The endolymphatic sac in the Mondini disorder

Summary The endolymphatic sacs are described in temporal bone specimens from a 31-year-old man with bilateral Mondini disorder. The ducts and sacs are thin-walled, cyst-like structures with complete absence of loose vascular perisac tissue, and are directly apposed to the bone of the vestibular aqueduct. Histological evidence of severe bone erosion is present in these specimens and is most marked in the intermediate and distal portions of the vestibular aqueduct. It is also present in the foveal region of the posterior temporal bone surface underlying the sac. Erosion of the bony wall of the paravestibular canaliculus (PVC) is demonstrable, with incorporation of the vein of the PVC inside the margin of the widened vestibular aqueduct. These findings suggest a causal relationship between pressure within the endolymphatic duct and sac and erosion of the surrounding bone. The absence of endolymphatic hydrops of the cochlea and vestibular organs in the Mondini disorder constrast significantly with the endolymphatic hydrops seen in Meniere's disease.Supported by The Hope for Hearing Foundation, UCLA     

The vascular pattern of the endolymphatic sac in the human embryo

The venous vascular anatomy of the endolymphatic sac in human embryos was examined. The endolymphatic sac was found to be covered by sinusoid-like blood vessels arising from the sigmoid sinus. A rich and extensive capillary network was present on the epithelial surface of the endolymphatic sac. Connections between this capillary bed and the vein in the paravestibular canaliculus were seen. The blood of the endolymphatic sac can therefore drain either into the vein of the vestibular aqueduct in the paravestibular canaliculus or directly into the sigmoid sinus. The vessels lying on the endolymphatic sac are thin-walled and irregular. The endothelial cells lies in direct contact with the epithelial cells of the endolymphatic sac. The reduction of the dense capillary bed in the young embryo to only a few vessels in the order embryo is described.     

The endolymphatic sac in the Mondini disorder

The endolymphatic sacs are described in temporal bone specimens from a 31-year-old man with bilateral Mondini disorder. The ducts and sacs are thin-walled, cyst-like structures with complete absence of loose vascular perisac tissue, and are directly apposed to the bone of the vestibular aqueduct. Histological evidence of severe bone erosion is present in these specimens and is most marked in the intermediate and distal portions of the vestibular aqueduct. It is also present in the foveal region of the posterior temporal bone surface underlying the sac. Erosion of the bony wall of the paravestibular canaliculus (PVC) is demonstrable, with incorporation of the vein of the PVC inside the margin of the widened vestibular aqueduct. These findings suggest a causal relationship between pressure within the endolymphatic duct and sac and erosion of the surrounding bone. The absence of endolymphatic hydrops of the cochlea and vestibular organs in the Mondini disorder contrast significantly with the endolymphatic hydrops seen in Meniere's disease.     

豚鼠内淋巴管与内淋巴囊微血管模式及解剖差异

为研究内淋巴管及内淋巴囊微血管分布模式，通过墨汁血管灌流技术和图像分析方法对１０只豚鼠的颞骨（２０侧）内淋巴管和内淋巴囊做全面观察分析。结果：①２０侧颞骨中有１７侧（８５％）内淋巴管、内淋巴囊有脑膜后动脉和前庭后动脉两条供血来源，其余３例（１５％）则发现前庭后动脉缺如；②脑膜后动脉在内淋巴囊的分布频率明显高于前庭后动脉（Ｐ〈０．０１），但两者在内淋巴管的分布频率无显著性（Ｐ〉０．０５）。结论：内淋     

Periductal vessels of the endolymphatic duct.

Light microscope was used to examine the rich vascular plexus surrounding the human endolymphatic duct, both in the periductal loose connective tissue and in the bony channels surrounding the bony vestibular aqueduct. We also performed computer-aided three-dimensional reconstruction on one serially sectioned region of the endolymphatic duct. We found an anastomotic and looping network of vessels residing in the loose connective tissue close to the epithelium of the endolymphatic duct. This network often received a vascular contribution from the vessels in the periaqueductal bony channels. These findings were verified by light microscopic examination of 50 temporal bone specimens. Concurrent with this finding, histologic examination also showed different characteristic features of the vascular system of the endolymphatic duct-proximal sac areas and of the more distal parts of the endolymphatic sac. These features include the arrangement, quantity, and contents of the periaqueductal bony channels, as well as the organization of the bone containing these periductal bony channels. Findings from this study help the understanding of the anatomy of the human endolymphatic duct. In addition, they support and supplement earlier observations of the structure of the endolymphatic duct. We suggest the possible existence of a periductal vasculature system, similar in pattern to that in the endolymphatic sac, but specialized to work with the duct to aid its function.     

