Round window membrane and labyrinthine pathological changes: an overview

The round window membrane is considered the most likely pathway from the middle to the inner ear. Various substances placed in the middle ear have been seen to pass through the round window membrane. Once toxic substances or inflammatory mediators such as cytokines and nitric oxide enter the inner ear, various inner ear sequelae such as labyrinthitis, endolymphatic hydrops, sensorineural hearing loss or more insidious diseases can occur.     

Round window membrane rupture

Round Window Membrane Rupture is a surgically correctable cause of sudden hearing loss and vertigo. Reported is a 19-year-old male who had proven round window membrane rupture secondary to barotrauma. Surgical exploration revealed an abnormally large round window niche and membrane, possibly predisposing him to this injury. Diagnostic and therapeutic modalities of this entity are presented.     

Round window membrane defect in divers]

BACKGROUND: The rupture of the round window membrane is a special form of traumatic inner ear deafness. Because of the changing pressure levels, divers are at risk of developing such a membrane rupture, especially if tube function is disturbed. As the popularity of diving as a sport increases, ENT specialists have to deal with diving related problems increasingly frequently. PATIENTS AND METHODS: Seven cases of divers are presented in whom a tympanotomy was performed following the diagnosis of a rupture of the round window membrane. The symptoms and intraoperative findings are discussed and the otologic and diving literature is reviewed. Following a case report, the pathophysiology, clinical symptoms and differential diagnosis of round window ruptures are discussed controversially. Possible therapeutical consequences are described. RESULTS: None of our patients exhibited the classical triad of deafness, tinnitus, and vertigo as described in the diving literature. The leading symptom in our patients was the loss of hearing; only two patients had vertigo. Tinnitus was found in half of the patients. Intraoperative a rupture of the round window membrane was presumed in five divers. CONCLUSIONS: If disturbance of inner ear function does occur concurrently with diving, a rupture of the round window membrane must be considered. An otologic examination must be performed in any diver with a loss of hearing and/or signs of a barotrauma of the middle ear. After differential diagnosis to exclude other possibilities, a tympanotomy to cover the round window membrane should be performed if symptoms persist more than 24 hours.     

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.     

Round window membrane rupture and acquired sensorineural hearing loss in children

Round window membrane rupture and acquired sensorineural hearing loss in children The aetiology of acquired sensorineural hearing loss includes many conditions. The disparity between the number of children affected by the conditions which are supposed to cause hearing loss and the number of children who are actually deaf, has never been satisfactorily explained. Clinical features observed in children with surgically proven round window membrane rupture have been noted in all conventional aetiological groups. These features include otitis media, doubt about the hearing status in early life, disturbance of balance and other occasional neurological phenomena. Wide variation in the appearance of round window niche has been observed in children with secretory otitis and similar appearances have been observed in children with proven round window membrane rupture. The appearances may represent a reaction to perilymph. Round window membrane rupture is probably common and may prove to be a unifying factor for many cases of acquired sensorineural hearing loss. Occasional neurological phenomena may be related to it.     

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 gentamicin absorption: an in vivo human model

OBJECTIVE/HYPOTHESIS: Using a novel human labyrinthine sampling model, in vivo gentamicin absorption through the round window can be measured. STUDY DESIGN: A prospective study. METHODS: Gentamicin was delivered either transtympanically (preoperative) or through a facial recess approach (intraoperative). The lateral semicircular canal and vestibule were opened, and by means of a microsyringe, labyrinthine fluid was aspirated. A sample of serum was also drawn. In all patients cerebrospinal fluid was also drawn. The samples were analyzed using a standard chemistry analyzer. RESULTS: Intratympanic gentamicin diffused through the round window membrane and achieved concentrations in the labyrinthine fluid ranging from 0 to 16 mg/L. Intratympanic gentamicin was absorbed into the systemic circulation in 4 of 11 patients with serum levels ranging from 0.3 to 0.4 mg/L. No gentamicin was detected in the cerebrospinal fluid. CONCLUSIONS: Intratympanic gentamicin diffuses rapidly through the round window membrane and achieves significant levels in the inner ear. Thus, this new model can be used to assess round window permeability to clinically relevant medications such as steroids and ototopical antibiotics.     

