[Frequency response of the semicircular canals--on semicircular canal function test by pendular rotation].
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Humans↗
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CT detection of facial canal dehiscence and semicircular canal fistula: comparison with surgical findings.
OBJECTIVE: The purpose of this study was to determine the accuracy of high resolution CT (HRCT) in the detection of facial canal dehiscence and semicircular canal fistula, the preoperative evaluation of both of which is clinically very important for ear surgery. MATERIALS AND METHODS: We retrospectively reviewed the HRCT findings in 61 patients who underwent mastoidectomy at Yamagata University between 1989 and 1993. The HRCT images were obtained in the axial and semicoronal planes using 1 mm slice thickness and 1 mm intersection gap. RESULTS: In 46 (75%) of the 61 patients, the HRCT image-based assessment of the facial canal dehiscence coincided with the surgical findings. The data for the facial canal revealed sensitivity of 66% and specificity of 84%. For semicircular canal fistula, in 59 (97%) of the 61 patients, the HRCT image-based assessment and the surgical findings coincided. The image-based assessment in the remaining two patients, who both had massive cholesteatoma, was false-positive. CONCLUSION: HRCT is useful in the diagnosis of facial canal dehiscence and labyrinthine fistula, but its limitations should also be recognized.
Adolescent↗
Posterior semicircular canal dehiscence: a morphologic cause of vertigo similar to superior semicircular canal dehiscence.
The aim of this study was to assess imaging findings of posterior semicircular dehiscence on computed tomography and to evaluate incidence of posterior and superior semicircular canal dehiscence in patients presenting with vertigo, sensorineuronal hearing loss or in a control group without symptoms related to the inner ear. Computed tomography was performed in 507 patients presenting either with vertigo ( n=128; 23 of these patients suffered also from sensorineuronal hearing loss), other symptoms related to the inner ear, such as hearing loss or tinnitus ( n=183) or symptoms unrelated to the labyrinth ( n=196). All images were reviewed for presence of dehiscence of the bone, overlying the semicircular canals. Twenty-nine patients had superior semicircular canal dehiscence. Of these patients, 83% presented with vertigo, 10% with hearing loss or tinnitus and the remaining 7% with symptoms unrelated to the inner ear. In 23 patients dehiscence of the posterior semicircular canal was encountered. Of these patients, 86% presented with vertigo, 9% with hearing loss or tinnitus and 5% with symptoms unrelated to the inner ear. Defects of the bony overly are found at the posterior semicircular canal, in addition to the recently introduced superior canal dehiscence syndrome. Significant prevalence of vertigo in these patients suggests that posterior semicircular canal dehiscence can cause vertigo, similar to superior semicircular canal dehiscence.
Case-Control Studies↗
Semicircular canal plane head impulses detect absent function of individual semicircular canals.
We studied the human vestibulo-ocular reflex (VOR) in response to head 'impulses': brief, unpredictable, passive, high-acceleration (up to 4000 degrees/s2), low-amplitude (20-30 degrees) head rotations. We delivered the head impulses approximately in the plane of the semicircular canal (SCC) being tested. To test the anterior and posterior SCCs, the head impulses were delivered in a diagonal plane, midway between the frontal (roll) and sagittal (pitch) planes. We recorded head and eye position in three dimensions with scleral search coils in nine normal subjects, seven patients following unilateral surgical vestibular neurectomy and three patients following unilateral posterior SCC occlusion. In the post-surgical patients we demonstrated a severe, permanent VOR gain deficit (0.2-0.3) for head impulses directed toward any single non-functioning SCC. The sensitivity of the test depends on the physiological properties of primary vestibular afferents, and its specificity depends on the anatomical orientation of the SCCs. The diagonal head impulse is the first test of individual vertical SCC function in humans, and together with the horizontal head impulse, forms a comprehensive battery of SCC-plane tests. These canal-plane impulses could be useful in evaluating patients with vertigo or other vestibular disorders.
Adult↗
[Clinical and histological findings after extirpation of the lateral semicircular canal in cholesteatoma suppuration with fistula of the semicircular canal].
