Anatomy and embryology of ear

1. SCOTT BROWN LEARNING 2020
ANATOMY AND EMBYOLOGY OF
THE EXTERNAL AND MIDDLE EAR
PRESENTER :Dr.NAGA NANDHINI MS PG
VOLUME – 2
CHAPTER – 46
PAGES – 525 to 543

2. EXTERNAL EAR
FUNCTIONS :
Early warning system by detecting & locating potentially threatening
environmental sounds
Major role in balance system, giving important information about sudden
changes in environment both external & self, to avoid falls and injury
CONSISTS OF
Auricle
External auditory canal

3. AURICLE (PINNA)
Function in collecting sound
Lateral surface has characteristic prominences & depressions which are
unique in every individuals even in identical twins
Curved rim is the HELIX ,has a small prominence DARWIN’s TUBERCLE at
its posterosuperior aspect
Anterior to and parallel with the helix is another prominence, the
ANTIHELIX
Superiorly this divides into two crura, between is the TRIANGULAR FOSSA
SCAPHOID FOSSA lies above the superior of two crura

4. In front of antihelix is the CONCHA , it is divided into two portions by descending
limb of anterior superior portion of helix known as CRUX OF HELIX , smaller superior
portion is the CYMBA CONCHAE – Direct lateral relation to suprameatal triangle of
temporal bone , Larger inferior portion is known as CAVUM CONCHAE.
Below the crux of helix and overlapping the external auditory meatus is the
TRAGUS is a blunt triangular prominence pointing posteriorly.
Opposite the tragus,at the inferior limit of antihelix is ANTITRAGUS , intertragic
notch separates tragus from antitragus .
LOBULE lies below the antitragus is soft being composed of fibrous and adipose
tissue.Medial (cranial) surface has elevations corresponding to depressions
eg:EMINENTIA CONCHAE
Body of auricle is formed by elastic fibrocartilage is
a continuous plate except for a narrow gap between
Tragus and crux of helix where it is replaced by dense
Fibrous band – Incisura terminalis the site for
ENDAURAL INCISION

5. TWO EXTRINSIC LIGAMENTS – Which connects cartilage of pinna to temporal
bone, ANTERIOR LIGAMENT – Runs from tragus and from a cartilaginous spine on
the anterior rim of the crux of helix to zygomatic arch, POSTERIOR LIGAMENT – Runs
from medial surface of concha to lateral surface of mastoid prominence
INTRINSIC LIGAMENTS – Connect various parts of cartilaginous auricle
between tragus and helix and another runs from antihelix to posteroinferior portion
of helix
EXTRINSIC MUSCLES – Auricularis anterior , posterior , superior all three
radiate out from auricle to insert into epicranial aponeurosis
INTRINSIC MUSCLES – 6 In number are small inconsistent and without useful
function
Skin of pinna is thin & closely attached to
perichondrium on lateral surface.
On medial surface there is a definite subdermal
adipose layer that allows dissection during
pinnaplasty surgery

6. BLOOD SUPPLY
ARTERIAL SUPPLY : Branches of external carotid artery
Posterior auricular – dominant artery supplies medial surface(except
lobule) ,concha ,middle & lower portion of helix and lower part of antihelix
Anterior auricular branch of superficial temporal artery supply upper
portion of helix , antihelix, triangular fossa, tragus and lobule
Superior auricular artery
VENOUS DRAINAGE :Auricular veins corresponds to arteries of auricle
Arteriovenous anastomosis are numerous in skin of auricle helps in regulation of
core temperature
Cartilage is covered by perichondrium from which
It derives its nutrients as cartilage itself is avascular.
stripping the perichondrium following injury leads to
cartilage necrosis with crumpled up BOXER’s EAR

7. NERVE SUPPLY
LYMPHATIC DRAINAGE
Posterior surface – mastoid tip.
Tragus & upper part of anterior surface
to preauricular nodes.
Rest of the auricle to upper deep
cervical nodes.

