On the Sound Reactions of Tullio

Vestibular Evoked Myogenic Potential (VEMP) Testing for Diagnosis of Superior Semicircular Canal Dehiscence

Superior semicircular canal dehiscence is a bony defect of the superior semicircular canal, which can lead to a variety of auditory and vestibular symptoms. The diagnosis of superior semicircular canal dehiscence (SCD) can be challenging, time consuming, and costly. The clinical presentation of SCD patients resembles that of other otologic disease, necessitating objective diagnostics. Although temporal bone CT imaging provides excellent sensitivity for SCD detection, it lacks specificity. Because the treatment of SCD is surgical, it is crucial to use a highly specific test to confirm the diagnosis and avoid false positives and subsequent unnecessary surgery. This review provides an update on recent improvements in vestibular evoked myogenic potential (VEMP) testing for SCD diagnosis. Combining audiometric and conventional cervical VEMP results improves SCD diagnostic accuracy. High frequency VEMP testing is superior to all other methods described to date. It is highly specific for the detection of SCD and may be used to guide decision-making regarding the need for subsequent CT imaging. This algorithmic sequential use of testing can substantially reduce radiation exposure as well as cost associated with SCD diagnosis.

Evolutionary changes in the cochlea and labyrinth: Solving the problem of sound transmission to the balance organs of the inner ear

This review article examines the evolutionary adaptations in the vertebrate inner ear that allow selective activation of auditory or vestibular hair cells, although both are housed in the same bony capsule. The problem of separating acoustic stimuli from the vestibular end organs in the inner ear has recently reemerged with the recognition of clinical conditions such as superior canal dehiscence syndrome and enlarged vestibular aqueduct syndrome. In these syndromes, anatomical defects in the otic capsule alter the functional separation of auditory and vestibular stimuli and lead to pathological activation of vestibular reflexes in response to sound. This review demonstrates that while the pars superior of the labyrinth (utricle and semicircular canals) has remained fairly constant throughout evolution, the pars inferior (saccule and other otolith, macular, and auditory end organs) has seen considerable change as many adaptations were made for the development of auditory function. Among these were a relatively rigid membranous labyrinth wall, a variably rigid otic capsule, immersion of the membranous labyrinth in perilymph, a perilymphatic duct to channel acoustic pressure changes away from the vestibular organs, and different operating frequencies for vestibular versus auditory epithelia. Even in normal human ears, acoustic sensitivity of the labyrinth to loud clicks or tones is retained enough to be measured in a standard clinical test, the vestibular-evoked myogenic potential test.

Vestibular Responses to Sound

Research into vestibular responses to sound has evolved in four stages. The first, largely the work of Tullio in the 1920s, involved inspection of the eye, head, and postural responses to sound of alert animals with surgical fenestrae into various parts of the bony labyrinth. The second, begun in 1964 by Bickford and his group and continued by our group and then by others in the last 10 years, involves the measurement of evoked myogenic potentials to air-conducted and bone-conducted clicks and tones in normal humans. The third, begun by Mikaelian at about the same time as Bickford and continued by McCue, our group, and others, involves electrophysiological recordings of primary vestibular afferent neuron responses to sound in anesthetized animals. The fourth involves measurements of vestibulo-ocular responses to sound in humans with the Tullio phenomenon. It was begun by Minor and his group in 1998 with the observation that sound-induced nystagmus in humans, the Tullio phenomenon, aligned with the rotation axis of the superior semicircular canal. They then showed a defect in the temporal bone between the apex of the superior semicircular canal and the middle cranial fossa, which was the cause of most, if not all, cases of sound-induced nystagmus. Here some of the key observations made in each of these four stages are reviewed.

Clinical Manifestations of Superior Semicircular Canal Dehiscence

OBJECTIVES/HYPOTHESES

To determine the symptoms, signs, and findings on diagnostic tests in patients with clinical manifestations of superior canal dehiscence. To investigate hypotheses about the effects of superior canal dehiscence. To analyze the outcomes in patients who underwent surgical repair of the dehiscence.

STUDY DESIGN

Review and analysis of clinical data obtained as a part of the diagnosis and treatment of patients with superior canal dehiscence at a tertiary care referral center.

