Hyperectasis: the hyperinflated tympanic membrane: the middle ear as an actively controlled system

Rare case of ballooning herniation of the tympanic membrane

Herniation of the tympanic membrane is a rare benign malformation of the tympanic membrane into the external auditory canal. It may be asymptomatic or associated with symptoms such as aural fullness, tinnitus, otalgia or hearing loss. We present a case of a symptomatic herniation of the tympanic membrane and its surgical therapy with hernia excision and tympanoplasty. An internal review board exemption was obtained.

Eustachian Tube Function

The fibrocartilaginous eustachian tube is part of a system of contiguous organs including the nose, palate, rhinopharynx, and middle ear cleft. The middle ear cleft consists of the tympanic cavity, which includes the bony eustachian tube (protympanum) and the mastoid gas cells system. The tympanic cavity and mastoid gas cells are interconnected and allow gaseous exchange and pressure regulation. The fibrocartilaginous eustachian tube is a complex organ consisting of a dynamic conduit with its mucosa, cartilage, surrounding soft tissue, peritubal muscles (ie, tensor and levator veli palatine, salpingopharyngeus and tensor tympani), and superior bony support (the sphenoid sulcus).

Hernia of the tympanic membrane

Although tympanic bulging is commonly encountered, tympanic herniation occupying the external auditory canal is extremely rare. A 66-year-old man was presented to our hospital with left aural fullness, bilateral hearing loss and otorrhea. Preoperative findings suggested tympanic membrane (TM) hernia located in the left external auditory canal. We performed total resection of the soft mass by a transcanal approach using endoscopy. Ventilation tubes were inserted into bilateral ears. Histopathological findings confirmed diagnosis of TM hernia. Passive opening pressure of this patient was higher than normal condition of the Eustachian tube, where active opening was not observed. Hernia of the TM most likely resulted from long-term excessive Valsalva maneuver.

Surgical anatomy and pathology of the middle ear

Middle ear surgery is strongly influenced by anatomical and functional characteristics of the middle ear. The complex anatomy means a challenge for the otosurgeon who moves between preservation or improvement of highly important functions (hearing, balance, facial motion) and eradication of diseases. Of these, perforations of the tympanic membrane, chronic otitis media, tympanosclerosis and cholesteatoma are encountered most often in clinical practice. Modern techniques for reconstruction of the ossicular chain aim for best possible hearing improvement using delicate alloplastic titanium prostheses, but a number of prosthesis-unrelated factors work against this intent. Surgery is always individualized to the case and there is no one-fits-all strategy. Above all, both middle ear diseases and surgery can be associated with a number of complications; the most important ones being hearing deterioration or deafness, dizziness, facial palsy and life-threatening intracranial complications. To minimize risks, a solid knowledge of and respect for neurootologic structures is essential for an otosurgeon who must train him- or herself intensively on temporal bones before performing surgery on a patient.

Mastoid geometry in a cross-section of humans from infancy through early adulthood with a confirmed history of otitis media

OBJECTIVE

This study describes the changes in mastoid air cell system (MACS) geometry with age in ears with a history of otitis media (OM), without (GR-I) or with (GR-II) middle ear fluid on the CT scan.

METHODS

Thirty-seven (74 MACSs) CT scans were selected to approximate 4 MACSs/year between 1 and 18 years. For each MACS, the volume, surface area and surface area/volume ratio were reconstructed using standard procedures. Correlation analysis was used to define the left-right relatedness for the geometric parameters, and regression analysis was used to determine the effect of age on those parameters for each group.

RESULTS

Twenty scans were from female and 17 from males. Fluid was observed in 12 left, 4 right and 10 bilateral MACSs. The MACS volume and surface area of GR-I increased with age, were significantly greater than those for age-matched MACSs in GR-II, but show large variability. Those measures in GR-II were independent of age and a large percentage of these MACS volumes was <5 ml. The surface-area/volume ratio for MACSs in both groups was independent of age and group assignment. The left-right correlations for the three geometric parameters of the MACS were significant for all MACS in the two groups, and for bilateral MACS concordant for group assignment. The left-right correlations for surface area and volume were not significant for bilateral MACSs discordant for group assignment.