Three-dimensional analysis of 61 human endolymphatic ducts and sacs in ears with and without Menière's disease

We used light microscopy and computerized graphic reconstruction techniques to examine the endolymphatic duct and sac in 20 pairs of bones from patients with Menière's disease and 21 bones from controls. The diameters of the endolymphatic duct and the proximal portion of the vestibular aqueduct were significantly smaller in Menière's disease ears than in controls. Graphic reconstructions showed the Menière's sacs to be smaller and to have fewer tubular epithelial structures in the intraosseous portion than in the control ears. The median volume of the sac in the Menière's disease side was substantially lower than in the contralateral ear. The width of the external aperture of the vestibular aqueduct was significantly smaller in Menière's disease ears than in controls. These findings indicate that the size not only of the vestibular aqueduct but also of the sac is reduced in Menière's disease. The results may suggest that the endolymphatic sac is pathologically changed in Menière's disease and that a reduced resorptive capacity of a small endolymphatic sac could result in endolymphatic hydrops.     

Ischemia of the endolymphatic sac.

A decrease in vascular density in the endolymphatic sac was suspected as a factor in the pathogenesis of endolymphatic hydrops in Meniere's disease. The present study was undertaken to explore this possibility by cutting the posterior meningeal artery and the sigmoid sinus above and below the external aperture of the vestibular aqueduct or by incision of the dura adjacent to the sinus in 18 guinea pigs. The lesions in the sac were greater in the segmental ablation of the artery and sinus and were consistently associated with the development of endolymphatic hydrops. Among the lesions shown in the sac epithelia, the intermediate portion was most often and most severely affected with a decrease in rugose formation and a flattening of the tall epithelial cells or replacement of epithelial cells by squamous type cells. A high correlation between the lesions in the intermediate portion and occurrence of hydrops suggests that the intermediate portion plays a greater role in the pathogenesis of endolymphatic hydrops. The sac luminal precipitates known to be increased in human Meniere's cases were decreased or absent in this study, which suggests that the increased amount is unlikely to be the cause of endolymphatic hydrops. The evidence supports the hypothesis that these substances are secreted by the endolymphatic sac. The limited sensory cell lesions seen in the cochleae and saccules are likely to be due to a temporary vascular ischemia and endolymphatic hydrops.     

The vein of the vestibular aqueduct with potential pathologic perspectives.

HYPOTHESIS: Pathologic changes around the vein of the vestibular aqueduct (VVA) may cause obstruction to the flow of blood toward the sigmoid sinus. Furthermore, a distal obstruction of this vessel may be responsible for a development of a retrograde flow of blood with concomitant drainage of endolymphatic sac (ES) substances to the inner ear. BACKGROUND: The VVA is responsible for the venous drainage of the vestibular apparatus and endolymphatic duct and ES. Previous studies have linked the VVA to Ménière's disease. The aim of the present article was a 3-dimensional perspective study of the VVA with its adjacent anatomic structures. METHODS: In 14 rats, the VVA was examined by 3-dimensional reconstruction of 2-microm serial sections, corrosion cast technique, and scanning electron microscopy. RESULTS: From the external aperture of the vestibular aqueduct, the VVA is interposed between the ES and the operculum. Three to 4 collecting venules from the ES drain into the VVA. The VVA merges at an oblique angle with the sigmoid sinus. CONCLUSION: The VVA courses near the ES, operculum, and sigmoid sinus and is potentially vulnerable to expanding structures in the cranial posterior fossa. The possible role of the VVA for the function of the ES under normal and pathologic conditions is discussed.     

The vestibular aqueduct and endolymphatic sac and duct in endolymphatic hydrops.

The histologic features of the endolymphatic sac and duct in 23 serially sectioned temporal bones with idiopathic or secondary endolymphatic hydrops were blindly compared with 22 randomly selected, normal temporal bones. In idiopathic hydrops, the pars rugosa of the endolymphatic sac extended out of the vestibular aqueduct into the dura in 29% of bones, compared with none of normal bones (P less than .01). In the other 71%, the pars rugosa in the vestibular aqueduct was surrounded by dura more commonly than normal. Functional studies are required to assess the relationship of these findings to hydrops. In secondary hydrops (eg, due to labyrinthitis), the endolymphatic duct was obliterated in the isthmus of the vestibular aqueduct by bone or fibrosis in seven of nine bones. Because of similar ossification and fibrosis elsewhere in the vestibular labyrinth, a direct relationship with hydrops cannot be assumed.     

