Lymphocyte-macrophage activity in the endolymphatic sac. An ultrastructural study of the rugose endolymphatic sac in the guinea pig

The irregular epithelial layer which delimits the intermediate part of the endolymphatic sac, and the surrounding perisaccular tissue, were examined morphologically in the guinea pig by transmission electron microscopy. Specialized areas of the epithelium which have previously been designated as "non-vascularized epithelial processes" (NVP) were constantly observed. These proliferative areas showed a close topographical relation to the free luminal cells and contained an abundance of lymphoid cells. Lymphocytes and macrophages were intimately associated with each other in a manner similar to that seen in these two types of cells in antigen-stimulated lymphoid tissues. There was a marked degeneration and phagocytosis of cells. The richly vascularized perisaccular tissue was rich in plasma cells, monocytes, mast cells and lymphocytes. The latter could be seen to migrate through the endothelial cells in the thin post-capillary venules into the sac tissue. The authors consider that the endolymphatic sac plays a role as an immunological defence organ for the internal ear. A hypothetical model concerning circulation and turnover of certain of the free intraluminal cells in presented.     

The endolymphatic sac in a mouse mutant with cochleo-saccular degeneration. Electrophysiological and ultrastructural correlations

The response of the endolymphatic sac to a disturbance in endolymph homeostasis was investigated by examining the sac in a mouse mutant, viable dominant spotting, which is known to exhibit primary strial dysfunction and cochleo-saccular degeneration. The function of the vascular stria was assessed by measuring the endocochlear potential and the sacs were then studied by light and transmission electron microscopy. The endolymphatic sac was found to be morphologically abnormal in these mutants, the main abnormality being the presence of granular epithelial cells, which showed clear histological signs of secretory activity. A stainable precipitate, believed to be secreted by the granular cells, was observed in the lumen of the endolymphatic sac in the mutants. The findings strengthen the view that the sac is involved in the regulation of endolymph volume and pressure.     

Innervation of the endolymphatic sac.

Previous studies suggest that the endolymphatic sac plays an important role in the homeostasis of endolymph. Factors that influence blood flow in the sac may affect its function. This blood flow may be influenced by autonomic innervation; however, no such innervation has been demonstrated. The purpose of this study was to demonstrate catecholaminergic and cholinergic fibers on the endolymphatic sac. Endolymphatic sacs from Hartley guinea pigs were stained either immunocytochemically for tyrosine hydroxylase to reveal catecholaminergic fibers or histochemically for acetylcholinesterase to reveal cholinergic fibers. For tyrosine hydroxylase immunostaining, the endolymphatic sacs were treated with dilute hydrogen peroxide and then incubated in the primary antiserum. The tissue was further processed by the avidin-biotin immunoperoxidase method and reacted with diaminobenzidine. For acetylcholinesterase histochemistry, the tissue was processed by a modification of the direct thiocholine method. Light microscopy of the whole-mounted endolymphatic sacs revealed tyrosine hydroxylase-positive and acetylcholinesterase-positive fibers. Some of the acetylcholinesterase-positive fibers were clearly associated with vessels. This innervation, which has not been described previously, may significantly influence blood flow and function of the endolymphatic sac.     

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.     

Changes in ultrastructural characteristics of endolymphatic sac ribosome-rich cells of the rat during development

It has recently been demonstrated that endolymphatic sac (ES) ribosome-rich (dark) cells respond to induced endolymph changes and are thus likely to be involved in endolymph homeostasis. Therefore, we studied the ultrastructural characteristics of rat ES ribosome-rich cells during development in order to determine the cellular distribution of organelles involved in protein metabolism, secretion and absorption, indicative for their contribution to endolymph homeostasis. During embryonal stages ribosome-rich cells contain a limited number and variety of organelles and are predominantly involved in the production of components for cell growth and differentiation. In the young adult stage (P60) three different states of ribosome-rich cells may be distinguished. State A resembles a cell with only limited metabolic activities whereas state B is characterized by numerous different intracellular organelles and is considered to be involved in production and secretion as well as absorption and degradation of complex proteins. A third cellular state, state C, is filled with phagolysosomes and contains very few other organelles. This is considered to be a final (pre)apoptotic state. Autoradiography data suggest that ES ribosome-rich cells are capable of synthesis and secretion of tyrosine-containing proteins and may thus be involved in regulation of the osmolarity of endolymph based on the capacity to bind cations as well as water molecules. In addition, ES ribosome-rich cells appear to synthesize and secrete fucosylated glycoproteins into the endolymph. In conclusion, the present data suggest that ES ribosome-rich cells are actively involved in endolymph homeostasis through secretion and absorption of complex proteins and it is hypothesized that they are able to adapt their function or activities in response to changes in endolymph composition.     