CONCLUSIONS

These results suggest that: the growth of MACS volume and surface area is genetically programmed but that this is disrupted by long-lasting OM; the effect of OM on MACS growth may depend on the duration and timing of the disease, and the MACS surface area/volume ratio does not explain the effect of MACS volume on the rate of gas exchange between middle ear and blood.

Surgery for tympanic membrane retraction pockets

BACKGROUND

Tympanic membrane retractions are commonly managed by ENT surgeons. There is currently no consensus as to the indications, timing and options for management of this condition.

OBJECTIVES

To study the effectiveness of different surgical options in the management of tympanic membrane retractions.

SEARCH STRATEGY

We searched the Cochrane Ear, Nose and Throat Disorders Group Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2010 Issue 1); PubMed (1950 to 2010); EMBASE (1974 to 2010); CINAHL (1982 to 2010); BIOSIS Previews; ISI Web of Science; CAB Abstracts; LILACS; KoreaMed; IndMed; PakMediNet; China National Knowledge Infrastructure; ISCTRN; UKCRN; ICTRP and Google. The date of the search was 17 March 2010.

SELECTION CRITERIA

Randomised controlled trials (RCTs) of the surgical management of tympanic membrane retraction pockets in adults or children. Staging of the retraction using a known system must have been performed. Studies of cholesteatoma or perforations were excluded.

DATA COLLECTION AND ANALYSIS

Two authors independently collected and analysed data to minimise the effects of selection and reporting bias.

MAIN RESULTS

Two RCTs were included, involving 71 participants. The first study showed no statistically significant benefit of cartilage graft tympanoplasty over a watch and wait policy for either disease progression or hearing outcome. The second showed no additional benefit from the insertion of ventilation tubes over cartilage tympanoplasty alone with regards to hearing outcome.

AUTHORS' CONCLUSIONS

No evidence currently exists to either support or refute the role of surgery in the management of tympanic membrane retractions. Higher quality studies are much needed to ascertain this.

The mastoid as a functional rate-limiter of middle ear pressure change

INTRODUCTION

The physiological function of the mastoid air cell system (MACS) with respect to middle ear (ME) pressure-regulation remains controversial because predictive mathematical models and experimental data to formulate and test hypotheses are lacking.

OBJECTIVE

A mathematical description of MACS volume effects on the rate of ME pressure change is presented; the agreement between published data and model prediction is examined for consistency with the hypothesis that the MACS acts as a functional rate-limiter of ME pressure change, and an explanation for the relationship between MACS volume and otitis media is discussed.

METHODS

The mathematical description shows that the value of a single, free parameter, termed the "MACS buffering efficiency" (M) determines if MACS volume affects the rate of ME pressure change caused by diffusive gas exchange. The MACS serves no rate-limiting function for M=0, acts as a gas sink for M>1 and acts as a gas reserve (rate-limiter) for M<1.

RESULTS

Fitting the model equation to published adult human data yielded an estimate for M of 0.2. This implies that larger MACS volumes are associated with lesser rates of change in ME pressure caused by diffusive gas exchange and lesser required frequencies of effective Eustachian tube openings to maintain near ambient ME pressures.

CONCLUSION

If well-controlled studies confirm M<1 for children and adults, larger MACS volumes will increase the time required to develop sufficient ME underpressures to cause otitis media by hydrops ex vacuo during transient or prolonged periods of Eustachian tube dysfunction.

The effects of slight pressure oscillations in the far infrasound frequency range on the pars flaccida in gerbil and rabbit ears

