Etiology of the Retraction Pocket in the Posterosuperior Quadrant of the Eardrum Avinash
Bhide, MS
\s=b\ The tympanic membrane meets the posterosuperior bony canal wall at a wide angle and thus makes the posterosuperior quadrant of the eardrum the most vulnerable part against the thrust effect of the air column in the external auditory canal compared with the rest of the pars tensa.
The air column thrust effect becomes active when there is a decrease in the middle ear pressure because of Eustachian tube obstruction. The medial displacement of the eardrum exposes the posterosuperior quadrant of the eardrum to the venturi effect in the isthmus tympanicus posticus and the region below. The retraction pocket is the end result.
ventilated during the normal conditions. Additional obstructing factors cause further impairment of function and reduce the middle ear pressure over the tympanic mem¬ brane." A prolonged decrease in mid¬ dle ear pressure leads to a chain of events resulting in a retraction pock¬
ear
et.
The retraction pockets occur in the PSQ and the pars flaccida of the eardrum. Why the PSQ is highly prone for retraction has not been properly understood until this time. This article will try to explain the principal factors involved in the consequent production of the retraction pocket in the PSQ of the eardrum.
Fig 1.—Two connections—isthmus tympanicus posticus and isthmus tympanicus anticus in tympanic diaphragm between mesotympanum and epitympanum (from Proctor2).
(Arch Otolaryngol 103:707-711, 1977)
pocket Theterosuperior quadrant (PSQ) retraction
in the pos¬ of
the pars tensa of the tympanic membrane poses a problem for man¬ agement because of the poor under¬ standing of its etiopathology. The problem persists even after successful
tympanomastoidectomies are per¬ formed using the intact canal wall technique, especially in those cases having transantral wide atticotomies.
Once established, a well-formed re¬ traction pocket progresses to the formation of a cholesteatoma and causes the destruction and disruption of middle ear structures and the mastoid air cell system. Holmquist and Renwall' have precisely summa¬ rized their observations regarding Eustachian tube dysfunction in some patients: "Eustachian tube function is primarily poor in some ears but it is just good enough to keep the middle Accepted
for publication April 13, 1977. From the "Ashwini," Vijayanagar Colony, Maharashtra State, India.
Reprint requests to "Ashwini," Vijayanagar Colony, 2108, Sadashiv Peth, PUNE-411 030,
Fig 1.—Two connections—isthmus tympanicus posticus and isthmus tympanicus anticus in tympanic diaphragm between mesotympanum and epitympanum (from Proctor2).
Maharashtra State, India (Dr Bhide).
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
changes and the stages of the retrac¬ tion of the tympanic membrane; and (5) application of principles of physics to explain the succession of events leading to retraction pocket.
BASIS FOR HYPOTHESIS
on
The the
hypothesis presented is based understanding of the following:
(1) the anatomical features of the middle ear cleft; (2) the PSQ of the eardrum and its relationship with the adjacent posterosuperior bony canal wall; (3) middle ear cleft aerodynam¬ ics; (4) clinical observations of the
Anatomical Features of the Middle Ear Cleft
The air-containing portion of the middle ear cleft for descriptive pur¬ poses is classified into the following:
eardrum movements with pressure
(1) the tubotympanic portion that contains the pro tympanum, the hypo¬ tympanum, and the mesotympanum, and (2) the epitympanoantral portion that consists of the epitympanum, the mastoid antrum, and air cells. This division is caused by the tympanic diaphragm that is made up of the body of the incus, the head of the malleus, and the lateral and medial mucosal folds (Fig 1). The gaps in the tympanic diaphragm are named the isthmus tympanicus posticus (ITP) and the isthmus tympanicus anticus (ITA). The isthmus tympan¬ icus posticus is the narrowest passage in the tympanic diaphragm and the whole of the middle ear cleft. The volume of the epitympanoantral por¬ tion is much more than the tubotym¬ panic portion (Fig 2). This difference in volume is one of the factors respon¬ sible for air movement toward the epitympanum across the ITP and the ITA. Further discussion will be focused on the ITP, the portion of the tympanic cavity just below that, and the adjacent posterosuperior portion of the tympanic membrane. PSQ of the Eardrum and
Relationship With the Adjacent Posterosuperior Bony Canal Wall
Its
Fig 2.—Marked portion.
