Round window membrane rupture following blunt force trauma

Round window rupture following barotrauma such as diving and air travel is well documented. However, we describe a case of round window rupture following a slap to the ear, which has not been described previously. A 12-year-old boy was slapped by his teacher in rural Nepal over his left ear and immediately noted hearing loss. There was no dizziness or tinnitus. He presented to our unit 21 days after the trauma and examination showed a perforation of the tympanic membrane in the anterior inferior quadrant with an otherwise normal ear examination and no nystagmus seen. Audiogram showed a left profound hearing loss, which was supported by auditory brainstem response test. Exploratory tympanotomy showed active perilymph leakage from the round window niche as demonstrated in the video attached. The round window was packed with cartilage and fascia to address the perilymph leakage. The patient was discharged the following day without any complications. This is an unusual cause for round window membrane rupture where the patient presented with hearing loss as his only symptom. Tympanotomy is recommended for patients with hearing loss following trauma with normal computed tomography imaging to exclude perilymph leak secondary to inner ear barotrauma.

The effects of round window membrane injury and the use of a model electrode application on hearing in rats

We conducted an animal experiment to investigate the effects of mechanical trauma to the round window with the placement of a model electrode inserted into the scala tympani on the cochlear reserve, and to determine the efficacy of topical steroids in preventing hearing loss in such a situation. Our subjects included 21 male Wistar albino rats that were assigned into three groups of 7 each. In all three groups, an initial mechanical injury to the round window was created. At that point, group 1 received no further treatment, group 2 received a dexamethasone injection into the cochlea, and group 3 underwent implantation of a multichannel cochlear implant guide followed by dexamethasone administration. After a few minutes, the round window opening was obliterated with muscle, and the incision was sutured with 4-0 Vicryl Rapide polyglactin in all 3 groups. Distortion-product otoacoustic emissions were obtained before and immediately after the surgical injury, and again on postoperative day 7. Mean signal/noise ratios (S/Ns) obtained at 2, 3, and 4 kHz were calculated, and datasets were compared with nonparametric statistical tests. We found that the early postoperative mean S/N values were significantly lower than the preoperative values in groups 1 and 2, but there was no difference between the mean preoperative values and those obtained on postoperative day 7 in those two groups. In group 3, there were statistically significant differences among the mean preoperative, early postoperative, and postoperative day 7 S/N values. We observed that an electrode insertion into the cochlea via the round window subsequent to mechanical trauma seemed to cause a progressive hearing loss. Therefore, we conclude that special care must be taken to avoid injury to the round window membrane during placement of a cochlear implant electrode, as well as during surgery for chronic otitis media.

Predicting the location of missing outer hair cells using the electrical signal recorded at the round window

The electrical signal recorded at the round window was used to estimate the location of missing outer hair cells. The cochlear response was recorded to a low frequency tone embedded in high-pass filtered noise conditions. Cochlear damage was created by either overexposure to frequency-specific tones or laser light. In animals with continuous damage along the partition, the amplitude of the cochlear response increased as the high-pass cutoff frequency increased, eventually reaching a plateau. The cochlear distance at the onset of the plateau correlated with the anatomical onset of outer hair cell loss. A mathematical model replicated the physiologic data but was limited to cases with continuous hair cell loss in the middle and basal turns. The neural contribution to the cochlear response was determined by recording the response before and after application of Ouabain. Application of Ouabain eliminated or reduced auditory neural activity from approximately two turns of the cochlea. The amplitude of the cochlear response was reduced for moderate signal levels with a limited effect at higher levels, indicating that the cochlear response was dominated by outer hair cell currents at high signal levels and neural potentials at low to moderate signal levels.

Round window versus cochleostomy technique in cochlear implantation: histologic findings

HYPOTHESIS

Cochleostomy or round window enlargement techniques for cochlear implant electrode insertion result in more abnormal tissue formation in the basal cochlea and are more apt to produce endolymphatic hydrops than round window electrode insertion.

METHODS

Twelve temporal bones from implanted patients were examined under light microscopy and reconstructed with 3-dimensional reconstruction software to determine cochlear damage and volume of neo-ossification and fibrosis after electrode insertion. Amount of new tissue was compared between 3 groups of bones: insertion through the round window (RW), after enlarging the RW (RWE) and cochleostomy (Cochl). The probable role of the electrode was evaluated in each case with hydrops.

RESULTS

More initial damage occurred in the Cochl and RWE groups than in the RW group, and the difference was significant between RWE and RW in cochlear segment I (p < 0.026). The volume of new bone in Segment I differed significantly between groups (p < 0.012) and was greater in the RWE group than in either the Cochl or RW groups (post hoc p's < 0.035 and 0.019, respectively). Hydrops was seen in 5 cases, all in the Cochl and RWE groups. Blockage of the duct was because of new tissue formation in 4 of the 5 hydrops cases.

