Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SEMICIRCULAR CANALS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56Linked to original sources
PubMed1976

Labyrinthine anomalies in trisomy 13 mosaicism.

The temporal bone histopathology of a 2-month-old male with a bilateral cleft palate, cleft lip and polydactylia due to trisomy 13 mosaicism was studied. Anomalies in the ear involved a partial absence of the superior semicircular canal, an abnormally wide lateral semicircular canal, underdeveloped cochlear coils, an abnormally broad modiolus, an undeveloped organ of Corti and an underdeveloped basilar membrane in the basal turn of the cochlea, an unusually wide cochlear aqueduct, and deformed stapedial crura.

Adult↗
PubMed1998

Inner ear blood flow in the rat after unilateral arterial occlusion in the vertebrobasilar arterial system.

It is generally accepted that certain kinds of vertigo and hearing disturbances are caused by blood flow insufficiency in the vertebrobasilar arterial system. Using the microsphere method we investigated whether unilateral vertebral artery or unilateral posterior inferior cerebellar artery occlusion could cause an imbalance between right and left inner ear blood flow in rats. We also studied the differential vulnerability between blood flow in the cochlea and in the ampullae of the three semicircular canals. We counted the numbers of microspheres distributed to the cochlea (CO) and microspheres distributed to three ampullae of semicircular canals (SC) under a microscope with the surface preparation method. The results were as follows: i) no imbalances were observed between bilateral CO or SC even in animals with arterial occlusion, and ii) the CO/SCs of animals with arterial occlusion were not significantly different from that of the control animals. These findings suggest that total inner ear blood flow over a certain period of time was even between the ears bilaterally even in animals with arterial occlusion. The blood flow in the ampullae of the three semicircular canals was not more or less affected by arterial occlusion than the blood flow in the cochlea.

Animals↗
PubMed1996

Three-dimensional organization of otolith-ocular reflexes in rhesus monkeys. II. Inertial detection of angular velocity.

1. The dynamic contribution of otolith signals to three-dimensional angular vestibuloocular reflex (VOR) was studied during off-vertical axis rotations in rhesus monkeys. In an attempt to separate response components to head velocity from those to head position relative to gravity during low-frequency sinusoidal oscillations, large oscillation amplitudes were chosen such that peak-to-peak head displacements exceeded 360 degrees. Because the waveforms of head position and velocity differed in shape and frequency content, the particular head position and angular velocity sensitivity of otolith-ocular responses could be independently assessed. 2. During both constant velocity rotation and low-frequency sinusoidal oscillations, the otolith system generated two different types of oculomotor responses: 1) modulation of three-dimensional eye position and/or eye velocity as a function of head position relative to gravity, as presented in the preceding paper, and 2) slow-phase eye velocity as a function of head angular velocity. These two types of otolith-ocular responses have been analyzed separately. In this paper we focus on the angular velocity responses of the otolith system. 3. During constant velocity off-vertical axis rotations, a steady-state nystagmus was elicited that was maintained throughout rotation. During low-frequency sinusoidal off-vertical axis oscillations, dynamic otolith stimulation resulted primarily in a reduction of phase leads that characterize low-frequency VOR during earth-vertical axis rotations. Both of these effects are the result of an internally generated head angular velocity signal of otolithic origin that is coupled through a low-pass filter to the VOR. No change in either VOR gain or phase was observed at stimulus frequencies larger than 0.1 Hz. 4. The dynamic otolith contribution to low-frequency angular VOR exhibited three-dimensional response characteristics with some quantitative differences in the different response components. For horizontal VOR, the amplitude of the steady-state slow-phase velocity during constant velocity rotation and the reduction of phase leads during sinusoidal oscillation were relatively independent of tilt angle (for angles larger than approximately 10 degrees). For vertical and torsional VOR, the amplitude of steady-state slow-phase eye velocity during constant velocity rotation increased, and the phase leads during sinusoidal oscillation decreased with increasing tilt angle. The largest steady-state response amplitudes and smallest phase leads were observed during vertical/torsional VOR about an earth-horizontal axis. 5. The dynamic range of otolith-borne head angular velocity information in the VOR was limited to velocities up to approximately 110 degrees/s. Higher head velocities resulted in saturation and a decrease in the amplitude of the steady-state response components during constant velocity rotation and in increased phase leads during sinusoidal oscillations. 6. The response characteristics of otolith-borne angular VORs were also studied in animals after selective semicircular canal inactivation. Otolith angular VORs exhibited clear low-pass filtered properties with a corner frequency of approximately 0.05-0.1 Hz. Vectorial summation of canal VOR alone (elicited during earth-vertical axis rotations) and otolith VOR alone (elicited during off-vertical axis oscillations after semicircular canal inactivation) could not predict VOR gain and phase during off-vertical axis rotations in intact animals. This suggests a more complex interaction of semicircular canal and otolith signals. 7. The results of this study show that the primate low-frequency enhancement of VOR dynamics during off-vertical axis rotation is independent of a simultaneous activation of the vertical and torsional "tilt" otolith-ocular reflexes that have been characterized in the preceding paper. (ABSTRACT TRUNCATED)

