"Reversed polarization" of Na/K-ATPase-a sign of inverted transport in the human endolymphatic sac: a super-resolution structured illumination microscopy (SR-SIM) study.

The human endolymphatic sac (ES) is believed to regulate inner ear fluid homeostasis and to be associated with Meniere's disease (MD). We analyzed the ion transport protein sodium/potassium-ATPase (Na/K-ATPase) and its isoforms in the human ES using super-resolution structured illumination microscopy (SR-SIM). Human vestibular aqueducts were collected during trans-labyrinthine vestibular schwannoma surgery after obtaining ethical permission. Antibodies against various isoforms of Na/K-ATPase and additional solute-transporting proteins, believed to be essential for ion and fluid transport, were used for immunohistochemistry. A population of epithelial cells of the human ES strongly expressed Na/K-ATPase α1, ß1, and ß3 subunit isoforms in either the lateral/basolateral or apical plasma membrane domains. The ß1 isoform was expressed in the lateral/basolateral plasma membranes in mostly large cylindrical cells, while ß3 and α1 both were expressed with "reversed polarity" in the apical cell membrane in lower epithelial cells. The heterogeneous expression of Na/K-ATPase subunits substantiates earlier notions that the ES is a dynamic structure where epithelial cells show inverted epithelial transport. Dual absorption and secretion processes may regulate and maintain inner ear fluid homeostasis. These findings may shed new light on the etiology of endolymphatic hydrops and MD.

Maximizing Exposure of the Internal Auditory Canal Via the Retrosigmoid Approach: An Anatomical, Radiological, and Surgical Study.

OBJECTIVE: The purpose of this study was to identify anatomic landmarks and surgical techniques that maximize bone removal for exposure of the distal internal auditory canal (IAC) to avoid labyrinthine injury during retrosigmoid removal of tumors within the IAC. STUDY DESIGN: Anatomic dissection, radiological assessment and retrospective case series. SETTING: Tertiary referral center. METHODS: On the basis of previously conducted temporal bone anatomic dissections of the temporal bone, the authors performed intraoperative measurement of the undissected distal IAC, performed pre- and postoperative radiological assessment of vestibular schwannoma (VS) patients. The surgical and anatomic information was used to determine the anatomic limits of labyrinth sparing bone dissection and the landmarks most critical to maximal IAC exposure. The authors describe surgical techniques using these data. An edited video of representative surgery highlights important principles. Review of 251 patients requiring IAC bony dissection for tumor removal from January 2005 through October 2017 is described. RESULTS: Achieving complete exposure of the IAC fundus is not possible, without labyrinthine injury, via retrosigmoid approach. Anatomic dissection, intraoperative photography, and postoperative radiographs demonstrate that bone removal within 2 to 3 mm of the fundus is routinely possible. The endolymphatic sac and duct is the optimal landmark for optimizing IAC exposure. CONCLUSION: The course of the endolymphatic sac and duct in the posterior petrous bone is the most important landmark determining the lateral limit of bony removal during IAC exposure for tumor resection. Surgical techniques based on these anatomic findings facilitate tumor resection while preserving the labyrinth.

Lamellar projections in the endolymphatic sac act as a relief valve to regulate inner ear pressure.

The inner ear is a fluid-filled closed-epithelial structure whose function requires maintenance of an internal hydrostatic pressure and fluid composition. The endolymphatic sac (ES) is a dead-end epithelial tube connected to the inner ear whose function is unclear. ES defects can cause distended ear tissue, a pathology often seen in hearing and balance disorders. Using live imaging of zebrafish larvae, we reveal that the ES undergoes cycles of slow pressure-driven inflation followed by rapid deflation. Absence of these cycles in lmx1bb mutants leads to distended ear tissue. Using serial-section electron microscopy and adaptive optics lattice light-sheet microscopy, we find a pressure relief valve in the ES comprised of partially separated apical junctions and dynamic overlapping basal lamellae that separate under pressure to release fluid. We propose that this lmx1-dependent pressure relief valve is required to maintain fluid homeostasis in the inner ear and other fluid-filled cavities.

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.

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.

Trautmann's triangle anatomy with application to posterior transpetrosal and other related skull base procedures.