CONCLUSION

With the electrodes in this series, implantation through the RW minimized initial intracochlear trauma and subsequent new tissue formation, whereas the RW extension technique used at the time of these implantations produced the greatest damage. Future studies may clarify whether today's techniques and electrodes will produce these same patterns of damage.

[Perilymphatic fistula: diagnosis and treatment]

INTRODUCTION

Diagnosis and management of perilymphatic fistula (PLF) is a controversial topic in the international neurotologic literature. An illustrative case of post traumatic PLF with clear surgical indications is presented. This manuscript also reviews the various clinical presentations, pathogenesis, diagnostic examinations, and management options of PLF.

MATERIALS AND METHODS

Case report and literature review.

RESULTS

A 40 y/o female presented with paroxysmal vertigo, imbalance and severe sensorineural hearing loss (SNHL) following minor occipital head trauma from a fall six months prior to presentation. Laboratory examination included intermittently positive fistula sign on video-nystagmography. Patient failed to respond to trials of pharmacologic treatment and bedrest and ultimately underwent surgical exploration and repair. Patient had earlobe fat placed in the round and oval windows. Postoperatively, she had prompt resolution of vestibulopathy and ultimate full return of sensorineural function.

CONCLUSIONS

Patients with appropriate antecedent history demonstrating fluctuating SNHL and vestibulopathy, failing to respond to conservative medical treatments, should be considered for exploratory tympanotomy. In the absence of any other violations of labyrinthine integrity, connective tissue grafting of the round and oval windows should be performed even if no obvious flow of fluid is observed. This management protocol is safe and effective in properly selected patients.

Cochleostomy site: implications for electrode placement and hearing preservation

CONCLUSIONS

With recent increased interest in minimizing intracochlear trauma and preserving residual hearing during cochlear implantation, increased attention must be paid to the cochleostomy site. The results of this paper demonstrate that the cochleostomy must be made inferior, rather than anterior, to the round window to ensure scala tympani insertion and to decrease the likelihood of insertion-induced intracochlear damage during electrode insertion.

OBJECTIVE

To describe the complex anatomy of the hook region of the cochlea, specifically in relation to the optimal placement of the cochleostomy for cochlear implant electrode insertion to potentially achieve hearing preservation. The authors believe that previous industry recommendations and described surgical techniques have resulted in cochleostomies being placed in anatomical positions that possibly result in electrode insertions that damage the basilar membrane and/or other cochlear structures.

MATERIAL AND METHODS

The results of a number of temporal bone studies were reviewed with attention being paid to the anatomical relationship of the basilar membrane and spiral ligament to the round window membrane. For different cochleostomy sites the potential for damage to intracochlear structures, particularly the basilar membrane and organ of Corti, was assessed.

RESULTS

The review of electrode insertion studies into human temporal bones, as well as a post-mortem anatomical study of implanted temporal bones, showed an increased risk of scala vestibuli insertions and insertion-induced damage to intracochlear structures when the cochleostomy was performed more anterior to the round window. These results were endorsed by studies detailing the anatomy of the hook region of the cochlea.

Behandlung akuter kochleovestibul�rer Sch�digungen nach dem Tauchen

BACKGROUND

There has been a steady in-crease of recreational scuba divers in the last years. The majority of diving associated diseases involve otorhinolaryngology, the most important of which are cochleovestibular dysfunctions as these can lead to permanent inner ear failure.

MATERIAL AND METHODS

We discuss the origin and clinical symptoms, as well as the therapy, of both inner ear barotrauma and inner ear decompression illness. Our own experiences are considered together with a review of the literature from the last decade.

RESULTS

Inner ear decompression illness seems to be a relatively common diving associated incident and is not as rare as previously thought.

DISCUSSION

Hyperbaric oxygen therapy is the treatment of choice for patients with inner ear decompression sickness, but is contraindicated in patients with inner ear barotrauma. As long as an inner ear decompression illness can not be ruled out, we suggest that every patient should be treated using hyperbaric oxygen therapy but only after bilateral paracentesis.