This study was designed to clarify whether the pars flaccida (PF) as a flexible part of the tympanic membrane is capable of reacting to pressure oscillations (PO) with amplitudes and frequencies typical for natural atmospheric pressure fluctuations in the far infrasound frequency range (APF). If so, the PF mechanical reactions to APF might be involved in the overall physiologic regulation processes, which make organisms susceptible to APF. The displacements of the PF in response to PO were measured in vitro in ears of gerbils and rabbits by means of laser Doppler vibrometry. The index of the PF reactivity (R(a)) was determined as the ratio of the amplitude of the PF oscillations (PFO) to the amplitude of the PO. All kinds of PO applied caused PFO. The amplitude of the PFO increased when the amplitude of the PO was increased. In gerbils, a decrease in R(a) with the increase in amplitude of the PO was observed. In the range of PO lowest amplitudes (4-20 Pa) R(a) proved to be 1.4 times higher than in the range of highest amplitudes (90-105 Pa). Considering that the natural APF are usually within the range of +/-20 Pa, this fact points to an important contribution of the PF to the pressure dynamics in the middle ear (ME) of gerbils. In rabbit ears, R(a) was lower and recovery from plastic deformation was slower than in gerbils. Our findings are in line with the suggestion that the PF might play an important role in respect of adaptation to natural APF.

The mechanical reaction of the pars flaccida of the eardrum to rapid air pressure oscillations modeling different levels of atmospheric disturbances

Atmospheric pressure fluctuations (APF) might induce mechanical effects in the pars flaccida (PF) of the eardrum. To clarify these effects, different kinds of pressure oscillations (PO), chosen within the range of naturally occurring APF, were applied to the middle ears (ME) of gerbils. The linear displacement of the PF during a PO in the ME was measured by laser interferometry. The compliance of the PF to PO was calculated as the ratio of the amplitude of a PF oscillation to the amplitude of a PO. The displacement of the PF traced the PO in the entire range of frequencies (from 10mHz to 200mHz) and amplitudes (from 10Pa to 110Pa) applied to the ME. Moreover, the PF is found to be displaced by pressure pulses of a few pascals only using a PO with a complex shape. The differences found in the compliance of the PF due to PO with low (less than 20Pa) and high (more than 90Pa) amplitude point out that the mechanism of pressure regulation in the ME through the mechanical reaction of the PF in gerbil ears is better adapted to ordinary levels of natural APF than to extraordinary levels. The implications of these findings for the physiology of the human ME with respect to adaptation to natural APF are discussed.

The Effects of Positive and Negative Middle Ear Pressures on Auditory Threshold

HYPOTHESIS

To assess the effects of positive and negative middle ear pressures on auditory threshold.

BACKGROUND

Nonatmospheric middle ear pressures can alter auditory threshold by their effects on tympanic membrane and ossicular chain mobility.

METHODS

Experiments were conducted on guinea pigs by inducing alterations in pressure (positive and negative) with a syringe connected to the middle ear bulla cavity, the magnitude of the pressure being assessed with a water manometer. Elevated middle ear fluid pressures were also induced by attaching a saline-filled vertical tube to the saline-filled middle ear. The effect of these altered middle ear air and fluid pressures were assessed by recording auditory nerve-brainstem evoked responses.

RESULTS

There was no effect on auditory threshold of positive middle ear air pressures (up to 250 mm H2O). A negative middle ear air pressure of -50 mm H2O induced a significant 9.5-dB threshold elevation, whereas more negative pressures (up to -150 mm H2O) did not induce an additional threshold elevation. Filling the middle ear cavity with saline induced a 10- to 16-dB elevation, whereas additional fluid pressures (up to 200 mm H2O) did not induce further elevations.

CONCLUSION

The major factor inducing threshold elevation in serious otitis media is not the alteration in middle ear pressure but rather the reduction in the volume of compressible air in the middle ear by the fluid.

Gas Flow Into and Within the Middle Ear

HYPOTHESIS

Both a normal and a narrowed eustachian tube (ET) are capable of equilibrating pressures between the middle ear (ME) and the atmosphere almost instantaneously.

OBJECTIVES

The objective of this study was to assess experimentally the effect of narrowing a simulated ET isthmus on air passage into the ME.

METHODS

A Perspex ME model (0.5 mL) was constructed in which a 1.5-mm long ET of 0.07- to 1.0-mm diameter and a "mastoid" of 0- to 10-mL volume were changeable. The ET could be opened and closed with a valve. A -5 mm H2O pressure difference between the system and the atmosphere was created by withdrawing gas from the system. The time required to equalize these pressures after opening the valve to the atmosphere were measured with a pressure transducer.