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Cholesteatoma↗
[Surgical block of the horizontal semicircular canals for the elimination of peripheral positional vertigo and positional nystagmus with preservation of hearing; at the same time a confirmation of the theory concerning the semicircular canals].
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Humans↗
Clinical, experimental, and theoretical investigations of the effect of superior semicircular canal dehiscence on hearing mechanisms.
HYPOTHESIS: A superior semicircular canal dehiscence affects hearing by introducing a third window into the inner ear that 1) lowers cochlear input impedance, 2) shunts air-conducted sound away from the cochlea resulting in conductive hearing loss, and 3) improves bone-conduction thresholds by increasing the difference in impedance between the vestibule and the round window. BACKGROUND: Superior semicircular canal dehiscence has been linked to a "conductive" hearing loss characterized by a decrease in the sensitivity to air-conducted sound and hypersensitivity to bone-conducted sound. METHODS: Four investigations were performed: 1) laser-Doppler vibrometer measurements of sound-induced umbo velocity in patients with computed tomographic scan-confirmed superior semicircular canal dehiscence; 2) laser-Doppler vibrometry of sound-induced motions of the vestibular lymph (either perilymph or endolymph) exposed in a chinchilla model of superior semicircular canal dehiscence; 3) studies in chinchillas of the effect of superior semicircular canal dehiscence on the cochlea's sensitivity to bone-conducted sounds; and 4) anatomically based theoretical analyses of sound flow through the human cochlea and semicircular canals. RESULTS: The low-frequency umbo velocity in superior semicircular canal dehiscence patients without previous middle ear surgery ranged from normal through high normal. This tendency toward hypermobility suggests a decrease in cochlear impedance. Measurements of sound-induced velocity of the lymph within a superior semicircular canal dehiscence in chinchillas demonstrated sound flow through the dehiscence. Measurements of the cochlear potential demonstrated a superior semicircular canal dehiscence-induced increase in response to bone-conducted sound in eight of nine chinchillas. An anatomically based model of the human ear predicts changes in auditory sensitivity similar to audiometric changes in superior semicircular canal dehiscence. CONCLUSION: The results suggest that superior semicircular canal dehiscence can affect hearing function by introducing a third window into the inner ear.
Animals↗
Acoustic stimulation of the semicircular canals.
Stimulation of the semicircular canals provides an alternative method of vibratory stimulation of the auditory system. The frequency response characteristics of stimulation of the tympanic membrane, malleus, stapes, round window, and fenestrated semicircular canal are presented in this article.
Animals↗
An electrokinetic model of transduction in the semicircular canal.
Transduction in the semicircular canal was studied by focusing an infrared beam on either side of exposed ampullae from the posterior canals of Rana pipiens. The direction of fluid movement resulting from a stimulus was inferred by observing the polarity of the change in afferent impulse mean rate relative to the spontaneous value. On the basis of the accepted functional polarization of this receptor, the results indicate that fluid moved toward the warmer side of the ampulla. Convection and thermal reception were shown to be unlikely explanations for these results. Morover, cupular displacements toward the warmer side would not be expected. Because thermo-osmosis can cause fluid to move toward the warmer side in a gelatin membrane, the results can be interpreted as evidence that thermo-osmosis occurred in the gelatinous cupula and influenced the transduction mechanism. Thermo-osmosis of liquids appears to be due to an electric field that is set up in a charged membrane; hence, the hair cells might have detected an electric field that occurred in the cupula during thermo-osmosis. Electroreception might be an important link in the transduction of physiological stimuli also. Rotational stimuli could result in weak electric fields in the cupula by the mechanoelectric effect. Cupular displacements could be important for large stimuli, but extrapolations to threshold stimuli suggest displacements of angstrom amplitudes. Therefore, electroreception by the hair cells could be an explanation of the great sensitivity that has been observed in the semicircular canal and other labyrinthine receptors.
Animals↗
Head impulses reveal loss of individual semicircular canal function.
