Morphometric Study of the Vestibular Aqueduct in Patients With Enlarged Vestibular Aqueduct.

OBJECTIVE: To test whether there are significant differences in the morphologic features of the enlarged vestibular aqueduct (EVA) and its anatomic relationships with adjacent structures between EVA patients with and without other inner ear malformations. METHODS: The morphology of vestibular aqueduct, volume of vestibule, and anatomic location of facial nerve (FN) were compared among 3 groups. Group A, 18 control subjects; group B, 32 EVA patients without other inner ear malformations; group C, 14 EVA patients with other inner ear malformations. RESULTS: The isthmus of the aqueduct and vestibular volume in group C were larger than those in group B (P < 0.05). Positive correlations were identified between the length of the aqueduct and the vestibular volume in groups B and C. The vertical FN segment in group C located more anteriorly than that in groups A and B (P < 0.05). CONCLUSIONS: Compared with EVA patients without other inner ear malformations, the aqueduct, and vestibule in EVA patients with other inner ear malformations are larger, the vertical FN segment locates more anteriorly.

Image-guided, microsurgical topographic anatomy of the endolymphatic sac and vestibular aqueduct via a suboccipital retrosigmoid approach.

The endolymphatic sac (ES) and the vestibular aqueduct (VA) are often in the surgical field when posterior fossa lesions are targeted using retrosigmoid approaches. The purpose of this work is to validate neuronavigator accuracy in predicting VA location as well as to give guidelines to preserve the ES and VA. A retrosigmoid approach was performed bilaterally in six specimens in the semisitting position. Preoperatively, we registered in the CT scans the position of the VA genu (virtual genu). After the approach execution, ES and VA genu topographic relationships with evident posterolateral cranial base structures were measured using neuronavigation. Next, we exposed the VA genu: its position coincided with the virtual VA genu in all the specimens. On the average, the ES was 17.93 mm posterosuperolateral to the XI nerve in the jugular foramen, 12.26 mm posterolateral to the internal acoustic meatus, 20.13 mm anteromedial to the petro-sigmoid intersection at a point 13.30 mm inferior to the petrous ridge. The VA genu was located 7.23 mm posterolateral to the internal acoustic meatus, 18.11 mm superolateral to the XI nerve in the jugular foramen, 10.27 mm inferior to the petrous ridge, and 6.28 mm anterolateral to the endolymphatic ledge at a depth of 3.46 mm from the posterior pyramidal wall. Our study demonstrates that is possible to use neuronavigation to reliably predict the location of the VA genu. In addition, neuronavigation may be effectively used to create a topographical framework that may help maintaining the integrity of the ES/VA during retrosigmoid approaches.

Correlation of air-bone gap and size of Enlarged Vestibular Aqueduct in children.

OBJECTIVE: Enlarged vestibular aqueduct (EVA) is an inner ear malformation that represents an important cause of pediatric hearing loss. While certain elements in the history or audiogram may suggest EVA, it is most often diagnosed using computed tomography (CT). The present investigation was conducted to determine if the size of the audiometric air-bone gap (ABG) is correlated with the size of the vestibular aqueduct in the pediatric population using three vestibular aqueduct measurements. These included the fundus, midpoint, and porous widths of the vestibular aqueduct. STUDY DESIGN: This is a retrospective cohort study. SETTING: This study took place at a tertiary care referral center. PATIENTS: Fifty-five children (33 female; 22 male) with a confirmed diagnosis of unilateral or bilateral EVA as determined by prior imaging of the inner ear were included in the study. MAIN OUTCOME MEASURES: Associations of EVA measurements with ABGs at 0.5 and 1 kHz were evaluated using Pearson correlation coefficients. RESULTS: All of the correlation coefficients were positive, indicating that as EVA measurements increased so did the ABG. Only the correlation between fundus width and ABG at 1 kHz was not statistically significant. CONCLUSIONS: ABGs measured during audiometric testing correlate with the size of the EVA and ABGs can be clinical predictors of the severity of the bony abnormality. These data support the third window theory of conductive hearing loss in pediatric EVA.

A high jugular bulb and poor development of perivestibular aqueductal air cells are not the cause of endolymphatic hydrops in patients with Ménière's disease.

