanic and mastoid segment respectively in guinea pigs, while EFP in the sciatic nerve was around 2 cm H2O. The higher pressure in the facial nerve may be related to the proximo-distal flow of the endoneurial fluid in peripheral nerves.

Early alterations of cochlear function in experimental perilymph fistulas

Alterations of cochlear function secondary to perforation of the round window membrane in guinea pigs were expected to reveal sensitive and/or specific audiometric parameters in perilymph fistulas. A perforation of the round window membrane either did not affect acoustic compound action potential thresholds, or induced a delayed, possibly conductive, inner ear hearing loss. Also, evoked suprathreshold responses deteriorated progressively and independently of the increase of compound action potential thresholds. A sudden (conductive) hearing loss and a poor response to suprathreshold stimulation might indicate inner ear damage secondary to a perilymphatic fistula.

[Sudden unilateral deafness and geotropic positional nystagmus--a special form of acute cochleo-vestibular disorders?]

Three patients with complete sudden unilateral hearing loss suffered from delayed vertigo and presented a strong geotropic positional nystagmus during the evolution of their disease. Significant direction-fixed spontaneous nystagmus was absent, although two of the three patients had markedly decreased caloric responses on the diseased side. These findings are considered as a special form of peripheral cochleovestibular disorder restricted mainly to the cochlea and the otolith organs.

A novel L-glutamate oxidase from Streptomyces endus. Purification and properties

A new flavoenzyme using molecular oxygen to oxidize L-glutamic acid has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis, from the culture medium of Streptomyces endus. Hydrogen peroxide, 2-oxoglutaric acid and ammonia are formed as products. Among 25 amino acids tested including D-glutamic acid, L-glutamine and L-aspartic acid, only L-glutamic acid is converted. The molecular mass of the enzyme was estimated to be about 90 kDa by gel chromatography and 50 kDa by SDS/PAGE. The subunit contains 1 molecule noncovalently bound FAD. The absorption spectrum shows maxima at 273, 355 and 457 nm and the isoelectric point is at pH 6.2. The Km value for L-glutamic acid in air-saturated phosphate pH 7.0 was estimated to be 1.1 mM, the Km for oxygen was calculated to be 1.86 mM at saturating concentration of L-glutamic acid. The enzymic reaction is inhibited by Ag+ and Hg2+ ions. The enzyme described here distinctly differs from two microbial L-glutamate oxidases purified hitherto, with regard to extremely high substrate specificity and to the subunit structure.

Maintenance of hydrostatic pressure gradients in the membranous labyrinth

In normal guinea pig ears, hydrostatic perilymphatic pressure is equal to endolymphatic pressure. Alterations of perilymphatic pressure induced, for example, by laceration of the round window membrane are transmitted immediately to the endolymphatic compartment, probably via Reissner's membrane. In guinea pigs with experimental endolymphatic hydrops, however, pressure gradients between the endolymph and perilymph remained preserved after rupture of the round window membrane. This is considered as further evidence that after long-standing distention of Reissner's membrane the membranous labyrinth loses its ability to equalize endolymphatic and perilymphatic pressure.

The surgical approach to the endolymphatic sac and the cochlear aqueduct in the guinea pig

The endolymphatic sac and cochlear aqueduct are primary passages of the endolymphatic and perilymphatic fluid compartments in the labyrinth. Closure of the endolymphatic sac and duct in the guinea pig will result in the development of endolymphatic hydrops. Although obstruction of the cochlear aqueduct in this species does not seem to result in any dysfunction, this structure may serve in the dynamics of inner ear fluid physiology. The anatomy of the guinea pig temporal bone is described with special emphasis on the endolymphatic sac and cochlear aqueduct. Surgical techniques to gain access to these structures through both a middle and posterior cranial fossa approach are described.