External Canal Research Articles

Nodular fasciitis of the external auditory canal in six Egyptian children

Nodular fasciitis of external auditory canal may mimic a malignant tumor due to its progressive course, so it was the aim of this study to focus on a new etiology for aural masses to avoid unnecessary aggressive treatment. Retrospective study on six children presented with aural masses that were diagnosed pathologically to have nodular fasciitis. Presentation of the cases clinically, radiologically and pathologically was carried out. Surgical excision of the lesions was done through the external canal with follow up of the cases for 1 year. Recurrence was detected in two cases, one after 2 months and the other after 4 months. Re-excision was carried out without recurrence till the end of the follow up period. Proper diagnosis of this lesion is mandatory to avoid aggressive treatment (radical surgery and/or radiotherapy) as the disease has favorable prognosis with local excision.

外耳道癌の臨床的検討

Carcinoma of the external auditory canal is infrequent and the prognosis is poor, especially in the advanced stage. Over the 15-year period, from 1992 to 2006, 17 patients with carcinoma of the external auditory canal were treated in our hospital. Eight patients (47%) were male, and nine (53%) were female. The mean patient age was 60 years old, ranging from 24 to 82 years. On pathological analysis, 11 patients (65%) showed squamous cell carcinoma, four (24%) adenoid cystic carcinoma, one (6%) basal cell carcinoma, and one (6%) verrucus carcinoma. Thirteen patients underwent external canal resection, lateral temporal bone resection, or subtotal temporal bone resection. Four advanced patients treated with radiation or chemotherapy without surgical treatment died within one year. The 3-year survival rate was 76.5%, and the 5-year survival rate was 68.0% using the Kaplan-Meier method. The main finding of this study was that radical resection is a reasonable approach and postoperative radiotherapy is helpful for carcinoma of the external auditory canal.

Meaningful novelty processing during sleep in humans

Event Abstract Back to Event Meaningful novelty processing during sleep in humans Jean-Baptiste Eichenlaub1*, P. Ruby1 and Dominique Morlet1 1 INSERM U821, France How does the sleeping brain process external stimuli, and in particular, up to which extent does it detect and process modifications in its sensory environment? In order to address this issue, we investigated brain reactivity to verbal and meaningful novel auditory stimuli during wakefulness and sleep in young healthy subjects. EEG (23 scalp electrodes referenced to nose), EOG and EMG were recorded during wakefulness and all-night sleep, while a passive oddball paradigm including standards, deviants and two types of novels was applied. Novel sounds were first names uttered by a neutral masculine voice: the subject’s own name (‘own’) and an unfamiliar first name (‘other’). They were presented rarely (p = 0.02) in a background of regularly presented tone-bursts. Stimuli were presented at a level of 50 dB SL via two mini-earphones inserted into the external acoustic canals. During wakefulness recordings, subjects watched a silent movie with subtitles. During sleep recordings, stimuli were presented continuously during the whole night. During wakefulness, ‘own’ and ‘other’ names evoked expected N1 and P3a components. Interestingly, the P3a component peaked significantly earlier (15 ms) for the ‘own’ name. In addition, analysis of the data revealed that the ‘own’ name only, evoked a large parietal positivity peaking at 550 msec. An enhanced response to the ‘own’ name was also detected during sleep, at late latencies, with a similar topography as the one observed during wakefulness (Figure), in sleep stages 2, 4 and REM (Rapid Eye Movement) sleep. These results demonstrate that, during wakefulness, the own first name induces an earlier reorientation of attention than another first-name, possibly due to its greater familiarity or to its meaning. The ‘own’ name subsequently evoked a late positivity which may be interpreted as a complex cognitive processing such as a recall of memory associated to the ‘own’ name. Only late positivities were found in sleep stages 2, 4 and REM suggesting that only the latter effect is preserved during sleep. In conclusion this study demonstrates verbal discrimination for the first time in all sleep stages and suggests a possible preservation of stimulus-driven recollection during sleep. pic Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Poster Presentation Topic: Perceptual Processing and Recognition Citation: Eichenlaub J, Ruby P and Morlet D (2008). Meaningful novelty processing during sleep in humans. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.357 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Dec 2008; Published Online: 15 Dec 2008. * Correspondence: Jean-Baptiste Eichenlaub, INSERM U821, Lyon, France, jb.eichenlaub@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jean-Baptiste Eichenlaub P. Ruby Dominique Morlet Google Jean-Baptiste Eichenlaub P. Ruby Dominique Morlet Google Scholar Jean-Baptiste Eichenlaub P. Ruby Dominique Morlet PubMed Jean-Baptiste Eichenlaub P. Ruby Dominique Morlet Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