OBJECTIVE: The presence of endolymphatic hydrops in the inner ear, which can be detected with gadolinium-enhanced magnetic resonance imaging (Gd-MRI), is widely recognized as the main pathological cause of Ménière's disease (MD). However, the precise mechanisms underlying the development of endolymphatic hydrops remains unclear. One hypothesis proposes a relationship between the presence of a high jugular bulb (HJB) and MD, which disrupts the vestibular aqueduct leading to the development of endolymphatic hydrops. This study sought to identify anatomical features in MD patients using computed tomography (CT) images of the temporal bone. METHODS: Fifty-nine MD patients meeting the AAO-HNS diagnostic criteria and exhibiting endolymphatic hydrops in Gd-MRI were enrolled between July 2009 and December 2015. We only included MD patients who showed unilateral endolymphatic hydrops in Gd-MRI. Sixty-six patients with otosclerosis or facial palsy were also enrolled as control participants. In both groups, patients with other pathologies (e.g., chronic otitis media or cholesteatoma) and patients <16years old were excluded. HJB was defined as a JB that was observable in the axial CT image at the level where the round window could be visualized. JB surface area was measured on the axial image at the level where the foramen spinosum could be visualized. Finally, to investigate the relationship between the pneumatization of perivestibular aqueductal air cells and the existence of endolymphatic hydrops, the development of the air cells was rated using a three-grade evaluation system and the distance between the posterior semicircular canal (PSCC) and the posterior fossa dura was measured. RESULTS: The presence of HJB was observed in 22 of 59 affected sides of MD patients and in 17 healthy sides. The likelihood that HJB was detected on an affected side (22/39) was not significantly above chance (50%). The HJB detection rate did not significantly differ between the three groups (MD affected side, MD healthy side, and control patients). Furthermore, there were no significant group differences in JB surface area, distance between the PSCC and posterior fossa dura, or the development of perivestibular aqueductal air cells. CONCLUSION: We did not find any relationship between the anatomy of the temporal bones and the existence of endolymphatic hydrops. Moreover, we found no evidence suggesting that HJB or poor development of perivestibular aqueductal air cells were the cause of endolymphatic hydrops in MD patients.

When is the vestibular aqueduct enlarged? A statistical analysis of the normative distribution of vestibular aqueduct size.

BACKGROUND AND PURPOSE: The size of vestibular aqueducts (VAs) seen on CT studies varies. The current practice of calling a VA enlarged when it exceeds a certain threshold (eg, 1.5 mm at the midpoint) is arbitrary. Our hypothesis was that statistical analysis of the range of VA widths in a normal-hearing population would lead to a mathematic definition of the upper-limit-of-normal VA width. MATERIALS AND METHODS: The VA midpoint and opercular widths were measured in 73 children with normal hearing. Statistical analysis yielded values of the 99 th, 97.5th, 95th, 90th, 75th, and 50th percentiles for this normal distribution. RESULTS: The upper-limit-of-normal (95th percentile) values for the VA midpoint and opercular widths were 0.9 and 1.9 mm, respectively. The VAs with greater widths may reasonably be considered enlarged. CONCLUSION: The VAs with midpoint or opercular widths of 1.0 and 2.0 mm or greater, respectively, are enlarged.

Morphological analysis of the vestibular aqueduct by computerized tomography images.

OBJECTIVE: In the last two decades, advances in the computerized tomography (CT) field revise the internal and medium ear evaluation. Therefore, the aim of this study is to analyze the morphology and morphometric aspects of the vestibular aqueduct on the basis of computerized tomography images (CTI). MATERIAL AND METHOD: Computerized tomography images of vestibular aqueducts were acquired from patients (n=110) with an age range of 1-92 years. Thereafter, from the vestibular aqueducts images a morphometric analysis was performed. Through a computerized image processing system, the vestibular aqueduct measurements comprised of its area, external opening, length and the distance from the vestibular aqueduct to the internal acoustic meatus. RESULTS: The morphology of the vestibular aqueduct may be funnel-shaped, filiform or tubular and the respective proportions were found to be at 44%, 33% and 22% in children and 21.7%, 53.3% and 25% in adults. The morphometric data showed to be of 4.86 mm(2) of area, 2.24 mm of the external opening, 4.73 mm of length and 11.88 mm of the distance from the vestibular aqueduct to the internal acoustic meatus, in children, and in adults it was of 4.93 mm(2), 2.09 mm, 4.44 mm, and 11.35 mm, respectively. CONCLUSIONS: Computerized tomography showed that the vestibular aqueduct presents high morphological variability. The morphometric analysis showed that the differences found between groups of children and adults or between groups of both genders were not statistically significant.