Trautmann's triangle (TT) faces the cerebellopontine angle and is exposed during posterior transpetrosal approaches. However, reports on the morphometric analysis of this structure are lacking in the literature. The goal was to better understand this important operative corridor. TT was exposed from an external approach (transmastoid) in ten cadavers (20 sides) and from an internal approach on 20 dry adult temporal bones. Measurements included calculation of the area of TT and the distance of the endolymphatic sac from the anterior border of the sigmoid sinus. The area range of TT was 45-210 mm(2) (mean 151 mm(2); SD 37 mm(2)). Three types of triangles were identified based on area. Type I triangles had areas less than 75 mm(2), Type II areas were 75-149 mm(2), and Type III areas were 150 mm(2) and greater. These types were observed in 37.5%, 35%, and 27.5% of sides, respectively. The distance from the jugular bulb's anterior border to the posterior border of the posterior semicircular canal ranged from 6 to 11 mm (mean 8.5 mm). The endolymphatic sac was located in the inferior portion of TT and traveled anterior to the sigmoid sinus. The horizontal distance from the anterior edge of the sigmoid sinus to the posterior edge of the endolymphatic sac ranged from 0 to 13.5 mm (mean 9 mm). Additional anatomic knowledge regarding TT may improve neurosurgical procedures in this region by avoiding intrusion into the endolymphatic sac and sigmoid sinus.

Noninvasive evaluation of endolymphatic space in healthy volunteers using magnetic resonance imaging.

CONCLUSIONS: A new method for noninvasive standard evaluation of normal endolymphatic space and endolymphatic hydrops using magnetic resonance imaging (MRI) is indicated. OBJECTIVE: To standardize the evaluation of endolymphatic space in the cochlea and the vestibule in healthy volunteers by applying noninvasive intratympanic gadolinium (Gd) perfusion through the eustachian tube and three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI). METHODS: This was a prospective study. 3D-FLAIR MRI was performed with a 3 Tesla (3 T) unit 24 h after intratympanic administration of Gd through the eustachian tube in 20 healthy volunteers. Pure tone test and tympanometry were performed 24 h before Gd was administered, and 24 h and 1 month after Gd administration. RESULTS: Gd was present in the perilymph of the inner ear, which clearly displayed the endolymphatic space on 3D-FLAIR MRI with a visible borderline between the perilymph and the endolymph. In healthy volunteers, the normal value for the endolymphatic space in the cochlea ranged between 9% and 28%, and that in the vestibule was between 14% and 40%. No significant changes in pure tone test and tympanometry were noted.

Hypothetical mechanism for vertigo in Meniere's disease.

Past theories that have been proposed to account for the attacks of vertigo during the course of Meniere disease are reviewed. In the past, vascular theories and theories of perilymph and endolymph mixing due to ruptures or leakages were proposed. Recent research concerning the basic mechanisms of the inner ear anatomy and function cast doubt on these theories. The anatomy, physiology, and pathophysiology of the inner ear, and in particular of the endolymphatic sac and endolymphatic duct are reviewed. Recent studies suggest that in people the endolymph ionic content is replenished without any flow of fluid and that longitudinal endolymph flow only occurs in response to volume excess. Furthermore audiological and electrophysiological studies have revealed little or no change in the cochlear function during episodes of vertigo. The longitudinal drainage theory attempts to encompass the recent research findings. The theory hypothesizes that endolymph draining too rapidly from the cochlear duct (pars inferior) causes attacks of vertigo. The endolymph overfills the endolymphatic sinus and overflows into the utricle (pars superior), stretching the cristae of the semicircular canals, causing the attacks of vertigo.

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.

Quantitative anatomy of the guinea pig endolymphatic sac.

The endolymphatic sac is believed to represent one of the primary loci for endolymph volume regulation in the inner ear. Quantitative analysis of physiologic measurements from the endolymphatic sac requires knowledge of the anatomy of the structure, specifically the luminal volume and the variation of cross-sectional area with distance along the sac. Recently techniques have become available to make these measurements. In the present study, fixed, isolated specimens of the guinea pig endolymphatic sac were imaged by high-resolution magnetic resonance microscopy (MRM) or by histological serial sections. Structures were reconstructed and quantified using image analysis software. In specimens imaged by MRM the endolymphatic sac volume, including tissue and lumen, was 359 nl for the intraosseous region and 106 nl for the extraosseous region, totaling 465 nl for the entire structure. The luminal volumes were 131 nl for the intraosseous region and 13 nl for the extraosseous region, totaling 144 nl. In histological specimens the volume, including tissue and lumen, was 414 nl for the intraosseous region and 121 nl for the extraosseous region, totaling 535 nl for the entire structure. The luminal volumes were 152 nl for the intraosseous region and 26 nl for the extraosseous region, totaling 179 nl. Differences in volume estimates obtained by the two methods were not statistically significant and variation was dominated by inter-specimen variation. Pooling the data, the total volume of the endolymphatic sac in the guinea pig including tissue and lumen was 506 nl (S.D. 100, n=17) and the volume of the lumen was 169 nl (S.D. 48, n=14).