In Situ Location of the Temporal Branch of the Facial Nerve

The purpose of this radiologic study was to determine the precise location of the temporal branch of the facial nerve in relation to the most anterior aspect of the bony external acoustic canal without distortion of the position of the nerve by surgical manipulation or cadaveric fixation artifact. This was a retrospective study of 30 patients with a mean age of 38 years (range, 22 to 67 years) with no history of previous surgery or trauma. Thirty axial high-resolution magnetic resonance imaging examinations at the level of the zygomatic arch were examined to determine the location of the temporal branch. The nerve was identified by following its course from the stylomastoid foramen to an area lateral to the frontozygomatic suture. Three individuals made 3 measurements of each image with digimatic calipers. The high and low values were discarded, and the remaining 3 values were analyzed. These examiners were trained in locating the nerve and bony landmarks and were tested for accuracy in measurement. No inter- or intraoperative variability was noted. The mean distance of the most posterior ramus of the temporal branch of the facial nerve to the most anterior aspect of the external acoustic canal was 2.12 cm +/- 0.21 cm (range, 1.68 to 2.49 cm). The course of the temporal branch was easily identified, and the examiners were consistent in their measurements. In all cases examined, there was no evidence of facial trauma or other facial surgery in the patient histories. All nerves were found superficial to the zygomatic arch, just deep to the superficial musculoaponeurotic system, or the temporozygomatic fascia, which is the connective tissue layer just deep to the subcutaneous fat. The temporal branch of the facial nerve is at risk for injury during a variety of facial surgical procedures because of its location. This study found the nerve to be in a slightly less vulnerable position during a preauricular approach than Al-Kayat and Bramley's classic study (0.8-3.5 cm), and also established a narrower range of nerve position variability.

Electrode extrusion through the tympanic membrane in a pediatric patient

The medical literature contains an increasing number of reports that establish the safety of cochlear implantation in both adults and children. Complications, however, are not inexistent, with reported rates between 3% and 13% for major complications and 7% to 37% for minor complications. 1 Though the exact definitions vary between series, major complications are generally defined as those that require surgical intervention or result in permanent disability, whereas minor complications include those managed conservatively or with a simple procedure (eg, aspiration). 1-3 Although device exposure through the postauricular skin flap is not uncommon, only a limited number of reports describe extrusion of the electrode through the tympanic membrane. In this case report, we present a child who developed a retraction pocket with electrode extrusion six years after implantation. The patient is a 17-year-old girl who presented to our clinic at age 13, two years after right cochlear implantation at a different institution for progressive hearing loss. The patient was then lost to follow-up for three years when she presented with right otalgia. She denied any history of recent infections and had no signs of implant malfunction. Examination of her right ear revealed an anteriorinferior retraction pocket, with obvious visualization of the cochlear implant electrode through the tympanic membrane. After informed consent was obtained, the patient was taken back to the operating room for exploration. This revealed a retraction pocket with the electrode extruding through the membrane into the external canal in a loop fashion (Fig 1). The middle ear was full of granulation tissue. The stimulating electrode had advanced through the facial recess into the mesotympanum, eroding the malleus and the tympanic membrane and protruding into the canal (Fig 2). All 22 leads were still in the cochlea. The device was carefully freed of the surrounding scar tissue and repositioned back into the mastoid cavity. A cartilage tympanoplasty was then performed. The internal receiver was in place and did not require manipulation. One year after the procedure, the tympanic membrane appears intact with no evidence of retraction or cholesteatoma. DISCUSSION

Results, Hearing Rehabilitation, and Follow-up with Magnetic Resonance Imaging after Tympanomastoid Exenteration, Obliteration, and External Canal Overclosure for Severe Chronic Otitis Media