Three-dimensional morphology of the vestibular cleft and its potential application.

HYPOTHESIS: To delineate quantitatively the spatial relationships of the utricle, saccule, and stapedial footplate, to locate the hole on the footplate, and to analyze the insertion depth into the vestibule and the direction of the piston during stapedotomy. BACKGROUND: The quantitative three-dimensional (3D) configuration of the utricle, saccule, and stapedial footplate is undetermined, and the stapedotomy procedures should be improved. METHODS: Four temporal bones were extracted from the fresh cadavers and were undecalcified polymer-embedded. The specimens were sectioned into serial 50-mum-thickness slices. After image processing and 3D reconstruction, a cartesian coordinate system was established to display the spatial relationships of the utricle, saccule, and stapedial footplate in the 3D Studio Max scene. The configuration of the utricle, the saccule, and the "vestibular cleft" was delineated quantitatively with the contour map method. With this contour map, any distance between one point at the surface of the footplate and another point at the surface of the utricle or saccule and its orientation can be measured. RESULTS: There was a V-shaped cleft between the utricle and the saccule named vestibular cleft. The angle of the cleft was 50.30 degrees +/- 19.90 degrees . The apex of the cleft always directed anterosuperiorly, whereas beneath the posteroinferior part of the footplate was an open and deep "seabed." The vertical distances between points on the tympanic surface of the footplate and points on the surface of the utricle or saccule were measured. The vertical distance from the center point of footplate to the vestibular end organs was 2.20 +/- 0.548 mm, the maximum distance being 3.0 mm, whereas the minimum distance was 1.6 mm. CONCLUSION: The posteroinferior area near the central point of the footplate is the optimal position for the fenestra through which the piston can be inserted relatively safely into a depth of 0.8 to 1.0 mm in the vestibule. If the deep end of the piston is inclined inferiorly and posteriorly by 8 to 10 degrees, respectively, the piston will be farther from the vestibular end organs. These manipulations may enhance surgical safety and efficiency in stapedotomy.

Clinical investigation and mechanism of air-bone gaps in large vestibular aqueduct syndrome.

OBJECTIVES: Patients with large vestibular aqueduct syndrome (LVAS) often demonstrate an air-bone gap at the low frequencies on audiometric testing. The mechanism causing such a gap has not been well elucidated. We investigated middle ear sound transmission in patients with LVAS, and present a hypothesis to explain the air-bone gap. METHODS: Observations were made on 8 ears from 5 individuals with LVAS. The diagnosis of LVAS was made by computed tomography in all cases. Investigations included standard audiometry and measurements of umbo velocity by laser Doppler vibrometry (LDV) in all cases, as well as tympanometry, acoustic reflex testing, vestibular evoked myogenic potential (VEMP) testing, distortion product otoacoustic emission (DPOAE) testing, and middle ear exploration in some ears. RESULTS: One ear with LVAS had anacusis. The other 7 ears demonstrated air-bone gaps at the low frequencies, with mean gaps of 51 dB at 250 Hz, 31 dB at 500 Hz, and 12 dB at 1,000 Hz. In these 7 ears with air-bone gaps, LDV showed the umbo velocity to be normal or high normal in all 7; tympanometry was normal in all 6 ears tested; acoustic reflexes were present in 3 of the 4 ears tested; VEMP responses were present in all 3 ears tested; DPOAEs were present in 1 of the 2 ears tested, and exploratory tympanotomy in 1 case showed a normal middle ear. The above data suggest that an air-bone gap in LVAS is not due to disease in the middle ear. The data are consistent with the hypothesis that a large vestibular aqueduct introduces a third mobile window into the inner ear, which can produce an air-bone gap by 1) shunting air-conducted sound away from the cochlea, thus elevating air conduction thresholds, and 2) increasing the difference in impedance between the scala vestibuli side and the scala tympani side of the cochlear partition during bone conduction testing, thus improving thresholds for bone-conducted sound. CONCLUSIONS: We conclude that LVAS can present with an air-bone gap that can mimic middle ear disease. Diagnostic testing using acoustic reflexes, VEMPs, DPOAEs, and LDV can help to identify a non-middle ear source for such a gap, thereby avoiding negative middle ear exploration. A large vestibular aqueduct may act as a third mobile window in the inner ear, resulting in an air-bone gap at low frequencies.