[Effects of round window membrane rupture on cochlear blood flow and endocochlear potential]

The degree of hearing loss and audiogram shape vary in patients with perilymphatic fistula. The cause of variability is not well known. To determine the effect of perilymphatic fistula on cochlear function, we studied the effect of round window membrane rupture on cochlear blood flow (CBF) by placing a laser-Doppler probe to the basal turn in 20 guinea pigs. In 10, endocochlear potential (EP) was measured by inserting a glass microelectrode through the stria vascularis of the basal turn. During 60 minutes following round window membrane rupture, CBF decrease of more than 15% was observed in 9 of 20 animals, and EP decrease of more than 15% was observed in 5 of 10. A significant correlation was observed between the degree of CBF reduction and EP reduction. In 3 animals in which CBF decreased after round window membrane rupture, temporal bones were studied histologically. One cochlea showed endolymphatic hydrops and another cochlea showed significant hemorrhage in the scala tympani after rupture. These results suggested that CBF impairment is associated with cochlear dysfunction in perilymphatic fistula.

Persistent inner ear injury after diving

OBJECTIVE

The purpose of this multiple case report was to discuss the occurrence and cause of sudden sensorineural hearing loss after diving.

STUDY DESIGN

The study design was a retrospective case review.

SETTING

The study was conducted at an academic tertiary referral center.

PATIENTS

In this multiple case report, two teenagers with unilateral sudden sensorineural hearing loss after diving, one from a starting block and one from a 1-m board, while performing school swimsports were included.

INTERVENTION

The patients underwent diagnostic tympanotomy with sealing of the round and oval window membranes and a vasoactive rheologic therapy combined with corticosteroid treatment.

MAIN OUTCOME MEASURES

The average pure-tone bone-conduction thresholds were calculated. The appearance of nystagmus, vertigo, and tinnitus was analyzed.

RESULTS

Both patients experienced unilateral sudden deafness after performing a headfirst pike-type dive into a swimming pool. None of the patients contacted with the bottom of the pool. In one patient, a rupture of the round window was found intraoperatively. In the other patient, no rupture of the round or oval window was seen intraoperatively. In spite of sealing of the round window and application of vasoactive rheologic therapy, hearing did not improve significantly in either of the patients.

CONCLUSION

Rupture of the round window may occur after diving even if the dive is performed from a low height into the water and the bottom of the pool is not contacted. Besides direct contusion to the external ear and barotrauma, other causes such as whiplash mechanism have to be considered.

Imaging of the windows of the temporal bone

Imaging of the window of the temporal bone has became an important tool in the analysis of hearing loss, vertigo, tinnitus in a context of trauma, malformation, otosclerosis, and chronic otitis media. A good knowledge of the anatomy and a good technical procedure are necessary for making an efficient diagnosis. The increased thickness of the footplate may be delineated in otosclerosis, chronic otitis media, malformation, when it is measured at 0.7 mm or more in horizontal computed tomography (CT) sections. The traumatic displacement of the stapes, particularly within the labyrinths, is easily diagnosed in horizontal CT section. Imaging of the round window is now very important for the detection of otosclerotic foci, congenital stenosis, and perilymphatic fistula with or without fracture. Magnetic resonance imaging (MRI) with the high-resolution T2 plays an important role in the detection of a small amount of fluid in the round window recess, confirming the traumatic perilymphatic fistula without fracture.

[Rupture of the round window--detection with fluorescence endoscopy]

Rupture of the round window membrane as a special cause of inner ear deafness is widely accepted after changing pressure levels, e.g. in diving. However, even without a barotrauma before, the spontaneous rupture of the round window membrane is suspected occasionally in patients with sudden hearing loss and/or vertigo and tinnitus. To carry through the tympanotomy is decided by ENT surgeons often in cases of progressive hearing loss despite infusion therapy. Perilymph fistulas have been detected relatively seldom, compared to the number of reported operations by several authors. However, covering the round niche with connective tissue leads to the improvement of symptoms sometimes even in cases without microscopical evidence of fistula. Within the last 3 years 14 patients suffering sudden hearing loss of one ear underwent tympanotomy in our department. Of these patients 8 reached restitution of the hearing ability. Especially 2 patients with sudden deafness caused by spontaneous rupture of the round window membrane are reported in the following article. Perilymph fistulas were detected in these cases by IV-application of fluorescein and fluorescence endoscopy of the middle ear. Both patients obtained a normal hearing curve within 1 week after surgical intervention and obliteration of the round niche.

Rupture pressures of membranes in the ear

The rupture pressures of the tympanic membrane, Reissner's membrane, the round window membrane, and the annular ligament have all been measured in cadaver ears from Norwegian cattle. For the tympanic membrane, a static overpressure was applied to the ear canal; for Reissner's membrane, to the endolymph; and for the round window membrane, to the perilymph. The rupture pressure of the annular ligament equals the rupture force to the footplate divided by the area of the oval window. The mean rupture pressures are 0.39 atm for the tympanic membrane, 0.047 atm for Reissner's membrane, greater than 2 atm for the round window membrane, and 29.4 atm for the annular ligament. This last pressure corresponds to 0.68 kilogram force applied to the footplate. The ruptures of the tympanic membrane appeared without exception as small tears in the pars flaccida. The rupture pressure of the tympanic membrane was also measured in a few ears from foxes.

