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7/24/2019 Middle Ear, Ossicles, Eustachian Tube (Done)
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Middle ear cleft consists of:1. tympanic cavity: (Irregular, air filled space within the temporal bone between the
tympanic membrane laterally & the osseous labyrinth medially)a. Auditory ossiclesb. Tendons of ossicles which attach them to the
muscles of the middle earc. Tympanic segment of the Facial Nerve
2. Eustachian tube
3. Mastoid air cell system
Lies at the medial end of the external auditory canal. Forms the majority of lateral wall of the tympanic cavity Shape: Oval; Broader above than below Orientation:
o forming an angle 55 with the flooro placed obliquely forming acute angle with
meatus anteriorly and obtuse one posteriorly Diameters:
o Its longest diameter (posterosuperior to
anteroinferior)= 9-10mm, Perpendicular tothis the shortest diameter= 8-9mm
o So tympanic membrane is 9*9 mm in sizeo 0.1mm in thicknesso Surface area 85 mm3; Effective vibrating
area: 55 mm3
Color:o Pearly white-gray, shiny, The light reflex is
due to the concave position of the membraneo Red Tympanic membrane may be seen in:
OM, crying child, sneezing, nasal blowingo Blue tympanic membrane may be seen in:
Glue ear, Hemotympanum, High jugularbulb, Choleasterol granuloma
Tympanic membrane layers:1. Outer- stratified squamous Epithelial layer -ectoderm2. Middle- Fibrous layer: -mesoderm
Lamina propria which is made of:a- Outer Radiating fibrous layerb- Inner Circular fibrous layer
3. Inner- Mucosa layer.-endodermEmbryology of Tympanic membrane Layers:
1. 1ST Branchial Pouch/ tubotympanic recess (Endoderm)forms: eustachian tube middle ear space inner mucosal layer of the tympanic membrane
2. Mesodermof the 1st& 2ndbrachial arch: Arise from the neural crest mesenchyme Forms middle fibrous layer of the tympanic membrane
3. 1ST Pharyngeal Groove/meatal plug (Ectoderm) forms: EAC and the outer epidermal layer of the tympanic membrane
It is adult sized at birth but due in part to incomplete ossification of the external auditory canal, lies in a nearlyhorizontal position, impairing its visualization on neonatal ear examination.
The final vertical orientation of the eardrum is achieved with completion of canal ossification by approximately ageof 2 years
Umbo is the center point which divides the tympanic membrane Its most prominent land mark is the handle of malleus (directed in anterio-superior direction)Tympanic Membrane Relation to the Temporal Bone:
Most of the circumference is thickened to form fibrocartilaginous ring = tympanic annulus
Which sits in Tympanic sulcus (groove in the temporal bone)
sulcus does not extend into the Notch of Rivinus
Middle ear anatomy
T m anic membrane
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Notch of Rivinus(tympanic incisura):
Superior part of tympanic ring (roof of the canal) is made of the squamous part of thetemporal bone
where the pars flaccida is attached to squamous part
deficient in the annulus ringAnterior & Posterior malleolar folds:
From the superior limits of the sulcus, the annulus ring becomes fibrous band whichruns centrally to handle of malleous So it is a continuation of the annular ring & setsthe border between pars flaccida & tensa
Paras flacida (shrapnel's membrane):
Part of Tympanic membrane above the malleolar folds Does not have annular ring
Triangular in shape, small in size
Lamina propria has radially oriented fibers in the outer layers; circular, parabolic and transverse fibers in deep layersParas Tensa:
Forms the rest of the tympanic membrane (below the malleolar folds)
Lamina propria is less marked and orientation of fibers is random
Concave toward the ear canal except between:1. the lateral attachment of the annulus2. center of the membrane where the tip of the malleus handle is attached at the umbo
Note:
Induostapedial joint, stapedius muscle, chora tympani could be seen through normal Tympanic membrane
The Tympanic membrane is lined with cuboidal & respiratory epithelium
Paras flacida Paras Tensa
Above the malleolar folds Below the malleolar foldsDoes not have annular ring has annular ring
Triangular in shape Concave toward the ear canal
Non vibratory vibratory part
Made of 3 layers but the lamia propriafibers are less organized Made of 3 layers
More innervated Less innervated
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Embryology: Middle ear cavity: 1st
+ 2nd
pharyngeal pouch
Compartments of the tympanic cavity
1. epitympanum (attic): above the level of malleolar folds2. mesotympanum3. Hypotympanum: area below the tympanic sulcusDimensions of the Tympanic cavity:
Anterio-posterior (width): 15 mm
Vertical(height): 15 mm
Transverse (depth):
Epitympanum: 6mmMesotympanum: 2mmHypotympanum: 4mm
Note: the narrowest area is the mesotympanum due to the medialorientation of handleof the malleus Epitympanum is separated from the mesotympanum +
hypotympanum by series of mucosalfolds Mesotympanum + hypotympanum are continuouswith each otherBorders of the epitympanum/attic:
Superiorly Tegmen
Laterally squamosa (scutum)
Medially lateralsemicircular canal and VII nerve
Posteriorly Aditus
Inferiorly fossa incudis
Anteriorly zygomatic arch
Protympanum: anterior to Tympanic membraneretrotympanum: - posterior to Tympanic membrane,
- contains facial recess + sinus stympani
Hyrtl's triangle/fissure