Identification of operculum and surgical results in endolymphatic sac drainage surgery.

To increase the accuracy of identification of the endolymphatic sac during endolymphatic sac drainage surgery, we focused on the intra-operative identification of the operculum as a structural marker of the endolymphatic sac and the vestibular aqueduct at the rugose portion. Then, we examined the relationship between identification of the operculum and surgical outcomes. We used 100 cases with intractable Meniere's disease who received endolymphatic sac drainage with local steroid administration, superior to traditional endolymphatic sac drainage surgery and non-surgical medical treatment. According to operation records, we divided these 100 cases into those with intra-operative identification of the operculum (n=72) and those without (n=28) and compared the surgical outcomes. The ratio of intra-operative identification of operculum (OPC(+)) was 72.0%. Better hearing results were observed significantly more often in patients with OPC(+), although there were no significant differences in vertigo results between OPC(+) and OPC(-). We concluded that the endolymphatic sac might be exposed adequately at rugose portion and opened for the drug delivery, resulting in better surgical results.

The Human Vestibular Aqueduct: Anatomical Characteristics and Enlargement Criteria.

HYPOTHESIS: The human vestibular aqueduct (VA) shows great anatomical variations, and imaging can be difficult, so we need more data on the normal anatomy of the VA for better radiologic evaluation of large vestibular aqueduct syndrome (LVAS). BACKGROUND: The normal anatomy of the human VA was analyzed in micro-dissected human temporal bones. METHODS: The study is based on two sets of human temporal bones. One set of 32 human temporal bones was selected from a collection of 50 micro-dissected specimens. The outline of the intraosseous portion of the VA was drawn and digitized, and dimensions were assessed. The other set of 20 plastic molds were randomly selected from a collection of 324 specimens, and the VA dimensions were assessed. RESULTS: Measurements from this study are presented in means, standard deviations, and ranges. The results from these measurements are considered normal and compared with previously published data. The variations in the normal anatomy of the VA are presented and discussed. CONCLUSION: The VA courses sagittal in the human skull. Therefore, we recommend the lateral projection (reformatted) to demonstrate the VA in LVAS patients. We advocate assessing: 1) the width (or height) of the external aperture (EA), 2) the width at the half distance between the EA and the common crus (CC), and if possible 3) the width of the proximal portion of the VA. Based on the measurements, our criteria for enlargement are 2.0 mm or greater, 1.5 mm or greater, and more than 1 mm at these sites.

Vestibular Aqueduct Measurements in the 45° Oblique (Pöschl) Plane.

BACKGROUND AND PURPOSE: The 45° oblique (Pöschl) plane allows reliable depiction of the vestibular aqueduct, with virtually its entire length often visible on 1 CT image. We measured its midpoint width in this plane, aiming to determine normal measurement values based on this plane. MATERIALS AND METHODS: We retrospectively evaluated temporal bone CT studies of 96 pediatric patients without sensorineural hearing loss. Midvestibular aqueduct widths were measured in the 45° oblique plane by 2 independent readers by visual assessment (subjective technique). The vestibular aqueducts in 4 human cadaver specimens were also measured in this plane. In addition, there was a specimen that had undergone CT scanning before sectioning, and measurements made on that CT scan and on the histologic section were compared. Measurements from the 96 patients' CT images were then repeated by using findings derived from the radiologic-histologic comparison (objective technique). RESULTS: All vestibular aqueducts were clearly identifiable on 45° oblique-plane CT images. The mean for subjective measurement was 0.526 ± 0.08 mm (range, 0.337-0.947 mm). The 97.5th percentile value was 0.702 mm. The mean for objective measurement was 0.537 ± 0.077 mm (range, 0.331-0.922 mm). The 97.5th percentile value was 0.717 mm. CONCLUSIONS: Measurements of the vestibular aqueduct can be performed reliably and accurately in the 45° oblique plane. The mean midpoint width was 0.5 mm, with a range of 0.3-0.9 mm. These may be considered normal measurement values for the vestibular aqueduct midpoint width when measured in the 45° oblique plane.

