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B. C. Buzo et al.
Multiple physiological mechanisms contribute to bone
conduction hearing. Simply put, sound energy is the conduction of vibrations in the skull to the cochlea, which ultimately
results in the propagation of waves along the basilar membrane and stimulation of the cochlear nerve: the same end
point as air conduction hearing[8]. To this day, research is
still ongoing to fully describe the mechanisms by which
bone conduction hearing occurs and the relative contributions of each pathway. In 2005, Stenfelt and Goode nicely
summarized ve major pathways [9]. In this excellent review
about the bone conduction, the authors describe ve main
appliances responsible for this type of conduction: (1) radiation of sound to the external auditory canal, (2) inertia of the
middle ear bones, (3) inertia of the cochlear uids, (4) compression of the cochlear walls (compression of the inner ear),
and (5) pressure transmission from the cerebrospinal uid
(CSF). These are the main contributors to bone conduction,
but cochlear uids inertia is considered to be the most important contributor; for further details, we suggest consulting:
[9] (Stenfelt S., Goode R.L. Bone-conducted sound:
Physiological and clinical aspects. Otol. Neurotol. 2005;
26:1245–1261).
Hence, in the words of Professor Stefan Stenfelt, “direct
stimulation of the cochlea by bone-conducted sound is
achieved through inertia of the cochlear uids and compression and expansion of the cochlear space. The rst
refers to the set of windows (oval window and round window) mainly, and the second, to the movement of the bone
surrounding the cochlea that compresses and expands the
cochlear space in phase with the bone movement wave”
[10].
Under these physical concepts of sound transmission, it is
clear that acoustic cochlea stimulation can be achieved by
bypassing the outer and middle ear. From this arises the technology of bone conduction devices (BCDs). These devices
take advantage of the above mechanisms by converting
sound energy into skull vibrations. Since the initial work of
Tjellström et al. [11], numerous commercial devices have
been introduced, including surgically implanted devices and
devices simply superimposed on the skull bone. These
devices are intended to assist with auditory rehabilitation for
patients with conductive or mixed hearing loss who cannot
use conventional air conduction hearing aids or even for
patients with single-sided deafness. The ability to use conventional transcranial devices is highly limited by recurrent
infections such as chronic otitis externa, previous surgical
intervention and altered physiology, microtia or anotia, canal
atresia or stenosis, or other anatomical limitations. In the
unilaterally deaf population, bone conduction devices direct
transcranial signals to the contralateral normal hearing
cochlea.
Bone Conduction Devices
This principle of bone conduction stimulation was already
known in the Renaissance by Girolamo Cardano, when he
demonstrated that a rod between the teeth, connected to a
musical instrument, transmitted sound stimuli to the ear.
Thus the development of dental stimulators began to improve
hearing, rst connected to a musical instrument and then to a
loudspeaker.
By virtue of the development of a carbon microphone, a
vibrator was rened as early as 1950, and it could be placed
in the mastoid area with the aid of glasses. They were
“audio- glasses” that held this vibrator in the retroauricular
area. The arms of the glasses contained the microphone, the
amplier, and the vibrator, which are applied to the bone
behind the ear. The effectiveness of these devices is inuenced by the thickness of the skin, the pressure exerted,
contact with the skull, and any complications arising from
skin irritation. Currently, some companies are re-investing
in such a device. Decades of subsequent studies corroborated this stimulation pathway and in 1977, Anders
Tjellstrom implanted the rst bone vibrator onto mastoid
[12].
Thus, a bone conduction device is an alternative to a conventional hearing aid for those with outer or middle ear problems. The device transmits sound by bone vibration directly
to the cochlea, bypassing the outer and middle ear. This
means it is useful for conductive and mixed hearing loss,
which the cochlea still works to send sounds to the brain with
the aim of achieving aural rehabilitation for patients.