difference in volume of
tubotympanic portion
and that of atticoantral
This brane
portion of the tympanic mem¬ margin is made up of the
Suprapyramidal (facial)
Section AB
Recess Air Column
Canal Wall A
Thrust
Tympanic Membrane
Tympanum External
Auditory Canal Air Col
Thrust
Tympanic Membrane
Infrapyramidal Recess
Canal Wall
Fig 3.—A, Angle between posterosuperior canal wall and that between inferior wall with tympanic membrane are shown for comparison. Pressure on both sides of eardrum is equal. B, Junction between posterosuperior canal wall and its relation with facial recess and sinus tympanum.
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
Middle Ear
,' 'Superior
.\\Malleus Section
T2—¡AX
'Floor of the
>/
VÇanal Wall/'
^2^"R"
/
/
'
Ri> R2 Section AB
^ 2
Radius of the Spherical Shell = Tension on the Membrane Shell Fig 4.—A, Section AB through posterosuperior quadrant of eardrum and anteroinferior quadrant passing through umbo. B, Segments (1) posterosuperior quadrant, (2) anteroR
=
superior quadrant of tympanic membrane in AB section. These segments membrane shells of sphericals of different radii.
act like
Aerodynamics
The Eustachian tube is normally closed (Fig 5). It opens when one swallows or yawns. Once the air enters into the tympanic cavity, it spreads over the cavity toward the ITP and ITA. The air, drawn toward the ITP and ITA, passes through them to the larger epitympanoantral portion of the middle ear cleft. The air in the epitympanoantral portion gets partially absorbed. This absorption, in addition to the greater volume of the epitympanoantral space compared with the tubotympanic por¬ tion creates a pressure gradient. This gradient helps the passage of air across the ITP to the smallest mastoid air cell. Clinical Observations of the Eardrum Movements
Eardrum movements with pressure and the stages of retraction of the tympanic membrane were observed clinically. Pneumatic ear speculum examination shows maxi¬ mum movements in PSQ. In the case of the patulous Eustachian tube, movements of the PSQ are evident with respiration. In cases of acute Eustachian tube obstruction, retrac¬ tion of the PSQ is prominent.
changes
Application of Principles of Physics Fig 5.—Medial wall of middle ear cleft removed to show air flow (arrows) from Eustachian tube orifice to antrum. Air reaches attic by passing through anterior isthmus located between tensor tympani tendon and long crus of incus. Air also passes lateral to long crus of incus and medial incudal fold and through posterior tympanic isthmus to enter mastoid antrum (from Proctor2). PSQ indicates posterosuperior quadrant. annulus tympanicus and the posterior malleal fold; anteriorly it is made up of the handle of the malleus (Fig 3). The annulus tympanicus ends at the beginning of the notch of Rivinus. The histological structure of this part of the eardrum is similar to the rest of the pars tensa. The bony posterosuperior canal wall slopes and merges with the eardrum very gradually, forming a wide angle or sometimes no well-defined angle at all. This particular structural pecu¬ liarity of the PSQ makes it more vul¬ nerable to air column thrust in the external auditory canal as compared with the rest of the tympanic mem¬ brane. The different quadrants of the tympanic membrane act like seg-
ments of membrane shells. The PSQ a longer radius of curvature
has
compared with the other quadrants. It is, therefore, a structurally weak quadrant that is more vulnerable to the stresses caused by the change of pressure over the membrane. (For the same thickness of a membrane shell,
the tensile
or
compressive
stresses
shell with a produced longer radius of curvature. The radius of curvature near the acute angle [a2] of contact is small, whereas it is long near the obtuse angle [ ] of contact [Fig 4]. The membrane stresses origi¬ nating as a result of external pressure are more near the obtuse angle of contact and so also the strain are more
produced.1)
for
a
The venturi effect and Bernoulli theorem were applied to explain the succession of events leading to retrac¬ tion pocket (Fig 6). The flow of fluid through a constricted passage is asso¬ ciated with a drop of pressure and an increase in the velocity. The drop in the pressure is known as the venturi effect, which is used in the construc¬ tion of venturimeters for the mea¬ surement of the quantity of fluid
flowing through pipes.
