The document discusses the embryology and anatomy of the external, middle, and mastoid parts of the ear. Regarding embryology, it describes how the external ear, auditory canal, middle ear spaces/folds, and ossicles develop from the branchial arches and pouches during fetal life. For anatomy, it outlines the structures of the external ear including the pinna, auditory canal, and tympanic membrane. It also details the walls, spaces, blood supply and contents of the middle ear, as well as the anatomy of the eustachian tube, mastoid air cells and their relationships.
3. EMBRYOLOGY OF THE EAR
External Ear - Auricle
1st and 2nd branchial arch gives rise to 6 mesodermal
thickenings (auricular tubercles) known as “HILLOCKS
of HIS” which fuse to form pinna.
1st hillock arises from 1st arch
Remaining 5 hillock arise from 2nd arch.
Takes definitive form by end of 3 month of IUL.
4. EMBRYOLOGY OF THE EAR
Dorsal part of 1st ectodermal cleft (or first branchial
groove grows medially and forms the external
auditory canal .
At birth, only the cartilaginous is completely
developed.
The bony part Of EAC continues to grow after birth .
(8th -10th week IUL)
EAC & Middle Ear
5. EMBRYOLOGY OF THE EAR
▪ Around 3rd week of Intra uterine life, the first pharyngeal pouch develops.
▪ Proximal narrow part forms eustachian tube.
▪ Distal dilated part forms tubotympanic recess.
▪ Diverticulum from tubotympanic recess forms the mastoid antrum .
▪ Antrum develops during 6th or 7th month .Mastoid air cells form at end of fetal life.
Development of Ossicles: They develop by 8th week iul.
1. Meckel’s cartilage: forms Head of the malleus and body of the Incus.
2. The second arch :forms the manubrium (handle) of the malleus and the long process of the incus and
the crura of stapes
3. The plate of the stapes develops from all the three sources of the otic capsule
6. MIDDLE EAR SPACES AND FOLDS
▪ The ossicles envelopment by the mucous membrane lining
of the tubotympanic recess occurs between 3-7 months of
IUL. It form numerous folds and spaces.
▪ Attic compartment
Superior malleolar fold divides it into anterior and posterior
compartment post comp. further divided into superior and
inferior incudal space.
Mesotympanum compartment
Ant. Malleolar fold and posterior malleolar fold.
Prussaks space
1ST potential space for cholesteatoma extension.
9. ANATOMY OF EXTERNAL EAR
▪ External ear consist of Pinna ,External auditory canal and Tympanic membrane.
10. ANATOMY OF EXTERNAL EAR – EXTERNAL
AUDITORY CANAL
▪ From bottom of concha to TM 24 m along with post wall
▪ Lateral cartilaginous and medial bony part
▪ Cartilage part -Outer 1/3 (8 mm), deficient at Incisura terminalis (root of helix and tragus)
▪ Skin is thick with hairs and sebaceous and ceruminous glands .
▪ Fissures in ant wall ‘fissures of Santorini’
▪ Bony Part -Medial 2/3 (16 mm)
▪ Two constrictions (Isthmus 6 mm lateral to TM) Ant recess sump for disc
▪ Skin has no subdermal layer, firmly attached to periosteum
11. ANATOMY OF EXTERNAL EAR
▪ Mixture of secretions of ceruminous and sebaceous glands
▪ Two types dry and wet
▪ Dry wax – yellowish or grey, dry and white
▪ Wet wax – yellowish brown, wet and sticky
▪ Contains amino acids, fatty acids, lysozymes and immunoglobulins.
▪ Has a bactericidal activity
▪ Migrates outside but may get impacted.
WAX
12. ANATOMY OF EXTERNAL EAR –
TYMPANIC MEMBRANE
▪ Separates auditory meatus of external ear from
tympanic cavity of middle ear.
▪ Measures 10mm in vertical diameter and 9mm in
horizontal diameter.
▪ Consists of 3 layers:
▪ Outer epithelial layer continuous with epithelial of
external ear
▪ Middle firous layer consist of radial and circular
fibres.
▪ Inner mucosal layerwhich is continuous with
mucosa of tympanum
This Photo by Unknown Author is licensed under CC B-SA
13. ANATOMY OF EXTERNAL EAR
▪ External ear
Blood Supply
Medial surface - Posterior auricular
Lat surface - Anterior auricular A (Sup temp A)
Nerve supply
▪ Greater auricular (C2-3).