[Traumatic perilymphatic fistula of round and oval windows (four cases reported)]

OBJECTIVE

To explore the diagnosis and treatment to traumatic perilymph fistula (PLF) of round and oval window.

METHOD

Traumatic PLF was diagnosed by the traumatic history of head, neck and ear, the examinations of auditory and vestibular function, and the exploratory tympanotomy. The PLF of round and oval windows were repaired by fascia graft or tragus perichondrium and gelform. Four cases with traumatic PLF of round and oval window were reported in this paper, which included 2 cases hitten by hand, 1 by brick, 1 insulted by middle ear surgery. Exploratory tympanotomy was performed from one and half to nine months after injury. One case was misdiagnosed as Meniere's disease before confirming PLF. Exploration and repair of PLF underwent in all cases.

RESULT

The symptom of vertigo relieved in all cases after surgery, while the hearing recovery was not evident.

CONCLUSION

1. Traumatic PLF is unrare, hence, traumatic PLF should be alerted if patients suffer from vertigo and hearing impairment after head and ear injury. 2. The features with vertigo attacks, fluctuating hearing loss and tinnutis should be distinguished from Meniere's disease. 3. Early exploratory tympanotomy and repair of PLF are effective for relieving vertigo and improving hearing.

[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.

Combined rupture of Reissner's membrane and round window: an experimental study in guinea pigs: experimental double-membrane rupture

OBJECTIVE

Hearing loss caused by combined rupture of Reissner's membrane and the round window (RW) membrane (the double-membrane rupture) may differ depending on the site of the lesion on Reissner's membrane. The purpose of this experimental study was to reveal the relationship between the hearing impairment and the site of the lesion on Reissner's membrane.

BACKGROUND

According to experimental studies on perilymphatic fistula (PLF), profound hearing loss is not induced by rupture of RW alone, but by the double-membrane rupture. However, the mechanism responsible for hearing loss in the double-membrane rupture remains unclear.

METHODS

Compound action potentials (CAPs) of the cochlear nerve in response to tone pip stimuli (1, 2, 4, and 8 kHz) were recorded before the lesion, 90 minutes after the Reissner's membrane rupture, and 90 minutes after subsequent laceration of the RW. Reissner's membrane was ruptured at one of the four turns for comparison.

RESULTS

The double-membrane rupture caused a more severe increase in CAP thresholds than seen with separate ruptures, when the Reissner's membrane was ruptured at the second turn. Such pronounced increase in threshold was not seen in ears with the rupture at other turns.

CONCLUSIONS

The double-membrane rupture causes varying degrees of hearing loss depending on the site of the lesion of Reissner's membrane. When the Reissner's membrane was ruptured at the second turn, the most severe hearing loss was detected.

Pathological features of healing of a ruptured human round window membrane

Pathology of a round window membrane rupture was demonstrated in a human temporal bone from a case in which labyrinthotomy had been performed through the round window membrane. Proliferation of mesothelial cells was seen in the inner layer of the membrane, and it appeared to be reinforced from the inside by these reactive cells. The middle layer of the membrane was thickened by increased collagen and elastin. The pathologic changes which take place during healing of the ruptured round window membrane are discussed.

Changes in cochlear function after double-membrane rupture in the guinea pig

We measured the transiently evoked otoacoustic emissions (TEOAEs), compound action potentials (CAPs) and cochlear microphonics (CMs) in guinea pigs after rupture of the round window membrane alone (n = 5) or of the round window membrane with localized cochlear damage (n = 10). The localized cochlear damage entailed rupture of Reissner's membrane with damage to the stria vascularis. We determined the time course of changes in the total echo power (TEP) in TEOAEs and the minimal detectable levels of CAPs and CMs. The endocochlear potential (EP) was measured in the cochlea with localized damage. There were no changes in TEOAEs, CAPs or CMs in the guinea pigs subjected to round window membrane rupture alone, but the minimal detectable levels of CAPs and CMs were increased in all the guinea pigs in which TEOAEs were absent after rupture of the round window membrane with localized cochlear damage. Our results suggest that double-membrane rupture (rupture of the round window membrane with localized cochlear damage) produces acute sensorineural hearing loss. The hearing loss appeared to be related to damage to the cochlea, which may be induced by influx of potassium-rich endolymph into the perilymph, and by morphological damage to the scala media.