Nowadays, we have several types of bone conduction
devices, which allow us to choose the most appropriate t for
each patient, adapting each to their hearing characteristics
and needs. They are divided by their amplication characteristics (passive or active), sound transmission (percutaneous
or transcutaneous), and technology (electromagnetic and
piezoelectric). Moreover, they could be implantable or nonimplantable, and osseointegrated or anchored. In the following section, each of them will be presented.
Types ofBone Conduction Devices
Bone conduction devices transform acoustic sound waves
into mechanical vibrations, which are conducted to the inner
ear through direct contact with the skull. As already mentioned, the contact with the skull can be classied into two
main groups: percutaneous devices and transcutaneous
devices (Fig.36.4).
The major difference between the two types is that in percutaneous devices an abutment is surgically positioned on
ab
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331
Fig. 36.4 Diagram showing present modalities of bone conduction devices
Fig. 36.5 (a) Percutaneous device. (b) Transcutanous device. (1) The
sound processors captures sounds in the air. (2) The sound processor
turns the sound into vibrations and sends them through the abutment (a)
the skin connecting the processor to the internal implant,
while in transcutaneous devices two magnets will make the
connection between the processor and the internal implant
(Fig.36.5).
Percutaneous: Percutaneous implants have a skinpenetrating abutment that transmits sound vibrations very
efciently because it does not suffer from attenuation of the
skin and soft tissues of the skull. While the vibration is transmitted more successfully by the skin-penetrating abutment,
such a coupling system potentially leads to infections and
chronic at the abutment site. Technological improvements
tend to reduce infection resistance and skin tolerance [13].
or magnetic (b) connection to the implant. (3) The implant transmits the
vibrations through the bone directly to your inner ear. Source: images
courtesy of Cochlear
®
However, its acceptance by some patients remains being psychologically difcult [14].
All percutaneous devices are considered passive, as all
vibrations transmitted to the skull are generated by the external processors and from there, transmitted via the abutment
to the bone implant within the skull bone. Some of commercial brands are Baha®Connect (Cochlear BAS, Sweden) and
Ponto (Oticon Medical AB) (Fig.36.6).
Transcutaneous: The skin limitations observed with percutaneous devices have led manufacturers to seek a solution
for direct energy transmission to the bone with the skin
closed. As a result, in 2012, a transcutaneous active implant
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B. C. Buzo et al.
Fig. 36.6 Devices commercial names. ** Headbands are commercially available as Baha® Start(Cochlear BAS), Alpha 2 sound processor on a
headband Sophono® (Medtronic), Ponto Softband (Oticon Medical AB)
was launched on the market. The advantage of this device is
the absence of a permanent abutment in the head, which signicantly reduces postoperative complications and facilitates patient acceptability [15].
Active implantable transcutaneous devices contain an
external microphone and processor that send electronic signals to an implanted vibrating device in direct contact with
the skull. With an active system, the external processor is
static and transmits electronic signals. Vibration happens
only at the level of the implanted device. Available devices
are Bonebridge (MED-EL) and Osia® System (Cochlear
BAS) (Fig.36.6). Although both are active, the amplication
mechanisms are different.
Bonebridge (MED-EL) has a oating mass electromagnetic transducer attached by cortical screws to the cranial
bone that transmits vibrations to the bone without soft tissue
attenuation. The external processor is xed to the subcutaneous coil by a magnet that transmits information and energy to
the implant. The bone conduction oating mass transducer
under closed skin minimizes skin complications and provides direct connection to the bone with greater efciency
compared to external vibrators through closed skin. The
great difference between Osia® System (Cochlear BAS)and
Bonebridge(MED-EL)is the Osia® has an amplication gen-
erated by a piezoelectric system, which is far superior,
mainly because of its low impedance at high frequencies
and, respectively, more amplication on that frequency
range. Thus, the new technology is capable of generating
greater gain never achieved at high frequencies, mainly
improving speech distinction with noise [16].
