Use of the malleus handle as a landmark for localizing the round window membrane

Localization of the round window membrane is desirable in order to allow a more direct application of medication to the inner ear. A new procedure has been developed to deliver direct, near-continuous inner ear perfusion to the round window with the Silverstein MicroWick. In this office procedure, the wick is inserted through a tympanostomy tube into the round window niche. Accurate localization of the round window is a necessary component of this procedure. In an effort to ascertain the precise location of the round window, we examined 25 cadaveric human temporal bones and measured the distance from the umbo to the round window in each sample. We found that the round window was an average of 3.44 mm (+/- 0.68) from the umbo and was situated at an average angle of 113.2 degrees (+/- 9.8) from the long process of the malleus. Our simple and reliable determination of the relationship between the malleus handle and the round window niche allows for the accurate placement of the Silverstein MicroWick and other devices.     

Round window reflex and oval window fistulae

The round window reflex is normally absent in stapedial fixation. In this study, six cases of oval window fistula are described in which the round window reflex was absent. This is probably because there is insufficient pressure transmitted to the round window membrane through the perilymph because of leakage from the oval window. This is considered as an important diagnostic sign of oval window/stapes footplate ligament disruption.     

Round window membrane permeability. An in vitro model

The round window membrane is regarded to be the main route for passage of potentially ototoxic substances from the middle ear cavity into the inner ear. This may be of clinical importance in acute otitis media and chronic otitis media, where sensorineural hearing impairment sometimes develops. The accuracy and reliability of an in vitro round window membrane permeability model was studied. The round window membrane of the mongolian gerbil was resected, together with its bony niche. The preparation was mounted between two glass chambers representing the middle ear and the inner ear. Passage through the round window membrane did not occur within 3 h for low density lipoprotein with a molecular weight of 2,300 kD. Only minute amounts of highly density lipoprotein, of molecular weight 115-350 kD, passed the round window membrane. The passage rate of horseradish peroxidase, which has previously been shown to pass the round window membrane in vivo, was estimated. The design of the present model is considered to make feasible controlled permeability studies on the round window membrane. Passage rates for different substances through the round window membrane can be calculated under controlled conditions by using this type of in vitro model.     

Computer-aided three-dimensional reconstruction and measurement of the round window niche

The goal of this study was to clarify the three-dimensional shape of the round window niche and to measure this structure three-dimensionally using the computer-aided reconstruction method we developed. The equipment used in this study included a personal computer (NEC 98-XA), a high-resolution 14-inch color CRT, a digitizer (Hitachi HDG-1111), and a printer. We studied five normal temporal bones obtained from five individuals with negative otologic histories, who had been 5 months and 14, 15, 18, and 59 years old at death. In each case the round window niche was located posteroinferior to the round window. The round window niches had wide openings to the middle ear cavity that became narrower near the aperture; thus, the round window niche seemed to be shaped like a pouch. The maximal diameter of the round window niche was 2.98 +/- 0.23 mm. The shortest distance between the aperture of the round window niche and the margin of the round window was 0.66 +/- 0.16 mm. The volume of the round window niche, on average, was 4.65 +/- 0.67 mm3. The volume of the round window niche was found to be correlated with the area of the round window.     

Anatomy of the round window. A histopathological study with a graphic reconstruction method

The round window was studied in normal adult and infant temporal bones to provide a knowledge base for the study of congenital anomalies of the round window, and to determine whether the round window develops postnatally. Fifty-three temporal bones were studied. Specimens were processed histologically, sectioned horizontally, stained with hematoxylin and eosin, and studied under the light microscope and microprojector. A special method of graphically reconstructing the round window was developed for this study, and was used to define the contour, area, and angle of the round window. We found that the round window is fan shaped. The area of the superoposteriorly located horizontal part (three-sevenths of the round window) and of the inferoanteriorly located vertical part (four-sevenths of the round window) totals approximately 2.29 mm2. In addition the angle between the plane of the tympanic sulcus and the vertical part of the round window was measured, and found to average 73.3 degrees. Lastly, the round window was found not to develop postnatally.     