The development of the endolymphatic duct and sac. A light microscopical study

The development and maturation of the endolymphatic sac were studied in the CBA/CBA mouse. The otocyst is developed at gestational day 10 and the primitive endolymphatic sac is present as a large slit-like appendage at day 12 of gestation. At day 18 the endolymphatic sac is clearly detached from the rest of the otocyst, forming a true sac. The epithelial lining consists of only one layer of immature cells containing large vesicles. The endolymphatic sac is surrounded by a rich network of vessels. One day before birth, the epithelial lining is uneven and the first signs of differentiation into light and dark cells is visible. This situation is more pronounced 2 days post partum when the sac also seems to be filled with a stainable material. At day 6 post partum the otic capsule fuses around the sac, forming the vestibular aqueduct. At 14 days post partum the sac is mature, with clearly developed light and dark cells and widened lateral intercellular spaces, constituting the rugose epithelium. The lumen is filled with a stainable precipitate and a few free-floating cells.     

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.     

Advanced techniques in magnetic resonance imaging in the evaluation of the large endolymphatic duct and sac syndrome

The purpose of this report is to compare temporal bone computed tomography (CT) to high-resolution magnetic resonance (MR) imaging using a novel thin-section fast spin echo (FSE) pulse sequence in identifying and characterizing patients with large vestibular aqueduct syndrome. Sixteen patients with sensorineural hearing loss and a CT diagnosis of large vestibular aqueduct(s) underwent high-resolution fast spin echo magnetic resonance imaging with dual, 3-in phased array receiver coils centered over the external auditory canals. Magnetic resonance imaging parameters included axial and oblique sagittal fast spin echo with an effective slice thickness of 1 mm contiguous. Thirty-eight patients with 76 normal inner ears who underwent MR imaging using this technique had their endolymphatic duct measured. MR alone identified the enlarged endolymphatic sac seen along with the large endolymphatic duct in all cases. Three cases (five inner ears) with enlarged bony vestibular aqueducts on CT showed no evidence of endolymphatic duct or sac enlargement on MR. MR alone identified a single case of mild cochlear anomaly in conjunction with an enlarged endolymphatic duct and sac. In the normal population the size of the normal endolymphatic duct at its midpoint measured from 0.1 to 1.4 mm. Thin-section, high-resolution fast spin echo MR imaging of the inner ear may be superior to CT in the evaluation of patients with the large vestibular aqueduct syndrome.     

磁共振内耳水成像在大前庭水管综合征诊断中的应用

目的：研究磁共振内耳水成像技术在大前庭水管综合征诊断中的作用。方法：应用三维高级快速自旋回波序列横断扫描大前庭水管综合征患者的整个颞骨岩部,将所有原始图像传给网上工作站,应用最大密度投影法将图像进行三维重建,获内耳立体像。结果：患者的磁共振内耳水成像表现为：后颅窝乙状窦前方、内听道后方硬脑膜外的高信号强度结构膨大,呈长条形,边缘光整。患者内淋巴囊骨内部分中点的最大宽度为2．470mm,远大于MRI诊断内淋巴囊扩大的标准。结论：磁共振内耳水成像是诊断大前庭水管综合征的有效方法,临床上可以用此技术做最终诊断。     

The surgical approach to the endolymphatic sac and the cochlear aqueduct in the guinea pig

The endolymphatic sac and cochlear aqueduct are primary passages of the endolymphatic and perilymphatic fluid compartments in the labyrinth. Closure of the endolymphatic sac and duct in the guinea pig will result in the development of endolymphatic hydrops. Although obstruction of the cochlear aqueduct in this species does not seem to result in any dysfunction, this structure may serve in the dynamics of inner ear fluid physiology. The anatomy of the guinea pig temporal bone is described with special emphasis on the endolymphatic sac and cochlear aqueduct. Surgical techniques to gain access to these structures through both a middle and posterior cranial fossa approach are described.     

Histological evidence of specialized microcirculation of the endolymphatic sac

Summary A specialized type of blood vessel is demonstrated within the dense soft tissue areas of the vestibular aqueduct and vascular channels of the surrounding bone, including the paravestibular canaliculus (PVC). The vessel wall is formed by the collagen-smooth muscle bundles of these areas. The lumen of these vessels is irregular, and segments appear to be closed by apposition of the bundles. The vessels are continuous with the capillaries of the endolymphatic sac. It is not clear whether they are on the venous side of the capillary system, or on the arterial side and might possibly be part of an arteriovenous anatomoses system. Their possible role in some cases of Meniere's disease must be considered.Supported by USPHS Grant NS-06606 from the National Institute of Neurological and Communicative Disorders and Stroke     

Vestibular aqueduct in Menière's disease and non-Menière's disease with endolymphatic hydrops: a computer aided volumetric study.