[Blood patch therapy of the perilymphatic fistulas--an experimental study]

Blood patch is a therapeutic procedure that uses a perilymphatic fistula to repair an inner ear window rupture by filling the tympanic cavity with autologous blood. The experimental study was conducted in 13 guinea pigs. Autologous blood or commercially available fibrin glue was poured into the otic bulla after artificial rupture of the round window. The animals were sacrificed immediately, or 1 to 7 days after the operation. The results showed that the blood or the fibrin glue successfully closed the window rupture by closing directly and by facilitating the formation of granulation at the margin of the rupture. Fibrin glue seemed to be preferable to autologous blood due to its non-toxic nature in the inner ear.

Effects and management of barometric change on cavities in the head and neck

Changes in atmospheric pressure may result in barotrauma to a variety of head and neck structures including the middle and inner ears, the sinus cavities, the teeth and some cranial nerves. This article outlines the pathophysiology of these injuries and suggestions are offered for prevention and treatment.

[Cochlear histopathological changes following chronic extracochlear electrical stimulation in kittens]

Histopathological investigation of the cochlea following chronic extracochlear electrical stimulation was carried out in 5 kittens. The auditory nerves were electrically stimulated with round window or tympanic promontory electrodes for periods of 1276-1526 h using charge-balanced biphasic current pulses at charge densities of 1.27-5.73 microC/cm2. geom. phase. The histopathological changes were examined with a light microscope. The findings were as follow: 1. The fixations of round window and tympanic promontory electrodes were very firm. Six round window membranes became thicker in the area which contacted the electrode. One was pushed into the scala tympani and adhered to the spiral lamina of the hook region. 2. There was some outer hair cell loss, mild inner hair cell loss and disappearance of Corti's organ structures in a small area of lower basal turns. 3. Decrease of spiral ganglion cell density was found over a 2% basilar membrane length in 2 stimulated cochleas. 4. There was no change in normal control cochleas. These results indicate that mild histopathological changes occurred even though chronic electrical stimulation was performed with non-invasive extracochlear electrodes. The mechanism behind these changes should be further investigated.

[Experimental defects of the round window membrane]

Previous and current studies of experimentally induced fistulas in the round window membrane (RWM) are reviewed. After puncture (or "micro-perforation") of the RWM leaking perilymph was not been observed and auditory evoked potentials have remained unaltered. In contrast, most publications have reported that gross incisions ("macro-perforations") of the RWM have resulted in the deterioration of auditory evoked potentials, with leaking perilymph and/or cerebrospinal fluid and/or with entrance of air bubbles into the scala tympani depending on the site of the perforation. Spontaneous healing was then observed within 4 to 8 days and was associated with normalization of the auditory evoked potentials. In a very few experimental studies pathophysiological mechanisms were simulated that may be involved clinically in patients with RWM fistulas, i.e. implosive rupture of the RWM due to an acute increase in middle ear pressure or explosive rupture of the RWM that may occur in patients trying to use forced Valsalva maneuvers to equalize decreased middle ear pressures due to blocked Eustachian tubes.

Morphologic and electrophysiologic effects of cochlear implantation and electrical stimulation

The nondeafened guinea pig model was utilized in this study to assess the functional and morphologic effects of cochlear implantation and electrical stimulation. Auditory brainstem responses (ABRs) were recorded prior to and following intrascalar implantation of a 3M-House cochlear electrode (n = 41 ears), as well as after electrical stimulation (n = 23 ears). The experimental population was divided into the following groups according to implantation and stimulation parameters: 200 microA for 3 hours (group I); 200 microA for 24 hours (group II); 400 microA for 3 hours (group III); implanted, but not stimulated (group IV); and nonimplanted, not stimulated ears (group V). Of those cochleae that sustained the trauma of implantation, 32 percent had no detectable ABR to 110 dB SPL clicks, while only 7 percent additionally failed to respond to 130 dB SPL clicks. No significant difference (one-way ANOVA with repeated measures at the 95 percent confidence limit) could be detected when comparing those ears that retained ABRs according to experimental grouping. Morphologic analysis was performed on 29 cochleae. Spiral ganglion "packing densities" were not found to be significantly different among the groups (ANOVA). The status of the organ of Corti was significantly better in groups II and V in comparison to the other groups (Kruskal-Wallis test with pairwise comparisons, p less than 0.05); there was no discernible dose-response relationship. Morphologic and electrophysiologic changes correlated with insertion trauma and infection rather than with electrical stimulation at the levels tested in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrode insertion trauma in cochlear implantation