Animals↗
PubMed1995

Persistent direction-changing positional nystagmus: another variant of benign positional nystagmus?

Positional nystagmus that does not fatigue, persists as long as the position is held, and changes direction in different head positions has typically been attributed to central vestibular lesions. We recently studied three patients who presented with positional nystagmus having these features but almost certainly of benign peripheral origin. All three had an initial history typical of benign positional vertigo and, in two, the persistent direction-changing positional nystagmus occurred after the patient underwent a maneuver to remove debris from the posterior semicircular canal. The positional nystagmus profile and clinical course are consistent with the debris leaving the posterior semicircular canal and becoming attached to the cupula of the horizontal semicircular canal.

Aged↗
PubMed2003

Timing of low frequency responses of anterior and posterior canal vestibulo-ocular neurons in alert cats.

The pitch vertical vestibulo-ocular reflex (VOR) is accurate and symmetrical when tested in the normal upright posture, where otolith organ and central velocity storage signals supplement the basic VOR mediated by the semicircular canals. However, when the animal and rotation axis are together repositioned by rolling 90 degrees to one side, head forward pitch rotations that excite the anterior semicircular canals elicit a more accurately timed VOR than do oppositely directed rotations that excite the posterior canals. This suggests that velocity storage of posterior canal signals is lost when the head is placed on its side. We recorded from 47 VOR relay neurons, second-order vestibulo-ocular neurons, of alert cats to test whether asymmetries are evident in the responses of neurons in the medial and superior vestibular nuclei during earth-horizontal axis rotations in the normal upright posture. Neurons were identified by antidromic responses to oculomotor nucleus stimulation and orthodromic responses to labyrinth stimulation, and were classified as having primarily anterior, posterior, or horizontal canal input based on response directionality. Neuronal response gains and phases were recorded during 0.5 Hz and 0.05 Hz sinusoidal oscillations in darkness. During 0.5 Hz rotations, anterior canal second-order vestibulo-ocular neurons responded approximately in phase with head velocity (mean phase re head position, +/- SE, 80 degrees +/- 3 degrees, n=18), as did posterior canal second-order vestibulo-ocular neurons (mean phase 81 degrees +/- 1 degree, n=25). Lowering the rotation frequency to 0.05 Hz resulted in only slight advances in response phases of individual anterior canal second-order vestibulo-ocular neurons (mean phase 86 degrees +/- 6 degrees, mean advance 7 degrees +/- 5 degrees, n=12). In contrast, posterior canal second-order vestibulo-ocular neurons behaved more like semicircular canal afferents, with responses markedly phase-advanced (mean advance 28 degrees +/- 5 degrees, n=14) by lowering rotation frequency to 0.05 Hz (mean phase 111 degrees +/- 5 degrees, n=14). In summary, low frequency responses of anterior and posterior canal second-order vestibulo-ocular neurons recorded during horizontal axis pitch correspond to the VOR they excite during vertical axis pitch. These results show that velocity storage is evident at anterior but not posterior canal second-order vestibulo-ocular neurons. We conclude that responses of posterior canal second-order vestibulo-ocular neurons are insufficient to explain the accurate low frequency VOR phase observed during backward head pitch in the upright posture, and that velocity storage or otolith signals required for VOR accuracy are carried by other neurons.

Action Potentials↗
PubMed1988

Responses of single neurons in the parietoinsular vestibular cortex of primates.