Surgical anatomy and pathology of the round window

A study of the surgical anatomy and pathology of the round window was performed on a total of 292 serially sectioned temporal bones. The surgical approach to the round window is discussed with consideration of the anatomical findings. In the pathological study obliteration of the round window niche occurred as a congenital anomaly, in otosclerosis, chronic otitis media and as an end result in suppurative labyrinthitis. Clinical reports seem to indicate that obliteration of the window is associated with a significant hearing loss, contrary to the findings in experimental animals. In chronic otitis media the round window is a pathway for spread of infection to the labyrinth, but also the finding of perilymphatic precipitates adjacent to the window in some ears suggests that certain inflammatory products may enter the scala tympani through the round window and so lead to high tone sensorineural hearing loss.     

1～6岁儿童振动声桥圆窗植入术相关解剖结构的CT测量

目的应用颞骨高分辨率CT测量儿童振动声桥圆窗植入术的相关解剖结构,为术前评估提供理论参考。方法以50例15个月～6岁因重度感音性聋拟行人工耳蜗植入术且术前颞骨薄层CT扫描示中耳、内耳均正常的患儿为研究对象,在其术前颞骨高分辨率CT扫描轴位片上测量振动声桥圆窗植入术的相关解剖结构数据,如圆窗龛的宽度和深度、锥隆起的高度、面神经至圆窗龛和外耳道后壁的距离等,并比较不同耳别、性别及年龄组间的差异。结果 50例儿童各指标测量均值分别为:圆窗龛的宽度2.02±0.20mm,圆窗龛的深度1.25±0.19mm,圆窗龛层面面神经管外缘至骨性外耳道后壁的最短距离3.99±0.53mm,面神经骨管内缘至圆窗龛的距离5.21±0.37mm,锥隆起的高度2.09±0.23mm。各测量指标耳别间、不同性别间、不同年龄组间差异均无统计学意义(P>0.05),锥隆起高度与面神经至圆窗龛的距离之间无明显相关性(r=0.331,P>0.05)。结论面神经隐窝等相关解剖结构在出生后可能已经基本发育完成;对国人1～6岁儿童行振动声桥圆窗植入术从解剖理论上具有可行性;术前相关结构的CT测量可为手术提供重要参考。     

Microscopic characteristics of round window problems in otology

Round window membrane ruptures and perilymph leakage can present the complication or concomitant of sudden deafness and barotrauma. Pathological involvement of the round window membrane can occur in many otological diseases such as otosclerosis, otitis media, tumors, etc. Microscopic manipulations might result in an inadvertent round window membrane lesion and cochlear deafness. In recent years purposeful surgical lesions, including procedures for vertigo and cochlear implant surgery, are being made in the round window membrane. Examples of pathology involving the round window in human temporal bones are described. To understand better the clinical features of early round window rupture in humans, controlled punctuate lesions were made in 36 chinchilla ears and studied sequentially. Round window membrane healing occurred as early as 3 days post-lesion, and was complete in all ears but 1 of the combined 7, 9 and 11-day group. Healing occurred primarily as a result of middle ear epithelial ingrowth and mesothelial cell reaction in the adjacent perilymphatic space of the scala tympani. These cellular events are described and discussed from an histological and clinical point of view.     

Non-syndromal round window atresia: an autosomal dominant genetic disorder with variable penetrance?

Round window atresia can be seen in association with syndromal anomalies such as mandibulofacial dysostosis, Mondini type anomalies or cretinism, or with extensive otosclerosis. Non-syndromal round window atresia is extremely rare and until today there is no proof whether non-syndromal round window atresia can be inherited. We present two family members with non-syndromal round window atresia. Based on this case and on an extensive literature review, we discuss the possible ways of sound transmission with round window occlusion as well as the possibility of an autosomal dominant inheritance pattern of these two non-syndromal cases. Evaluating the hearing test results, the effect of round window atresia in non-syndromal cases cannot be thoroughly explained by current theories of sound transmission. In general, full occlusion of the round window should result in a complete air-bone-gap and a surgical procedure to open the window, e.g. a cochlear fenestration which creates a new pressure outlet for the inner ear fluids, should result in normalizing the hearing levels. Astonishingly, patients with non-syndromal round window atresia, show hearing tests similar to those in patients with otosclerosis. In contrast to otosclerosis, complete closure of the air-bone-gap by surgery in patients with round window atresia does not seem to be possible according to currently reported cases. Therefore, routine examination of the round window in stapes surgery should be part of every stapes surgery and a high resolution CT scan should be considered in particular prior to revision of unsuccessful stapes surgery. As a genetic inheritance pattern can be assumed, specific emphasis should also be laid on the patient’s family history.     