Mechanism of Retraction in the Normal Eardrum
Eustachian tube function when im¬
paired because of its blockage fails to equalize middle ear pressure. The pressure in the tympanum decreases as compared with that in the external auditory canal. The decrease in the tympanic pressure leads to a thrust effect on the outer surface of the tympanic membrane causing medial
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
Relationship Between
Venturi Effect
the PSQ and ITP and
Infra-ITP
Region
Antrum "
Tympanic Diaphragm Level
Incus Air
Pathway fra-ITP
Region =
Pressure
on
PSQ
the Wall
Fig 6.—A, Schematic diagram showing venturi effect. B, Marked portion of posterosuperior quadrant (PSQ) exposed to venturi effect produced at isthmus tympanicus posticus (ITP) and infra-ITP region.
is
Retracted Eardrum in Various Positions
Suprapyramidal (facial) Recess
Air Column Thrust
Retracted Eardrum Various Positions
Air Column Thrust
External
Tympanum
Auditory Canal Tympanic Membrane
Infrapyramidal Recess
Canal Wall Disturbed pressure equilibrium over eardrum. Posterosuperior quadrant (PSQ) of eardrum is more Fig 7.—A, subjected to air thrust in external auditory canal than other portion of eardrum. B, Retraction of PSQ and adhesion of that part with long process of incus making that part more vulnerable to venturi effect.
displacement, ie, retraction (Fig 7). In chronic Eustachian tube dysfunc¬ tion, the thrust effect will be persis¬ tent on the structurally vulnerable portion of the eardrum, ie, on the PSQ of the eardrum. This portion of the
eardrum overlies the facial recess and the sinus tympanum just below the ITP. Retraction of the PSQ narrows or
obstructs the region of the tympanum just below the ITP (Fig 6,B) which in turn accentuates the venturi effect deep to the PSQ. This produces a
further drag effect on the retracted PSQ of the eardrum. A persistent retraction and simultaneous mucosal changes cause adhesions between the eardrum and the long process of the
incus (Fig 7,B). Long-standing retrac¬ tion causes thinning and the loss of elasticity of the eardrum which is mainly because of atrophy of the lamina propria. The consequent result will be a plastic stage of the PSQ of the eardrum, ie, there is a loss of elasticity of the membrane with some permanent determination. Flaccid
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
Canal Wall
Canal Wall
Newly Reconstructed
Posterior
Tympanotorny
Newly Reconstructed Tympanic Membrane
Tympanic Membrane
jSJ~ Interposed
i¿¿
Interposed Bone
Bone
Stapes
Fig 8.—A and B, Persistence of weak zone in posterosuperior region because of more wide weak angle between canal wall and posterosuperior quadrant to air column thrust.
PSQ causes permanence of the retrac¬ pocket. The retraction pocket progresses to the posterior epitym¬ tion
panum, the aditus, and the antrum. This progress is due to the thrust effect acting maximally in the depth
of the retraction pocket against di¬ minished pressure on the medial aspect of the retracted portion of the eardrum. The medial pressure fall is due to reduced total air volume (air cushion) in the closed epitympanomastoid cavity. A cholesteatoma formation takes place because of squamous epithelium in the epitympanum and the antrum. It helps expansion of the sac thus causing erosion of the bone. METHOD Mechanism of Retraction in Ears That Have Been Operated On Most of the intact canal wall techniques (Fig 8) and the combined approach techniques with modifications preserve the eroded posterosuperior canal wall. The following few factors are thought to be responsible for the retraction pockets. 1. The canal wall eardrum angle is more obtuse because of lateral placement of the newly reconstructed eardrum as shown in Fig 8. 2. Annulus tympanicus and sulcus tym¬ panicus being absent in the PSQ, the weak¬ ness is aggravated. 3. The venturi effect is lessened because of the wide posterior tympanotomy, but it is still present. The site of maximum venturi effect corresponds to the weakened area of the eardrum. The resulting retracted portion of the eardrum causes obstruction to the air passage across the posterior tympanotomy and is subjected to a drag effect.