METHODS

Clinical manifestations of superior semicircular canal dehiscence were studied in patients identified with this abnormality over the time period of May 1995 to July 2004. Criteria for inclusion in this series were identification of the dehiscence of bone overlying the superior canal confirmed with a high-resolution temporal bone computed tomography and the presence of at least one sign on physiologic testing indicative of superior canal dehiscence. There were 65 patients who qualified for inclusion in this study on the basis of these criteria. Vestibular manifestations were present in 60 and exclusively auditory manifestations without vestibular symptoms or signs were noted in 5 patients.

RESULTS

For the 60 patients with vestibular manifestations, symptoms induced by loud sounds were noted in 54 patients and pressure-induced symptoms (coughing, sneezing, straining) were present in 44. An air-bone on audiometry in these patients with vestibular manifestations measured (mean +/- SD) 19 +/- 14 dB at 250 Hz; 15 +/- 11 dB at 500 Hz; 11 +/- 9 dB at 1,000 Hz; and 4 +/- 6 dB at 2,000 Hz. An air-bone gap 10 dB or greater was present in 70% of ears with superior canal dehiscence tested at 250 Hz, 68% at 500 Hz, 64% at 1,000 Hz, and 21% at 2,000 Hz. Similar audiometric findings were noted in the five patients with exclusively auditory manifestations of dehiscence. The threshold for eliciting vestibular-evoked myogenic potentials from affected ears was (mean +/- SD) 81 +/- 9 dB normal hearing level. The threshold for unaffected ears was 99 +/- 7 dB, and the threshold for control ears was 98 +/- 4 dB. The thresholds in the affected ear were significantly different from both the unaffected ear and normal control thresholds (P < .001 for both comparisons). There was no difference between thresholds in the unaffected ear and normal control (P = .2). There were 20 patients who were debilitated by their symptoms and underwent surgical repair of superior canal dehiscence through a middle cranial fossa approach. Canal plugging was performed in 9 and resurfacing of the canal without plugging of the lumen in 11 patients. Complete resolution of vestibular symptoms and signs was achieved in 8 of the 9 patients after canal plugging and in 7 of the 11 patients after resurfacing.

CONCLUSIONS

Superior canal dehiscence causes vestibular and auditory symptoms and signs as a consequence of the third mobile window in the inner ear created by the dehiscence. Surgical repair of the dehiscence can achieve control of the symptoms and signs. Canal plugging achieves long-term control more often than does resurfacing.

Acoustic Responses of Vestibular Afferents in a Model of Superior Canal Dehiscence

HYPOTHESIS

Afferents innervating the superior semicircular canal are rendered especially sensitive to acoustic stimulation when there is a dehiscence of the superior canal. Other vestibular end organs are also more sensitive to acoustic stimulation.

BACKGROUND

Dehiscence of the superior semicircular canal is associated with vertigo and nystagmus caused by loud sounds (Tullio phenomenon) or changes in middle ear or intracranial pressures. The mechanisms by which acoustic stimuli act on the vestibular end organs are unclear. The nystagmus caused by acoustic stimuli generally aligns with the affected superior canal.

METHODS

Responses to acoustic stimuli in the superior vestibular nerves of anesthetized chinchillas were recorded before and after fenestration of the superior canal.

RESULTS

Two acoustic response patterns were seen: rapid phase locking and slow tonic changes in firing rate. Phasic responses principally occurred in irregular afferents and tonic responses in regular afferents. Afferents from all of the vestibular end organs encountered could respond to acoustic stimuli, even before fenestration. However, fenestration lowered the thresholds for acoustic stimulation in superior canal afferents with phasic responses and increased the magnitude of tonic responses.

CONCLUSIONS

Superior canal dehiscence may render the irregular afferents innervating the superior canal particularly sensitive to loud sounds. Rapid phase-locking responses may explain the short latency of nystagmus seen in patients with superior canal dehiscence syndrome. The mechanisms by which acoustic stimuli activate the vestibular end organs may differ from the damped endolymph motion associated with head acceleration.