Cochlear fluid space dimensions for six species derived from reconstructions of three-dimensional magnetic resonance images.

OBJECTIVES: To establish the dimensions and volumes of the cochlear fluid spaces. STUDY DESIGN: Fluid space volumes, lengths, and cross-sectional areas were derived for the cochleas from six species: human, guinea pig, bat, rat, mouse, and gerbil. METHODS: Three-dimensional reconstructions of the fluid spaces were made from magnetic resonance microscopy (MRM) images. Consecutive serial slices composed of isotropic voxels (25 microm3) representing the entire volume of fixed, isolated cochleas were obtained. The boundaries delineating the fluid spaces, including Reissner's membrane, were resolved for all specimens, except for the human, in which Reissner's membrane was not consistently resolved. Three-dimensional reconstructions of the endolymphatic and perilymphatic fluid spaces were generated. Fluid space length and variation of cross-sectional area with distance were derived by an algorithm that followed the midpoint of the space along the length of the spiral. The total volume of each fluid space was derived from a voxel count for each specimen. RESULTS: Length, volume, and cross-sectional areas are provided for six species. In all cases, the length of the endolymphatic fluid space was consistently longer than that of either perilymphatic scala, primarily as a result of a greater radius of curvature. For guinea pig specimens, the measured volumes of the fluid spaces were considerably lower than those suggested by previous reports based on histological data. CONCLUSIONS: The quantification of cochlear fluid spaces provided by this study will enable the more accurate calculation of drug and other solute movements in fluids of the inner ear during experimental or clinical manipulations.

Endolymphatic sac tumours.

This review article surveys clinical and pathological literature on endolymphatic sac tumours (ELST) and summarizes characteristics that describe the entity. ELST are rare neuroectodermal neoplasms in the petrous bone, originating from inner ear structures. They can be encountered sporadically or in von Hippel-Lindau disease. The most prominent symptom is sensorineural deafness. Historically, nomenclature of invasive adenoid tumours in the petrous bone has been divergent, the term papillary adenocarcinoma used most frequently. Histologically, they have a follicular or papillary and adenoid pattern that can be easily confused with various other neoplastic conditions including metastatic carcinoma. It remains to be verified whether similar tumours (papillary adenocarcinomas) can originate from the middle ear. Middle ear adenomas have a similar appearance but probably originate from neural crest cells in the middle ear. ELST can express a variety of epitopes (including cytokeratin and neuroectodermal markers) which can be detected immunohistochemically. In cases in von Hippel-Lindau disease the cerebello-pontine angle should be included in routine radiological examinations to detect ELST before the tumours lead to deafness. In apparently sporadic cases of ELST, genetic testing for von Hippel-Lindau disease should be considered. Correct distinction of ELST from metastatic carcinoma prevents futile searches for unknown primary tumours.

[3-D morphological study of the temporal bone].

OBJECTIVE: To establish the 3-D(three-dimensional) morphological study of the temporal bone by means of computer graphic techniques. METHODS: The serial sections of the temporal bone were processed by the technique of computer-aided 3-D reconstruction. The 3-D images of the multi-structures in the temporal bone were displayed on the monitor. The 3-D parameters of these structures were measured by a special software. The stereo-images of the structures in the temporal bone were obtained by stereoscopy and stereo-pairs. RESULTS: Most structures of the temporal bone were reconstructed in 37 instances for the different purpose of study. Each set of the stereo-pair corresponding to the structures in the temporal bones and many 3-D parameters were obtained. The complex spatial relationship among the reconstructed structures such as the facial nerve, endolymphatic sac, posterior tympanum and posterior ampullary nerve was revealed and the mechanic model of the ossicular chain was set up. According to these results, the surgical approach of the posterior ampullary nerve transection was designed and simulated on the graphic computer. CONCLUSION: The technique of computer-aided 3-D reconstruction provides a new tool for the study of the temporal bone. It is also helpful for the designs and simulations of the surgical approaches. The results of this study contribute to developmout of a new branch of pathology of the temporal bone and a primary 3-D morphological study of the temporal bone.