The volume of the vestibular aqueduct was studied by a computer-aided volumetric method in 9 temporal bones with endolymphatic hydrops from individuals with Menière's disease (MD), 7 temporal bones with endolymphatic hydrops from individuals without a history of Meniere's disease (non-MD hydrops), and 10 normal temporal bones (controls) to investigate the cause of endolymphatic hydrops in both MD and non-MD hydrops. A hypoplastic vestibular aqueduct was found significantly more often in the MD group than in either the non-MD hydrops group (chi 2-test, chi 2 = 4.063, p less than 0.05) or the control group (chi 2-test, chi 2 = 6.363, p less than 0.05). The difference in volume between the non-MD hydrops group and the control group was not significant. It is speculated that a small vestibular aqueduct (presumably containing a small endolymphatic sac) might be a predisposing factor in Menière's disease. In contrast, in non-MD hydrops, there seems to be no correlation of endolymphatic hydrops with a hypoplastic vestibular aqueduct and endolymphatic sac.     

Vascular patterns of the saccule of the rat: a microcorrosion cast study

Summary A scanning electron microscope study of corrosion cast preparations of the vessels of the saccule was carried out in adult rats. This method shows the microvasculature of the saccule in the three-dimensional model. As a result of this technique we have been able to demonstrate a particular microvasculature of the saccule in the rat's inner ear. The main blood supply of the saccule consists of the arterioles coming from the vestibulocochlear artery entering the anterior margin of the macula sacculi. A few branches of the anterior vestibular artery enter the macula sacculi from the superior margin. The saccular vein drains the venous blood from a dense capil lary area underneath the striola to the posterior vestibular vein which eventually ends in the vein of the cochlear aquaduct.     

Familial enlarged vestibular aqueduct syndrome

Enlarged vestibular aqueduct syndrome is a clinical disease entity associated with anatomic abnormality of the bony canal in the temporal bone containing the endolymphatic duct and sac. The definition of this syndrome is progressive sensorineural hearing loss with an isolated enlarged vestibular aqueduct. Familial inheritance of enlarged vestibular aqueduct syndrome is rare, and the correct mode of inheritance has not been discovered. This report is the study of familial inheritance with enlarged vestibular aqueduct syndrome. Clinical audiological, radiographic, and chromosomal analyses were performed in this case, which reports on two female probands who are offspring of normal parents. According to the study of pedigree, familial inheritance of enlarged vestibular aqueduct syndrome is strongly suspected as an autosomal recessive trait. Further study should be focused on discovering the genetic evaluation of familial inheritance of enlarged vestibular aqueduct syndrome.     

A potential portal flow in the inner ear

OBJECTIVES/HYPOTHESIS: The aim of the present study was to visualize the flow direction of blood in the extraosseous part of the vein of the vestibular aqueduct (VVA) and to explore the effect of an induced obstruction in the distal part of the VVA before it merges with the sigmoid sinus. The endolymphatic sac has been implicated as a potential endocrine gland, which venules drain to the VVA. A reversal of the direction of flow in the VVA toward the inner ear could, through vestibular arteriovenous anastomosis, cause portal circulation in the inner ear. STUDY DESIGN: The authors conducted an experimental animal study using in vivo fluorescence microscopy. RESULTS: Obstructing the distal part of the VVA just before it empties into the sigmoid sinus immediately reverses the flow of blood in the VVA toward the inner ear. CONCLUSIONS: After an obstruction of the VVA, the drained venous blood from the endolymphatic sac may enter a portal circulation in the inner ear, which could cause disturbances in the endolymph homeostasis and potentially symptoms as seen in Meniere disease.     

Obstructing lesions of the endolymphatic sac and duct mimicking Ménière's disease

In this retrospective case series and literature review, we demonstrate that temporal bone lesions that obstruct the endolymphatic sac or duct can cause symptoms of Ménière's disease. This finding is likely attributable to endolymphatic hydrops; initially, such cases typically masquerade as Ménière's disease. Between July 1995 and April 2002, a total of 379 patients were treated for an initial diagnosis of Ménière's disease at our institution. Among this group, 3 patients were found to have an obstructing lesion of the endolymphatic sac or duct that we felt was causally related to their Ménière's-like symptomatology. We reviewed these cases and noted the similarities in each patient's presentation, including a common pathophysiology. On imaging studies, each patient had a different pathologic lesion that involved the endolymphatic sac or duct: patient 1 had a jugular megabulb, and she was ultimately treated with vestibular nerve section; patient 2 had a cholesterol granuloma, which was treated with surgical excision; patient 3 had an endolymphatic sac tumor that was treated with surgical excision. As has been suggested in previous reports, not all cases of Ménière's disease are idiopathic. We conclude that obstruction of the endolymphatic sac or vestibular aqueduct by a mass lesion or vascular anomaly can lead to vestibulocochlear pathology that mimics Ménière's disease.