We sought to evaluate the results, auditory rehabilitation, and follow-up with magnetic resonance imaging (MRI) after tympanomastoid exenteration with obliteration of the mastoid cavity and overclosure of the external ear canal in patients with severe chronic otitis media that was resistant to medical therapy and conventional surgery and was associated with a profound sensorineural or severe conductive hearing loss. Twenty-nine patients were analyzed and underwent this surgical technique. Twelve patients had, during the same or later stage, either cochlear implantation, fixture implantation for a bone-anchored hearing aid, or middle ear implantation. For follow-up control of the obliterated cavity, delayed gadolinium-enhanced, T1-weighted MRI in combination with non-echo planar imaging diffusion weighted sequences were used. No patient had recurrent otorrhea after an average follow-up period of 4.75 years. One patient had a residual cholesteatoma as shown by new MRI techniques, and this was successfully resected. One patient developed complications 6 months after 1-stage tympanomastoid exenteration and cochlear implantation. This technique is very useful in selected patients with severe chronic otitis media that is resistant to medical therapy and surgery and is associated with a profound sensorineural or severe conductive hearing loss. New sequences in MRI are used for postoperative follow-up of these obliterated cavities and seem reliable for the detection of residual or recurrent cholesteatoma. Middle ear implantation and cochlear implantation can be relatively safely performed in these patients in a second stage.

Canal Wall Reconstruction Mastoidectomy

ObjectiveTo investigate the advantages of canal wall reconstruction (CWR) mastoidectomy, a single-stage technique for cholesteatoma removal and posterior external canal wall reconstruction, over the open and closed procedures in terms of cholesteatoma recurrence. Methods:Between June 2002 and December 2005, 38 patients (40 ears) with cholesteatoma were admited to Sun Yat-Sen Memorial Hospital and received surgical treatments. Of these patients, 25 were male with ages ranging between 11 and 60 years(mean = 31.6 years) and 13 were female with ages ranging between 20 and 65 years (mean = 38.8 years). Canal wall reconstruction (CWR) mastoidectomy was performed in 31 ears and canal wall down(CWD) mastoidectomy in 9 ears. Concha cartilage was used for ear canal wall reconstruction in 22 of the 31 CWR procedures and cortical mastoid bone was used in the remaining 9 cases. ResultsAt 0.5 to 4 years follow up, all but one patients remained free of signs of cholesteatoma recurrence, i.e., no retraction pocket or cholesteatoma matrix. One patient, a smoker, needed revision surgery due to cholesteatoma recurrence 1.5 year after the initial operation. The recurrence rate was therefore 3.2% (1/31). Cholesteatoma recurrence was monitored using postoperative CT scans whenever possible. In the case that needed a revision procedure, a retraction pocket was identified by otoendoscopy in the pars flacida area that eventually evolved into a cholesteatoma. A pocket extending to the epitympanum filled with cholesteatoma matrix was confirmed during the revision operation, A decision to perform a modified mastoidectomy was made as the patient refused to quit smoking. The mean air-bone gap in pure tone threshold was 45 dB before surgery and 25 dB after (p < 0.05). There was no difference between using concha cartilage and cortical mastoid bone for the reconstruction regarding air-bone gap improvement, CT findings and otoendoscopic results. ConclusionCWR mastoidectomy can be used for most patients with acquired middle ear cholesteatoma, including children. The CWR technique provides improved exposure of the middle ear, especially the anterior epitympanum, without creating a mastoid bowl and reduces the incidence of residual and recurrent disease, including cholesteatoma and otorrhea.

Otitis Externa

Otitis Externa

TWO NEW SPECIES OF AUSTROBDELLA (HIRUDINIDA: PISCICOLIDAE) FROM CHILE

Austrobdella coliumicus n. sp. is described from Coliumo Bay, Chile. It is characterized by a continuous, external coelomic canal (= marginal lacuna), 5 pairs of testisacs, accessory gland cells, a body not distinctly divided into trachelosome and urosome, 2 pairs of dorsal ocelli on the trachelosome, dorsal and ventral segmental ocelli present on the urosome, green overall pigmentation with transverse brown bands, and the absence of conducting tissue. Austrobdella coliumicus is distinguished from other species of Austrobdella by the presence of 2 pairs of ocelli on the trachelosome and a more cylindrical body. It is unusual that this leech was collected from inside the mantle cavity of the razor clam, Ensis macha. Austrobdella losmoliniensis n. sp. is described from the electric ray, Discopyge tschudii, collected at Los Molinos, Chile. It is characterized by a continuous, external coelomic canal; 5 pairs of testisacs; accessory gland cells; a body distinctly divided into trachelosome and urosome; 1 pair of eyes on the oral sucker; overall black pigmentation with unpigmented areas; and the absence of conducting tissue. Austrobdella losmoliniensis can be distinguished from other species of Austrobdella by the combination of 1 pair of eyes on the oral sucker and black pigmentation.