4. Adhesions form between the new eardrum and the raw medial wall of the tympanic cavity thus making the retrac¬ tion irreversible.
COMMENT
The onset of the retraction pocket is initiated by Eustachian tube obstruc¬ tion in patients with poor Eustachian tube function. It causes a more effec¬ tive air column thrust effect on the structurally weak PSQ and activates the suction force produced by the venturi effect at and below the ITP on the PSQ of the tympanic membrane. The aforementioned theory of re¬ traction pocket is capable of offering a
angle
and exposure of
1. Holmquist J, Renwall U: Eustachian tube function in secretory otitis media. Arch Otolar¬ yngol 99:59-61, 1974. 2. Proctor B: The development of the middle ear spaces and their surgical significance. J Laryngol Otol 78:631-648, 1964. 3. Timoshenko SP, Woinoswky Kreiger S: Theory of Plates and Shells. New York, McGrawHill Book Co Ine, 1959, pp 554-555.
reasonably satisfactory explanation
for some of the commonly observed clinical findings. One finding, attic retraction with cholesteatoma, is caused by total blockage of the epitympanum at the level of the tympanic diaphragm. This blockage is mainly caused by mucosal edema and adhesions at the isthmuses. Another finding, retraction of the PSQ without retraction of the attic part of the eardrum, is due to the patency of the ITA. The ITP may or may not be blocked due to retraction of the pars tensa of the eardrum. With the retraction pocket of the attic portion and the PSQ, the retrac¬ tion of the PSQ that develops at the beginning obstructs the ITP. Asso¬ ciated mucosal swelling at the ITA and ITP could be a contributory factor for the development of attic retrac¬ tion. Another clinical finding is absence of the retraction pocket after a
stapedectomy procedure in a patient having prolonged Eustachian tube dysfunction. The posterosuperior ca-
nal wall is removed in part for the exposure of the ossicles and the oval window niche. The PSQ is made weak and a retraction pocket should develop but that seldom happens, probably because the reduced canal wall eardrum angle strengthens the PSQ
region.
There
are
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
possible applications of
Bhide, MS
\s=b\ The tympanic membrane meets the posterosuperior bony canal wall at a wide angle and thus makes the posterosuperior quadrant of the eardrum the most vulnerable part against the thrust effect of the air column in the external auditory canal compared with the rest of the pars tensa.
The air column thrust effect becomes active when there is a decrease in the middle ear pressure because of Eustachian tube obstruction. The medial displacement of the eardrum exposes the posterosuperior quadrant of the eardrum to the venturi effect in the isthmus tympanicus posticus and the region below. The retraction pocket is the end result.
ventilated during the normal conditions. Additional obstructing factors cause further impairment of function and reduce the middle ear pressure over the tympanic mem¬ brane." A prolonged decrease in mid¬ dle ear pressure leads to a chain of events resulting in a retraction pock¬
ear
et.
The retraction pockets occur in the PSQ and the pars flaccida of the eardrum. Why the PSQ is highly prone for retraction has not been properly understood until this time. This article will try to explain the principal factors involved in the consequent production of the retraction pocket in the PSQ of the eardrum.
Fig 1.—Two connections—isthmus tympanicus posticus and isthmus tympanicus anticus in tympanic diaphragm between mesotympanum and epitympanum (from Proctor2).
(Arch Otolaryngol 103:707-711, 1977)
pocket Theterosuperior quadrant (PSQ) retraction
in the pos¬ of
the pars tensa of the tympanic membrane poses a problem for man¬ agement because of the poor under¬ standing of its etiopathology. The problem persists even after successful
tympanomastoidectomies are per¬ formed using the intact canal wall technique, especially in those cases having transantral wide atticotomies.
Once established, a well-formed re¬ traction pocket progresses to the formation of a cholesteatoma and causes the destruction and disruption of middle ear structures and the mastoid air cell system. Holmquist and Renwall' have precisely summa¬ rized their observations regarding Eustachian tube dysfunction in some patients: "Eustachian tube function is primarily poor in some ears but it is just good enough to keep the middle Accepted
for publication April 13, 1977. From the "Ashwini," Vijayanagar Colony, Maharashtra State, India.