We studied individual semicircular canal responses in three dimensions to high-acceleration head rotations ("head impulses") in subjects with known surgical lesions of the semicircular canals, and compared their results to those of normal subjects. We found that vestibular-ocular reflex (VOR) gains at close to peak head velocity in response to yaw, pitch and roll impulses were reliable indicators of semicircular canal function. When compared to normals, lateral canal function showed a 70-80% decrease in VOR gain at peak of yaw head velocity during ipsilesional yaw impulses. After the loss of one vertical canal function there was a 30-50% decrease in vertical and torsional VOR gain in response to ipsilesional pitch and roll impulses respectively. Bilateral deficits in anterior or posterior canal function resulted in a 80-90% decrease in vertical VOR gain during ipsilesional pitch impulses, while the loss of ipsilateral anterior and posterior canal functions will result in a 80-90% decrease in torsional VOR gain in response to ipsilesional roll impulses. Three-dimensional vector analysis and animation of the VOR responses in a unilateral vestibular deafferented subject to yaw, pitch and roll impulses further demonstrated the deficits in magnitude and direction of the VOR responses following the loss of unilateral lateral, anterior and posterior canal functions.
Adult↗
Differential processing of semicircular canal signals in the vestibulo-ocular reflex.
Selective semicircular canal inactivation and three-dimensional eye movement recordings have been used to investigate the spatial organization of vestibular signals in the vestibulo-ocular reflex (VOR) of rhesus monkeys. In animals with one pair of semicircular canals inactivated, afferent activity no longer codes all spatial components of head angular velocity. if it were the activation pattern of semicircular canal afferents alone that determines VOR slow phase eye velocity, the head velocity components along the sensitivity vectors of the remaining intact semicircular canals would determine the orientation of slow phase eye velocity. Thus, angular head velocity and slow phase eye velocity would not necessarily always align. Alternatively, if vestibulo-ocular signals coded absolute angular head motion in space based on both semicircular canal and otolith afferent information, one might expect a spatial transformation of the encoded head angular velocity signals such that slow phase eye velocity and angular head velocity continue to spatially align. Examination of the VOR at different frequencies between 0.01 Hz and 1 Hz revealed a frequency-specific spatial organization of vestibulo-ocular signals. Mid and high frequency vestibulo-ocular responses were determined exclusively by the orientation of the sensitivity vectors of the remaining intact semicircular canals. In contrasts, low frequency vestibulo-ocular responses were largely determined by the orientation of the head relative to gravity. These low frequency responses after selective semicircular canal inactivation could be predicted and simulated by a simple model where semicircular canal signals are spatially transformed from a head-fixed to a space-fixed (inertial) representation of angular head velocity. These findings suggest that low frequency vestibulo-ocular responses are dominated by inertial vestibular signals that detect absolute head motion in space based on both semicircular canal and otolith afferent information. Inertial vestibular signals are likely to contribute to head control and motor coordination of gaze, head and body posture.
Animals↗
[Horizontal canal benign paroxysmal positional vertigo--its affected side and horizontal semicircular canal function].
We report horizontal canal BPPV (HC-BPPV) targeting its pathophysiology, the affected side, and the function of the horizontal semicircular canal, together with a review of the literature. Subjects were 13 patients with HC-BPPV visiting our vertigo outpatient clinic at Nara medical university hospital and a related hospital in the 2.5 years from January 2000 to June 2002. Subjects were classified into 7 with canalolithiasis and 6 patients of cupulolithiasis after a neurotological examination. CP was positive in 54% of all patients, 71% of those with canalolithiasis, and 33% of those with cupulolithiasis. To determine the affected side in HC-BPPV, we used the affected side by using the law of Ewald in canalolithaisis patients and the detection of a neutral diminishing nystagmus in cupulolithiasis patients. CP positive in caloric testing indicated insignificant dysfunction of the horizontal semicircular canal in canalolithiasis patients compared to that in cupulolithasis patients. The mechanism behind caloric nystagmus was thought to be a convection of endolymphatic fluid interrupted consequently by an otolith in the semicircular canal in canalolithiasis patients. In contrast, CP was positive in cupulolithiasis patients regarded as having no convection of endolymphatic fluid. The mechanism causing a difference in caloric test results between canalolithiasis and cupulolithiasis patients thus requires a larger patient population and further examination to be conclusive.