Residual hearing conservation may be important in cochlear implantation of children and of adults with disabling tinnitus responsive to extracochlear stimulation. Damage to the neural elements of the cochlea during electrode insertion may have a negative impact on residual hearing conservation. Histologic analysis of eight temporal bones with cochlear implants reveals trauma at essentially two locations: the round window insertion site and along the basal turn of the cochlea. In four of the bones, insertion at the round window resulted in damage to the osseous spiral lamina and the electrode was inserted through the scala media into the scala vestibuli. Evidence of secondary reactive osseous formation was also noted in these bones. This paper relates the surgical anatomy of the round window to histologic findings and microanatomical dissections. Recommendations for implantation surgery include creation of a cochleostomy by removal of the floor of the round window niche and a superior-to-inferior angle of electrode insertion.

[Recurrence of perilymphatic fistula]

Recurrence of the perilymphatic fistula is not rare and may be a tough problem for surgical treatment. This is because a graft is usually applied on the ruptured window(s) from the middle ear and therefore the perilymphatic pressure directly acts on the graft. The recurrence may be caused by a technical failure, use of an unsuitable graft material, poor postoperative bedrest, trauma, increased inner ear pressure, etc. In our clinic, the recurrence occurred in 7 of 48 cases surgically treated. Vertigo accompanied with spontaneous or positional nystagmus was seen in all 7 recurrent cases, while only 2 of them complained of worsening of the existing hearing loss. Re-operation was carried out in two patients. In the first case, closure of the round window by the previous operation was found incomplete, and the perilymph leaked through the gap around the graft. In the second case, closure of the round window was complete, but perilymph leaked from the oval window. In order to prevent the recurrence, the operation should be carefully performed by using strong and adhesive tissue as a graft material, applying a glue between the graft and the inner ear window(s), and keeping strict postoperative bedrest.

Histopathologic study of the perilymph-suctioned labyrinth

A small amount of perilymph was suctioned from the scala tympani through the round window membrane of guinea pigs. The animals either were killed immediately after the suctioning or were kept alive for 1 to 3 months. For morphologic study, the conventional celloidin embedding method was employed, and the temporal bones were serially sectioned. Various kinds and degrees of changes in the membranous labyrinth were observed: hydrops, collapse, and rupture. Loss of outer hair cells in the upper turns of the cochlea was noted in the 1- to 3-month recovery specimens. These findings are identical to those found in animals in which artificial perilymph was injected into the subarachnoid space in order to produce experimental perilymphatic fistula. After comparing morphologic changes of the membranous labyrinth following use of each method, we concluded that perilymph suctioning from the round window can be used as an animal model of perilymphatic fistula.

Role of perilymphatic fistula in sudden hearing loss: an animal model

The electrophysiologic response of the guinea pig cochlea was monitored after sequential lesions to Reissner's membrane and the round window (RW). Action potential (AP) responses to click stimuli were recorded from the RW before and after discrete puncture-type lesions were created in the cochlear partition of the second turn. Observed decrements were typically minor, comparable to no greater than 10 dB attenuation of stimulus intensity. The RW membranes then were perforated to create perilymphatic fistulas. Further monitoring demonstrated a rapid (within 5 to 10 minutes), severe decrement in AP amplitude and latency, with complete loss of the AP within 1 hour. Control animals with RW perforations alone did not show these decrements. Correct placement of the second turn lesions was documented by histology. We conclude that discrete lesions in the cochlear duct are not reflected in the AP input-output functions unless there is a fluid leak from the RW, and thus present a possible model for idiopathic sudden hearing loss.

Maintenance of hydrostatic pressure gradients in the membranous labyrinth

In normal guinea pig ears, hydrostatic perilymphatic pressure is equal to endolymphatic pressure. Alterations of perilymphatic pressure induced, for example, by laceration of the round window membrane are transmitted immediately to the endolymphatic compartment, probably via Reissner's membrane. In guinea pigs with experimental endolymphatic hydrops, however, pressure gradients between the endolymph and perilymph remained preserved after rupture of the round window membrane. This is considered as further evidence that after long-standing distention of Reissner's membrane the membranous labyrinth loses its ability to equalize endolymphatic and perilymphatic pressure.

Healing of experimentally produced round window membrane rupture

The healing mechanism of experimentally produced ruptures of the round window was histologically studied in guinea pigs. Surgically created rupture of the round window resulted in spontaneous closure within 2 weeks. Light microscopical examination indicated that the rupture closed with proliferation of connective tissue which usually appeared to protrude into the middle ear cavity, each case showing a unique shape. In one case, the wound was covered with granulation tissue at the site of closure on the middle ear surface. Although the rupture was closed by connective tissue, the elastic fibres of the middle layer remained disrupted at the early stage of healing.