RESULTS

A pressure difference of -5 mm H2O was created in the system when 1.3 to 6.5 microL of ME gas was removed. On ET valve opening, the pressure was equalized within 0.1 and 0.15 to 0.3 seconds for ET diameters of 1.00 and 0.07 mm, respectively, depending also on the "mastoid" volume. Similar results were obtained when the pressure was measured through the "tympanic isthmus" and "aditus ad antrum."

CONCLUSIONS

Our model shows that under ordinary physiological conditions, the amount of gas that can pass through the ET during swallowing time (0.4 sec) is potentially higher than required to equalize a negative pressure. This is also the case when the ET is very narrow and open for a very short time. It is unlikely that any narrowing of the tube will, by itself, hamper gas transfer into or within the ME, as long as the ET is not totally obstructed.

Effects of non-invasive ventilation on middle ear function in healthy volunteers

OBJECTIVES

To evaluate the effects of non-invasive ventilation (NIV) with facial mask or helmet on middle ear (ME). DESIGN. Prospective, randomised study.

SETTING

University hospital.

PARTICIPANTS

Ten healthy subjects randomly allocated in two groups of five subjects each.

INTERVENTIONS

NIV for 1 h, with helmet (group H) or facial mask (group M). Flow-triggered pressure support was 10 cmH(2)O, PEEP 5 cmH(2)O, FiO(2) 0.21.

MEASUREMENTS AND RESULTS

Impedenzometry was performed before NIV and 5 min after NIV ended; it was repeated 60 min later. In group H the acoustic compliance increased after NIV from 2.0+/-.6 ml to 2.3+/-.6 ml ( P<.01), suggesting that the tympanic membrane became less stiff; 1 h later the compliance returned to basal values (2.0+/-.7 ml); in group M the compliance was unaffected (from 2.0+/-.5 ml to 2.0+/-.4 ml; 1.9+/-.4 ml 1 h later). The acoustic reflex, i.e., the contraction of the stapedial muscle in response to an auditory stimulus, involving the acoustic and facial nerves, was also evaluated during impedenzometry at 250 Hz, 500 Hz, 1,000 Hz, and 4,000 Hz; no significant change of the threshold was observed.

CONCLUSIONS

The tympanic membrane is tighten by the tensor tympani and a reversible loosening suggests muscle fatigue in response to the application of intermittent positive pressure applied to the external ear during NIV with helmet. The loss of tensor tympani protective action could theoretically predispose the middle and inner ear to mechanical damage during NIV with helmet, suggesting the use of protective devices (ear plugs) in selective cases requiring long-term, high-pressure treatment.

Barotrauma vis-a-vis the "chronic otitis media syndrome": two conditions with middle ear gas deficiency Is secretory otitis media a contraindication to air travel?

We compared 17 patients (29 ears) with barotrauma with 171 patients suffering from "chronic ears" (secretory otitis media, atelectasis, or previously operated cholesteatoma). The patients with "chronic ears" were followed up prospectively, and none were found to suffer from barotrauma after flying on a commercial airplane. The mastoid pneumatization (seen on lateral mastoid radiographs) was significantly larger in ears with barotrauma, averaging 16.85 cm2, versus 12.9 cm2 in normal controls, whereas in "chronic ears" it was only 3.6 cm2. During flight on a commercial airplane, the middle ear has to equalize about 20% of its gas volume with the ambient pressure. This equalization must happen within 15 to 20 minutes of ascent and descent in order to avoid barotrauma. This 20% is a fivefold greater task for ears with a large mastoid pneumatization than for ears with an undeveloped pneumatization; "chronic ears" usually have an undeveloped mastoid pneumatization. The smaller the middle ear (mastoid) volume, the smaller the volume of gas needed to pass through the eustachian tube in order to equalize pressure changes during flying. This factor may explain why "chronic ears" rarely suffer from barotrauma. It also implies that eustachian tubes of secretory otitis, atelectatic, and cholesteatomatous ears have little problem in equalizing large pressure differences (over 2,000 mm H2O) within 15 to 20 minutes of landing, in contrast to what has been traditionally believed. Individuals with "chronic ears" can be advised that they can fly safely.