Passive implantable transcutaneous devices have an
implanted part of the device directly connected to the skull
and a separate external part held in place magnetically that
drives the vibration through the skin to the implanted device.
In a passive system, the vibration occurs at the level of the
external processor and the vibrations are transmitted in a
transcutaneous manner to the implanted device. Available
commercial options are Baha® Attract (Cochlear BAS) and
Sophono® (Medtronic) (Fig.36.6).
Still, transcutaneous passive devices could be divided in
implanted and non-implantable devices: The rst generations of bone conduction systems were the passive and nonimplantable transcutaneous devices. An external vibrator is
held with a headband on the skin behind the ear. In fact, the
skin and soft tissues attenuate sound mainly at high frequencies, and this attenuation varies according to the frequency
and can attenuate from 8 to 20dB [17].
The headbands (Fig.36.6) allow to test the devices, or to
use them prior to surgery. This is how pediatric population,
while waiting to meet the presurgical anatomical requirements, stimulates their hearing early. It is very important that
the child perceives the benet of these devices and develops
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an attachment to them. They are commercially available as
Baha® Start(Cochlear BAS), Alpha 2 sound processor on a
headbandSophono® (Medtronic), and Ponto Softband
(Oticon Medical AB).
For those who need a different nonsurgical option of
headbands, Baha®SoundArc (Cochlear BAS) (Fig. 36.6)
could be an excellent option. It allows high-quality demonstrations, evaluations, and trials with the Baha processors.
The Baha®SoundArc (Cochlear BAS) was designed to sit
above the ears and be worn behind the head, with the Baha
sound processor attached to a connector disk just behind
the ear.
Finally, instead of headbands it still is available an adhesive nonsurgical solution composed of two parts: the thin
adhesive adapter and the audio processor. The adhesive
adapter is glued behind the ear in the area where there is no
hair. Its commercial name is Adhear® (MED-EL) (Fig.36.6).
Fig. 36.7 Bone conduction audiometry (in situ)
Evaluation ofBone Conduction Device
Candidates
333
When choosing a bone conduction device, many factors
must be considered. Each patient has unique needs that are
related to their degree and type of hearing impairment, anatomy, vocational or educational needs, and personal preferences. Finding this information in a consolidated location
can be a challenge for patients and providers.
In the evaluation of candidates, several aspects of the
audiological and medical indications are analyzed as well as
integral aspects to the patient such as age, living environment, lifestyle and work environment, expectations regarding the results, motivation, family support, their education,
and the possibility of follow-ups. Candidates for a bone conduction device directly attend the audiology department after
being referred by the otolaryngologist. An interview with the
audiologist is scheduled so that they can get to know the
device and clarify their doubts. The patient wants to see the
device, its size, its texture, color options, among others, to
imagine their personal appearance while wearing it. Thus,
the esthetic factor is very important.
Once these aspects are examined, a test of the bone conduction device is performed, instance in which the patient
can test how the bone conduction amplication would work.
Through the programming software, a sound processor
anchored to a headband is calibrated and placed around the
patient’s head, positioning the processor in the mastoid
region. This device is calibrated mainly on the basis of previous audiometry and in situ tests (bone conduction audiometry) allowed by the calibration software (Fig.36.7).
Once the processor is calibrated, the patient is able to feel
and experience hearing again through the bone conduction
Fig. 36.8 Free-eld audiometry to measure functional gain of the
speech processor
device, although we know that once the patient is operated,
the benet will be greater after.
Candidates for a bone conduction device directly attend
the audiology department after being referred by the otolaryngologist. An interview with the audiologist is scheduled so
that they can learn about the device and clarify their doubts.
The patient wants to see the device, its size, its texture, its
color options, among others, to imagine their personal
appearance while wearing it, and the esthetic factor is very
important.
The nal performance of the device is studied in a silent
camera with free-eld audiometry (Fig.36.8).