Round window vibroplasty: Long-term results

Abstract Conclusions: The round window (RW) approach in the use of the Vibrant Soundbridge? (VSB) is a safe and effective treatment of conductive and mixed hearing losses for a period of more than 3 years of device use. Objective: To investigate the long-term safety and efficacy as well as user satisfaction of patients with conductive and mixed hearing losses implanted with the VSB using RW vibroplasty. Methods: Twelve patients with conductive and mixed hearing losses were evaluated after 40 months of daily VSB use. Safety was assessed by evaluating reports of postoperative medical and surgical complications as well as by changes in bone conduction hearing thresholds. Efficacy outcome measures included aided and unaided hearing thresholds, speech recognition in quiet and in noise and subjective benefit questionnaires. Results: The safety results revealed no significant medical complications. One subject experienced sudden hearing loss after 18-24 months of device use, but still continues to wear the device to her satisfaction. With regard to efficacy, there were no significant changes from short- to long-term results in aided word understanding, functional gain or speech recognition threshold, suggesting that the outcomes are stable over time. Subjective questionnaires revealed either the same or better results compared with the short-term data.     

Round window membrane in young and aged C57BL/6 mice

Although there have been many studies on the round window membrane (RWM), little information has been reported about changes in the membrane associated with aging. We have undertaken morphological studies of RWMs using young (7-8 weeks old) and aged (27-29 months old) C57BL/6 mice. The RWM was thinner in mice from the aged group compared with that of the young group. The cell density in the epithelial and inner layers was also reduced in the aged group. In the middle layer of the RWM in aged mice, transmission electron microscopy revealed many degenerated short and thick elastic fibers. Confocal laser microscopy using fluorescein isothiocyanate(FITC)-wheat germ agglutinin (WGA) staining was used to identify WGA-positive fibers in the middle layer of the RWM, which changed in a similar manner to the fibers in aging skin.     

Round window membrane permeability to human serum albumin in antigen-induced otitis media

The round window membrane (RWM) permeability to human serum albumin (HSA) was investigated in both normal chinchillas and chinchillas sensitized with HSA. The effect of a corticosteroid agent (triamcinolone) on the RWM permeability was also analyzed. It was found that HSA could not be detected in either the perilymph or the cerebrospinal fluid of normal chinchillas within 1 hour after instillation into the middle ear bulla. Perilymph levels of HSA peaked 24 hours after instillation. In antigen-induced otitis media, the HSA level in the perilymph at 12 hours after challenge was significantly higher than that in normal chinchillas (P less than .01), but it did not increase with the development of otitis media. A significant difference of HSA level in the perilymph of animals with and without steroid treatment was noted (P less than .025 at 24 hours and P less than .05 at 48 hours). It is concluded that little HSA passes through the normal RWM in a short time and that the RWM permeability to HSA increases in the early stage (about 12 hours) of antigen-induced otitis media. Corticosteroids can affect the RWM permeability to HSA by reducing the level of antigen-induced otitis media.     

Clinical aspects of round window membrane permeability under normal and pathological conditions

Current research and an overall review of 25 years of round window membrane studies are presented. The approach, rationale and concepts that have evolved from these studies are described. Ultrastructural studies of the round window membrane of humans, monkeys, felines and rodents have disclosed three basic layers: an outer epithelium, a middle core of connective tissue and an inner epithelium. Interspecies variations are mainly in terms of thickness, being thinnest in rodents and thickest in humans. Morphologic evidence suggests that the layers of the round window participate in resorption and secretion of substances to and from the inner ear, and that the membrane could play a role in the defense system of the ear. Different substances, including antibiotics and tracers, when placed in the middle ear side traverse the membrane. Tracers placed in perilymph become incorporated into the membrane by the inner epithelial cells. Permeability is selective and factors affecting permeability include size, concentration, electrical charge, thickness of the membrane and tacilitating agents. Passage of substances through the membrane is by different pathways, the nature of which is seemingly decided at the outer epithelium of the membrane. Round window membrane studies have provided increased knowledge of the anatomy and function of this structure, as well as new insights into pathology and pathogenesis. The concepts that have evolved from these studies are potentially useful for understanding middle and inner ear interactions, and for eventual drug delivery (based on permeability) to the inner ear.     