Embryological connection between the subarachnoid space& hypotympanum
Located anteriorinferiorto the roundwindow near the inferiorganglion of the (IX) glossopharyngeal nerve
Closes as the infant grows
If persistsit will afford a rout for direct extension of the middle ear infection into the subarachnoid space
Tympanic Cavity
Content of the epitympanum:
1- head & neck of the malleus
2- body & short process of the incus
3- lateral semicircular canal
4- tympanic part of the fallopian canal of facial nerve
5- aditus
Content of the Mesotympanum:
1. handle of the malleus
2. long process of the incus
3. stapes4. round, oval windows
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1- Lateral wall (Membranous wall):
Divisions:
Superiorly:bonylateral wall of the epitympanum= outer attic wall/scutum = Squamous boneo It is wedge shape in section (shield-like)o With sharp inferior portiono Thin & easily eroded by cholesteatoma leaving a telltale signon the CT scan
Centrally:Tympanic membrane
Inferiorly: bonylateral wall of the Hypotympanum = tympanic bone
Holes:a- Petrotympanic fissure (Glaserian fissure):is a slit about 2 mm long which opens anteriorly just above the attachment of
the tympanic membrane. It receives the anterior malleolar ligament and transmits the anterior tympanic branch of the maxillary
artery to the tympanic cavity.
b- iter chord anterius (canal of Huguier) (ant canaliculus): see nerve course of chorda tympani
c- iter chord posterius:see nerve course ofchorda tympani
Chorda Tympani:
see nerve course of chorda tympani
Walls of tympanic cavity
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2- Roof of the tympanic cavity (tegmen tympani):
Roof of epitympanum = tegmen tympani
Thinbony plate that separates the middle ear from the middlecranial fossa (temporal lobe)
It is made up of petrous and squamous portions of temporal bone
It is continuous with tegmen antri
It contains the petrosquamous fissure The fissure contains superior tympanic canaliculus through which the superior petrosal nervepasses Veins from the tympanic cavityrunning to thesuperior petrosal sinuses through thissuture line Petrosquamous suture line does not close untiladult life so can provide a routeof infection into the
extraduralspace in children
3-
Floor of tympanic cavity (jugular wall) It is made of tympanicplate+ part of the petrous bone (??) may consists of compact or pneumonized bone Separates the Hypotympanumfrom the Jugular fossa Occasionally, the floor is deficient& the jugular bulb lies in themesotympanumis covered onlyby fibrous
tissue & mucous membrane (May be at risk during myringotomy) At the junction of the floor & medialwall there is inferior tympanic canaliculusthrough which tympanicbranch
of glossopharyngeal nerveenters the tympanic cavity IX, X, XIare nerve that emerge through jugular foramen, so they are found beneath the floor of the middle ear
4- Anterior wall (Carotid wall) Anterior wall narrowsas the medial & lateralwalls converge Elements:
o The petrousportion of the bonyInternalCarotid artery canalo Eustachian tubeo Tensor tympani muscle & its semi-canal
1. Lower 1/3 of the Anterior wall:o Consists of thinplate of bone covering the carotidartery as it enters the skull before it turns anteriorlyo This plate is perforated by (through the opening of the carotid canal Glasserian fissure)
- superior& inferiorcaroticotympanic nerves carring sympathetic fibers to tympanic plexus- tympanicbranch of the internal carotid artery
2. Middle 1/3 of the Anterior wall:
o Comprises the tympanic orifice of the Eustachian tube, which isoval &is 5x2 mm in size.o Just aboveit is a canal that contains the tensor tympani musclethat subsequently runs along the medial
wall of the tympanic cavity, enclosed in athinbony sheath3. Upper 1/3 of the anterior wall:o Usuallypneumonized, may house the epitympanic sinuso Epitympanic sinus: is a small niche anterior to the ossicular heads, which can hideresidual cholesteatoma in
canal wall up surgery
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5- Medial wall (labyrinthine wall):
- The medial wall separates the middle from the inner ear, Composed of:A- promontory: see page 475 netter The most prominentportion in themedial wall Occupying mostof the centralportion of the medial wall of the middle ear It covers partof the basal coilof the cochlea. it inclines gently forward to merge with the anterior wall, but is more steeply sloped posteriorly Groovedbecause of branches of the tympanic plexuswhich lie under its mucous membrane Sometimes the groove that contains the tympanic branch of the glossopharyngeal nerve may be covered
with bone which forms a small canal
B-
two fossa:The oval vestibular window (fenestra vestibule):
Lie above& behindthe promontory, in thebottomof a depression which varies in depthdependingon the position of the Facial nervesuperiorly and the promontory inferiorly
Connect the tympanic cavity with the vestibule The opening is closed in life by the footplate
stapesand its surrounding annular ligament. Kidney shape The long axis of the fenestra vestibuli is horizontal The size of the oval window varies according to the
size of footplate but on an average it is 3.25mmlong & 1.75 mmwide
The round window (fenestra cochlea):Round window niche:
Vestibulethat leads to the round window. Belowand a little behindthe oval windowniche
from which it is separated by a posterior extension of the
promontory called the subiculum.