Ultrastructure of the endolymphatic sac in two-phase endolymphatic hydrops in the guinea pig.

Two-phase endolymphatic hydrops is a subtle experimental model for Meniere's disease. Chronic dysfunction of the endolymphatic sac, induced by dissection of the most distal part without causing damage to the intermediate part, is combined with increased endolymph production induced by administration of aldosterone which stimulates the N/K-ATPase in the stria vascularis. A transmission electron microscopic study was performed on the endolymphatic sacs of four groups of guinea pig cochleas: controls: non-operated aldosterone-treated cochleas; operated (dissection of the endolymphatic sac) cochleas; operated and aldosterone-treated cochleas. Light and electron microscopy showed a normal morphology in the controls. Aldosterone treatment had no visible effect. Dissected ears revealed severe deviations. The epithelium of the intermediate sac was low, showed dilated lateral intercellular spaces indicating elevated fluid transport and displayed serious degenerative processes. Distally, the endolymphatic sac was completely blocked by newly formed bone. Additional aldosterone treatment had no cumulative effect on the dissected ears.     

The vascular supply of the endolymphatic sac.

The vascular anatomy of the endolymphatic sac in guinea pigs was examined following intravascular injection of silicone rubber (Microfil). Methacrylate resin of low viscosity (Mercox) was used to obtain vascular corrosion casts for scanning electron microscopy, which allowed more accurate differentiation between arteries and veins. The extensive vascular system around the sac comprises both arteries and veins, as well as lymphatic vessels. The arterial supply is derived mainly from the posterior meningeal artery in the posterior cranial fossa. In some cases a small artery also leads to the sac from the posterior vestibular artery in the labyrinth (in 7 of the 35 animals investigated). It courses together with the vein of the vestibular aqueduct along the walls of the endolymphatic duct. The blood is drained over the intermediate portion of the endolymphatic sac, which becomes lodged in a rich meshwork of capillaries, venules, veins and a few small arteries. A few venous trunks from both sac walls fuse with the vein of the vestibular aqueduct, which drains blood from the vestibule to the sigmoid sinus. Scanning electron microscopy also revealed numerous anastomosing vessels within bone channels with adjacent bone marrow sinusoids, which also probably contribute to the vascular supply of the endolymphatic sac.     

Effect of labyrinthectomy on the endolymphatic sac. A histological, ultrastructural and computer-aided morphometric investigation in the mouse

A time sequence study of the effect of hemilabyrinthectomy on the endolymphatic sac was performed in mice. Light and transmission electron microscopy of the sac showed significant morphological changes of the epithelial lining and adjacent structures. Initially (2 and 4 days post-labyrinthectomy) the sac lumen was collapsed, but later (7 days post-labyrinthectomy) it was dilated or 'ballooned' and filled with a darkly staining homogeneous substance. This substance, which has been identified histochemically as a proteoglycan, appeared to be secreted from the epithelium of the endolymphatic sac. This finding suggests that the endolymphatic sac may be capable both of absorbing and of secreting endolymph.     

Osmotically induced macrophage activity in the endolymphatic sac. On the possible interaction between periaqueductal bone marrow cells and the endolymphatic sac.