8. EXTERNAL AUDITORY CANAL
Extends from concha of auricle to tympanic membrane & it is 2.4 cm long.
Canal wall is cartilage in lateral 1/3( 8mm) & bone in medial 2/3(16mm).
In adults , the cartilaginous portion runs inwards, downwards, forwards & it is
straightened by moving auricle upwards & backwards. In neonates , there is no bony
meatus as tympanic bone is not developed and tympanic membrane is more
horizontal so that the auricle must be gently drawn downwards & backwards.
Two constrictions in canal one at junction of cartilaginous and bony portion and
the other is the isthmus, 5mm from tympanic membrane . Deep to the isthmus the
anteroinferior portion of wall dips to form wedge shaped ANTERIOR RECESS –
Difficult for access.
Two fissures, SANTORINI – in cartilaginous part &
FORAMEN OF HUSCHKE in anteroinferior part of bony
canal both permitting infections to and from parotid

9. Skin of ear canal is lined by keratinizing stratified squamous epithelium contains
fine vellus hairs & terminal hairs called tragi
Also contains clusters of ceruminous & sebaceous glands. CERUMINOUS GLANDS
–are modified apocrine sweat glands which produce watery white secretions turns
semisolid & sticky as it dries. SEBACEOUS GLANDS- Produce oily material(sebum)
WAX – Mixture of desquamated cells, cerumen, sebum. DRY WAX – Lacking
cerumen is yellowish or grey & brittle WET WAX – brownish & sticky.
ARTERIAL SUPPLY :
Auricular branches of superficial temporal artery – roof & anterior portion of canal
Deep auricular branches of maxillary artery – anterior meatal skin
Auricular branches of posterior auricular artery – posterior portion of canal
NERVE SUPPLY :
Trigeminal , facial, glossopharyngeal & vagus . Patient can cough during micro
suction of canal because of stimulation of ARNOLD’s NERVE – auricular branch of
vagus

10. MIDDLE EAR CLEFT
Consists of
Tympanic cavity
Eustachian tube
Mastoid air cell system
TYMPANIC MEMBRANE
Lies at medial end of meatus & forms lateral wall of tympanic cavity ,Oval in
shape , forming an angle of 55 degree with floor of meatus Most of circumference is
thickened to form fibrocartilaginous ring, TYMPANIC ANNULUS, which sits in a
groove in tympanic bone , TYMPANIC SULCUS. Sulcus doesn’t extend into the notch
of Rivinus at roof of canal which is formed by squamous part of temporal bone.
From the superior limits of sulcus the
annulus becomes a fibrous band which runs
centrally as anterior & posterior malleolar fold
to lateral process & handle of malleus.

11. PARS FLACCIDA – Small triangular region of tympanic membrane above the
malleolar folds within notch of Rivinus ,which doesn’t have annulus at its margin ,
PARS TENSA – Rest of tympanic membrane. Centre of membrane where the tip of
malleus handle is attached at UMBO.
LAYERS :
Outer epithelial layer – Skin of external meatus
Middle fibrous layer – Lamina propria
Inner mucosal layer – Lining of tympanic cavity
ARTERIAL SUPPLY Epidermal & mucosal branches of maxillary artery
NERVE SUPPPLY Branches of auriculotemporal nerve
Auricular branch of vagus
Tympanic branch of glossopharyngeal nerve

12. TYMPANIC CAVITY
COMPARTMENTS :
Epitympanum (Upper )
Mesotympanum (Middle)
Hypotympanum (Lower)
Retrotympanum
Protympanum
LATERAL WALL – Bony lateral wall of epitympanum superiorly , Tympanic membrane
centrally , Bony lateral wall of hypotympanum inferiorly .
Lateral epitympanic wall is wedge shaped in section & its
inferior portion – Outer attic wall or SCUTUM – Thin and easily eroded in
cholesteatoma

13. MEDIAL WALL
Separates tympanic cavity from internal ear .
PROMONTORY – Rounded elevation occupying much of central portion of
medial wall. Behind & above the promontory – OVAL WINDOW –Kidney shaped
opening covered by footplate of stapes.
ROUND WINDOW –Lies below & behind oval window from which it is
separated by posterior extension of promontory forming bony ridge- SUBICULUM .
PONTICULUS – Ridge of bone leaves the promontory above the subiculum & runs to
pyramid on posterior wall of cavity .
FACIAL NERVE CANAL (FALLOPIAN CANAL) – Runs above promontory &
oval window in anteroposterior direction .Facial canal is marked anteriorly marked by
PROCESSUS COCHLEARIFORMIS – Curved projection of bone , houses tendon of
tensor tympani muscle as it turns laterally to handle of malleus.

14. POSTERIOR WALL
ADITUS AD ANTRUM– leads back from posterior epitympanum to mastoid
antrum, FOSSA INCUDIS – Small depression below aditus , houses short process of
incus & suspensory ligament, PYRAMID – Conical projection below fossa incudis ,
houses stapedius muscle FACIAL RECESS – Groove lies between pyramid & facial
nerve& annulus of tympanic membrane, bounded medially by facial nerve &
laterally by chorda tympani nerve.
SINUS TYMPANI – Posterior extension of mesotympanum into
posterior wall & lies deep to facial nerve , pyramid, stapedius muscle , bounded
superiorly by ponticulus inferiorly by subiculum . Most inaccessible site in middle ear
when operating with microscope , cholesteatoma extended here from
mesotympanum is difficult to eradicate.