1. Neurons activated by stimulation of the horizontal and/or vertical vestibular semicircular canals were recorded in the parietoinsular vestibular cortex in four awake Java monkeys (Macaca fascicularis) and three squirrel monkeys (Saimiri sciureus). Steady tilt in darkness or during illumination of a vertically striped cylinder or of the normal laboratory surroundings did not lead to a significant change in PIVC neuron activity. Thus vestibular input to this cortical region seems to be restricted to signals originating in the semicircular canal receptors. 2. Vestibular stimulation in the three main experimental planes (roll, yaw, and pitch) and in planes in between provided clear evidence that optimum activation can be found in planes that do not coincide with the planes of the semicircular canals but are distributed over all possible spatial planes through the head. 3. Definite evidence of clustering in subdivisions of PIVC of neurons responding to the same optimum rotation plane was obtained in squirrel monkeys and is also suggested to exist in PIVC of Java monkeys. 4. Nearly all neurons responding to vestibular stimulation were also activated by visual large-field movement (optokinetic stimulation). Responses to optokinetic stimuli were always at optimum when the direction of the movement pattern corresponded to the optimum vestibular plane. Two classes of visual-vestibular interaction were found: Synergistic neurons were those PIVC cells with the strongest response to visual movement stimulation in the opposite direction to that leading to a maximum response to vestibular stimulation. Antagonistic neurons had a response maximum when the visual stimulus was moved in the direction of optimum vestibular stimulation. 5. Most PIVC neurons responded to stimulation of the deep mechanoreceptors in the neck region. This input from the neck receptors was tested quantitatively only in the horizontal plane (trunk rotation with the head fixed in space or head rotation with the trunk fixed in space). It interacted with vestibular signals at the PIVC neurons either in an antagonistic or a synergistic manner, the latter meaning activation during rotation of the head in the same direction as that leading to activation induced by semicircular canal stimulation. 6. In addition to the direction-specific vestibular, visual, and neck receptor inputs, a rather complex somatosensory input to PIVC neurons exists, including responses to stimulation of mechanoreceptors of the skin, the muscles, and the joint receptors of legs and arms. Total body vibration also led to activation of some of the neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Head and eye movements following vestibular stimulus in squirrel monkeys.

Head and eye movements induced by vestibular stimuli (rotational velocity steps) were studied under several experimental conditions in squirrel monkeys. Monkeys showed prominent head nystagmus under a free head condition. Slow phase gaze velocity (SPGV) was calculated by summing the slow phase speed of coupled head and eye nystagmus. A statistical test showed no significant difference between slow phase eye velocities in a fixed head versus SPGV in a free head condition. This indicates that an accurate negative feedback control of eye movements is performed by the vestibular system when sensing active head movements. Bilateral lateral semicircular canal block eliminated these responses in subjects without amphetamine injection. However, in amphetamine-injected animals, 14-21% of preoperative response could be found even after this operation. Since the plane of rotation was not parallel to that of the lateral semicircular canals, the result was considered to be due to vertical semicircular canal stimulation.

Animals↗
PubMed1996

Differential central projections of vestibular afferents in pigeons.

The question of whether a differential distribution of vestibular afferent information to central nuclear neurons is present in pigeons was studied using neural tracer compounds. Discrete tracing of afferent fibers innervating the individual semicircular canal and otolith organs was produced by sectioning individual branches of the vestibular nerve that innervate the different receptor organs and applying crystals of horseradish peroxidase, or a horseradish peroxidase/cholera toxin mixture, or a biocytin compound for neuronal uptake and transport. Afferent fibers and their terminal distributions within the brainstem and cerebellum were visualized subsequently. Discrete areas in the pigeon central nervous system that receive primary vestibular input include the superior, dorsal lateral, ventral lateral, medial, descending, and tangential vestibular nuclei; the A and B groups; the intermediate, medial, and lateral cerebellar nuclei; and the nodulus, the uvula, and the paraflocculus. Generally, the vertical canal afferents projected heavily to medial regions in the superior and descending vestibular nuclei as well as the A group. Vertical canal projections to the medial and lateral vestibular nuclei were observed but were less prominent. Horizontal canal projections to the superior and descending vestibular nuclei were much more centrally located than those of the vertical canals. A more substantial projection to the medial and lateral vestibular nuclei was seen with horizontal canal afferents compared to vertical canal fibers. Afferents innervating the utricle and saccule terminated generally in the lateral regions of all vestibular nuclei in areas that were separate from the projections of the semicircular canals. In addition, utricular fibers projected to regions in the vestibular nuclei that overlapped with the horizontal semicircular canal terminal fields, whereas saccular afferents projected to regions that received vertical canal fiber terminations. Lagenar afferents projected throughout the cochlear nuclei, to the dorsolateral regions of the cerebellar nuclei, and to lateral regions of the superior, lateral, medial, and descending vestibular nuclei.

