Andrew Phillip Bradshaw

Superior semicircular canal dehiscence simulating otosclerosis

This is a report of a patient with an air-bone gap, thought 10 years ago to be a conductive hearing loss due to otosclerosis and treated with a stapedectomy. It now transpires that the patient actually had a conductive hearing gain due to superior semicircular canal dehiscence. In retrospect for as long as he could remember the patient had experienced cochlear hypersensitivity to bone-conducted sounds so that he could hear his own heart beat and joints move, as well as a tuning fork placed at his ankle. He also had vestibular hypersensitivity to air-conducted sounds with sound-induced eye movements (Tullio phenomenon), pressure-induced nystagmus and low-threshold, high-amplitude vestibular-evoked myogenic potentials. Furthermore some of his acoustic reflexes were preserved even after stapedectomy and two revisions. This case shows that if acoustic reflexes are preserved in a patient with an air-bone gap then the patient needs to be checked for sound- and pressure-induced nystagmus and needs to have vestibular-evoked myogenic potential testing. If there is sound- or pressure-induced nystagmus and if the vestibular-evoked myogenic potentials are also preserved, the problem is most likely in the floor of the middle fossa and not in the middle ear, and the patient needs a high-resolution spiral computed tomography (CT) of the temporal bones to show this.

Tuning Characteristics of Ocular and Cervical Vestibular Evoked Myogenic Potentials in Intact and Dehiscent Ears

Cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) to air-conducted tone bursts (250–2000 Hz) were recorded in 14 patients with superior canal dehiscence (SCD) and 32 healthy controls. For cVEMPs, the most common ‘optimal frequency’ in control ears (48.2%) was 500 Hz; for oVEMPs, it was 1000 Hz (51.8%). We found a significant interaction between age and frequency, with a shift towards higher-frequency tuning in older subjects. cVEMP and oVEMP tuning in SCD was characterised by a broadening of amplitude and threshold tuning curves. The tendency of cVEMPs to tune to lower frequencies compared to oVEMP was enhanced in SCD. Differences in cVEMP and oVEMP ‘optimal frequencies’, demonstrated in 57.1% intact ears and 81.3% dehiscent ears, imply differences in the recruitment of hair cells generating these two reflexes. Age-matched oVEMP amplitudes provided excellent separation between SCD and control ears. Although cVEMP amplitudes overlapped between SCD and control ears, better separation was achieved by using a 2-kHz stimulus.

Rapid fluctuations in dynamic semicircular canal function in early Ménière’s disease

Ménière’s disease (MD) is characterized by fluctuations in labyrinthine function which are well known and objectively established for the auditory symptoms [1, 2]. It is also well known that it is disorders of balance, rather than hearing, which are the major symptoms during the early stages of the disease [3]. But to date there have been only a few measurements of the fluctuations in vestibular function around the time of the attack. This has been due to two factors. First, the difficulty of testing early MD patients around the time of their attack, which can have highly variable duration: each attack may last from 10 min to hours [2, 3]. Second, the limited range of vestibular tests available and the fact that the usual tests of vestibular function are so demanding that they are not feasible in patients around the time of the attack. However, recently, we published results of a new nondemanding test of otolith function—the n10 of the ocular vestibular-evoked myogenic potential which showed that there are fluctuations in vestibular function, with enhanced dynamic utricular function at the time of the attack compared to quiescence [4]. Here, we wish to address the complementary question as to whether dynamic semicircular canal function fluctuates as auditory and dynamic otolith function does and we present evidence of variations in dynamic semicircular canal function around the time of the MD attack. The development of the video head impulse test (vHIT) has allowed non-demanding objective measures of semicircular canal function [5]. This is a very simple, fast way of measuring dynamic semicircular canal function accurately and has been validated by directly comparing it to simultaneous measures by the ‘‘gold standard’’ search coil test [6]. The gain measurements of the two tests are not significantly different and show very high concordance correlations [6]. With vHIT it is possible to test patients very quickly at short intervals and this kind of easily repeatable, high accuracy, minimally demanding test allows the measurement of the sequential changes in semicircular canal function at the time of the attack. The vHIT test involves the clinician delivering brief, passive, high acceleration head impulses of yaw head rotation unpredictably to the right or left through an angle of about 10 –20 while the patient is instructed to keep looking at an earth-fixed target. The patient wears a set of minimal-slip goggles to which is attached a small lightweight high speed video camera to measure eye position and a 3-d sensor to measure head velocity. We used vHIT to measure the yaw VOR response of patients with evidence of early MD, both at quiescence and during an acute attack. Here, we report that the repeated tests at short intervals show that the VOR response changes substantially around the time of an attack (Fig. 1). One important issue is that the patients for this study were a homogeneous group with early MD (6 subjects, 3 L. Manzari (&) MSA ENT Academy Center Cassino, Via Riccardo da S.Germano 41, 03043 Cassino (FR), Italy e-mail: leonardomanzari@virgilio.it

The configuration and attachment of the utricular and saccular maculae to the temporal bone. New evidence from microtomography-CT studies of the membranous labyrinth.