Microperforation and removal of the round window membrane. Short- and long-term study in animal experiments using electrocochleography and evoked response audiometry

Our earlier animal experiments on guinea pigs showed that instrumental perforation of the round window membrane by a 0.2 mm platinum wire leads to an instant loss of the inner ear functions. The membrane defect healed in a few days, the cochlear structures remained intact, and the compound action potential of the auditory nerve and the brain-stem responses could be evoked again with normal latency times within 2 weeks. 1. In the studies reported here we first carried out microperforations with a 1 micron needle electrode, which caused no changes of the hearing potentials (cochlear microphonics, compound action potential of the auditory nerve, brain-stem responses), and no visible defect of the round window membrane and no perilymph outflow. 2. The removal of the round window membrane and the withdrawal of the perilymph led to a loss of the cochlear microphonics and to a considerable increase of the latency times of wave I (Jewett). The hearing potential regained their original values after 2 weeks without closure of the round window niche. The round window membrane had regenerated spontaneously and the scala tympani was again filled with perilymph. After covering the round window niche with a connective tissue graft, the hearing potentials regained their original values after 2 weeks, as they had done without cover of the round window niche. The round window membrane regenerated below the tissue graft and the scala tympani was also filled again with perilymph.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental grafting of the round window membrane: Part I

The histology and permeability of cats' round window membranes were described following surgical grafting with gelatin foam or fascia. An increase in the thickness of the round window membrane due to fibrosis, neovascularization, and epithelial metaplasia was observed 2 months following grafting with gelatin foam. Grafting with fascia did not increase the thickness of the round window membrane, but did form a thick layer of granulation tissue adjacent to and overlying the round window membrane, with occasional adhesions between. The layer of granulation tissue consisted of cuboidal or columnar ciliated epithelial cells, fibrous tissue, lipid, and undigested grafted material. The granulation tissue did not always completely cover the round window membranes. Horseradish peroxidase placed in the round window niche of cats with grafts on the round window membrane remained a significant distance further from the inner ear when compared to its migration through nongrafted membranes.     

Round window atresia in association with congenital stapes fixation

Objective: To document an association of round window atresia with congenital stapes fixation, discuss the diagnostic role of computed tomography, and implicate the clinical significance of these anomalies. Study Design: Retrospective chart review and review of the literature. Results: The authors report three pediatric cases of round window atresia. All cases presented with hearing loss of a conductive nature (two cases bilateral, one unilateral). Two patients underwent middle ear exploration, demonstrating stapes fixation and the absence of a round window. Stapedectomy was performed in both cases without postoperative hearing improvement. Subsequent revision stapedectomy was also unsuccessful in one of these cases. The unoperated case represents the fraternal twin of one patient. In all cases, computed tomography scanning demonstrated findings consistent with atresia of the round window niche without cochlear anomaly. Conclusions: An association of round window atresia and congenital stapes fixation is apparent. The mechanism of the conductive hearing loss following stapedectomy remains poorly understood. Computed tomography imaging and surgical confirmation are probably both necessary to establish the diagnosis of round window atresia.     

Permeability of the round window membrane to middle-sized molecules in purulent otitis media

The effect of pneumococcal otitis media on the permeability of the round window membrane was evaluated using tetraethylammonium ions as a tracer. Round window membrane permeability is reduced significantly at resolved stages of purulent otitis media. In contrast, measurements of round window membrane permeability indicate that acute purulent otitis media has a tendency to facilitate such permeability. Moreover, histologic observations of the round window membrane following bacterial inoculation further support the evidence of functional changes in round window membrane permeability. These findings indicate that the round window membrane in resolved stages of purulent otitis media plays a protective role in preventing the penetration of harmful substances into the inner ear.     

Computer-aided three-dimensional reconstruction and measurement of microfissures.