Animals↗
PubMed2006

Analysis of mastoid findings at surgery to treat middle ear cholesteatoma.

OBJECTIVES: To analyze mastoid findings, such as facial nerve dehiscence (FND), labyrinthine fistula, and dural exposure; to review its incidence at cholesteatoma surgery; to analyze its association with semicircular canal fistula; and to elucidate its relationship with dural exposure. DESIGN: One hundred fifty-two patients (65 males and 87 females; 155 ears) were enrolled in a retrospective study of tympanoplasty with or without mastoidectomy. SETTING: Medical university center hospital. RESULTS: The incidence of FND after exenteration of disease was 29.7% (46/155 ears) for total surgical procedures, 29.7% (43/145 ears) for initial procedures, and 30% (3/10 ears) for revision procedures. The prevalence of FND in the tympanic segment only was 87%, with 8.7% in the vertical segment only and 4.3% in both segments. Three patients (2.0%) developed facial palsy postoperatively, with 8 lateral semicircular canal fistulas (5.2% of total ears operated on), half of these with concomitant FND. The incidence of dural exposure of the mastoid tegmen in the entire surgical group was 16.8% (26 ears), 38.5% with concomitant FND. CONCLUSIONS: The overall incidence of FND in our sample was high at 29.7%, with rates of lateral semicircular canal fistula and dural exposure of 5.2% and 16.8%, respectively. The relationship between FND incidence and presence of lateral semicircular canal fistula was positive in our study. The surgeon should bear in mind that the location of FND with cholesteatoma coincides with the most common area of iatrogenic facial nerve injury during otologic surgery.

Adolescent↗
PubMed1994

A cure for benign positional vertigo.

Benign positional vertigo is a common clinical entity encountered in any dizzy clinic. It is easily diagnosed on the basis of historical information and a positive Dix-Hallpike position test. The available evidence suggests that this condition is due to involvement of the posterior semicircular canal. The pathophysiology of this condition can be explained theoretically on the basis of free-floating particles within the endolymph of the posterior semicircular canal that move under the influence of gravity with certain provocative positional changes. Based on this theoretical model, a variety of particle-repositioning manoeuvres have been developed that attempt to relocate the loose particles from the posterior semicircular canal to the utricular sac. If the particles are kept in the utricular sac for a period of 48 h by maintaining the patient in an upright position, the clinical symptoms are relieved in a high proportion of patients. If the manoeuvre is unsuccessful on a first attempt, or if the benign positional vertigo recurs at a later date, the condition can usually be relieved by a second manoeuvre. Bilateral benign positional vertigo can be treated by performing a manoeuvre on one side followed by a manoeuvre on the other side at a later date. On occasion, posterior canal benign positional vertigo is converted to horizontal canal benign positional vertigo, but this subsides readily within the 48-h post-manoeuvre period.

Humans↗
PubMed2005

Gbx2 is required for the morphogenesis of the mouse inner ear: a downstream candidate of hindbrain signaling.

Gbx2 is a homeobox-containing transcription factor that is related to unplugged in Drosophila. In mice, Gbx2 and Otx2 negatively regulate each other to establish the mid-hindbrain boundary in the neural tube. Here, we show that Gbx2 is required for the development of the mouse inner ear. Absence of the endolymphatic duct and swelling of the membranous labyrinth are common features in Gbx2-/- inner ears. More severe mutant phenotypes include absence of the anterior and posterior semicircular canals, and a malformed saccule and cochlear duct. However, formation of the lateral semicircular canal and its ampulla is usually unaffected. These inner ear phenotypes are remarkably similar to those reported in kreisler mice, which have inner ear defects attributed to defects in the hindbrain. Based on gene expression analyses, we propose that activation of Gbx2 expression within the inner ear is an important pathway whereby signals from the hindbrain regulate inner ear development. In addition, our results suggest that Gbx2 normally promotes dorsal fates such as the endolymphatic duct and semicircular canals by positively regulating genes such as Wnt2b and Dlx5. However, Gbx2 promotes ventral fates such as the saccule and cochlear duct, possibly by restricting Otx2 expression.