At this time, surgical procedures related to bone conduction implants are minimally invasive with increasingly sim-
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plied surgical techniques and a postsurgical period very
well tolerated by the patient that allows them to resume his
usual activities promptly.
The minimum age for implantation varies according to
the device chosen and the ones authorized by the regulatory
authority that governs the country. For instance, the minimum age for implanting an active conduction device such as
Osia® System (Cochlear BAS) according to the FDA in the
United States is 12years and for European countries governed by the EC is 5years.
Usually, the surgeon requests an ear scanner to verify that
the bone thickness of the calotte allows the anchorage of the
implant. For example, in the case of the implants which require
osseointegration of a titanium implant of 3 or 4mm, it will
require a bone thickness the measures above mentioned. In
addition to the ear scanner, routine presurgical examinations
will be requested following health condition of each patient.
The initial tting procedure for the sound processor
should be scheduled approximately four weeks after the
operation, for example, in Osia® System or Baha® Attract
Systems(Cochlear BAS). In the event that the tissue is still
too swollen, consider a later tting. Fitting should be checked
in regular intervals as per clinic protocol.
B. C. Buzo et al.
Fig. 36.9 Audiogram shows bilateral mixed hearing loss
Clinical Cases
Case 1: Bone Conduction Device—Passive,
Transcutaneous, andPiezoelectric
A 56-year-old woman, with a history of bilateral chronic otitis media since childhood, has undergone several tympanoplasties in both ears. As of now, the right ear has an opaque
and scarred eardrum, but it is closed and does not ooze, and
she consistently wears a hearing aid in that ear. In the left ear,
the eardrum is perforated.
The patient is an active woman who works daily and
requires better hearing.
The audiometry shows a mixed hearing loss in both ears
(Fig.36.9), with signicant air–osseous gap in the low frequencies and good discrimination of disyllabic words (left
ear: 96% at 95dB and right ear: 88% at 100dB).
A softband with sound processor test was performed in
the left ear, considering direct bone conduction and piezoelectric technology as the best option for the perforated eardrum conditionin this ear.
The patient reported immediate improvement during
device testing and underwent left ear surgery on 2018 with a
passive, transcutaneous, and piezoelectric bone conduction
implant.
Today, in 2022, the patient is still a consistent user of a
hearing aid in her right ear and she made an upgrade for the
sound processor in her left ear.
The latter processor features innovative speech sound
processing and optimal noise handling, which greatly
facilitates speech distinction in different sound
environments.
Case 2: Bone Conduction Device—Passive,
Transcutaneous, andPiezoelectric
This case is that of a 30-year old woman, architect, and very
active at work, who consulted an ENT doctor in October
2021. The audiological examination shows mixed hearing
loss with an average pure tone of 90dBs HL in the right ear
by air conduction and neurosensorial hearing loss in the left
ear (Fig.36.10).
Physical examination showed microtia of the right ear
with stenosis of the external auditory canal. Radiological
examinations, on the other hand, showed malformation of
the middle ear ossicles.
She reported having undergone cosmetic ear surgery a
few years earlier.
We proceeded to test a headband with a sound processor
on the patient so that she could feel the performance of the
external device, and she reacted positively to the test, stating
that no conventional hearing aid previously tested had
achieved such audiological performance.
She underwent surgery on her right ear with a passive,
transcutaneous, and piezoelectric bone conduction implant
on December 21, 2021.
36 Evaluation andAuditory Rehabilitation inChronic Otitis Media (COM)
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References
Fig. 36.10 Audiogram, October 2021
10. Stenfelt S. Cochlear boundary motion during bone conduction
11. Tjellström A, Lindström J, Hallén O, Albrektsson T, Brånemark
12. Mudry A, Tjellström A.Historical background of bone conduction
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Fig. 36.11 Free-eld audiometry with a bone conduction device
17. Verstraeten N, Zarowski AJ, Somers T, Riff D, Offeciers
She is an excellent user of the bone conduction device
who has never presented a problem with the adhesion of the
magnet and her skin, and her performance in a free-eld
audiometry is shown in Fig. 36.11 that shows a great
improvement at low and high frequencies.