Round window membrane visibility related to success of hearing preservation in cochlear implantation

Objectives: This study was designed to evaluate the relationship between the degree of round window membrane (RWM) exposure and hearing outcome.

Materials and methods: Forty-six ears with cochlear implantation (CI) were enrolled. The degree of RWM exposure was divided into Grade I (<25%), Grade II (25–50%), and Grade III (>50%). The hearing outcomes were evaluated at 1.5 and 12 months postoperatively.

Results: Twenty-seven ears were Grade I, 13 were Grade II, and 6 were Grade III. RW approach was used in all ears of Grades II and III and 20 ears of Grade I and cochleostomy was used in 7 ears of Grade I. The pattern of bony overhang was multidirectional in 41 ears. Threshold shift significantly decreased proportional to the increase of RWM exposure after CI. The mean RWM exposure was 32.1?±?24.4% in ears with more than partial preservation (n?=?17), and 13.3?±?11.7% in the other ears (n?=?6) at 12 months post-CI (p?=?.061). Age at CI differed significantly between ears that had more than partial preservation and the other ears at 1.5 months post-CI.

Conclusions and significance: Degree of RWM exposure and age at CI might be factors predicting hearing outcome after CI using the RW approach.     

Canal wall window mastoidectomy for extensive labyrinthine cholesteatoma: total dissection and hearing preservation

This case report highlights outcomes of a 6-year-old patient who preserved functional hearing after complete dissection of an extensive labyrinthine cholesteatoma causing two semicircular canals fistulas with endolymph leak, tympanic and labyrinthine fallopian canal erosion of the facial nerve and internal auditory canal invasion with cerebrospinal fluid leak. The patient preserved 40 dB average of bone conduction threshold and 92% of speech discrimination score at 26 months postoperatively. This article reveals that canal wall window mastoidectomy might be an option even in cases of extensive cholesteatomatous labyrinthine fistula therefore avoiding hearing loss and long life cleaning of a canal wall down mastoid cavity.     

Round window gentamicin application: an inner ear hair cell damage protocol for the mouse

It is important to develop an inner ear damage protocol for mice that avoids systemic toxicity and produces damage in a relatively rapid fashion, allowing for study of early cellular and molecular mechanisms responsible for hair cell death and those that underlie the lack of hair cell regeneration in mammals. Ideally, this damage protocol would reliably produce both partial and complete lesions of the sensory epithelium. We present a method for in vivo induction of hair cell damage in the mouse via placement of gentamicin-soaked Gelfoam in the round window niche of the inner ear, an adaptation of a method developed to study hair cell regeneration in chicks. A total of 82 subjects underwent the procedure. Variable doses of gentamicin were used (25, 50, 100 and 200 microg). Saline-soaked Gelfoam, sham-operations and the contralateral, non-operated cochlea were used as controls. Survival periods were 1, 3 and 14 days. Damage was assessed on scanning electron microscopy. We found that this method produces relatively rapid hair cell damage that varies with dose and can extend the entire length of the sensory epithelium. In addition, this protocol produces no systemic toxicity and preserves the contralateral ear as a control.     

Round window application of an active middle ear implant (AMEI) system in congenital oval window atresia

Conclusion: Application of the Vibrant Soundbridge to the round window (RW) membrane can be utilized as an efficient therapy for congenital oval window (OW) atresia. Objective: To report the surgical technique and auditory outcome of an active middle ear implant (AMEI) system used in patients with congenital OW atresia. Methods: Nine subjects with congenital OW atresia (six males and three females, ranging in age from 5.5 to 25 years, average 12.5 years) were implanted with an AMEI (Vibrant Soundbridge) at the round window (RW-Vibroplasty). Five cases were diagnosed as having isolated congenital OW atresia while four patients presented with combined external/middle ear malformation. Results: An improvement of 30 dB in average pure-tone air conduction thresholds (0.5–4 kHz) was achieved, with the high frequencies showing greater results. The subjects achieved postoperative speech recognition scores of 80–100% on the Computerized Mandarin Speech Test System (CMSTS) sentence test. Bone conduction thresholds were confirmed as stable in all subjects postoperatively. Decline in auditory benefit was noticed in two subjects, who then underwent revision surgery. One of these revision surgery patients then experienced stable hearing recovery, while the other patient’s hearing declined.