Animals↗
PubMedDate not supplied

Acute vestibular paralysis in herpes zoster oticus.

A case of herpes zoster oticus is presented in which the lateral and superior semicircular canals of the labyrinth were affected unilaterally. The results of several electronystagmographic examinations are described and correlated with the patient's description of symptoms. This case study indicates that disease affecting the lateral semicircular canal is reliably detected by the conventional caloric test. However, the fact that the posterior semicircular canal remained intact could not be inferred from the results of the caloric test in this case. Also the appearance of nystagmus upon eye closure appears to have been a more sensitive index of the state of the disease process than was the caloric test.

Adult↗
PubMed2001

Virtual endoscopic evaluation of labyrinthine fistulae resulting from cholesteatoma.

OBJECTIVES/HYPOTHESIS: Fistulae of the otic capsule occur in approximately 10% of cholesteatoma cases. Preoperative imaging of this complication is valuable in limiting intraoperative morbidity. Three-dimensional virtual endoscopic imaging provides a new method for analysis of conventional computed tomography (CT) imaging data. The purpose of the study was to examine the feasibility and efficacy of this technique in detecting labyrinthine fistulae caused by cholesteatoma. STUDY DESIGN: Retrospective case study. METHODS: Fifteen patients with surgically confirmed lateral semicircular canal fistula and preoperative CT scan were included. Scans meeting inclusion criteria were imported into a software program for production of virtual endoscopic images. Dehiscent and normal lateral semicircular canals were navigated while varying threshold values for surrounding bone. Changes in threshold values produce the effect of thickening or thinning the bone enveloping the semicircular canal. Threshold parameters that produced easy circumnavigation ("open") and intact inner surface of the lateral canal ("closed") were recorded. RESULTS: The fistula group demonstrated a significantly lower "closed" threshold level and, consequently, a greater range of navigation between "open" and "closed" thresholds. Intrasubject absolute differences in threshold values between normal and abnormal ears appeared to be the most accurate method for detecting a fistula. The suggested imaging parameters displayed an overall sensitivity for fistula detection of 67% with a specificity of 93%. CONCLUSIONS: The three-dimensional virtual endoscopic algorithm shows promise as a method for confirmation of otic capsule dehiscences. Sensitivity for detection is suboptimal but can be improved by alterations in image acquisition parameters.

Adolescent↗
PubMed1999

Ectopic noggin blocks sensory and nonsensory organ morphogenesis in the chicken inner ear.

Bone morphogenetic protein 4 (Bmp4) is expressed during multiple stages of development of the chicken inner ear. At the otocyst stage, Bmp4 is expressed in each presumptive sensory organ, as well as in the mesenchymal cells surrounding the region of the otocyst that is destined to form the semicircular canals. After the formation of the gross anatomy of the inner ear, Bmp4 expression persists in some sensory organs and restricted domains of the semicircular canals. To address the role of this gene in inner ear development, we blocked BMP4 function(s) by delivering one of its antagonists, Noggin, to the developing inner ear in ovo. Exogenous Noggin was delivered to the developing otocyst by using a replication-competent avian retrovirus encoding the Noggin cDNA (RCAS-N) or implanting beads coated with Noggin protein. Noggin treatment resulted in a variety of phenotypes involving both sensory and nonsensory components of the inner ear. Among the nonsensory structures, the semicircular canals were the most sensitive and the endolymphatic duct and sac most resistant to exogenous Noggin. Noggin affected the proliferation of the primordial canal outpouch, as well as the continual outgrowth of the canal after its formation. In addition, Noggin affected the structural patterning of the cristae, possibly via a decrease of Msx1 and p75NGFR expression. These results suggest that BMP4 and possibly other BMPs are required for multiple phases of inner ear development.

Animals↗
PubMed1993

Gravity load related asymmetries in the sagittal vestibulo-collic reflex.