Perilymph fistula: the Stanford experience

Seventy-eight tympanotomies were performed to determine the presence of perilymph fistulas (PLFs); of these, 51% were found. The oval and round windows of all patients were grafted, whether PLFs were present or not. Of those patients with PLFs, 64% had resolution of their major symptom; when no PLF was found, 44% had a similar outcome. We concluded that 1) PLFs often behave as if they are epiphenomena in relation to hearing and balance, 2) PLFs can be intermittent, 3) PLF surgery is disappointing for restoration of hearing in sudden hearing loss when compared to the rate of spontaneous recovery, 4) stabilizing a fluctuating or progressive loss is a more realistic goal, and 5) establishing preoperative criteria for exploration is still a problem.

[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)

Surgery of the round window

Tympanotomy is routinely performed in our institution to control the round window membrane for patients with recurrent sudden deafness, with Meniere-like attacks, and those with Meniere's disease. In a large number of these patients, especially those with vertigo, perilymph fistula has been diagnosed. Most patients are free of attacks after the fistula has been closed, and in those with a short history of illness, hearing can become normal. In the future, closure of the round window membrane should be considered an important procedure in the treatment of inner ear dysfunctions.

Pressure transmission properties from the externa ear canal to the inner ear. An experimental study using guinea pigs

The inner ear pressure (PIE) in response to pressure changes in the external ear canal was measured in guinea pigs while alternatively opening and closing the perforation of the otic bulla. When the bulla was opened, only a transient degree of applied pressure was transmitted to the inner ear and the amplitude of the PIE was smaller than that of the corresponding PIE when the bulla was closed. This was because the applied pressure was exclusively transmitted to the inner ear via the ossicular chain. When the otic bulla was closed, the pressure was transmitted not only via the ossicular chain but also via the round window (RW) through the middle ear cavity. When the bulla was closed, the amplitude of PIE was larger by a positive pressure load than by the corresponding negative one. The amplitude of PIE showed a linear relationship to ear canal pressure of at least within the +/- 200 mmH2O range, as long as pressure was slowly applied to the ear canal. When the loading pressure was abruptly changed, a bouncing response, possibly reflecting elasticity of the RW, was evoked, which diminished or disappeared when the round window was artificially ruptured.

Effects of round window membrane rupture on cochlear blood flow and inner ear pressures

Effects of round window membrane rupture on cochlear blood flow and inner ear pressures were investigated using non-radioactive microspheres and a servo-micropipet system in guinea pigs. When perilymphatic pressure was raised through a glass capillary tube inserted into the perilymphatic space, both endolymph pressure and perilymph pressure rose. When these inner ear pressures were raised to relatively high levels, cochlear blood vessels could be compressed and endocochlear potential decreased to a negative value due to the interruption of cochlear blood flow. However, in the case when the round window membrane was ruptured by further increase in perilymph pressure, the inner ear pressures decreased and restoration of cochlear blood flow and endocochlear potential was observed. When the round window membrane was ruptured with a fine needle under ordinary inner ear pressures, cochlear blood flow did not change significantly.

The effect of round window membrane rupture on endolymphatic and perilymphatic pressures

We used a guinea pig model to investigate the effect of round window membrane rupture on endolymphatic and perilymphatic pressures under conditions known to increase these pressures: anoxia, hypercapnia, increased intracranial pressure, and occlusion of the vein of the cochlear aqueduct. When the round window membrane was not ruptured, increases in endolymphatic pressure paralleled the perilymphatic pressure following exposure to each of the experimental conditions. After the round window membrane had been ruptured, however, no increases in perilymphatic pressure or endolymphatic pressure were seen. These results suggest that endolymphatic pressure is dependent on perilymphatic pressure, even when the round window membrane is ruptured.

Pneumolabyrinth in perilymphatic fistula: report of three cases

In three patients with perilymphatic fistula, exploratory tympanotomy revealed air bubbles emerging through the ruptured round window membrane. Review of the literature disclosed three case reports in which air was demonstrated in the labyrinth in association with perilymphatic fistula. Experimental evidence that air could enter the labyrinth through a defect of the round window membrane was described in two articles. In our patients, the perilymphatic fistula was produced by implosive force. When a perilymphatic fistula was produced by implosive force, or in the case of a pre-existing perilymphatic fistula, we assume, air may enter the scala tympani through the defect of the round window membrane if the middle ear pressure rises beyond a certain limit. Sudden onset of deafness and reversibility of hearing in perilymphatic fistula could be attributable to the presence of air bubble in the scala tympani--pneumolabyrinth--which might disturb propagation of the traveling wave of the basilar membrane.