The entranceto this vestibule (the round windowniche) is usually triangularin shape, withanterior, posteriosuperior and posterioinferiorwalls, The later 2 meet Posteriorly and lead to the
sinus tympaniBounderies of the vestibule: The medial lip (subiculum of the promontory):
posterior extension of the promontory which
separates it from the oval window. occasionally, another ridge of bone (the
ponticulus) runs above the subiculum & runs tothe pyramid on the post wall of the cavity
The lateral lip is created by the posteriormarginof the promontory.
The round window membrane:
The round window is closed in life by roundwindow membrane(secondary tympanic
membrane). Out of sight, obscured by the overhangingedge
of the promontoryforming the nicheand themucosal folds within it
almostoval in shape, lies inright angle to theplane of thestapes footplate, its dimensions=1.9*2.3 mm
it curves toward thescala tympani of the basalcoil of cochlea= concave when viewed frommiddle ear
appears to be divided bytransverse thickening into anterior & posterior portions The ampullaof the posteriorsemicircularcanal is the closestvestibular structure to this
membrane.
The nerve supplying the ampullaof the posteriorsemicirular canal (singular nerve) lies close to it.So The secondary tympanic membrane forms a landmarkfor the position of the singularnerve.
This is useful during surgical procedures like singularneurectomyfor treatment of intractablevertigo.
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Oval window Round window
Plane Sagittal Transverse
Orientation Facing inferior post lateral
Relation to the promontory Posterior superior Poaterio-inferior
Relation to perilymphatic duct Sacla vestibule Sacla tympani
C- Two prominences in the medial wall:1. the lateral semicircularcanal: The most superiorin the medial wall Majorfeature of the posteriorportion of the
epitympanum.
Land Mark:It is used as a land mark of theepitympanum from which you start reading the CT
temporal The dome of the lateralsemicircular canal above,
posterior & extends a little lateralto the facial canal In well pneumatizedmastoid bone the labyrinthine
over the superiorcanal can be very prominent,
running in Rightangle to the lateral semicircular canal& joining it anteriorlyat a swelling which houses theampullaeof the twocanals
In frontand a little belowthis, abovethecochleariformis process, may be a slight swelling
corresponding to the geniculateganglionwith thebony canal of the greater superficial petrosal nerverunning for short distance anteriorly
2. The facial canal (fallopian canal): Lies abovethe promontory and oval window in an anteroposteriordirection Behindthe fenestra vestibuli, the facial nerve turns inferiorlyto begin its descent in the
posteriorwall of the tympani cavity, also superior petrosal artery travels in it Region abovethe level of the facial nerve canal forms the medial wallof the epitympanum/
attic.Medial wall outline:
A-promontoryB- widows: oval + roundC- Canals: lateral semicircular canal + tympanic/horizontal segment
of the facial nerve
D- cochleariformis process +/- sup semicircular canal, ampulla of thesuperior & lateral canal geniculate gangilion, greater petrosal
The sequence of medial prominence from superior to inferior:
prominence of the lateral semicircular canal prominence of the facial canal promontoryThe most anterior structure in the medial wall is:
cochleariformis processThe oval window & round window niche relation to the
promontory:
ovalwindow lies posterior superiorto the promontory roundwindow lies posterior inferiorto the promontory6- Posterior wall
Widerabove than below1. aditus ad antrum:
o largeirregular openingo in the upperpart of the medial wallo leads back from the posteriorepitympanum into the mastoid antrumo lateralsemicircular canal form the floorof the antrum
o Mastoid antrum lies abovethe middle ear cavity & about 2 mm deep2. Fossa incudis:
o Small depression below the adituso Houses the shortprocess of the incus and its suspensory ligamento Forms a land mark for:
