Anatomy of ear and mastoid

Anatomy of ear and mastoid

1. Anatomy of ear and
mastoid
Dr. Krishna Koirala
Dr. Krishna Koirala // Anatomy of Ear and Mastoid

2. •Pairedsensoryorganscomprisingof
–Auditorysysteminvolvedinthedetectionofsound
–Vestibularsysteminvolvedinmaintainingbodybalance
andequilibrium
•Dividedanatomicallyandfunctionallyinto
–Externalear
–Middleear
–Innerear
•Allthreesubdivisionsareinvolvedinhearing
•Innerearisinvolvedinbodybalanceandequilibrium

3. External Ear (Outer Ear)

4. Pinna
•Frameworkformedbyyellowelasticcartilageexceptinthe
lobuleandincissuraterminalis
•Functions
–Collectanddirectsoundwaves
throughtheearcanaltotheTM
−Protectthetympanicmembrane
•Importance:Perichondrium/cartilageusedasagraftmaterial
formiddleearandotherreconstructivesurgeries

5. Parts of pinna
Helix:Slightlycurvedrimofthe
auricle
Antihelix:Broadercurvedeminence
anteriortohelix
Concha:Deepcavityinfrontofthe
antihelix
•Cymbaconchae:Depressionbetweentheantitragusand
ascendingcrusofthehelix(surfacelandmarkofmastoidantrum)
•Tragus:prominenceinfrontofandpartlyclosingtheexternal
auditorycanal
•Lobule:lowerportionofpinnamadeupofareolartissue&fatwithoutcartilage

6. Sensory Nerve supply of pinna
•Lateral surface
–Upper 2/3 : Auriculotemporal nerve (cranial nerve V)
–Lower 1/3 : Greater auricular nerve (C2,3)
•Medial Surface
–Upper 1/3: Lesser occipital nerve (C2)
–Lower 2/3 : Greater auricular nerve (C2, 3)
•Posterior concha and antihelix : Auricular b/o Vagus
•Facial : Small region at the root of concha

7. External Auditory canal

8. •Extendsfrombottomofconchatothetympanic
Membrane
•24 mm long in adults
–Lateral 1/3 (8 mm) : Cartilaginous, directed
upwards, backward and medially
–Medial 2/3 (16 mm) : Bony, directed downwards,
forward and medially
•Pinna to be pulled upwards, backwards and laterally
to straighten the external auditory canal in adults

9. Onlycartilaginousskinhashairfollicles,
ceruminousandpilosebaceousglands(wax)
CartilaginousfissureofSantoriniandbony
foramenofHuschkepresentinanteriorwall
infection/metastasistoandfromtheparotid
gland

10. Middle Ear

11. Middle ear cleft
Contents
−Middle ear cavity
−Attic ,aditus, antrum
−Mastoid air cell system
−Eustachian tube
Develops from tubo -tympanic
recess
Middle ear cavity
Epitympanum
Mesotympanum
Hypotympanum
Protympanum
Post-tympanum

12. ET
ME
ATTIC
AD
Ant

13. Contents of middle ear
3Ossicles:malleus,incus,stapes
2Nerves :Chordatympani,Tympanicplexus
2Muscles :Tensortympani,stapedius
Air
Mucosalfolds&ligaments
Bloodvessels

14. Tympanic Membrane
•Partitionbetweentheexternalandmiddleear
•Obliquelysetwith55
0
tofloor
•Dimension:10mmx8mmx0.1mm
•Parts
–ParsTensa
–ParsFlaccida(Shrapnel'smembrane)

15. PF
PT

16. •Landmarks of TM
–Lateral process of malleus
–Anterior and posterior
malleal folds
–Handle of malleus
–Umbo
–Cone of light
–Annulus tympanicus

17. •Layersoftympanicmembrane
1)Outerlayerofsquamousepitheliumcontinuous
withthatofthemeatus
2)Middlelayeroffibroustissuethathasradialand
circularfibres
3)Innerlayerofmucousmembranecontinuouswith
theliningofthetympaniccavity
•Fibrouslayerdisorganizedinparsflaccida
•AnnulusdeficientsuperiorlyasnotchofRivinus

18. Four Quadrants of pars Tensa
AS
AI
PS
PI

19. Borders of middle ear cavity
•Roof :Tegmen tympani
•Floor : Separates tympanic cavity from jugular bulb
•Medial wall
−Promontory: Bulge formed by basal turn of cochlea
−Oval window: Communicates between middle ear and the
vestibule of the inner ear, closed by footplate of stapes
−Round window : Communicates between scala tympani and
tympanic cavity, covered by secondary tympanic membrane