Residual cholesteatoma after performing the mastoid obliteration technique with middle ear cholesteatoma

This report describes a case with the re-growth of a residual recurrence of cholesteatoma in a patient who had previously undergone mastoid obliteration using bone putty. At the first visit to the clinic, his external canal resembled one that had undergone canal wall down surgery and his symptoms resembled a cavity problem. Because this recurrent cholesteatoma showed an unusual development, it was not possible to distinguish the cholesteatoma recurrence and a neoplasm using CT and MRI. Surgical removal of the cholesteatoma was extremely difficult because the obliteration covered most of the surgical landmarks. No continuity was identified between the matrix of the cholesteatoma and the eardrum /external ear canal epithelium. The follow-up CT 2 weeks after the initial surgery revealed a residual mass in the mastoid cavity, which required a second surgery for complete removal. This experience indicated that confirmation of the complete removal of a cholesteatoma matrix is critical before deciding to obliterate the mastoid cavity, and that, it is never easy to determine if the procedure is complete. The goal is pneumatization at the mastoid cavity, thereby making it possible to both confirm the recurrence of the cholesteatoma and allowing surgeons to remove it safely.

Epidermal hyperplasia of the tympanic membrane and deep external ear canal: novel histo‐pathological features, embryological and clinical correlates

Objectives. To study the histology and developmental biology of epidermis of tympanic membrane and deep ear canal and to correlate the histo‐pathological features with clinical conditions.Method. Histo‐pathological and electron microscopic examination was performed of deep meatal skin, keratosis, keratosis obturans, external canal cholesteatoma, retraction pockets, acquired cholesteatoma and tympanic membrane perforations.Results. In some mature ears, a marked change in the normal flat thin epidermis to one resembling that of the fetus is seen in the presence of local inflammation. This hyperplastic epidermis is present in varying lengths on the tympanic membrane and deep ear canal and displayed as hyperplastic bands growing down into sub‐epidermal tissue and sometimes penetrated the collagen layer of the tympanic membrane to enter the middle ear. Keratosis was frequent on the surfaces of the tympanic membrane and deep ear canal, which may also be found in the invading bands, where they produced small keratin cysts.Conclusions. Severe chronic otitis media, with inflammatory exudates, glandular metaplasia or tympanosclerosis, may be associated with hyperplasia. This type of epidermal hyperplasia appeared to be pathogenic and was observed in several structurally distinct entities such as keratosis, keratosis obturans, retraction pockets, and cholesteatoma of the deep external canal. Invading epidermis in the middle ear, in some cases, is indistinguishable from acquired cholesteatoma. This reverse differentiation highlights a primordial property of auditory epithelium, which was not previously recognised. Furthermore, hyperplastic epidermis appears to be pathogenic and may be the cause of some specific conditions or their complications.References 1 Johnson A., Hawke M., Berger G. (1984) Hodge memorial Award‐surface wrinkles, cell ridges, and desquamation in the external auditory canal. J Otolaryngol.13, 345–3542 Johnson A., Hawke M. (1985) Cell shape in the migratory epidermis of the external auditory canal. J Otolaryngol.14, 273–281

CT recognition of traumatic pneumomyelogram

CT recognition of traumatic pneumomyelogram

両側小耳症・外耳道閉鎖に対する手術―２つの耳の形と機能を再建する―

In two stages of total ear reconstruction surgery for children with microtia and atresia, plastic surgeons and otologists have cooperated to reduce the number of surgeries and to achieve both esthetically and functionally better results. Ear elevation, external canal plasty and tympanoplasty are performed cooperatively in the second stage of surgery.In the past 5 years we have experienced 70 cases of combined surgery as the second stage of microtia reconstruction: 59 boys and 11 girls, 12 cases of bilateral microtia and atresia and 58 cases of unilateral microtia and atresia. Analysis of the 3D CT scan was useful to plan total reconstruction surgery for microtia and atresia, and was important for education and design of surgery. Esthetically and functionally combined surgery at the second stage is convenient to make a natural orifice of the external canal, elevate the external ear and reconstruct the ossicular chain.After bilateral reconstructive surgery, patients with bilateral microtia and atresia can localize sounds in the right and left auditory spaces.