335
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Pathogenesis ofChronic Otitis Media
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andtheContinuum: TheBasics, Further
andBeyond
SadySelaimenda Costa andMichaelM.Paparella
37
Otitis Media: TheBasics
Otitis media (OM) is dened as an inammatory process
(associated or not to infection), in the middle ear cleft (MEC)
[1–3]. It might affect the ME as a whole (generalized) or
focally. It is one of the most prevalent infectious diseases
being associated with an immense social impact worldwide
[4]. The morbidity (and even mortality) of this condition still
poses a formidable challenge to otolaryngologists, pediatricians, and generalists.
Due to its immense social impact, otitis media has been
exhaustively studied, but even so, a consensus on its complete understanding is far from being achieved. Pending
questions remain regarding the epidemiology, pathogenesis,
and treatment of this condition. Even the classication and
denition of otitis media among its different subgroups is
very controversial. It is clear the struggle of the authors to
agree upon a denitive classication which would only be
unquestionable if it could accommodate all features of a
given subgroup. As an example, the so-called acute otitis
media (AOM), as a rule, would be always associated with a
suppurative, purulent, or mucopurulent component.
However, in special situations—such as large variations in
atmospheric pressure—a typical serous collection can sud-
S. S. da Costa (*)
Department of Otolaryngology, Head and Neck Surgery, School of
Medicine-Universidade Federal do Rio Grande do Sul,
Porto Alegre, Brazil
International Hearing Foundation, Minneapolis, MN, USA
American Academy of Otolaryngology and Head & Neck Surgery,
Alexandria, VA, USA
Department of Otolaryngology, University of Minnesota,
Otopathology Laboratory, Minneapolis, MN, USA
M. M. Paparella
American Academy of Otolaryngology and Head & Neck Surgery,
Alexandria, VA, USA
Department of Otolaryngology, University of Minnesota,
Otopathology Laboratory, Minneapolis, MN, USA
denly develop lling completely the middle ear. In the same
way, a wide perforation of the pars tensa of the tympanic
membrane (TM) can arise as a sudden complication in the
course of some infectious disease (measles as an example) or
as a consequence of a temporal bone trauma [5].
Years ago, an International Study Group was organized to
discuss topics related to otitis media. According to the conclusions of this committee, the following classication was
proposed [6].
Suppurative Otitis Media
– Acute (AOM)
– Chronic otitis media without cholesteatoma (NCCOM)
– Chronic otitis media with cholesteatoma (CCOM)
Nonsuppurative Otitis Media
– Serous (SOM)
– Secretory (MOM)
The same committee dened chronic otitis media as an
inammatory condition always associated with a perforation
of the tympanic membrane (TM) and otorrhea. This denition is quite traditional and has been echoed in many publications around the world [5–10].
Chronologically, acute otitis media is dened as a short
duration inammatory process with a gap between its beginning and resolution no longer than three weeks. This gap is
extended to three months when subacute otitis media is considered and the term chronic is reserved only for those cases
when, even after three months, the resolution does not ensue.
We will adopt this classication (although we recognize
that it is incomplete and subject to well-founded criticism) as
a starting point for future discussions. The authors themselves identify its obvious limitations, remembering that this
is just another “working” classication widely publicized
and, therefore, simple and accessible. It fullls purely didactic objectives as we seek new operational hypotheses in relation to the pathogenesis of OM.In this sense, several works
have demonstrated that the mechanisms involved in the
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
M. V. Goycoolea et al. (eds.), Textbook of Otitis Media, https://doi.org/10.1007/978-3-031-40949-3_37
337
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S. S. da Costa and M. M. Paparella
installation and perpetuation of the ME inammatory processes are much more complex [2, 11–13].
Despite all its limitations, we will employ this working
classication to build up a prototype model of pathogenesis.