Reformatted planar 'Christmas tree' MR appearance of the endolymphatic sac.

A high-resolution three-dimensional Fourier transform technique and prototype bilateral dual phased-array surface coil technique was used to make inner ear structures visible on MR. Multiplanar reformatted images, parallel to the plane of the vestibular aqueduct, allowed viewing of the entire endolymphatic sac/vestibular aqueduct on one section, producing a "Christmas tree" shape. The reformation was obtained using a double oblique angle, 45 degrees from true sagittal and 70 degrees from the orbital-meatal axis.

Anatomy and physiology of the gerbil cochlear nucleus: an improved surgical approach for microelectrode studies.

A new, improved surgical approach to the cochlear nucleus is developed in the gerbil. This new approach involves making a small hole in the lateral wall of the temporal bone located within the perimeter of the superior semicircular canal. Microelectrodes are passed through the intact parafloccular lobe of the cerebellum to the cochlear nucleus. One advantage of the new approach is that no removal of any CNS vasculature or neural tissue is necessary. Relations between the bulla, temporal bone and cochlear nucleus are presented in detail. The new approach is demonstrated by making single unit recordings from the cochlear nucleus and classifying response patterns as measured in PST histograms. All of the response types found in cat are found in the gerbil.

Estimation of the endolymphatic sac and vestibular aqueduct using magnetic resonance imaging.

OBJECTIVE: To evaluate the diagnostic accuracy of magnetic resonance imaging for assessment of the endolymphatic sac and vestibular aqueduct. STUDY DESIGN: Imaging and histological study of the cadaver. METHODS: Five cadavers were studied by a 1.5-T magnetic resonance imaging system with a 3-inch-diameter surface coil. Magnetic resonance imaging scans were obtained with proton density-weighted and T2-weighted fast spin-echo sequences. Histological sections were made with an epoxy resin-embedding method and were compared with magnetic resonance imaging scans. RESULTS: The visibility of the endolymphatic sac on both sequences corresponded well to the presence of the endolymphatic sac on histological sections. On the histological sections, the width of the external aperture of vestibular aqueduct (endolymphatic sac including surrounding connective tissue) was 0.96 +/- 0.18 mm (mean +/- SD) and the width of lumen of endolymphatic sac at the same point was 0.47 +/- 0.17 mm. The width of the endolymphatic sac was 1.02 +/- 0.19 mm on proton density-weighted images and was 0.81 +/- 0.15 mm on T2-weighted images. The widths of endolymphatic sac measured on proton density-weighted image and those of vestibular aqueduct on histological section did not show statistically significant differences (P >.05). On the other hand, the endolymphatic sac as measured on T2-weighted image tended to be smaller than the vestibular aqueduct (P <.05) and tended to be larger than the lumen of the endolymphatic sac (P <.0005). CONCLUSION: Both sequences can precisely depict the endolymphatic sac; however, the proton density-weighted image is a more appropriate indicator of the actual anatomical configuration of the endolymphatic sac with surrounding connective tissue and vestibular aqueduct.

Anatomic basis for labyrinthine preservation during posterior fossa acoustic tumor surgery.

Earlier diagnosis of acoustic tumors promises to increase our opportunity to identify patients with serviceable hearing. Critical to a posterior fossa transmeatal approach for acoustic tumor resection is preservation of the underlying labyrinth. Although the labyrinth has been recognized as a limiting factor in exposure of tumor in the internal auditory canal, few reports have detailed the microscopic surgical anatomy posterior to the internal auditory canal. An anatomic study was undertaken to determine consistent relationships between critical structures within the temporal bone relevant to hearing preservation surgery. The results of this study indicate that, whereas topographic landmarks are helpful for orientation, the more consistent relationship of the labyrinth to the vestibular aqueduct and singular canal allows a more accurate localization of the underlying labyrinth. Although the vestibule frequently prevents direct visualization of the transverse crest, a dissection based upon the microsurgical anatomy will maximize visualization of the lateral fundus while preserving the integrity of the labyrinth.