Single Scrotal Incision Orchiopexy for Palpable Undescended Testis

To prospectively evaluate the Bianchi single scrotal incision technique for orchiopexy in boys with palpable undescended testis. A total of 35 orchiopexies were performed in 28 patients. The patent processus vaginalis was dissected and cut high without ligation, while in Bianchi's original procedure, the patent processus vaginalis is dissected up to the external inguinal canal, ligated high and divided. Testicular size and position were assessed at 2 and 6 weeks and 6 months. The single incision technique was successful in all cases. All testes were satisfactorily positioned in the scrotum. All testes showed good anatomical and cosmetic results at 6-month follow-up. Single scrotal incision orchiopexy without ligation of the patent processus vaginalis has proved to be simple, safe and effective in selected cases compared with the standard two-incision approach in the treatment of palpable undescended testis.

Bone-Conduction Hearing and the Occlusion Effect in Otosclerosis and Normal Controls

The goal of this study was to better understand bone-conduction hearing in subjects with normal hearing and in those with otosclerosis through the occlusion effect. With this study, the authors hope to lend credence to commonly accepted theories of bone-conduction hearing and the effect of lateralization during the Weber tuning fork test. There are three accepted theories defining bone-conduction hearing: compressional bone conduction describes an auditory percept produced by the compression and expansion of the cochlea leading to basilar membrane vibration; inertial bone conduction describes the inertia of the ossicular chain as a result of skull vibration during bone conduction testing; whereas skull vibration may also be transmitted to the external auditory canal, surrounding soft tissues, and para-auditory structures to illicit tympanic membrane vibration known as osseotympanic bone conduction. Twenty normal volunteers and 17 unilateral otosclerosis patients underwent external canal sound pressure level measurement during bone-conduction testing using a standardized bone oscillator placement and stimulation paradigm. Sound was detected with a probe microphone placed in the external auditory canal in nonoccluded and occluded conditions after a 50-dB hearing level bone-conduction stimulus. There was no significant difference in sound pressure level between otosclerosis and normal subjects when the external auditory canals were nonoccluded. With occlusion, sound pressure level increased in both groups, but at a statistically significantly higher level for the otosclerosis group. Sound measured in the external canal likely represents energy lost to the environment transmitted through the middle and external ear systems, aided by the effect of both inertial and osseotympanic bone conduction. Occluding the ear leads to sound trapping and amplification. Also, the pressure exerted against the tympanic membrane reduces middle ear compliance and increases the impedance mismatch between air and the middle ear system, reflecting sound back into the external canal. This effect is further enhanced by stapes fixation to explain our data in both groups of subjects. The final common pathway in "lateralization" is probably a product of higher than normal impedance mismatch at the oval window.

An intradermal nevus of the external auditory meatus

We herein describe a rare case of an intradermal nevus arising in the external auditory meatus. A 36-year-old woman presented with progressive hearing loss on the right ear, and otomicroscopic examination revealed the presence of a large, violaceous, dome-shaped, papillomatous lesion originating from the posterior wall of the external canal of the right ear. Upon excisional biopsy, the tumor was diagnosed as an intradermal nevus. Thus, this is a unique case of intradermal nevus obstructing the external ear canal with the patient presenting with progressive hearing loss. The possibility of a benign nevomelanocytic nevus should not be underestimated when evaluating a lesion obstructing the ear canal, and all melanocytic nevi should be excised instead of biopsied to rule out melanoma.

A case of osteoma with cholesteatoma in the external auditory canal

Osteoma in the external auditory canal (EAC) is an uncommon benign lesion, which presents as a solitary, unilateral, and slow-growing pedunculated mass in the outer half of the bony canal. It is usually asymptomatic; but symptoms can arise if a canal obstruction occurs. External canal cholesteatoma is also a rare lesion of the external auditory canal. Cholesteatoma of the external auditory canal may arise via several mechanisms. However, an occlusion or narrowing of the external auditory canal is the basic pathogenesis. The association of an osteoma with a cholesteatoma is extremely rare, and there have been very few reports published. We encountered a rare case of a 49-year-old man with an osteoid osteoma that was complicated by a cholesteatoma in the external auditory canal. The canal wall down mastoidectomy and tympanoplasty successfully removed the osteoma and the cholesteatoma, and no recurrence or complications had occurred in the first 6 months postoperatively.