CT evaluation of bone dehiscence of the superior semicircular canal as a cause of sound- and/or pressure-induced vertigo

PURPOSE

To describe the computed tomographic (CT) findings at different collimation widths associated with superior semicircular canal (SSC) dehiscence syndrome and to determine the frequency of these findings in a control population.

MATERIALS AND METHODS

Temporal bone CT scans with 1.0-mm and/or 0.5-mm collimation were obtained in 50 patients with sound- and/or pressure-induced vestibular symptoms. The control population consisted of 50 patients undergoing CT at 1.0-mm collimation and 57 patients undergoing CT at 0.5-mm collimation for other reasons.

RESULTS

SSC dehiscence was documented on CT scans in all 36 patients with the clinical syndrome, with bilateral findings in six patients. Six other patients without specific clinical signs appeared to have dehiscence on 1.0-mm-collimated scans. Intact bone overlaying the SSC was subsequently identified with 0.5-mm-collimated CT in each case. On the 1.0-mm-collimated scans in 50 control patients, an area judged as possible or definite dehiscence was identified in 18 of 100 ears. The bone overlaying the SSC was intact in each of the 114 control ears evaluated with 0.5-mm-collimated CT. CT findings from the patients with vestibular symptoms combined with those in the control population indicated that the positive predictive value of an apparent dehiscence in the diagnosis of SSC dehiscence syndrome improved from 50% with 1.0-mm-collimated CT with transverse and coronal images to 93% with 0.5-mm-collimated CT with reformation in the plane of the SSC.

CONCLUSION

The positive predictive value of CT in identification of SSC dehiscence syndrome improves with 0.5-mm-collimated helical CT and reformation in the SSC plane.

Tullio phenomenon with dehiscence of the superior semicircular canal

HYPOTHESIS

The goal of the investigation was to determine if vector analysis of nystagmus in a patient with the Tullio phenomenon could determine the source of the nystagmus.

BACKGROUND

The Tullio phenomenon consists of the combination of vertigo and abnormal eye and/or head movements provoked by sound. Dehiscence of the superior semicircular canal can be found in certain patients with the Tullio phenomenon.

METHODS

The patient was tested with pure tones ranging from 250 to 3,000 Hz at 95dB HL. The time course of the three-dimensional vector of eye movement, including torsion and vertical and horizontal displacement angles was determined by individual stop-frame analysis of digitized video.

RESULTS

Torsion amplitude varied from 1 to 7 degrees; vertical amplitude varied from 1 to 5 degrees; and horizontal amplitude varied less than 1.5 degrees. The maximal response occurred on stimulation of the right ear with a 1,250-Hz 95-dB HL tone. This elicited a reliable counterclockwise torsional and down-beating fast phase nystagmus as seen from the examiner's point of view. Comparison of the nystagmus with known canal vectors identified the right superior semicircular canal as the source of stimulation. High-resolution computed tomography scan of the temporal bone showed a definite right superior canal dehiscence.

CONCLUSION

The origin of nystagmus from the Tullio phenomenon can be identified by calculating the three-dimensional vector of the observed nystagmus. We show that vector analysis of the observed eye movement can be used to infer the source of nystagmus in these patients. The development of real-time, three-dimensional vector analysis of nystagmus is desirable.

Effect of white noise "masking" on vestibular evoked potentials recorded using different stimulus modalities

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses (L-VsEPs) are initiated in the otolith organs (saccule and utricle). Some of the saccule afferents have been reported to respond not only to linear acceleration, but also to high intensity acoustic stimuli. If so, the L-VsEP recorded from the saccule (elicited with the stimulus orientated relative to the head so as to optimally activate the saccule, i.e. stimulus in the vertical plane, Z-VsEP) should be reduced during high intensity broad band noise (BBN) "masking". Conversely, the utricular afferents have been reported to be less auditory-sensitive. Therefore, an L-VsEP which is mainly utricular in origin (stimulus in the horizontal plane, X-VsEP) should be less affected by this noise "masking". This was investigated in rats by recording X-VsEPs and Z-VsEPs and angular VsEPs (A-VsEPs), originating in the lateral semi-circular canals, before, during and after exposure to short duration, high intensity (113 dB SPL) BBN. This intensity completely masked auditory nerve evoked responses. The Z-VsEP did appear to be slightly more affected by the noise "masking" than the X-VsEP, implying the presence of more auditory-sensitive elements in the saccule. The A-VsEP was also affected by the BBN. The overall effect was relatively small (on average, 10-25% depression of the first wave of the different VsEPs). The responses showed recovery 5 min later.