15. ROOF
TEGMEN TYMPANI – Thin bony plate separates middle ear from middle
cranial fossa. Petrosquamous suture line doesn’t close until adult life , route of
access of infection into extradural space. COG – Bony crest project from tegmen
tympani ,divides the posterior epitympanic space from small anterior epitympanic
space, where residual cholesteatoma may be left .
FLOOR
Separates hypotympanum from dome of jugular bulb. Occasionally, it is
deficient covered only by fibrous tissue ,should be kept in mid while raising inferior
portion tympanomeatal flap. At junction of floor & medial wall INFERIOR TYMPANIC
CANALICULUS allows Jacobson’s nerve into middle ear from its origin below the
base of skull.

16. ANTERIOR WALL
In lower third ,it consists of plate of bone covering carotid artery, perforated
by superior & inferior carticotympanic nerves carrying sympathetic fibres to
tympanic plexus. In middle third , it contains tympanic orifice of Eustachian tube ,
just above this is a canal containing Tensor tympani muscle. In upper third, usually
pneumatized & contain Supratubal recess
ARTERIAL SUPPLY
Branches of internal & external carotid artery
CONTENTS
Ossicles,
Two muscles,
Chorda tympani,
Tympanic plexus.

17. MALLEUS (HAMMER)
Largest of 3 ossicles
Comprises of head , neck , handle(manubrium) , lateral& anterior process.
Head lies in epitympanum suspeneded by superior ligament, has saddle
facet articulates with body of incus by synovial joint. Lateral process is prominent
landmark on tympanic membrane & receives anterior & posterior malleolar folds .
On the medial surface of handle , a small projection where tendon of tensor tympani
muscle inserts . Chorda tympani crosses upper part of malleus handle above the
insertion tendon of tensor tympani. Handle runs between mucosal & fibrous layer of
tympanic membrane ,in lower end it is very closely attached, fine web of mucosa
separating handle from TM in upper end, this can be opened surgically to create a
slit without perforating the membrane to allow prosthesis

18. INCUS (ANVIL)
Has body , Long & Short process. Body lies in epitympanum suspended by
superior incudal ligament. Short process lie in fossa incudes by the attachment of
short suspensory ligament. Long process descends into mesotympanum behind&
medial to malleus handle and its tip is Lenticular process called 4th Ossicle.
STAPES
Like stirrup. Consists of head, neck, anterior & posterior crura and footplate.
Head has cartilage covered depression for synovial articulation with lenticular
process of incus. Stapedius tendon inset into neck & posterior crus

19. MUSCLES :
STAPEDIUS – Arises from apex of pyramid and inserts into stapes , supplied
by facial nerve.
TENSOR TYMPANI – Arises from walls of bony canal lying above Eustachian
tube , part of muscle also arises from cartilaginous portion & greater wing of
sphenoid , runs backwards lie on medial wall of tympanic cavity & the tendon hooks
around processus cochleariformis, and insert into handle of malleus , supplied by
mandibular nerve.
MUCOSA Mucus
Mucus secreting respiratory mucosa bearing
cilia on its surface, 3 distinct mucociliary pathway -
Epitympanic ,Promontorial , Hypotympanic.
These folds separate middle ear into compartments ,
Prussak space between pars flaccida & neck of
malleus bounded by malleolar fold, Important role
in retention of cholesteatoma.

20. CHORDA TYMPANI NERVE
Branch of facial nerve enters posterior canaliculus at junction of lateral &
posterior wall, runs across medial surface of tympanic membrane between mucosal
& fibrous layers and passes medial to upper portion of handle of malleus ,leave by
anterior canaliculus.
TYMPANIC PLEXUS ON PROMONTORY
Formed by tympanic branch of glossopharyngeal nerve(Jacobson’s nerve)
and caroticotympanic nerves arise from sympathetic plexus around internal carotid
artery, Provide branches to mucous membrane lining tympanic cavity, Eustachian
tube, mastoid antrum & air cells.