1- lateralsemicircular canal which lies medialto it2- facialnerve which lies inferiomedialto it
In cortical mastoidectomy the triangularrelationship between the facialcanal, lateral semicircular
canal& short process of the incusis very helpful
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3. Opening of the chorda tympani nerve
4. Pyramid:
o Small hollowconical projectionso Lays below the fossa incudis & medial to the opening of the chorda tympani
nerveo Its apex pointing anteriorlyo Houses the stapidusmuscleand tendon, which inserts into the posterior
aspect of the head of stapeso The canal withinthe pyramid curves downward & backwards to join the
descendingportion of the facial nerve canal
o The vertical part of the facial nerve divides the posterior wall of the tympaniccavity into 2 recesses:a- facial recess (suprapyramidal recess) (lateral to facial nerve):
Aeratedextension posteriorsuperiorportion of the middle ear
cavity Boundaries:
o Posterio-Medial: Facial nerve + pyramido Anterio-Lateral: tympanic annulus + chorda tympanio Superior: fossa incudis (near the short process of incus)
It is shallowerlowerdownwhere the facial canal forms onlyslightprominenceover the posterior wall
chordatympaninerveRuns obliquely through the wall between
the facial nerve and the annulus. Chorda tympani always runmedial to the tympanic membrane.
Drilling in this area between the facial nerve and annulus in theangleformed by the chorda tympani nerve leads into the middleear cavity with ability to keep the tympanic membrane intact.
This surgical approach to the middle ear cavity is known as facialrecessapproach.
This approach can be used for posteriortympanotomy site for hidden choleasteatoma
b- sinus tympani(medial to facial nerve) The largestsinus, Inferiomedial, Infrapyramidal deep to facialnerve & promontary
posterior extension of the mesotympanum extension of the mesotympanuum can be very extensive making it the most inaccessible part of
the middle ear cavity & mastoid, choleasteatoma in this region is very difficult to eradicate The extension into the mastoid may reach 9mmwhen measured from the pyramidal process The medial wall of the sinus is continuous with the posterior part of the medial wall of the tympanic
cavity in which it is related to the oval window, round window, promontory, subiculum
Sinus tympanilies between the ponticulus(superiorly) and subiculum (inferior) Subiculum: ridge of bone originating from the promontorythat separates the round window niche
(which is inferiorto it) from the sinus tympani. Ponticulus: bony ridge originating from the promontory, connecting the promontory to the pyramid
which separates the oval window (which is superiorto it) from the sinus tympani. So subiculum & ponticulus forms 3 depressionsin the posteriorpart of the medialwall Round window lies inferior to subiculum & inferio-posterior to the promontory Superiorinferior: oval windowponticulussinus tympanisubiculumround window The sinus tympani is the worst way for access because:
1- medial to facial nerve2- below the pyramid3- posterior to intact stapes
Retro-facial approach is impossibleas the posteriorsemicircular canal obstructs the view Facial recess is superficialto the sinus tympani and separatedfrom it by:
1- verticalpart of facial canal2- pyramidal process
Facial recessSuperior lateral
Above pyramide
2n genuof facial nerve
Pyramid
Sinus tympani
Inferior medial
Below the pyramid
Descendingpart of the facial Nerve
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The middle ear cavity is entered during combined approach tympanoplasty& cochlear implantvia facial recess
Summary of Boundaries of the tympanic cavity:
o Roof: tegmeno Floor: jugular wall and styloid prominenceo Posteriorly: mastoid, stapedius, pyramidal prominenceo Anteriorly: carotid wall, eustachian tube, canalfor tensor
tympanio Medially: labyrinthine wallo Laterally: tympanic membrane, scutum (latero-superior).