Relative humidity of the external auditory canal in normal and abnormal ears, and its pathogenic effect

To find the relative humidity of the normal external ear canal and to demonstrate that the relative humidity of the external auditory canal was higher in abnormal ears, i.e. ears commonly associated with chronic discharge. Secondary health care within the ENT departments of Addenbrooke's and Hinchingbrooke hospitals. A clinical observational study. Volunteers seen in ENT outpatients. Inclusion criteria for the normal ear group, was a normal ear with no history of infection or previous ear disease. Inclusion criteria for abnormal ear group commonly associated with chronic discharge. Exclusion criteria were the presence of pus or infection within the ear canal. The relative humidity of the external ear canal was measured in normal and abnormal ears. Abnormal ears were grouped as those commonly associated with chronic discharge, mastoid cavities, tympanic perforations, recurrent otitis externa and hearing-aided ears. The range of relative humidity of normal ears is 40-70%. The humidity in abnormal ears was found to be significantly higher than the humidity in normal ears (P < 0.0001). The raised relative humidity in the external canal may explain the predisposition of certain abnormal ears to chronic discharge and infection. If the humidity of the canal could be brought down to a normal level, this could offer a new therapeutic treatment.

Pediatric external canal cholesteatoma with extensive invasion into the mastoid cavity

Cholesteatoma in the external auditory canal (EAC) is an uncommon situation, and is especially rare in pediatric patients. We report two pediatric cases of external canal cholesteatoma with extensive invasion into mastoid cavity. Both cases had otalgia and poor hearing as the initial symptoms, and received operation according to the extent of the lesions. Since external canal cholesteatoma with extensive invasion into the mastoid cavity has the propensity to involve the vertical segment of the facial nerve, extreme care should be taken when performing any procedure in this area. Through thorough pre-operative evaluation and adequate surgical procedures, good outcomes can be achieved and hearing as well as facial nerve function can be preserved.

Gas diffusion across the tympanic membrane in chinchillas: effect of repeated perforations

Objective: Earlier studies documented a slow diffusion of gas across the tympanic membrane (TM) in humans and animals. However, structural changes caused by repeated TM perforations could affect gas diffusion rates. This possibility was evaluated using a chinchilla model. Methods: In six chinchillas, the right TM was perforated four times at 2-week intervals; the left TM served as a control. Approximately 12 weeks after the fourth perforation and when the right TMs had healed, a probe was introduced into the external canal and sealed to the environment. For 120 min, pressure in the probe was continuously monitored and probe gas was sampled at 10 min intervals and analyzed for composition by online mass spectrometry. Percent compositions for CO 2 and O 2 were calculated and these data were recast as partial-pressure versus time functions. The information contained in those functions was used to estimate time-constants for transTM O 2 and CO 2 diffusion. Results: In all experiments, CO 2 percent composition in the probe increased as a curvilinear function of time while that for O 2 decreased linearly. For all animals and both gases, the rate of change in probe partial-pressure was greater for the right TM. Average values of the right and left time-constants were (6.7 ± 2.4) × 10 −3 and (4.2 ± 2.2) × 10 −3 min −1 TM −1 for CO 2, and (2.3 ± 0.8) × 10 −3 and (1.5 ± 0.5) × 10 −3 min −1 TM −1 for O 2. Between side differences in these time-constants were statistically significant ( P < 0.05, 2-tailed, paired, Student's t-test). The average right/left, transTM time-constant ratio was 1.66 ± 0.43 for CO 2 and 1.61 ± 43 for O 2; both were significantly different from a value of 1.0 ( P < 0.05, 2-tailed Student's t-test). Conclusion: These results document an increased rate of diffusive gas exchange across TMs that had been repeatedly perforated. This effect may be caused by structural thinning secondary to scar formation and could have implications for middle ear pressure regulation in ears with a history of repeated myringotomies and/or tympanostomy tube insertions.