Reprint requests to "Ashwini," Vijayanagar Colony, 2108, Sadashiv Peth, PUNE-411 030,
Fig 1.—Two connections—isthmus tympanicus posticus and isthmus tympanicus anticus in tympanic diaphragm between mesotympanum and epitympanum (from Proctor2).
Maharashtra State, India (Dr Bhide).
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
changes and the stages of the retrac¬ tion of the tympanic membrane; and (5) application of principles of physics to explain the succession of events leading to retraction pocket.
BASIS FOR HYPOTHESIS
on
The the
hypothesis presented is based understanding of the following:
(1) the anatomical features of the middle ear cleft; (2) the PSQ of the eardrum and its relationship with the adjacent posterosuperior bony canal wall; (3) middle ear cleft aerodynam¬ ics; (4) clinical observations of the
Anatomical Features of the Middle Ear Cleft
The air-containing portion of the middle ear cleft for descriptive pur¬ poses is classified into the following:
eardrum movements with pressure
(1) the tubotympanic portion that contains the pro tympanum, the hypo¬ tympanum, and the mesotympanum, and (2) the epitympanoantral portion that consists of the epitympanum, the mastoid antrum, and air cells. This division is caused by the tympanic diaphragm that is made up of the body of the incus, the head of the malleus, and the lateral and medial mucosal folds (Fig 1). The gaps in the tympanic diaphragm are named the isthmus tympanicus posticus (ITP) and the isthmus tympanicus anticus (ITA). The isthmus tympan¬ icus posticus is the narrowest passage in the tympanic diaphragm and the whole of the middle ear cleft. The volume of the epitympanoantral por¬ tion is much more than the tubotym¬ panic portion (Fig 2). This difference in volume is one of the factors respon¬ sible for air movement toward the epitympanum across the ITP and the ITA. Further discussion will be focused on the ITP, the portion of the tympanic cavity just below that, and the adjacent posterosuperior portion of the tympanic membrane. PSQ of the Eardrum and
Relationship With the Adjacent Posterosuperior Bony Canal Wall
Its
Fig 2.—Marked portion.
difference in volume of
tubotympanic portion
and that of atticoantral
This brane
portion of the tympanic mem¬ margin is made up of the
Suprapyramidal (facial)
Section AB
Recess Air Column
Canal Wall A
Thrust
Tympanic Membrane
Tympanum External
Auditory Canal Air Col
Thrust
Tympanic Membrane
Infrapyramidal Recess
Canal Wall
Fig 3.—A, Angle between posterosuperior canal wall and that between inferior wall with tympanic membrane are shown for comparison. Pressure on both sides of eardrum is equal. B, Junction between posterosuperior canal wall and its relation with facial recess and sinus tympanum.
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
Middle Ear
,' 'Superior
.\\Malleus Section
T2—¡AX
'Floor of the
>/
VÇanal Wall/'
^2^"R"
/
/
'
Ri> R2 Section AB
^ 2
Radius of the Spherical Shell = Tension on the Membrane Shell Fig 4.—A, Section AB through posterosuperior quadrant of eardrum and anteroinferior quadrant passing through umbo. B, Segments (1) posterosuperior quadrant, (2) anteroR
=
superior quadrant of tympanic membrane in AB section. These segments membrane shells of sphericals of different radii.
act like
Aerodynamics
The Eustachian tube is normally closed (Fig 5). It opens when one swallows or yawns. Once the air enters into the tympanic cavity, it spreads over the cavity toward the ITP and ITA. The air, drawn toward the ITP and ITA, passes through them to the larger epitympanoantral portion of the middle ear cleft. The air in the epitympanoantral portion gets partially absorbed. This absorption, in addition to the greater volume of the epitympanoantral space compared with the tubotympanic por¬ tion creates a pressure gradient. This gradient helps the passage of air across the ITP to the smallest mastoid air cell. Clinical Observations of the Eardrum Movements
Eardrum movements with pressure and the stages of retraction of the tympanic membrane were observed clinically. Pneumatic ear speculum examination shows maxi¬ mum movements in PSQ. In the case of the patulous Eustachian tube, movements of the PSQ are evident with respiration. In cases of acute Eustachian tube obstruction, retrac¬ tion of the PSQ is prominent.