Connections of the middle ear:o Nasopharynx via: Eustachian tubeo Mastoid antrum via: aditus ad antrumo Vestibule via: oval windowo Cochlea via: the round window
Summary of bone components of the ear:
o Anterior + floor + posterior wall of the external auditory canal =tympanic plate
o Superior wall of external auditory canal = squamous parto Tegmen tympani = squamous + petrous parto Hypotympanum = tympanic plateo Lateral wall = squamous + tympanic plateo Anterior wall = petrous portion of internal carotid canal + ET + Tensor tympani muscle semi canal
Facial recess Sinus tympani
Relation to facial nerve Lateral medial
Relation to the pyramid Superior inferior
Posterior extension location Superior lateral Inferio-medial
Borders Post medial: facial nerveAnt-lateral: chordytympaniSuperior: fossa incudis (near the short process of incus)
Betweensubiculum & ponticulus
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Trautmanns triangle
Triangle between:
Anteriorly: ottic capsule (posteriorsemi-circular canal)
Posteriorly: sigmoid sinus
Superiorly: dura containg superficial petrosal vein
Or it is the triangle between:
Solid angle
Sigmoidal sinus
Sinuodural angle
This triangle is important in mastoidectomyPart of the bonyplate of the posteriorcranialfossa
Clinical application:
1. Potentialweakspot through which infections of temporal
bone may traverse and affect cerebellum.
2. Extra dural abscessinvolving the posterior cranial fossa is
also possible when thin bone (post semi-circular canal) in
this triangle gets breachedin infections /cholesteatoma
involving mastoid cavity.
3. Land mark for entry into the posterior cranial fossa: Since
bone in this area is rather thin it can be drilled out to enter
into the posterior cranial fossa. This can be used as anapproach to posterior cranial fossa lesions.
Citelli's angle (sinodural angle) 8:
It is located between the duraof the sigmoid sinus
and the middle fossa duraplate.
Importantlandmark in the mastoidectomy
Others consider the superiorside of Trautmann's
triangle to be Citelli's angle.
Solid angle:
It is the place where the three semicirculat canals meet.
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1- Ossicles: Malleus, Incus, Stapes (See ossicle page)2- muscles: tensor tympani muscle, Stapedius muscle3- Nerves: chorda tympani, Tympanic plexusStapedius muscle:
o Origin: the wall of the conical cavity within thepyramid +downward curved continuation of thecanal in front of the descending part of the facial
nerve
o A slender tendonemerges from the apex of thepyramido Insertion:posterior neck of the stapeso Innervation: small branch of the facial nerveo Action: pulls stapes posterior to the direction of the movement of the ossicular chain, attenuating low frequency
sounds
Tensor tympani muscle:o Long slender muscle (2 cm long)o Origin: the walls of the bonycanal lying above the Eustachian tube, Greaterwing of the sphenoid, Cartilaginous
portion of the Eustachian tubeo From its origin, the muscle passes backwards into the tympanic cavity where it lies on the medialwall, a little below
the level of the 1stgenu of facial nerve
o The bony coverage of the canal is often deficient in its tympanic segment where the muscle is replaced by slendertendon
o Insertion: The tendonenters cochlearformis process, where it is held down by transversetendon as it turnsthrough a right angle (90)to pass laterallyand inserts into the medial aspect of upper part of the handle of theMalleus
o Innervation: trigeminal Nervemadibular branchmedial pterygoid Nerveo Action: display the handle of the malleus medially to decrease the compliance of tympanic membrane & stiffening
the ossicular chain attenuating the lowfrequencyhighintensity sounds
o Its contraction could be audible causing tinnituso Note: Cochearformisprocessis located in the anteriorwall of the tympanic cavityo Note: it is an Important land mark for the 1stgenuof the facial nerveo The tensor tympani muscles fibers are continuous with fibers of tensor veli muscleso the tensor tympani muscle is above the Eustachian tube
THE MUCOSA OF THE TYMPANIC CAVITYo The middle ear mucosa is essentially mucus-secreting respiratory mucosa bearing cilia on its surface.o mucociliary epithelium varies in normal middle ears, being more widespread in the young.o Three distinct mucocilary pathways can be identified - epitympanic, promontorial and hypotympanic,
the latter being the largest. Each of these pathways coalesces at the tympanic orifice of the Eustachiantube.
o The mucous membrane lines the bony walls of the tympanic cavity, and it extends to cover the ossicles
and their supporting ligaments.o The mucosal folds also cover the tendons of the two middle ear muscles and carry the blood supply to
and from the contents of the tympanic cavity.
o These folds separate the middle ear space into compartments. As a result, the only route for ventilationof the epitympanic space from the mesotympanum is via two small openings between the variousmucosal folds -the anterior and posterior isthmus tympani. Likewise, Prussak's space is found betweenthe pars flaccida and the neck of the malleus, bounded by the lateral malleolar fold.