High‐resolution X‐ray microtomography (micro‐CT) was used to show the spatial configuration of the membranous labyrinth of the fixed guinea pig and human inner ear. Whole temporal bones were en bloc stained in 2% osmium tetroxide for 2 days or more to allow the osmium to attach to the membranes of the inner ear, and then scanned with a Skyscan 1172 micro‐CT with highest resolution of 8 microns. The scans were segmented and reconstructed. The findings for guinea pigs and humans are similar. The saccular macula is closely attached to the curved medial wall of the temporal bone, but in both human and guinea pig the utricular macula is attached to the temporal bone only at the anterior region of the macula, and, as others have reported previously, much of the caudal area of the utricular macula is tenuously supported by a thin membrane, just above the dorsal margin of the stapes. This tenuous support may have important consequences for the sensing of forces by the utricular macula. Combining information from a dissected human horizontal canal with CT images allows an estimate of the orientation of the horizontal canal crista in human subjects, data which are necessary for treatment of benign paroyxsmal positional vertigo of the horizontal canal. The very high resolution achieved by micro‐CT shows that reconstruction from inadequately sampled CT data produces images that are not anatomically correct, so that canal deformations and aplasias may appear to be present.

Augmented ocular vestibular evoked myogenic potentials to air-conducted sound in large vestibular aqueduct syndrome.

Objective: To demonstrate the value of recording air-conducted ocular Vestibular Evoked Myogenic Potentials (oVEMP) in a patient with bilaterally enlarged vestibular aqueducts. Design: Cervical VEMP and oVEMP were recorded from a patient presenting with bilateral hearing loss and imbalance, attributable to large vestibular aqueduct syndrome. The stimuli were air-conducted tone bursts at octave frequencies from 250 to 2000 Hz. Amplitudes and thresholds were measured and compared with the normal response range of 32 healthy control subjects. Results: oVEMP reflexes demonstrated pathologically increased amplitudes and reduced thresholds for low-frequency tone bursts. Cervical VEMP amplitudes and thresholds were within normal limits for both ears across all frequencies of stimulation. Conclusions: This study is the first to describe the augmentation of AC oVEMPs in an adult with large vestibular aqueduct syndrome.

Three-dimensional analysis of the vestibular end organs in relation to the stapes footplate and piston placement.

Objective: Measurements of the proximity of the membranous labyrinth to the stapes footplate show considerable variation. Largely, such measurements have been from histologic sections of fixed temporal bones, which may be affected by shrinkage artifact and perspective distortion in the 2-dimensional plane. To overcome these problems, the present study undertook an analysis of the 3-dimensional (3D) architecture of the relationship of the stapes to the membranous labyrinth using high-resolution X-ray micro-computed tomography. Methods: Eleven temporal bones were fixed with Karnovskys fixative (known to minimize shrinkage), soaked in 2% osmium tetroxide, and scanned in a micro-computed tomography scanner. The otic capsule was intact to exclude sectioning artifact, and no alcohol was used to avoid tissue shrinkage. Measurements were taken in a vertical plane to provide distances from the utricle and saccule to the footplate, and 3D reconstruction of the spatial relationship of these structures was carried out. The relationship of these structures to a stapes piston also was studied. Results: The safest area of piston placement was the central and inferior part of the footplate. This was safe up to 0.5 mm depth at all areas except posterosuperiorly where the utricular macula is, on average, only 0.61 mm away from the footplate. The angle of insertion of the piston also influences the end result. Conclusion: Two-dimensional information about vestibular end organ location should serve as a guideline only because the operative field is 3D, and the relationship of the piston to the vestibular labyrinth changes with the angle of placement.

Bedside Assessment of Acute Dizziness and Vertigo

Dizziness is a common symptom in emergency departments, general practice, and outpatient clinics. Faced with an acutely dizzy patient, the frontline physician must determine whether or not the symptoms are vestibular in origin and, if they are, which vestibular disorder they best fit. A focused history provides useful clues to the likely cause of dizziness, yet it is the clinical examination that yields the final answer. This article summarizes history and examination techniques that are useful in the assessment of acutely dizzy patients and discusses oculomotor signs that accompany common vestibular disorders.