21. •Lateral wall
−Largely by TM
−Scutum (outer attic wall)
−Bone inferior to TM
•Anterior wall
−Thin plate of bone
−Openings of canal for tensor tympani and
Eustachian tube
•Posterior wall
−Separates middle ear cavity from mastoid bone
−Contains aditus ,pyramid

22. Themastoidantrumandaircellsystem
Mastoid antrum : Largest and most consistent air cell of
mastoid air cell system, well developed at birth
Relations
Roof : Part of floor of MCF
Floor : Digastric muscle, sigmoid sinus
Posterior: Bony covering of sigmoid sinus
Lateral : Squamous temporal bone (corresponds to
suprameatalor Macewan’s triangle and Cymba conchae)

23. Mac Ewan’s Triangle (Suprameatal Triangle)
•Boundaries
−Superior:Posteriorprolongationofupperborderofrootof
zygoma(Supramatoidcrest)
−Anteroinferior:Posterosuperiormarginofbonyexternal
meatus
−Posterior:Verticaltangentdrawnthroughtheposterior
marginofbonyexternalmeatustothefirstline
•Contains spine of Henle
•Surgical landmark for mastoid antrum (Mastoid antrum lies 1.5
-2.0 cm deep to the triangle in adults)

25. Mastoid air cell system
Extensive system of interconnecting air filled cavities arising
from walls of mastoid antrum that extend throughout the
mastoid
Lined with flattened non ciliated squamous epithelium
Types
−Cellular ( pneumatized) : Honeycomb appearance on
plain X-Ray mastoid
−Diploic : Air cells interspersed with marrow containing
spaces
−Acellular (sclerotic)

27. Five Recognized regions of mastoid pneumatisation
(Allam -1969)
Middle ear: Epitympanum, Mesotympanum, Hypotympanum,
Protympanum, posterior tympanum
Mastoid: Antrum, central mastoid, peripheral mastoid
Perilabyrinthine: Supralabyrinthine, infralabyrinthine
Petrous apex : Apical, peritubal
Accessory: Zygomatic, squamous, occipital, styloid

28. Inner ear

29. Lies within the petrous temporal bone
Divisions
Bony labyrinth : consists of a series of bony cavities within
the petrous temporal bone
It is composed of cochlea, vestibule and semi-circular
canals. These structures are lined internally by periosteum
and contain perilymph
Membranous labyrinth: lies within the bony labyrinth. It
consists of the cochlear duct, utricle, saccule and semi-
circular ductsand is filled with endolymph

30. Bony labyrinth (Vestibule, Semicircular
canals , Bony cochlea)
Vestibule
−Central portion of bony labyrinth, ovoid in shape
−Oval window at the lateral wall, utricle and
saccule in the medial
−Openings of SCC (5) -lie on posterior, superior
and inferior walls of bony vestibule

31. Pink= Endolymph
Blue= Perilymph

32. Semicircular canals (3)
−Lieinplanesatrightanglestoeachother
−Ampullatedandnonampullatedends
−Ampullatedendscontainvestibularsensory
epitheliumandindependentlyopenintothe
vestibule
−NonampullatedendoflateralSCCopens
separatelywhereasthoseofsuperiorandposterior
SCCsjointoformcruscommunebeforeopeningin
thevestibule

33. Bony cochlea
Coiled tube like the shell of a
snail, contains 2
½
to 2
¾
turns
Height around 5mm,base
around 9 mm in diameter
Coils turn around the modiolus
-extends along the entire
length of cochlea except for
helicotrema (small channel at
the apex)

34. Threecompartments
−Scalavestibuli
−Scalatympani
−Scalamedia(membranouscochlea)
Withinthemodiolusliespiralganglion
Cochlearnervelieswithinthebonymodiolus
throughouttheentirelength

35. Membranous labyrinth
Membranous cochlea
−Triangular in cross section
−Bordered by Reissner's membrane, Basilar
membrane and stria vascularis
Utricle and saccule
Semicircular ducts
Endolymphatic ducts and sac

37. Organ of Corti
Sense organ of hearing
Situated on the basilar membrane
Components
−TunnelofCorti
−Haircells(outerandinner)
−Supportingcells(Deiter's,Hansen's)
−Tectorialmembrane

39. Differences between inner and outer hair
cells
Inner Hair CellsOuter Hair Cells
Numbers 3500 12,000
Rows Single row Three or four rows
Shape Flask-shaped Cylindrical
Stimuli Primarily afferentPrimarily efferent
Functions Transmit auditory
stimuli
Modulate inner hair
cell
Strength More Resistant to
damage
Vulnerable to
damage