Prussak's space:Boundaries
o Anteriorly + Superiorly+ Posteriorly: by the lateral malleolar foldo Medially:neckof malleuso Laterally:pars flaccida (Shrapnell'smembrane) (epitympanum area)o Inferiorly:lateralprocess of malleus
Clinical application: can play an important role in the retention of keratin and subsequent development of cholesteatoma Koerner's line/false bottom:
o Persistent petrosquamous suture line which separates The superfecial squamous air cells from the deep petrousalair cells by the Korner septum
o This line separates the mastoid air cells into medial & lateral air cellso The mastoid antrum lies deep to ito The antrum cannot be located unless this septum is removed during mastoid exploration
The contents of the tympanic cavity
Tensor tympani muscle & Stapedius muscle decreasethe dampen down the movement of the ossicles
Tensor tympani muscle: Medial pterygoid muscle
Stapedius muscle: Facial nerve
http://en.wikipedia.org/wiki/Neck_of_malleushttp://en.wikipedia.org/wiki/Neck_of_malleushttp://en.wikipedia.org/wiki/Neck_of_malleushttp://en.wikipedia.org/wiki/Pars_flaccidahttp://en.wikipedia.org/w/index.php?title=Lateral_process_of_malleus&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Lateral_process_of_malleus&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Lateral_process_of_malleus&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Lateral_process_of_malleus&action=edit&redlink=1http://en.wikipedia.org/wiki/Pars_flaccidahttp://en.wikipedia.org/wiki/Neck_of_malleus7/24/2019 Middle Ear, Ossicles, Eustachian Tube (Done)
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Temporal bone pneumonizationOnly 9 % of the population has pneumonized petrousportion of temporal bone (baily q p250)
The mastoid is completely pneumatized at the age of 2years
Located mainly in the atticarea (most of them are related to the neck of the malleus)- May limit infection1) Anterior malleal fold & Posterior malleal fold:
Both connected to:1. Neckof the malleus2. superiormargin of the tympanic sulcus:
A. anterior malleal fold: anteriosuperiormarginB. posteriormalleal fold: posteriosuperiormargin
Pouch of von Trltsch:lies between the malleal fold & segment of tympanic membraneanterio/post the handle of
malleus:a- Anterior pouch of von Trltsch:
Lies between the anteriormalleal fold & the portion of the tympanic membrane anteriorto the handleof the
malleus.b- Posteriorpouch of von Trltsch:
Lies between the posteriormalleal fold and the portion of the tympanic membrane posterior to the handle of the
malleus
2) Lateral medialmallear fold:neckto neck in an archform and to Shrapnell'smembrane.
Malleus ligaments:
Stabilization direction Name of the ligament Site of insertion over the malleus Insertion on the bone
Superiorly Superior malleal ligament Head of the malleus Tegmen tympani
Anteriorly Anterior malleal ligament Neck of the malleus near the anterior process Sphenoid bone viapetrotympanic fissure
Medial Tensor tympani muscle tendon Upper part of manibrium cochleariformis
Lateral Lateral malleal ligament Neck of the malleus Tympanic notch
Incus:superior incudal ligament:body to tegmen
posterior incudal ligament: short process to the floor of incudal fossa
stapes:stapedial tendon: apex of the pyramidal process to the posterioraspect of the stapedial neckannular ligament: footplate to the marginof vestibular fenestrum
Mucosal folds of middle ear
Note:Anterior & Posterior folds are the borders between:
1. epitympanum & mesotypanum: this is why they are attached to the superiormargin of the tympanic sulcus
2. paras flaccida & paras tensa: because they are attached to thesuperiormargin of the tympanic sulcusto
which paras tensaattaches.
3. 1st arch & 2nd arch derivatives: They are attached to the malleur neck which is the 1st arch derivative while
the manubrium is 2nd arch derivative
Ligaments
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How does the composition of gas in the middle ear differ from that of room air?
Lower oxygen level and higher carbon dioxide and nitrogen levels.