▪ Lesser occipital (C2),
Auricular branch of Facial (Concha),
▪ Auriculotemporal
Lymphatic drainage
▪ Mastoid tip, Pre-auricular,
▪ Deep cervical
15. External auditory canal
Blood supply
▪ External carotid system (Sup temporal, Maxillary, Post auricular)
Nerve supply
▪ Ant half Auriculotemporal N,
▪ Post half by Arnold’s N (X)
Relations
▪ Ant - TMJ
Post - Mastoid
▪ Sup - Middle fossa
▪ Inf - Parotid gland
16. EXTERNAL EAR-APPLIED ANATOMY
Developmental Anomalies of Pinna
▪ Pre-auricular Sinus,
▪ Microtia
▪ Anotia
▪ Darwin’s Tubercle.
Developmental Anomalies of EAC
▪ Complete atresia
▪ Shallow depression
▪ Changes in curvature of canal
▪ Stenosis
17. 1. Relatively less subcutaneous tissue makes the pinna more sensitive to frost bite.
2. Incisura terminalis is used for end-aural incision.
3. Referred otalgia .
4. Important donor of cartilage and fat.
5. Isthmus or anterior recess holds the foreign bodies .
6. Vagus stimulation to increase appetite.
7. Sagging of deep postero superior wall – Acute mastoiditis
8. Furuncles only in lateral part, very painful
9. Persistent cough by impacted wax .
10. Cymba conchae direct relation to suprameatal triangle
11. Skin has unique quality of migrating laterally from the tympanic membrane and forms wax.
loss of this property is seen in keratosis obturans.
18. 10. Cymba conchae direct relation to suprameatal triangle
11. Skin has unique quality of migrating laterally from the tympanic membrane and forms wax.
loss of this property is seen in keratosis obturans.
12 Infection can pass through fissures –fissure of Santorini and foramen of huschke from EAC to
parotid glands
20. ANATOMY OF MIDDLE EAR -MIDDLE EAR CLEFT
Middle ear cleft consists of:
• Tympanic cavity,
• Eustachian tube
• Mastoid air cell system.
The tympanic cavity is an irregular,
air-filled space within the temporal
bone between the tympanic
membrane laterally and the
osseous labyrinth medially.
It contains the ossicles, muscles
and structures, like the tympanic
segment of the facial nerve
This Photo by Unknown Author is licensed under CC BY
21. ANATOMY OF MIDDLE EAR -TYMPANIC CAVITY
Tympanic cavity consist of three compartments
1. Epitympanum (upper),
2. Mesotympanum (middle) and
3. Hypotympanum (lower).
23. ANATOMY OF MIDDLE EAR -THE LATERAL WALL
It is formed by the
• Bony lateral wall of the epitympanum superiorly(scutum)
• Tympanic membrane centrally and
• Bony lateral wall of the hypotympanum inferiorly.
Holes present in the bone of the medial surface of the
lateral wall of the tympanic cavity
• The petrotympanic fissure -anterior malleolar ligament and
transmits the anterior tympanic branch of the maxillary artery
to the tympanic cavity.
• Anterior canaliculus (canal of Huguier) -chorda tympani nerve
• Posterior canaliculus.
Course of chorda tympani nerve
24. ANATOMY OF MIDDLE EAR -ROOF
The roof of the epitympanum is the tegmen tympani
• It is a thin bony plate that separates the middle ear space from the middle cranial fossa.
• It is formed by both the petrous and squamous portions of the temporal bone .
• The petrosquamous suture line.
• Veins from the tympanic cavity running to the superior petrosal sinus pass through this suture line.
25. ANATOMY OF MIDDLE EAR -FLOOR
• The floor of the tympanic cavity separates the hypotympanum from the dome of the jugular bulb.
• Occasionally, the floor is deficient and the jugular bulb is then covered only by fibrous tissue and a mucous membrane.
• At the junction of the floor and the medial wall of the cavity there is a small opening that allows the entry of the tympanic
branch of the glossopharyngeal nerve into the middle ear.
26. ANATOMY OF MIDDLE EAR -ANTERIOR WALL
• Narrow as the medial and lateral walls converge.
• The lower-third -thin plate of bone covering the carotid artery. It is perforated by the – superior and inferior caroticotympanic
nerves and tympanic branches of the internal carotid artery.
• The middle-third - tympanic orifice of the Eustachian tube.
• Just above this is a canal containing the tensor tympani muscle
• The upper-third -pneumatized and may house the anterior epitympanic sinus, a small niche anterior to the ossicular heads,
which can hide residual cholesteatoma in canal wall up surgery
27. ANATOMY OF MIDDLE EAR -MEDIAL WALL
.