changes
Application of Principles of Physics Fig 5.—Medial wall of middle ear cleft removed to show air flow (arrows) from Eustachian tube orifice to antrum. Air reaches attic by passing through anterior isthmus located between tensor tympani tendon and long crus of incus. Air also passes lateral to long crus of incus and medial incudal fold and through posterior tympanic isthmus to enter mastoid antrum (from Proctor2). PSQ indicates posterosuperior quadrant. annulus tympanicus and the posterior malleal fold; anteriorly it is made up of the handle of the malleus (Fig 3). The annulus tympanicus ends at the beginning of the notch of Rivinus. The histological structure of this part of the eardrum is similar to the rest of the pars tensa. The bony posterosuperior canal wall slopes and merges with the eardrum very gradually, forming a wide angle or sometimes no well-defined angle at all. This particular structural pecu¬ liarity of the PSQ makes it more vul¬ nerable to air column thrust in the external auditory canal as compared with the rest of the tympanic mem¬ brane. The different quadrants of the tympanic membrane act like seg-
ments of membrane shells. The PSQ a longer radius of curvature
has
compared with the other quadrants. It is, therefore, a structurally weak quadrant that is more vulnerable to the stresses caused by the change of pressure over the membrane. (For the same thickness of a membrane shell,
the tensile
or
compressive
stresses
shell with a produced longer radius of curvature. The radius of curvature near the acute angle [a2] of contact is small, whereas it is long near the obtuse angle [ ] of contact [Fig 4]. The membrane stresses origi¬ nating as a result of external pressure are more near the obtuse angle of contact and so also the strain are more
produced.1)
for
a
The venturi effect and Bernoulli theorem were applied to explain the succession of events leading to retrac¬ tion pocket (Fig 6). The flow of fluid through a constricted passage is asso¬ ciated with a drop of pressure and an increase in the velocity. The drop in the pressure is known as the venturi effect, which is used in the construc¬ tion of venturimeters for the mea¬ surement of the quantity of fluid
flowing through pipes.
Mechanism of Retraction in the Normal Eardrum
Eustachian tube function when im¬
paired because of its blockage fails to equalize middle ear pressure. The pressure in the tympanum decreases as compared with that in the external auditory canal. The decrease in the tympanic pressure leads to a thrust effect on the outer surface of the tympanic membrane causing medial
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
Relationship Between
Venturi Effect
the PSQ and ITP and
Infra-ITP
Region
Antrum "
Tympanic Diaphragm Level
Incus Air
Pathway fra-ITP
Region =
Pressure
on
PSQ
the Wall
Fig 6.—A, Schematic diagram showing venturi effect. B, Marked portion of posterosuperior quadrant (PSQ) exposed to venturi effect produced at isthmus tympanicus posticus (ITP) and infra-ITP region.
is
Retracted Eardrum in Various Positions
Suprapyramidal (facial) Recess
Air Column Thrust
Retracted Eardrum Various Positions
Air Column Thrust
External
Tympanum
Auditory Canal Tympanic Membrane
Infrapyramidal Recess
Canal Wall Disturbed pressure equilibrium over eardrum. Posterosuperior quadrant (PSQ) of eardrum is more Fig 7.—A, subjected to air thrust in external auditory canal than other portion of eardrum. B, Retraction of PSQ and adhesion of that part with long process of incus making that part more vulnerable to venturi effect.
