Die Tulliosche Reaktion in Zusammenhang mit der Funktion des Mittelohres

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.

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.

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.

Hearing thresholds of normal and fenestrated deaf pigeons. A behavioural study on hearing with the vestibular organ

Hearing thresholds were measured for 5 normal pigeons with the heart-rate conditioning method. After extirpation of the membranous cochlea on both sides and fenestration of the lateral canals, hearing thresholds were measured again with the same method at 250, 750 and 1500 Hz. Hearing thresholds found in this way for deaf fenestrated pigeons correspond very well to threshold values for the "Tullio effect". Electrical activity in the vestibular nerve evoked by sound is thought to be the origin of these phenomena.

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.

Tullio phenomenon with torsion of the eyes and subjective tilt of the visual surround

A 44-year-old male patient had an acoustic trauma three years previously, after which he suffered from vertigo and tilting of the environment to the right when uttering the vowels u or e. At such times, a tonic eye torsion to the left, which lasted throughout the utterance, was observed under Frenzel's glasses along with head tilt to the left. The phenomenon could be elicited experimentally by right-ear stimulation with low-frequency noise (mean frequency, 125 Hz; 90 dB), as well as by constant pressure. The patient also reported observing the phenomenon with loud noises, nose blowing, obstruction of his right external meatus with the finger, and with altitude pressure changes in a car. This suggests that the phenomenon is elicited via the eardrum and the ossicular chain. Since lateral head tilt and counterrolling were tonic and without nystagmus, it is unlikely that one of the semicircular canals is involved as in usual Tullio cases. Rather, the otoliths may play a role in pathogenesis. Possible causative mechanisms are discussed along with the relevant literature.