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Forms semi-rigid bony chain for conducting sound
Embryology:
1. First Branchial Arch (Meckels cartilage):
Malleus( head and neck ,anterior malleal ligament, short process)
incus (body and short process)
2. Second Branchial Arch (Reicherts cartilage):
manubrium of the malleus
long process and lenticular process of the incus
stapes suprastructures* (except vestibular part of footplate)3. process of folius (mesenchyme bone):
anterior process of the malleus(so develops from the membranous bone)
4. otic capsule: the vestibularpart of the foot plate ; the annular ligament of the
footplate
footplate supra-structure: head+ neck+ both cura + tympanic part of the foot plate
note: stapes footplate has dual origin (2ndarch + otic capsule)
Development of the incus & malleus:
4thwk: the process of ossicles formation starts
6thwk:malleus & incus forms a singlemass
8thwk: they are separated by the malleoinsudal Joint
16th
wk: adultsize
ossification starts:
1stpart to ossify:beginsat thelong process of the incus
the following ossicularcomponents nevercompletelyossifies:
o manubrium of the malleus
o vestibular portion of the foot plate
at 25THwk: the ossiclesareadult size (endochondrial ossification is complete)
Development of The muscles attached to the ossicles:
Malleus The most lateralossicle
Largestof the 3 ossicles (9mm)
Made of:
1- Head: It has a saddle shapedfacet over the posteriomedialsurface to articulate
with bodyof the incus by synovial joint
2- Neck of malleus:
Connects the handle with the malleus
Belowthe neck of malleus, the bone broadens to form anterior & lateral processes and the hadle of malleus3- Lateral /short process:
Create the malleolarprominence(Prominent landmarkon Tympanic membrane)
Attach to Pars Tensaof Tympanic membrane
4- Handle of Malleus (manubrium):
Runs downward, medially and slightly backward
Between the mucosal & fibrous layers of Tympanic membrane
1- Lower end: very closely attached to the membrane
2- Upper end: there is a fine web of mucosa separating the membrane from the
handle before it becomes adherent again at the lateral process.
Tendon of tensor tympani muscle (V3) is inserted into the small projection over
theupper part of the handle of malleus Chorda tympani Nervecrosses theupper part medialsurface of the malleus
handle, above the insertion of the tensor tympani muscle but below the neck of
malleus
So amuptationof the headby cutting through the neck will leave the chorda tympani nerve & tensor
tympani muscle intact
Tensor tempani muscle Stapedius muscle
Attachment site Upperpart of the malleus handle Postsurface of the stapes neck
Arch 1starch 2ndarch
Nerve supply V3 Facial nerve
Ossicles
7/24/2019 Middle Ear, Ossicles, Eustachian Tube (Done)
15/17
Incus:Made of:
1- Body:
Has cartilage covered facet corresponding that on the head of Malleus
Suspended by superior incudal ligament that is attached to the tegmen tympani
2- Short process:
Project posteriorlyfrom the body to lie in fossa incudiusto which it is attached
by short suspensory ligament (posteriorligament)
Land mark for: lateral semicircular canal (medially), facial nerve (inferiomedially)
3- Long process (crus): descends into the mesotympanumBehind andmedial to handle of the Malleus (parallel)
4- Lenticular process: (is sometimes called the 4th
ossicles because of its incomplete fusion with the long process)
located at the tipof the long process, Mediallydirected
Articulates with the head of thestapes via diarthrodialjoints (ball and socket articulation)
Stapes: shortest bone of the body1) Head
points laterally, Has small cartilage covered depression (fovea) for articulation with lenticular process of Incus
Stapedius muscle (VII) is inserted into the posterior part of the neck and the upper portion of the posterior Crus
2) Crura (anterior and posterior):
Anterior Crus is thinner, shorter & less curved than posterior Crus (great variation in the shape of the 2 crura)
Hollowed on its concave surface (for optimal strength and lightness)
3) Footplate (base):
convexsuperiorsurface; Almost straightinferiorsurface; Curved anterior + posterior ends
Average dimensions= 2.99 mm long + 1.41 mm wide
Kidney shape (reniform)
attaches to the bony margins of the oval window by the annular ligament forming a joint (syndesmosis)
The long axis is almost horizontalwith the posteriorend being slightly lowerthan the anterior end
Footplate movement:
Mostmovement at the footplateoccurs at anterio-superiorportion
The safest site to create an opening in the footplate is the central portion
The minimal distance between the central portion and: Utricle: 1.2mm, Saccule:1.4mm
Ossicular joints types: Malleal-insudal joint: diarthrodial joint
Incudo-stapedial joint: diarthrodial joint
Stapedial-labyrinthin joint: synodesmotic joint
Diarthrodial:
freely mobile joint
surrounded by capsule
as knee joint
slightly mobile joint
Ossicle part Orientation
Head of malleus Medioposterior
Manubrium Inferior-medial-posterior
Short process of incus Posterior
Long process of incus Inferior
Lentiform process of incus Medial
Head of stapes Lateral
Allparts of the ossicles are situated in the Mesotympanicexcept:
Body & short process of the malleus