displacement, ie, retraction (Fig 7). In chronic Eustachian tube dysfunc¬ tion, the thrust effect will be persis¬ tent on the structurally vulnerable portion of the eardrum, ie, on the PSQ of the eardrum. This portion of the
eardrum overlies the facial recess and the sinus tympanum just below the ITP. Retraction of the PSQ narrows or
obstructs the region of the tympanum just below the ITP (Fig 6,B) which in turn accentuates the venturi effect deep to the PSQ. This produces a
further drag effect on the retracted PSQ of the eardrum. A persistent retraction and simultaneous mucosal changes cause adhesions between the eardrum and the long process of the
incus (Fig 7,B). Long-standing retrac¬ tion causes thinning and the loss of elasticity of the eardrum which is mainly because of atrophy of the lamina propria. The consequent result will be a plastic stage of the PSQ of the eardrum, ie, there is a loss of elasticity of the membrane with some permanent determination. Flaccid
Downloaded From: http://archotol.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/26/2015
Canal Wall
Canal Wall
Newly Reconstructed
Posterior
Tympanotorny
Newly Reconstructed Tympanic Membrane
Tympanic Membrane
jSJ~ Interposed
i¿¿
Interposed Bone
Bone
Stapes
Fig 8.—A and B, Persistence of weak zone in posterosuperior region because of more wide weak angle between canal wall and posterosuperior quadrant to air column thrust.
PSQ causes permanence of the retrac¬ pocket. The retraction pocket progresses to the posterior epitym¬ tion
panum, the aditus, and the antrum. This progress is due to the thrust effect acting maximally in the depth
of the retraction pocket against di¬ minished pressure on the medial aspect of the retracted portion of the eardrum. The medial pressure fall is due to reduced total air volume (air cushion) in the closed epitympanomastoid cavity. A cholesteatoma formation takes place because of squamous epithelium in the epitympanum and the antrum. It helps expansion of the sac thus causing erosion of the bone. METHOD Mechanism of Retraction in Ears That Have Been Operated On Most of the intact canal wall techniques (Fig 8) and the combined approach techniques with modifications preserve the eroded posterosuperior canal wall. The following few factors are thought to be responsible for the retraction pockets. 1. The canal wall eardrum angle is more obtuse because of lateral placement of the newly reconstructed eardrum as shown in Fig 8. 2. Annulus tympanicus and sulcus tym¬ panicus being absent in the PSQ, the weak¬ ness is aggravated. 3. The venturi effect is lessened because of the wide posterior tympanotomy, but it is still present. The site of maximum venturi effect corresponds to the weakened area of the eardrum. The resulting retracted portion of the eardrum causes obstruction to the air passage across the posterior tympanotomy and is subjected to a drag effect.
4. Adhesions form between the new eardrum and the raw medial wall of the tympanic cavity thus making the retrac¬ tion irreversible.
COMMENT
The onset of the retraction pocket is initiated by Eustachian tube obstruc¬ tion in patients with poor Eustachian tube function. It causes a more effec¬ tive air column thrust effect on the structurally weak PSQ and activates the suction force produced by the venturi effect at and below the ITP on the PSQ of the tympanic membrane. The aforementioned theory of re¬ traction pocket is capable of offering a
angle
and exposure of
1. Holmquist J, Renwall U: Eustachian tube function in secretory otitis media. Arch Otolar¬ yngol 99:59-61, 1974. 2. Proctor B: The development of the middle ear spaces and their surgical significance. J Laryngol Otol 78:631-648, 1964. 3. Timoshenko SP, Woinoswky Kreiger S: Theory of Plates and Shells. New York, McGrawHill Book Co Ine, 1959, pp 554-555.
reasonably satisfactory explanation
for some of the commonly observed clinical findings. One finding, attic retraction with cholesteatoma, is caused by total blockage of the epitympanum at the level of the tympanic diaphragm. This blockage is mainly caused by mucosal edema and adhesions at the isthmuses. Another finding, retraction of the PSQ without retraction of the attic part of the eardrum, is due to the patency of the ITA. The ITP may or may not be blocked due to retraction of the pars tensa of the eardrum. With the retraction pocket of the attic portion and the PSQ, the retrac¬ tion of the PSQ that develops at the beginning obstructs the ITP. Asso¬ ciated mucosal swelling at the ITA and ITP could be a contributory factor for the development of attic retrac¬ tion. Another clinical finding is absence of the retraction pocket after a
stapedectomy procedure in a patient having prolonged Eustachian tube dysfunction. The posterosuperior ca-
nal wall is removed in part for the exposure of the ossicles and the oval window niche. The PSQ is made weak and a retraction pocket should develop but that seldom happens, probably because the reduced canal wall eardrum angle strengthens the PSQ
region.
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possible applications of