This study aimed to investigate the origin of the free cells in the lumen of the endolymphatic sac (ES). Activation of the cells was accomplished through osmotic induction using glycerol. The ES and the perisaccular tissue were analyzed with special reference to the activity of periaqueductal bone marrow cells after different time intervals following the injection of hyperosmotic agents. The results show that the perisaccular or periaqueductal bone marrow space may constitute a source of some of the free cells occurring in the ES. Osmotic challenging of the inner ear may cause activation of the periaqueductal bone marrow, initiating the locomotion and migration of cells (mostly monocytes, neutrophils and eosinophilic leukocytes) along bone marrow sinusoids that frequently anastomose with the ES vessels. The free cells show signs of transepithelial diapedesis and, in the lumen of the ES, cells may develop into phagocytes which initiate the ingestion and degradation of secreted macromolecular aggregates. It is thought that osmotic alterations in the inner ear may give rise to local changes in or around the ES, leading to the chemotactic attraction of bone marrow cells. The results verify the existence of a complex sugar/protein aggregate metabolism over the wall of the ES, which is linked to the turnover of free cells. The findings may indicate that ES macrophages are important in the regulation of inner ear fluid homeostasis.     

Scanning electron microscopy of the endolymphatic sac epithelium.

In this study, scanning electron micrographs of the dog endolymphatic sac surface epithelium are presented. According to our morphological findings, three portions were recognized, the proximal, intermediate and distal part. The intermediate or 'rugose' portion was found the most differentiated where two types of cells were identified. These cells were seen to have many of the criteria for fluid absorption and phagocytosis. In man, alteration in the ability of these cells may lead to endolymphatic hydrops.     

Acidity in the endolymphatic sac fluid of guinea pigs.

The pH value and the DC potential in the endolymphatic sac (ES) were measured using H(+)-selective double-barreled electrodes and the intra- and extradural approach, the pH value in the ES fluid (6.65 +/- 0.12, n = 7) was markedly lower than that in the cerebrospinal fluid (7.39 +/- 0.07, n = 7). Acidity in the ES fluid, under normal (nontreated) conditions may be closely associated with metabolism in the epithelium of the ES.     

The endolymphatic sac and inner ear homeostasis. I: Effect of glycerol on the endolymphatic sac with or without colchicine pretreatment

The combined effects of glycerol and colchicine on the endolymphatic sac were investigated in mice. Glycerol induced signs of secretion from the epithelium with formation of secretory granules in the light epithelial cells. Other characteristics of the epithelial lining were also changed resulting in an increased widening of the lateral intercellular spaces, a partial collapse of the lumen and with a deposition of a stainable substance within the lumen. This reaction lasted from 30 min to 24 h following the injection. Pretreatment with colchicine was found to decrease or inhibit the glycerol-induced secretion of macromolecules into the sac. The lumen collapsed but frequently there was no presence of stainable substance. Animals treated with both glycerol and colchicine showed marked signs of inner ear malfunction which could indicate that the secretory activity in the sac might be closely related to the regulation of inner ear fluid homeostasis and that functional disturbances in this system may lead to disorders of inner ear function.     

Development of endolymphatic hydrops following immune response in the endolymphatic sac of the guinea pig.

The present study investigated immune injury associated with endolymphatic hydrops (e.hydrops) following locally mounted immune reaction in the endolymphatic sac (e.sac) of guinea pigs. E.hydrops occurred, progressing rapidly within the first week post secondary Keyhole limpet hemocyanin (KLH) challenge in the e.sac and developed into two phases, acute and chronic. On the other hand, primary KLH challenge of the e.sac, PBS inoculation into the e.sac or intradural secondary KLH challenge were incapable of inducing e.hydrops. These results indicate that reversible and irreversible e.hydrops are induced by the immune response of the e.sac, suggesting that local immunological events of the e.sac may provide an animal model of Meniere's disease.     

Hyaluronan synthesis in the adult guinea pig endolymphatic sac.

The endolymphatic sac is believed to play a major role in membranous labyrinth homeostasis by controlling the volume of endolymph, removing debris, and participating in the immune response of the inner ear. The endolymphatic sac is postulated to absorb endolymph and to synthesize and secrete high-molecular-weight and osmotically active glycosaminoglycans (GAGs). The present study examines the ability of in vitro adult guinea pig endolymphatic sac cells to synthesize complex proteins and polysaccharides. The intent is to characterize the nature of these compounds by studying carbon-14 (14C) glucose incorporation in tissue cultured endolymphatic sac specimens using autoradiographic and specific enzymatic digestion techniques. Our results suggest that sac cells can synthesize GAGs and proteins in vitro in proportionately larger amounts than surrounding connective tissue and dura. The principal GAG synthesized by the endolymphatic sac appears to be hyaluronan.     