Head & neck of the incus
7/24/2019 Middle Ear, Ossicles, Eustachian Tube (Done)
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Embryology:
Originatates from medial part of the tubotympanic
recess (ventral part of the 1st
pharyngeal pouch)
The length of the ET doubles from birth to adulthood
Dynamic channel that connects the middle ear with the
Nasopharynx
Directed:
Runs downward from middle ear at 45degree and is
turned forward and medially from the bony part in
the petrousportion of temporal boneAdult length: 36 mm longConsists of 2 unequal cones connected at their apices:
Bony portion (intratemporal):
Upper posteriolateral 1/3 (12 mm)
This portion is inactive and is always open
Arise from the anterior wall of the tympanic cavity 4 mm
above the most inferior part of the floor of the cavity
The diameter of the Ostium is 3-5 mm
Widest at its oval tympanic end & tapes down to its junction with cartilaginous part of the tube
In cross section the tube is triangular or rectangular with the horizontal diameter being greater
It passes through the squamous and petrous portions of the temporal bone A thin plate of the bone forms the roof of ET, separating the tube from tensor tympani muscle
The carotid canal lies medially and can impinge on the bony ET
The Isthmus:
The Narrowest part of the tube (diameter =
7/24/2019 Middle Ear, Ossicles, Eustachian Tube (Done)
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Muscles attached to the Eustachian tube:
Muscle arising from the posterior lower marginof the tubal orifice:
Salpingopharyngeal muscle( see pharyngeal wall: inner longitudinal muscle)supplied by pharyngeal plexus
Muscles arising from theundersurfaceof the Eustachian tube (para-tubal muscles):
Levatorpalati muscle: arise medially (withinthe pharynx)supplied by pharyngeal plexus
Tensorpalati muscle: arises laterally (outsidethe pharynx)seperates the tube from the otic ganglion, the
mandibular nerve, the chorda tympani nerve and the middle meningeal artery
Tensor tympani muscle
BothPara-Tubal muscles are partlyattached to the tube
Allmuscles helps in openingthe ET during the act of swallowing Tensorpalati muscle (predominate dilator, the medialbundle of tensor veli palatine forms the dilator tubae)
Note:
openingof the Eustachian tube is an active process that is done mainly by the tensor palate muscles
Closingof the Eustachian tube is a passive process
Nerve supply Blood supply
Bony part Inferior tympanic plexus of glossopharyngeal
nerve (IX)
Inferior tympanic branch of ascending pharyngeal artery
Cartilaginous part Nervous spinosum of Vc Middle menigeal artery
Ostium Pharyngeal branch of Pterygopalatine ganglion
Venous drainage: pharyngeal plexus
Lymphatic drainage: retropharyngeal LNsMucosal lining of the Eustachian tube:
The cartilaginous part of the tube is lined by respiratory mucosa containing goblet cells and mucous glands, with ciliated
epithelium on its floor (less towards ear): pseudostratifiedcolumnarciliated, but toward the tympanic orifice it is lined
by ciliatedcuboidalepithelium.
Lymphoid tissue within the tube:Tonsil of Gerlach
Functions:
Ventilation: equalization of the pressure between the nasopharynx & middle ear
Clearance: drainage of middle ear secretions
Protection: from nasopharynx sound and secretion
The eustachian tube features in infants
Length in infants is 1/2of the adult's length = 18 mm. more horizontal
Less angulated.
The bony portion is relatively longerand widerin diameter, the nasopharyngeal end of the cartilaginous portion
lies more inferiorly.
The adult length is reached at the age of 7years
Congenitalabsence of the Eustachiantubeis associated with 1starchsyndromeespecially treacherCollin
syndrome
It opens by the action of the tensor palati (innervated by the third division of the V nerve) acting synergistically with
the levator veli palatini (innervated by the vagus).
In children, the only muscle that works is the tensor palati because the levator palati is separated from the
eustachian tube cartilage by a considerable distance. Therefore, a cleft palate child with poor tensor palati functionis expected to have eustachian tube problems until the levator palati starts to function.
In a normal individual, a pressure difference of 200 to 300 mm H2O is needed to produce airflow.
It is easier to expel air from the middle ear than to get it into the middle ear (reason for more tubal problems when
descending in an airplane).
A pressure of30 mm Hg or lower for 15 minutes can produce a transudate in the middle ear. A pressure differential
of 90 mm Hg or greater may lock the Eustachian tube, preventing opening of the tube by the tensor palati muscle.
It is called the critical pressure difference.
If the pressure differential exceeds 100 mm Hg, the tympanic membrane may rupture.
A Valsalva maneuver generates about 20 to 40 mm Hg of pressure.
The tympanis ostium of the tube is at the anterior wall of the tympanic cavity about 4mm above the most inferior
part of the floor of the cavity. The diameter of the ostium is 3 to 5 mm. The size of the pharyngeal ostium variesfrom 3 to 10 mm in its vertical diameter and 2 to 5 mm in its horizontal diameter.
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