The spatial anatomy of microfissures in the round and oval window areas was investigated in 24 randomly selected normal human temporal bones by our computer-aided three-dimensional reconstruction and measurement method. Microfissures that communicated with the middle ear surface in the round window area were seen in 21 cases (87%) and were located on the posteromediosuperior aspect of the round window niche; whereas microfissures in the oval window area, seen in seven cases (29%), were located at various sites, but mostly in the area below the oval window. Of the 21 microfissures seen in the round window niche, only four were found to be visible through the aperture of the round window niche when viewed from the lateral direction. The mean lengths of the microfissures seen on the middle ear surface in the round and oval window areas were 0.95 +/- 0.66 mm and 0.74 +/- 0.44 mm, respectively. The microfissures in the round window area were significantly longer in individuals 20 years of age and older, than in those less than 20 years (Wilcoxon test, t = 21.5, p less than 0.01); this tendency for microfissures to be longer in older subjects was also found for microfissures in the oval window area. The possible clinical and pathologic significance of these results is discussed.     

Oval window absence, bony closure of round window, and inner ear anomaly

Unusual temporal bone findings are presented in a seven-and-one-half-year-old female with marked hearing impairment and multiple congenital anomalies. The oval window was absent bilaterally, with no stapedio-vestibular joint development on the right side and incomplete development on the left side. The round window membranes were normal, but on the left side the round window niche was walled off from the middle ear by bone continuous with the periosteum of the middle ear surface of the otic capsule. Surgically, this would have been interpreted as congenital absence of the round and oval windows. It should be recognized that the round window membrane may be present in the absence of an open round window niche. Bilaterally the cochlea consisted of 13/4 turns, and on the left side, the scalae tympani ended blindly in the second turn so that no helicotrema was present. Spiral ganglion cells were markedly reduced on the right side and entirely absent on the left, where there was marked thickening of the cribriform base of the cochlea. The organ of Corti was present in all turns. The bony semicircular canals were not formed. The embryological development and interference with development which probably resulted in these malformations are discussed. Oval window absence or congenital footplate fixation should probably be referred to as varying degrees of stapediovestibular joint malformation.     

明胶海绵和透明质酸在地塞米松圆窗灌注中对豚鼠圆窗膜形态及功能的影响

目的圆窗分别放置明胶海绵与透明质酸,观察地塞米松圆窗灌注对豚鼠圆窗膜形态及功能影响。方法①36只豚鼠随机分为3组,Ⅰ组圆窗龛放置明胶海绵并在圆窗置管;Ⅱ组圆窗龛放置含2%透明质酸明胶海绵置管,Ⅲ组圆窗龛放置明胶海绵置管,Ⅱ组和Ⅲ组经圆窗置管向圆窗灌注地塞米松7d后。用光学显微镜和扫描电镜观察圆窗膜变化。36只豚鼠中随机取6只左耳作为正常对照（Ⅳ组）。②另取18只豚鼠,按给药时间分为1、4、7d3组,每组各取3只分为实验组和对照组,实验组圆窗放置透明质酸明胶海绵,对照组圆窗放置明胶海绵。各组经圆窗置管圆窗灌注地塞米松后,用LC-6A高效液相色谱仪测定外淋巴液中地塞米松浓度。结果光镜和扫描电镜检查发现Ⅰ、Ⅱ和Ⅲ组圆窗膜厚度和形态与正常对照Ⅳ组比较无明显差异（P〉0.05）;圆窗放置透明质酸明胶海绵后豚鼠外淋巴液中地塞米松含量明显高于明胶海绵组（P〈0.01）。结论①圆窗放置明胶海绵和透明质酸对豚鼠圆窗膜形态无明显影响。②透明质酸明胶海绵能提高地塞米松的圆窗膜通透性。     

High variability of perilymphatic entry of neutral molecules through the round window

OBJECTIVE: To improve the efficacy of intratympanic therapy using perilymphatic entry through the round window membrane. MATERIAL AND METHODS: The perilymphatic entry characteristics of 2 neutral molecules, mannitol (182.2 Da) and inulin (7,000 Da), were studied. A polyethylene catheter was placed in contact with the guinea pig round window membrane and sealed with cyanoacrylate glue. This catheter was linked to an osmotic minipump that delivered 100 microl portions of 3H-mannitol or 3H-inulin solutions over a 7-day period at a constant rate (0.5 microl/h). Perilymph in the scala vestibuli and scala tympani, cerebrospinal fluid (CSF) and plasma were sampled after 4-7 days of delivery. RESULTS: Despite the constant rate of infusion, perilymphatic radioactivity varied widely from one animal to the other, probably as a function of the position of the microcatheter within the round window niche and/or the permeability of the round window. Even a large molecule such as inulin entered the perilymphatic space. Seven days after the beginning of 3H-mannitol administration, the radioactivity was higher in the perilymph of the scala tympani than in that of the scala vestibuli. The perilymphatic radioactivity on Day 7 was approximately 50% lower than that measured on Day 4 (p = NS). Finally, round window membrane delivery did not preclude distant spread of the molecules into the blood and CSF. CONCLUSIONS: Using round window membrane delivery, the perilymphatic entry of mannitol and inulin depended on their molecular weight. Intratympanic delivery induced a high inter-individual heterogeneity of the drug concentration within the inner ear, with subsequent variability of the therapeutic effects.     