In this process, we will try to frame all the subgroups (AOM,
SOM, MOM, NCOM, and CCOM) in a logical march from
normality to chronicity. The problem is that this model,
despite being attractive and easy to understand, collapses
when confronted with a series of key questions that are
extremely relevant and still not completely claried. To
exemplify, in the next paragraphs, we will review, point by
point, the traditional concepts just exposed and their pathogenic basis, later opposing them to a second hypothesis born
from the work developed by the group from Minneapolis: the
so-called continuum theory [13].
Acute Otitis Media andOtits Media
withEusion
Acute otitis media (AOM) is a sudden, suppurative infectious process marked by the presence of infected middle ear
uid and inammation of the mucosa lining the middle ear
cleft (MEC). Mechanisms involved in its development
include tubal dysfunction (secondary to physiological immaturity, obstruction, or edema resulting from upper airway
infections and/or allergy) and aspiration of infected secretions from the rhino pharynx [1, 2].
Eustachian tube (ET) dysfunction, when prolonged, can
cause negative pressure in the MEC with the consequent
transudation of liquid from the intravascular compartment to
the interstitial compartment and from there to the lumen of
the MEC.This establishes the so-called serous otitis media
or otitis media with effusion (OME) which may be dened as
the presence of middle ear uid without signs of acute
infection.
Chronic Otitis Media withandWithout
Cholesteatoma
The trademark® of chronic otitis media has always been the
presence of a tympanic perforation (which until then, who
knows how it was produced!) [5, 7–10]. In NCCOM, this
perforation can be subclassied as central or marginal. What
differentiates the rst from the second is the persistence
(central) or not (marginal) of an eardrum remnant around the
360° of the perforation. This brous ring would theoretically
prevent skin from the external auditory canal to migrate
through the perforation gaining access to the middle ear. On
the other hand, in marginal perforations (where there is a
partial or complete absence of this brous margin), the perforation itself can work as a gateway to the middle ear
(Fig.37.1).
When not encountering any resistance, the keratinized
stratied squamous epithelium from the EAC, fullling its
renewal cycle, can penetrate the MEC.There, it develops a
typical cycle to this type of epithelium when in an ectopic
location: it encysts and begins to produce keratin. In other
words, it gives rise to the so-called secondary cholesteatoma,
secondary to a NCCOM with a marginal perforation.
Important to stress that aural cholesteatoma is dened as the
presence of exfoliated keratin in any pneumatized area of the
temporal bone (Fig.37.2).
The next question is as obvious as it is pertinent. If there
is a secondary cholesteatoma, is there a primary cholesteatoma and, if so, how does it develop? The answer to this
question is yes, but its development does not require the
presence of a TM perforation since they arise from progressive TM retractions. In this regard, the region of the pars accida of the TM, of dimer composition, would be the most
prone to suffer a progressive retraction. The evolution of this
retraction follows through the stages of simple retraction (the
bottom diameter is smaller than the external opening), TM
Fig. 37.1 Central X marginal
perforations
37 Pathogenesis ofChronic Otitis Media andtheContinuum: TheBasics, Further andBeyond
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339
retraction pocket (the bottom diameter is greater than the
external opening making it prone to losing its self-cleaning
properties), and cholesteatoma (when accumulation of keratin nally ensues) (Fig. 37.3). The primary cholesteatoma
has two main gateways: the TM pars accida (attic cholesteatoma) and the TM posterior–superior quadrant (tensa cholesteatoma). Both may extend to other areas of the temporal
bone following preexistent pathways created by the unique
embryological development of the ME.
Potential Pitfalls oftheSo-Called Working
Classication
All those who are dedicated to the study and care of patients
with otitis media will agree that this model, despite being
attractive and easy to understand, collapses when confronted
with a series of key questions that are extremely relevant and
still not completely claried. In other words, with a few
exceptions, we present a classication composed of welldened (pseudo) subgroups but dissociated from each other
and with many “missing links” along the way. For example:
• What is the difference between serous and secretory
(mucoid) otitis—which, incidentally, are denitions inap-
propriately used as synonyms or both under the umbrella
name of otitis media with effusion?