21. EUSTACHIAN TUBE
Dynamic channel links middle ear with nasopharynx, In adult it is 36mm in
length. Consist of 2 unequal cones , lateral third (12mm) is bony arises from
anterior wall of tympanic cavity, joins medial cartilaginous(24mm) just after its
narrowest point, ISTHMUS . Cartilaginous end is bend to resemble like ‘J’ thereby
forming longer medial & shorter lateral cartilaginous lamina
Lined by respiratory epithelium containing goblet cells &
mucous glands. Apex of cartilage is attached to isthmus of bony portion, while the
wider medial end protrudes into nasopharynx , lying directly under the mucosa to
form TORUS TUBARIS. In nasopharynx, tube opens 1-1.25 cm behind & below the
posterior end of inferior turbinate . Behind the torus is Pharyngeal recess or fossa of
Rosenmuller.

22. MUSCLES ATTACHED TO EUSTACHIAN TUBE
TENSOR TYMPANI MUSCLE – Arises from scaphoid fossa of pterygoid plate,
lateral cartilaginous lamina ,converge to form tendon turns around pterygoid
hamulus & spread out within soft palate to meet fibres from other side in midline
raphe , supplied by Mandibular nerve.
SALPINGOPHARYNGEUS – Slender muscle attached to inferior part
cartilaginous tube, & blends with palatopharyngeus .
LEVATOR PALATI – Arises from lower surface of cartilaginous tube, petrous
bone, carotid sheath fascia, crosses to medial side & spreads into soft palate. Both
supplied by pharyngeal plexus.

23. MASTOID AIR CELL SYSTEM
MASTOID ANTRUM
Air filled sinus within petrous part of temporal bone. Communicates with
middle ear through aditus,& has mastoid air cells arising from its wall. Antrum is
well developed at birth & by adult life has volume of about 2 ml.
Roof form the floor of middle cranial fossa, medial wall relates to posterior
semicircular canal. Posterior belly of digastric muscle form groove in base of
mastoid bone, lies lateral to facial nerve & is a useful landmark. Outer wall is easily
palpable behind pinna.
MACEWEN’s TRIANGLE – Direct lateral relation to mastoid antrum , formed
by prolongation of line of zygomatic arch & tangent to this that passes through
posterior border of external auditory meatus.

24. Lining of mastoid – Flattened , non ciliated epithelium without goblet cells &
mucus glands. SCLEROTIC or ACELLULAR mastoid applies only when mastoid
antrum may be the only air filled space in mastoid process, seen in 20% adult
temporal bone & in chronic ear disease individuals.
PETROUS APEX is most medial aspect of temporal bone. Internal carotid
artery, internal auditory meatus, Trigeminal nerve running into Meckel’s cave with
abducent nerve. GRADENIGO’s SYNDROME- Infection of petrous apex causing
Lateral rectus palsy, Facial pain , Discharging ear.

25. INTERNAL AUDITORY MEATUS
Short canal 1cm ,lined by dura, passes into petrous bone in lateral direction
from cerebellopontine angle. Transmits Facial, Cochlear, Vestibular nerves & Internal
auditory artery & vein. Meatus covered by plate of bone for passage of nerves &
blood vessels to and from cranial cavity.
TRANSVERSE CREST( CRISTA FALCIFORMIS) – Separates meatus into
small upper & larger lower area. Above the crest & anteriorly is facial canal carrying
facial nerve, Separated by vertical ridge – BILL’s BAR, Posterior region transmits
Superior vestibular nerve, supply superior, lateral semicircular canal, Utricle &
Saccule. Below the crest ,Cochlear nerve lies anteriorly, Inferior vestibular nerve
passes posteriorly to supply Posterior semicircular canal.

26. DEVELOMENT OF EAR
From implantation of fertilized and dividing egg( blastocyst) to birth is divided
into 3 periods – Pre- embryonic - 21days,
Embryonic - 35 days,
Foetal - 210 days.
Embryonic phase – Rapid growth & differentiation of ecto-,meso-,and
endoderm, all major organ systems have been formed.
Foetal period – Change in shape, size & orientation of structure, but no new
tissue develop.
In mammals, during early embryonic life, Mesenchyme surrounding the
primitive foregut and pharynx differentiates into maxillary & mandibular swelling on
each side of midline just above& below the buccopharyngeal membrane. This then
breaks which will become both nasal& buccal cavities.