Aged↗
[Position of semicircular canals in humans and cryptogenetic cupulolithiasis].
Semicircular canals in humans are three membranous tubes each forming two-thirds of a circle, arranged in a coordinate system. The horizontal semicircular canal makes a 30 degree angle with the horizontal plane, a phenomenon neither easily understood nor explained in Literature. This paper reports a personal opinion based on the theory of evolution. Before man assumed erect posture (Australopithecus Afarensis), more than 3 million years ago, the head was bent forward (as in other primates) so that the temporal bone (structures inside included) laid on the horizontal plane. In the Author's opinion the present alignment might have come about after the gradual change in posture in human evolution. The ampulla of the posterior canal and the non ampullary branch of the horizontal semicircular canal became the lowest part of the utricule thereby allowing otoconial debris to settle. On the basis of this hypothesis the Authors attempt to explain the high prevalence of idiopathic cupulolithiasis.
Humans↗
[Three-dimensional reconstruction and measurement of the human membranous semicircular canal].
The planar relationship of the human semicircular canals was determined by Blanks et al. at a series of points measured from the dissected bony labyrinth of the human skull. The relationship of membranous canal planes have not, however, been measured from the human temporal bone. We reconstructed 3 semicircular canals by computer-aided 3-dimensional analysis and measured the angles formed between pairs of 3 osseous and membranous canal planes of temporal bones. Five temporal bones in adults were used for this study. Results indicated angles formed between pairs of ipsi-lateral canal planes of both the bony and membranous labyrinth. Angles formed between the horizontal-anterior, anterior-posterior, and posterior-horizontal canal planes of the bony labyrinth were 89.64 +/- 1.82 (mean +/- SD), 90.95 +/- 1.25, and 94.02 +/- 3.77 degrees. The same angles measured from the membranous labyrinth were 90.12 +/- 2.64, 90.18 +/- 2.75, and 91.48 +/- 6.32 degrees. Differences between the angles formed between bony and membranous canal planes were 2.11, 6.05, and 3.26 degrees in the anterior, horizontal, and posterior canal. Pairs of membranous canal planes were nearly perpendicular without exception, but pairs of osseous canal planes had a larger deviation from 90 degrees. This suggested that membranous canals could successfully be constructed in adequate alignment for canal function in the large perilymphatic space within osseous semicircular canals.
Adult↗
A quantitative analysis of the spatial organization of the vestibulo-ocular reflexes in lateral- and frontal-eyed animals--I. Orientation of semicircular canals and extraocular muscles.
The spatial relationship between extraocular muscles and semicircular canals was evaluated in cat (frontal-eyed animal) and rabbit (lateral-eyed animal). Semicircular canal orientations in the rabbit were determined by a principal components analysis of data points obtained from the exposed osseous canals using a three-axis micromanipulator. Canal orientations were presented in terms of unit sensitivity vectors. Orientation of extraocular muscles in rabbits and cats was derived from measurements of the insertion and origin of each muscle with respect to a reference point on the skull and a calculated estimate of the center of the eye. Muscle orientations were presented in terms of unit action vectors. Semicircular canal planes of the rabbit labyrinth were not orthogonal, having deviations up to 14 degrees. Pairs of antagonistically acting vertical semicircular canals, left (right) anterior-right (left) posterior deviated from coplanarity by 16 degrees, while the deviation for the horizontal canals was 9 degrees. In both animals, muscles of an antagonistic pair were coplanar to within 8 degrees, with the exception of the oblique muscles in the rabbit for which the deviation was 19 degrees. The three pairs of antagonistic muscles were almost orthogonal to each other, the maximum deviation between any of the pairs being 8 degrees in the cat and 18 degrees in the rabbit. Comparing extraocular muscle planes and semicircular canal planes reveals that they are roughly aligned. However, there were slight but consistent differences between a given semicircular canal plane and the planes of the muscles to which this canal is connected by the classical three-neuron-arc (principal vestibulo-ocular reflex circuits).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
In vitro electrogenic K secretion in the frog semicircular canal: absence of effect of streptomycin.