Effects of high intensity pure tone stimulation on the endolymphatic sac. Correlations between cochlear morphology and endolymphatic sac response

A systematic study of the effects of acoustic overstimulation on the endolymphatic sac (ES) in the guinea pig was performed. The ES was studied with light and transmission electron microscopy after exposure of the animals to a 3.85 kHz pure tone of 108 dB SPL or 120 dB SPL for 22.5 min (sound energy 9.4 and 150 Pa2 X h, respectively). The damage pattern in the organ of Corti was studied after various post-exposure times with SEM and correlated with the morphological characteristics of the ES in the same ear. This was made possible by using a modified technique for histological processing. In ears with induced structural abnormalities to the organ of Corti, the ES displayed few morphological changes without obvious signs of accumulation of cell debris within the lumen. Initially an increase in the amount of freely floating cells was found which persisted for at least 24 h. The role of the ES for disposal and digestion of locally produced degeneration products within the cochlea after acoustically generated structural damage is discussed.     

Surgery of the endolymphatic sac and preservation of hearing in endolymphatic hydrops

Vertigo is the most important symptom of Ménière's disease both from the standpoint of follow-up and indication for surgery. But although vertigo is an alerting symptom for both the patient and the physician, we believe that the hearing level is the most reliable and even the single sign in determining the recent status of the disease. Between 1983-1989, 42 patients with various types of Ménière's disease (MD) (34 typical MD, 3 cochlear MD and 3 vestibular MD) underwent endolymphatic sac surgery at ENT department of Gazi University School of Medicine. In the typical MD group, patients with a duration of symptoms of less than one year prior to surgery revealed better postoperative results; 91% fell into class A and B, whereas this rate was found to be lower (40%) in patients with symptomatology lasting for more than one year. In conclusion, especially in bilateral cases, given the importance of the hearing, early sac surgery is thoroughly recommended for the conservation of hearing.     

Intermediate filaments in the endolymphatic sac of the guinea pig.

The expression of the five main groups of intermediate filaments and their subgroups, especially cytokeratins, was investigated in the guinea pig endolymphatic sac at the light microscopic level using immunohistochemistry. Immunostaining for cytokeratin (PKK1, PKK2, PKK3) was found in the epithelial cell layer of the sac. Vimentin was seen to stain epithelial cell layer as well as subepithelial tissue. These findings may indicate that the cytokeratins are closely related to the inner ear fluid transport. The coexpression of cytokeratin and vimentin seemed to indicate the dual function of absorption and secretion of the endolymphatic sac epithelial cell to regulate the inner ear fluid homeostasis.     

Management of endolymphatic sac tumors: a case series report

Objective To study clinical characteristics of endolymphatic sac tumor (ELST) and its diagnosis and treatment. Methods ELST was diagnosed in 6 cases based on surgical and histological findings. These cases were reviewed for their clinical manifestations, differential diagnosis and surgical treatment techniques. Results There were 1 male and 5 females in this group, aged from 28 to 59 years (mean age=38.7 years). The tumor was in left ear in 4 cases and in right ear in the other 2 cases. Disease courses ranged from 5 to 30 years (mean duration= 12.6 years). Clinical presentations included sensorineural hearing loss (n=4), otorrhea and tinnitus (n=2), tinnitus and facial spasm(n=1), otorrhea with facial paralysis(n=l), and hearing loss with tinnitus (n=2). None of the cas-es was diagnosed as ELST preoperatively. Two cases were misdiagnosed as glomus jugulare tumor, 2 as chronic suppurative otitis media, 1 as sweat gland adenoma on biopsy and 1 as temporal bone tumor. Tumors were sprgi-tally resected in all 6 cases via the mastoidectomy (n=2) or combined oto-cervical or cranio-oto-cervical ap-proaches(n=4). Postoperative cerebrospinal fluid otorrhea occurred in 1 case. The tumors were confirmed on histo-logical examination to be a low-grade adenocarcinoma. All patients have survived at the time of this paper. Conclusion ELST is rare and commonly misdiagnosed and inadequately treated. Its prognosis is relatively favor-able because of its slow growth rate.