27. In the mesenchyme surrounding the pharynx, 5 or 6 parallel thickenings
develop , these are BRANCHIAL ARCHES, numbered 1 to 6 from head to tail.
On external surface a groove develops between each branchial arch and this
is matched by Cleft or Pouch on inner pharyngeal surface. In each branchial arch a
bar of cartilage, group of muscles, associated artery & cranial nerve supplying these
structures & their derivatives.
Cranial nerve – Post- trematic nerve, a nerve from the arch lower down
supplies the inner endodermal surface of arch above – Pretrematic nerve

28. DERIVATIVES OF BRACHIAL ARCHES
FROM FIRST AND SECOND BRACHIAL ARCHES
First pharyngeal pouch on inside expands due to rapid growth of surrounding
mesenchyme after dragging in some second pouch endoderm, result in –
EUSTACHIAN TUBE, MIDDLE EAR, MASTOID ANTRUM. Eustachian tube lumen,
middle ear spaces formed by 8 months, and epitympanum & mastoid antrum
developed by birth. At birth , Mastoid air cells filled with amniotic fluid, Development
of mastoid air cell system starts after birth , 90% completed at age of 6 yrs.
In 4th week , endoderm precursor of middle ear lies against ectoderm
of first pharyngeal groove, mesenchyme grows in between these 2 layers forming –
TYMPANIC MEMBRANE.

29. Ossicles developed from outer ends of First arch( Meckel’s) and Second arch
(Reichert’s) cartilage .
Tensor tympani developed from first arch , supplied by mandibular nerve.
EXTERNAL AUDITORY CANAL – Develops from first pharyngeal groove, meatus
deepens by proliferation of its ectoderm which will cover future tympanic membrane.

30. DEVELOPMENT OF AURICLE (PINNA)
6 Small cartilaginous tubercle that surround first pharyngeal groove –
‘Hillocks or Tubercles of His’ Majority of auricle develops from Second arch cartilage,
TRAGUS alone developed from first arch.

31. INTERNAL EAR DEVELOPMENT
Development of labyrinth can be thought as initial development of
generalized structure of membranous labyrinth followed by period of encasement by
bony labyrinth . Ectodermal thickening on side of head end of embryo form neural
tube and neural crest cells which becomes brain & brainstem and cranial nerves .
Ectodermal thickening is OTIC PLACODE ,deepens and sinks below the
surface to form OTIC PIT which loses communication – OTOCYST. Associated with
otocyst is cluster of neural crest cells that become facial( geniculate)
,auditory(spiral), and vestibular (Scarpa's) ganglion. Otocyst undergoes series of
spectacular changes to form – MEMBRANOUS LABYRINTH.

32. Semicircular canals start to develop at around 35 days as 3 flattened
pouches that grow out at right angles from each other form UTRICLE. Superior
semicircular canal is first to be fully formed.
As these developments are taking place, COCHLEA, starts to be
formed. SACCULE, has separated from utricle , starts to put out a single pouch like
process that grows and then begins to coil from base to apex to reach its full 2.5
coils by 25 weeks.
Within membranous labyrinth the Sensory cells of 3 cristae, 2 maculae and
organ of Corti develop from areas of ectoderm. Organ of Corti developing as single
block of heaped up ectodermal cells at 11 weeks, Within this mass develop inner
and outer hair cells & supporting cells. Epithelium close to sensory region develops
into specialized cell groups that maintain ionic and electrical stability of endolymph
– Stria vascularis of cochlear duct and ‘dark cell’ region of vestibular sensory
epithelium

33. DEVELOPMENT OF BONY LABYRINTH
Mesenchyme enclosing the otocyst becomes chondrified to form OTIC
CAPSULE. As membranous labyrinth expands , the otic capsule remodels and
undergoes dedifferentiation to form fluid filled spaces which becomes
Perilymphatic spaces. It become continuous and communication with CSF is formed
by development of Cochlear aqueduct.
Ossification of otic capsule fuse without leaving suture line , which forms
Petrous bone. Certain channels remain within otic capsule , one of most important
being OVAL WINDOW ,where part of otic capsule becomes stapes footplate.

34. DEVELOPMENT OF TEMPORAL BONE
4 separate elements fuse to form temporal bone , Petromastoid complex,
Squamous portion, Tympanic bone, Styloid process.
Petromastoid – Derived from petrous bone,form roof & floor of middle ear,
lateral wall of Eustachian tube , canal of facial nerve and petrous apex.
Squamous bone – Develops in mesenchyme, form roof of zygoma, lateral
wall of mastoid antrum.
Tympanic bone – Formed in mesenchyme, around external meatus, even by
late foetal life bony ear canal is unformed, only after birth crescentic swelling fuse
leaving a gap in floor of ear canal– Foramen of Huschke.
Styloid – Develops from second arch.
Much of growth of temporal bone occurs after birth, with enlargement of
whole structure and major growth of mastoid process takes place , so that
stylomastoid foramen initially close to surface become buried by mastoid tip
development.

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