In vitro, the frog semicircular canal secretes an endolymph-like fluid, i.e. a K-rich, positively polarized fluid. This electrogenic K secretion involved basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter and a luminal protein possessing sulfhydryl groups blocked by N-ethylmaleimide. Streptomycin, an ototoxic antibiotic, is known to block the non-specific mechano-dependent channels in the sensory cells of the ampulla of the semicircular canal. The aim of the present study was to investigate the possible effect of streptomycin on the K fluxes in the ampulla of the semicircular canal. The posterior frog semicircular canal was isolated and the lumen was filled with perilymph-like solution containing or not containing 0.5 mM streptomycin. The luminal K concentration and the transepithelial potential were measured and the unidirectional K fluxes calculated. The K influxes (into the lumen, pmoles/min/mm2) were 114 +/- 25.9 and 111 +/- 3.2 (mean +/- SE, n = 3) in the absence and presence of streptomycin, respectively. The transepithelial potential was not altered (4.0 +/- 1.08 mV versus 3.4 +/- 1.03 mV, n = 3). When ouabain (10(-3)M) was added to the basolateral solution together with luminal streptomycin, no further alteration occurred as compared with the effect of ouabain alone. These results suggest that in these conditions, the sensory organ does not have a major role in the endolymphatic K secretion in the ampulla of the frog semicircular canal.
Animals↗
Spatial orientation of semicircular canals and afferent sensitivity vectors in pigeons.
Rotational head motion in vertebrates is detected by the semicircular canal system, whose innervating primary afferent fibers carry information about movement in specific head planes. The semicircular canals have been qualitatively examined over a number of years, and the canal planes have been quantitatively characterized in several animal species. The present study first determined the geometric relationship between individual semicircular canals and between the canals and the stereotactic head planes in pigeons. Stereotactic measurements of multiple points along the circumference of the bony canals were taken, and the measured points fitted with a three-dimensional planar surface. Direction normals to the plane's surface were calculated and used to define angles between semicircular canal pairs. Because of the unusual shape of the anterior semicircular canals in pigeons, two planes, a major and a minor, were fitted to the canal's course. Calculated angle values for all canals indicated that the horizontal and posterior semicircular canals are nearly orthogonal, but the anterior canals have substantial deviations from orthogonality with other canal planes. Next, the responses of the afferent fibers that innervate each of the semicircular canals to 0.5 Hz sinusoidal rotation about an earth-vertical axis were obtained. The head orientation relative to the rotation axis was systematically varied so that directions of maximum sensitivity for each canal afferent could be determined. These sensitivity vectors were then compared with the canal plane direction normals. The afferents that innervated specific semicircular canals formed homogeneous clusters of sensitivity vectors in different head planes. The horizontal and posterior afferents had average sensitivity vectors that were largely co-incident with the innervated canal plane direction normals. Anterior canal afferents, however, appeared to synthesize contributions from the major and minor plane components of the bony canal structure to produce a resultant sensitivity vector that was positioned between the canal planes. Calculated angles between the average canal afferent sensitivity vectors revealed that direction orthogonality is preserved at the afferent signal level, even though deviations from canal plane orthogonality exist.
Afferent Pathways↗
Functional model of benign paroxysmal positional vertigo using an isolated frog semicircular canal.
Bull frogs posterior semicircular canals (psc) wee used to simulate the condition of benign paroxysmal positional vertigo (BPPV). The psc was isolated in frog Ringer's solution, and the saccular otoconia were used as a responsible material to stimulate the cupula. When the otoconia were placed on the cupular surface to mimic the condition of cupulolithiasis, the psc ampullary nerve action potentials instantaneously changed according to the direction of the gravity produced by otoconia. When the otoconia were dropped into the canal to mimic the condition of moving otoconia in the canal, the action potentials changed together with the otoconial flow after a latent period. Both cupulolithiasis and moving otoconia are possibly valid mechanisms of BPPV, since they effectively stimulate the cupula. However, moving otoconia with a latent period would better explain clinical features of BPPV.
Action Potentials↗