EMG recordings of the neck muscles (biventer cervicis, complexus, splenius, longus capitis) of decerebrate cats were obtained during pitch and roll stimulations (sinusoidal stimulation: 30 degrees p-p amplitude, 0.2 Hz frequency). Most of the EMG responses to pitch showed activation peaks leading the position stimuli by 56 degrees and inhibition peaks leading by 11 degrees. Conversely, in response to roll the activation peak led by 16 degrees and the inhibition peak by 10 degrees. The activation peaks of the pitch responses were, thus, more asymmetric and more leading than those of the roll responses. Consequently, the harmonic distortion coefficient was significantly higher in pitch than in roll. Moreover, when the vertical semicircular canals were activated in absence of otolithic modulation, the pitch and roll responses maintained the same difference in timing observed in the presence of otolithic coactivation. It appeared that the simultaneous stimulation of both anterior semicircular canals (pitch) induces a greater lead than that of combined anterior and posterior canals (roll). Thus the timing of neck muscle responses to vestibular stimulation depends on the pair of activated vertical semicircular canals.

Animals↗
PubMed1978

Histological effect of ultrasonic irradiation in Menière's disease.

The lateral semicircular canal and the crista ampullaris from five patients previously treated with ultrasound for Menière's disease showed the following histological and ultrastructural changes: 1. The lateral semicircular canal was completely obliterated by dense connective and osteoid tissue. 2. In the subepithelial tissue in Crista ampullaris no signs of degeneration was found. The nerve fibers were normal. 3. Also the sensory cells with nerve-endings and supporting cells appeared normal. 4. In the transitional epithelium there was vacuolization and extensive swelling with protrusion of the cells into the endolymphatic space. 5. The secretory cells showed pronounced cellular vacuolization and increased intercellular space. It is concluded that the massive destruction of the normal anatomy in the lateral semicircular canal may be the morphological basis of a functional endolymphatic fistula for drainage of the endolymphatic hydrops.

Humans↗
PubMed2003

Rotatory nystagmus synchronous with heartbeat: a treatable form of nystagmus.

PURPOSE: To describe a treatable form of nystagmus. METHODS: Two patients recently evaluated at the Mayo Clinic had experienced various forms of oscillopsia, imbalance, and worsening symptoms with a Valsalva maneuver. Close inspection of the eye revealed a subtle rotatory nystagmus that was synchronous with the heartbeat. RESULTS: The two patients had surgical treatment for dehiscence of the superior semicircular canal; postoperatively, their symptoms completely resolved. This is a relatively newly discovered condition that has not been described on either slit-lamp or ophthalmoscopic examination. The cause is related to a dehiscence of the superior semicircular canal that permits communication of variable pressures between the intracranial cavity and the perilymphatic spaces of the semicircular canal. CONCLUSION: Being aware of this unusual form of nystagmus may permit physicians to diagnose it--one of the few treatable forms of nystagmus.

Humans↗
PubMed1995

Sinus tympani: anatomic considerations, computed tomography, and a discussion of the retrofacial approach for removal of disease.

Surgical access to the sinus tympani remains a challenge for otologic surgeons. Usually, the retrotympanum is approached through the middle ear in an anterior to posterior direction during chronic ear surgery. Whether this is via a posterior tympanotomy or after canal wall down tympanomastoidectomy, visualization of the most posterior recess of the sinus tympani is often inadequate. The purpose of this investigation is two fold: (1) to describe the highly variable anatomy of the posterior tympanic cavity and (2) to review the retrofacial approach to the sinus tympani. Histologic sections, cadaver dissections, and diagrammatic illustrations are combined with computed tomographic (CT) imaging to provide a three-dimensional understanding of the sinus tympani and adjacent labyrinthine structures. Viewed from the mastoid, the anatomic structures that define the boundaries of the retrofacial approach include the facial nerve and stapedius muscle laterally, the lateral semicircular canal superiorly, the posterior semicircular canal posteromedially, the vestibule anteromedially, and the jugular bulb inferiorly. When the sinus tympani is well developed, saucerization within these boundaries gives wide access into the sinus and round window niche. The authors suggest that preoperative imaging can select patients who are candidates for a retrofacial approach to expose and remove disease in the sinus tympani. Contraindications to this approach include axial CT image measurements showing a contracted space between the posterior semicircular canal and the medial aspect of the facial nerve, lack of posterior expansion of the sinus tympani, and in cases where these measurements are marginal, the presence of a high jugular bulb or anteriorly positioned sigmoid sinus.

Ear Diseases↗