Vestibular responses to pressure variations: a review

A selected review of the literature concerning different forms of pressure stimulation of the normal and abnormal vestibular labyrinth is presented. On the basis of this review, it can be stated that there are definite vestibular signs and symptoms associated with pressure stimulation. The exact mechanisms remain in doubt. The responses, however, appear to be mediated through the vestibular hair cells.

Observations on the Tullio phenomenon

Vestibular responses (vertigo, nystagmus-like eye movements) to acoustic stimuli are known as the "Tullio phenomenon". Detailed electro-oculographic analysis of this reaction, as observed in a 30-year-old patient, revealed the following: a maximum amplitude of eye movement (mainly vertical) was achieved by sine wave bursts of high intensity, a frequency of 500 to 1000 Hz and a duration of 100 ms. The ocular deviation was composed of a fast initial component, followed by a slower resetting movement that was often divided into two parts of different velocities. At longer stimulus durations (more than 100 ms) the electro-oculogram showed a fractionation of the eye deviation, terminating in an "off-response". Various positions of the patient's head influenced the direction of the eye motion. The possibility that the Tullio phenomenon may be due to an abnormal excitation of the statolith organs is discussed.

Vestibular implications of noise-induced hearing loss

An extensive vestibular examination was carried out in a group of 29 noise-exposed technicians. A spontaneous nystagmus was found in 18 persons, and 24 had a positional nystagmus exceeding a velocity of the slow phase of 5 degrees/s in three or more positions. In 17 subjects a cervical nystagmus could be provoked, while a nystagmus preponderance of more than 20% in the rotation test was found in seven persons. A difference in excitability between the labyrinths of more than 20% was shown by seven subjects. None of the subjects showed pathology in the tests for central vestibular disorders. The technicians were divided into four groups, according to the severity of their hearing loss. No correlation was found between the grade of the hearing loss and the vestibular function disturbance. This can be explained in terms of the adaptive properties of the vestibular system. All subjects showed pathology in one or more of the vestibular tests. The medico-legal aspects of vestibular involvement in noise-induced hearing loss can be of some importance. Hearing loss itself does not affect work capability directly; however, a vestibular disorder might well do so. In consequence, noise-exposed individuals could be disabled because of vertigo or balance disorder--an important and perhaps neglected aspect of noise-induced hearing damage.

The incidence and significance of the Tullio phenomenon in man

The purpose of this study was to investigate the incidence and significance of the Tullio phenomenon in a group of human subjects. The subjects included 40 patients with complaints of auditory or vestibular symptoms. Ten otologically normal subjects were included in the study as a control group. All subjects underwent routine audiologic evaluation as well as electronystagmogram (ENG) testing. All subjects were then tested for the presence of the Tullio phenomenon by the method described. The results of this study showed that of the 40 subjects with known auditory or vestibular disorders, 90% (36) demonstrated nystagmus in response to high-intensity sound stimulation. All patients in the otologically normal control group demonstrated the presence of the Tullio phenomenon. No specific correlations were made between the presence of the Tullio phenomenon and specific audiologic or ENG findings. Studies on the effects of sound on the vestibular system are reviewed and lend support to the finding that the Tullio phenomenon may be a normal physiologic response in man under certain test conditions.

The occurrence of the Tullio phenomenon in congenitally deaf children

One hundred and fifty deaf children between 5 and 16 years old of the 'Rudolf Mees' Institute were investigated in search of the Tullio phenomenon with nystagmus as a criterion. Seventy-six out of those 300 ears were positive. A functioning (calorically excitable) pars superior of the labyrinth was a 'conditio sine qua non' for this reflex. We may assume that deaf ears which show a positive Tullio phenomenon have a labyrinthine pathology of the Mondini-Alexander type and that this symptom is a pathologic one.