Labyrinthine window rupture with round window predominance: a long-term review of 32 cases

A retrospective series is presented of 32 cases of spontaneous labyrinthine window rupture proven at tympanotomy. There was no prior history of stapedectomy or other middle ear surgery. Seventy-eight per cent of cases involved the round window, in contrast to previous series on the subject. The pattern of hearing loss and vestibular symptoms varied widely and followed different antecedent factors, the commonest of which was head injury (46.9%). Including cases misdiagnosed initially, 92.9% of patients with vestibular symptoms experienced improvement following surgery, but only 20.7% of patients had improved hearing; these figures changed with long-term follow-up, which has been rarely reported previously. Seven patients, the majority oval window ruptures, required re-exploration, mainly for vertigo, and prolonged follow-up is required.

[Pressure measurements of the round window membrane in the guinea pig cochlea]

Some clinical observations suggest that sudden hearing loss or dizziness can be due to rupture of the round window membrane. Experiments on 16 guinea pigs showed that after injection of fluid the pressure in the scala tympani of the basal turn increases. This leads to rupture of the round window membrane. The pressure was recorded via a piezoresistant transducer. Morphological changes were visualised by scanning electron microscopy.

[The "window-fistula symptom" in lesions of the round and oval window]

22 tympanoscopies in suspected perilymph fistulas with clinical symptoms such as sudden hearing loss, tinnitus, vertigo, fluctuating hearing etc., histories and intraoperative findings were registered. In some cases a remarkable interval between the implicated event and the clinical manifestation of the symptoms was noticed. Besides on case history and audiometric data the diagnosis was based on vestibular investigations. In 14 of 22 cases the window-fistula-symptom was positive. The window-fistula-symptom is defined as a provocation nystagmus with maximal intensity in the lateral head position lying on the affected ear and in the head hanging position with the head rotated to the affected side. After abandoning these positions the nystagmus is decreased. Mostly the nystagmus is directed to the healthy side. With regard to the preoperative and postoperative findings a generous indication for tympanoscopy in suspected fistulas of the round and oval window membrane is recommended.

[Clinical and etiologic aspects of rupture of the membrane of the round window]

For more than 15 years, rupture of the round window membrane has been discussed as a possible cause of sudden sensineural hearing loss. With regard to the pathophysiological basis for such a rupture, an abnormality in the width of the aquaeductus cochlearis as well as anatomical variations of the round window membrane itself are presumed as causative factors. The authors report on six cases concerning this incidence. The indication for tympanoscopy and the technique for the closure of the round window fistula are reported. In 5 of the 6 patients treated in this manner, surgery the resulted in a significant and lasting hearing gain.

[Sudden deafness caused by rupture of the round window membrane. Surgical indications, course and prognosis]

Tympanotomy was performed on 39 of 247 patients with sudden hearing loss between 1980 and 1982. In 23 cases a round window membrane defect was found. Evaluation of the indications, intraoperative findings and postoperative course allows the following conclusions to be drawn. Only in patients treated in the second week was the rate of success significantly higher than the spontaneous remission rate in patients without perilymphatic fistula. If there is no improvement in the hearing level in the first week after covering a round window membrane defect the prognosis is poor. Stabilization of the hearing is complete in the first three weeks after treatment. Prognosis in extensive membrane defects with large perilymphatic fistulas is definitely worse than in small round window membrane defects. The best results were achieved for the following groups: physical exertion/barotrauma, sudden deafness, progressive hearing loss despite drug therapy.

Long-term study after perforation of the round window. Animal experiments using electric response audiometry

The round-window membrane of the inner ear of the guinea pig was perforated with a platinum wire under ketamine-xylazine anaesthesia. The latency times of waves I and V (Jewett) increased to 0.6 ms at 100 dB click HL stimulus loudness. The interpeak latencies did not change (4.0-4.2 ms). At 60 dB CHL stimulus loudness, no responses were discernible. Closure of the membrane damage by adhesive fibrin tissue had no effect on the auditory nerve potentials or the brain-stem responses. Normal latency times of waves I-V were seen 7 days after perforation. There was no difference between the animals with repaired and unrepaired membrane damage. We observed spontaneous healing of the round-window membrane 7 days after perforation, and a normal organ of Corti.

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.

Labyrinthine membrane rupture caused by elevated intratympanic pressure during general anesthesia

General anesthesia is not considered as a potential cause of hearing loss. However, three patients who sustained sensorineural hearing loss due to labyrinthine membrane rupture following general anesthesia with nitrous oxide have come to the authors' attention. These cases are presented and the mechanism causing labyrinthine membrane rupture is discussed.

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.