• What is the connection between the eminently physical
process of transudation and the complex inammation/
infection typical of suppurative and secretory (mucoid)
otitis media?
• What is the origin of the wide tympanic perforations char-
acteristic of COM (traditionally referred to as a conse-
quence of an acute necrotizing otitis media (a very unusual
condition) or induced by a temporal bone trauma that did
not spontaneously heal?
• What is the reason for the frequent association between
uid and gross pathological changes within the ME?
• Why are we increasingly exploring ME lled with granu-
lation tissue, cholesterol granuloma, and/or ossicular
destruction whose tympanic membranes are intact and
with an appearance close to normal?
• Why do studies demonstrate similar histopathological
proles between temporal bones with chronic otitis media
and intact and perforated eardrums?
• What is the relationship between compartmentalized
hypo-aeration of ME and associated pathological
ndings?
• Where did the concept of silent chronic otitis media come
from?
• In short, there is a number of waiting to be answered
questions waiting to be addressed and answered in order
to bring a better and more realistic understanding in the
pathogenesis of otitis media.
This is particularly true when human and animal temporal
Fig. 37.2 Cholesteatoma following a marginal perforation
Fig. 37.3 Cholesteatoma following progressive tympanic membrane retractions
bones with OM are studied through the powerful lenses of
340
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S. S. da Costa and M. M. Paparella
Fig. 37.4 Otitis media continuum
last-generation microscopes by the most talented otopathologists. These studies have shown that the histopathologic
boundaries between one form and another are tenuous if not
intersected suggesting that we are not dealing with specic
and isolated diseases but with one single condition which
may evolve through progressive stages. This progression
may not be linear, being inuenced by cofactors generally
linked to the aggressor, the subject, and facilitating or moderating circumstances. Aware of this possibility, in 1970
Paparella and colleagues suggested the hypothesis of the
continuum to explain the pathogenesis of OM.According to
these authors, the condition seems to exist along a continued
series of events in which, after a “triggering off” insult, with
early forms progressing to more chronic stages of the disease
(serous or purulent OM to seromucoid, mucoid, and, eventually, chronic) (Fig.37.4).
They also suggested that structural changes in the epithelial
and subepithelial spaces of the ME would be responsible for
this dynamic behavior. In their rst animal model, they
obstructed the ET of monkeys to develop experimental
OM. After this pioneering experiment, the hypothesis of the
“continuum,” or that all subgroups of OM (serous, purulent,
mucoid, and chronic) represent different phases of the same
evolving process, has been tested and conrmed by many elegant and well-designed studies. Independently of the animal
model used, they have shown that the histopathologic and bio-
chemical proles of these subgroups are progressive and, at
one time or another, overlapped. To exemplify, in the next paragraphs, we will review, point by point, the traditional concepts
just presented, and their pathogenic rationale developed by the
group from Minneapolis: the so-called continuum theory.
Otitis Media andtheContinuum Further
We will dedicate the next paragraphs to detailing how we
understand the paths taken by the disease from its earliest
stages to the most advanced forms. It is very important to
point out that the natural history of this journey can be
aborted midway by native defense barriers or by timely and
efcient medical intervention.
An initial trigger, in the reversible phase of this whole
process, would be functional or mechanical tubal dysfunction (persistent or temporary). Since the ET was unable to
balance atmospheric and intratympanic pressures (even with
the aid of voluntary maneuvers), middle ear aeration would
depend exclusively on the establishment of a pressure gradient between the nasopharyngeal and tympanic extremities of
the ET.This gradient would have to be big enough to displace air toward the middle ear. Physiologically, it would be
obtained through the constant absorption of gas in the middle
ear, which from a closed but ventilated system would be
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