Anomaly of the round window a histopathological study using a graphic reconstruction method

Although literature to date has reported that anomalies of the round window occur infrequently, no study to our knowledge has investigated such anomalies quantitatively. Thus, we developed a graphic reconstruction method and used it to study histology sections of the temporal bones. By this method we studied quantitatively the morphology of the round window of individuals with Mondini dysplasia of the inner ear and compared it to that of individuals with no anomaly. Iit was found that in 3 of 19 individuals with dysplasia, the total area of the round window was more than two standard deviations below the mean, thus small enough to be called anomalous. Moreover, the area of the round window was statistically significantly smaller in the ears from individuals with Mondini dysplasia, as a group, than in normal ears. This round window anomaly seems to be due to interruption of the normal development of the round window early in fetal life, as the result of poor development of the cartilage bar between the tympanic cavity and the subarachnoid space and also of the otic capsule in the hook portion of the basal turn of the cochlea.     

Comparison of microfissures between the oval and round window niche areas in human temporal bone

There are numerous reports on microfissures in the round window niche area, but not many reports have appeared on microfissures in the oval window niche area. In addition, few studies have compared microfissures between the oval and round window niche areas in the same subjects. Hence, the present study investigated the prevalence of microfissures in both areas in human temporal bones. The study was conducted on the 637 ears of 333 cases. Specimens were prepared according to the conventional methods: after fixation, decalcification and dehydration, each specimen was embedded in Celloidin, and the temporal bones were sectioned horizontally at 25-micron intervals. Every 10th section was stained with hematoxylin & eosin, and each section was analyzed under a light microscope. The prevalence of microfissures was analyzed in relation to the sex, left/right differences and age of the subjects. Microfissures were seen in the oval window niche area in 66.2%, and in the round window niche area in 92.0%. When a microfissure was seen in the oval window niche area, it was also detected in the round window niche area in every case. There were no sex or left/right differences in the prevalence of microfissures, and microfissures occurred bilaterally in most cases. The youngest subject with a microfissure in the oval window niche area was a 14-year-old, and the prevalence increased with age up to approximately 60 years. On the other hand, microfissures in the round window niche area were seen in a 3-year-old, and were seen in most cases over the age of ten. These findings suggest that microfissures are more likely to occur in the round window niche area as compared to the oval window niche area. However, the prevalence of microfissures in the oval window niche area was not low either, and it is important to pay attention to both the oval and round niche areas when microfissures are involved in the formation of perilymph fistulae. Given that the prevalence of microfissures in the oval window niche area increased up to about 60 years of age, not only growth, but also mastication, may be involved in the occurrence of microfissures.     

Instrumental perforation of the round window. Animal experiments using cochleography and ERA

The round window membrane of the inner ear of the guinea pig was perforated under Ketanest anaesthesia. A very rapid and almost total loss of cochlear microphonics, auditory nerve action potential and brain-stem response developed. Replacement of the perilymph with Ringer's solution and surgical closure of the membrane damage had no effect on auditory nerve action potential or brain-stem response. Further decline in the amplitude of cochlear microphonics was halted, however. When perfusion of the round window membrane was carried out whilst the bulla was full with Ringer's solution, no essential decline was seen in the amplitudes of microphonics and auditory nerve action. Only brain-stem response was reduced--temporarily by 40% of the original amplitudinal level--but this showed subsequent recovery. Preservation of cochlear microphonics and auditory nerve action after perforation in Ringer's solution, i.e. excluding air, indicates that air entering the scala tympani is the cause of the sudden hearing loss after round window perforation. Using a simple physical model, an attempt is made to demonstrate this process. The anatomic connections between the round window, cochlear aqueduct and scala tympani are discussed, as are the different ways in which the round window membrane can be perforated.