[The vascular pattern of the endolymphatic duct, endolymphatic sac and its anatomic differences in guinea pigs].

In order to study the vascular pattern of the endolymphatic duct and sac, endolymphatic duct and sac were examined with vascular Indian ink injection and image analysis. The Results were as follows: 1. In the 20 temporal bones, 17 (85%) had posterior meningeal artery (PMA) and posterior vestibular artery (PVA) supply and the rest (3 specimens, 15%) had no PVA supply; 2. The distribution frequency of PMA in the endolymphatic sac was much higher than that of PVA(P < 0.01), but the distribution of PMA and PVA in the endolympatic duct were not different (P > 0.05). The conclusions is that there are anatomic differences in vascular supply and pattern of the endolymphatic duct and sac, PMA is the main vascular structure in the endolymphatic sac.

Morphometric evaluation of the infralabyrinthine approach to the internal auditory canal.

Morphometric evaluation of the infralabyrinthine approach to the internal auditory canal (IAC) was performed using 20 fresh human temporal bones in order to assess the exposure limitations, inherent risks and technical difficulties that may arise due to common anatomic variations of this region. While performing the infralabyrinthine approach to the IAC, minor problems such as an anteriorly placed sigmoid sinus were easily managed. However, in 50% of the specimens, this approach was limited due to variations of the jugular bulb, restricting access to the IAC. Sacrificing the endolymphatic duct in these specimens did not significantly improve the surgical access to the eighth nerve. Furthermore, it was noted that this approach puts the facial nerve and cochlea under the risk of inadvertent damage during drilling. The authors conclude that vestibular nerve sectioning using the infralabyrinthine approach may be performed only in few selected cases and extreme care is needed in order not to damage the structures that limit this approach.

Pathophysiologic theories in the etiology of Meniere's disease.

The etiology of the attacks of vertigo that occur in Meniere's disease is discussed in this article. None of the current theories remain tenable in view of recent findings concerning the physiology and pathophysiology of the cochlea and endolymphatic sac. A new theory suggests that a narrowed duct becomes obstructed by debris that is cleared by a combination of the secretion of hydrophillic proteins within the sac and a hormone, saccin, that increases the volume of endolymph within the cochlea. It is proposed that the sudden restoration of longitudinal flow initiates the attacks of vertigo.

Endolymphatic hydrops after total dissection or cauterization of the distal portion of the endolymphatic sac.

In this study, a more subtle animal model of Menière's disease is investigated by damaging the distal portion of the endolymphatic sac by dissection or cauterization to produce mild dysfunction of endolymphatic outflow. Cauterization resulted in low degrees of hydrops without any correlation with the inflicted damage. Total dissection of the distal portion of the sac adjacent to the sigmoid sinus produced moderate to severe endolymphatic hydrops with interanimal variation. The consequences of these relatively severe effects, in relation to the mild damage of the endolymphatic sac, and the influence on damaged and undamaged parts of the endolymphatic sac will be discussed.

Comparison of endolymph cross-sectional area measured histologically with that measured in vivo with an ionic volume marker.

In order to establish how endolymph volume is regulated, it is essential to be able to measure endolymph volume or cross-sectional area in vivo. We have developed methods to accomplish this by injecting the volume marker ion hexafluoroarsenate (AsF6) into endolymph by iontophoresis. For an injection at a constant rate, the endolymph concentration is inversely dependent on the cross-sectional area of the scala into which injection occurred. Marker concentrations were monitored by inserting ion-selective microelectrodes into endolymph near the injection site. In a previous study we quantified the degree of hydrops in animals following ablation of the endolymphatic sac. In the present study we validated the technique by comparing the endolymphatic cross-sectional area measured in vivo with AsF6 with that measured by established histologic procedures. The correlation between the two measures was good, with a coefficient of .903, although the area measured histologically was a little lower than that measured in vivo.