Observation of the external aperture of the vestibular aqueduct using three-dimensional surface reconstruction imaging.

Observation of the external aperture of the vestibular aqueduct was hitherto possible only in cadavers or dry temporal bones; however, by applying three-dimensional surface reconstruction imaging, it is now possible to observe solid-looking images of this structure in living humans. When the width of the external aperture of the vestibular aqueduct was measured in 58 people, it was found to be significantly narrower in the affected ears of patients with Meniere's disease than in normal ears.

Variations in surgical anatomy of the endolymphatic sac.

Twenty-nine specimens of the extraosseous portion of the human endolymphatic sac (ES) were serially sectioned longitudinally. The length and width of the extraosseous ES were measured and the surface area was calculated. As the specimens included the sigmoid sinus (SS), the relationship between the ES and the SS was analyzed. The extraosseous ES varied considerably in size. The lumen either consisted of a single tube or was subdivided into several tubules. The distal part of the ES overlapped the SS in one third of the specimens. The results indicate that a minute extraosseous ES could explain the sometimes difficult task of localizing this structure at ES surgery. The great variability in size might perhaps also explain the varying results of this surgery.

Vascular mechanisms in Meniere's disease.

Normal venous drainage of the vestibular organs through the vein of the paravestibular canaliculus (PVC) may be crucial to inner ear fluid mechanics. It is proposed that increased venous pressure, with resultant venous insufficiency of the vestibular organs, may result in endolymphatic hydrops unless collateral venous circulation develops. Certain variations in pattern of venous drainage where the vestibular organs drain predominantly through the PVC vein may be a predisposing factor. In patients with Meniere's disease, different mechanisms can cause venous insufficiency. One suggested mechanism is morphologic change in the microcirculation of the intermediate portion of the endolymphatic sac. Microcirculation changes may be associated with fibrosis of the perisac tissues or shortening of the intermediate sac region or might be physiologically determined. Venous insufficiency may also result from anomalies of the PVC vein.

Course and contents of the paravestibular canaliculus.

The purpose of this study is to describe the anatomy of the paravestibular canaliculus (PVC) in detail, especially its course in relation to the vestibular aqueduct (VA) and its vascular contents. Serial horizontal sections of 20 normal human temporal bones were stained either with hematoxylin and eosin, by Verhoeff-van Gieson's method, or by Mallorys method, and studied under the light microscope. Graphic reconstruction of the VA and the PVC was performed in some of the cases. In this study, the following new anatomical information on the common course and vascular contents of the PVC was obtained: 1) two PVC are present in the area near the vestibular orifice of the VA; 2) the PVC merges with the VA in the area near its cranial orifice without any particular branching, and does not enter the posterior cranial fosa; 3) veins course through the entire length of the PVC whereas arteries course only through the posterior cranial fossa side of the PVC. It appears that veins are the major contents of the PVC and that these veins represent the main venous drainage system from the vestibule. It also appears that arteries in the PVC supply the blood from the posterior cranial fossa mainly to the PVC itself.

Postnatal development of the vestibular aqueduct in relation to the internal auditory canal. Computer-aided three-dimensional reconstruction and measurement study.

To investigate a possible developmental relationship between the internal auditory canal (IAC) and the vestibular aqueduct (VA), we made the following measurements in 10 normal temporal bones from individuals 4 months to 70 years of age at death, using a computer-aided three-dimensional reconstruction and measurement method: the volume of the VA, the length of the IAC, and the distance between the IAC and the external aperture of the VA. The degree of periaqueductal pneumatization was also assessed qualitatively by means of a light microscope. The three parameters increased postnatally in parallel with the development of the periaqueductal air cells, and all pairwise comparisons of these parameters showed a statistically significant correlation. Our results indicate that the IAC and VA develop synchronously and in parallel with the development of the periaqueductal air cells. We believe that an understanding of this relationship will be of help during surgery involving the IAC and VA, and may shed some light on the morphological features of Meniere's disease.