• The medial wall separates the tympanic cavity from the
internal ear.
The promontory.
• It covers part of the basal coil of the cochlea . The
promontory gently inclines forwards to merge with the
anterior wall of the tympanic cavity
28. ANATOMY OF MIDDLE EAR-MEDIAL WALL CONTD..
• Oval window behind and above the promontory, kidney-shaped opening that connects the tympanic cavity with the
vestibule, which is closed by the footplate of the stapes and its surrounding annular ligament.
• The round window, subiculum , the ponticulus, the sinus tympani
• The facial nerve canal (or Fallopian canal) runs above the promontory and oval window in an anteroposterior direction.
It is marked anteriorly by the processus cochleariformis
• The dome of the lateral semicircular canal.
32. ANATOMY OF MIDDLE EAR-POSTERIOR WALL
• The posterior wall is wider above than below
• Upper part a large irregular opening - the aditus ad antrum, that leads back from the posterior epitympanum into the
mastoid antrum
• Below the aditus is a small depression, the fossa incudis,.
• Below the fossa incudis and medial to the opening of the chorda tympani nerve is the pyramid,
• The canal within the pyramid curves downwards and backwards to join the descending portion of the facial nerve canal.
34. ANATOMY OF MIDDLE EAR-POSTERIOR WALL
The Facial recess wall.
Boundaries –
• Medially by the facial nerve .
• Laterally by the tympanic annulus,
• The chorda tympani nerve running obliquely
through the wall between the two.
36. ANATOMY OF MIDDLE EAR - POSTERIOR WALL
• The sinus tympani is a posterior extension of the
mesotympanum and lies deep to both the promontory and the
facial nerve.
• This extension of air cells into the posterior wall can be
extensive, and is probably the most inaccessible site in the
middle ear and mastoid.
• The sinus can extend as far as 9 mm into the mastoid bone
when measured from the tip of the pyramid.
• The medial wall of the sinus tympani becomes continuous with
the posterior portion of the medial wall of the tympanic cavity
where it is related to the oval and round window niches and the
subiculum of the promontory
37. ANATOMY OF MIDDLE EAR–
CONTENTS OF TYMPANIC CAVITY
Tympanic cavity contains
• The ossicles,
• Two muscles-tensor tympani and stapedius muscle
• Chorda tympani
• The tympanic plexus.
The ossicles are the malleus, incus and stapes that form a
semi-rigid bony chain for conducting sound
. The malleus is the most lateral and is attached to the
tympanic membrane, whereas the stapes is attached to the
oval window
38. ANATOMY OF MIDDLE EAR - EUSTACHIAN TUBE
• It is a dynamic channel that links the middle ear with
the nasopharynx from the middle ear at 45° and is
turned forwards and medially.
•
• Consists of two unequal cones, connected at their
apices. (36mm)
• The lateral third is bony and arises from the anterior
wall of the tympanic cavity(about 12mm)
• Medial two-thirds cartilagenous part.( 24mm)
• Its narrowest portion is called the isthmus, where the
diameter is only 0.5 mm or less.
39. ANATOMY OF MIDDLE EAR- EUSTACHIAN TUBE
• In the nasopharynx, the tube opens 1-1.25 cm behind and below the posterior end of the interior turbinate.
• The opening is triangular in shape and is surrounded above and behind by the torus.
• The salpingopharyngeal fold stretches from the lower part of the torus downwards to the wall of the pharynx.
• The levator palati, as it enters the soft palate, results in a small swelling immediately below the opening of the tube.
• Behind the torus is the pharyngeal recess or fossa of Rosenmuller.
• Lymphoid tissue is present around the tubal orifice and in the fossa of Rosenmuller, and may be prominent in
childhood.
40. ANATOMY OF MIDDLE EAR- EUSTACHIAN TUBE
• It is lined with respiratory mucosa containing goblet cells and mucous glands, having ciliated epithelium on its
floor.
• At its nasopharyngeal end, the mucosa is truly respiratory; but in passing along the tube towards the middle ear,
the number of goblet cells and glands decreases, and the ciliary carpet becomes less profuse.
• It runs through the squamous and petrous portions of the temporal bone, gradually tapering to the isthmus.
• A thin plate of bone forms the roof, separating the tube from the tensor tympani muscle above.
• The carotid canal lies medially and can impinge on the bony Eustachian tube.
41. ANATOMY OF MIDDLE EAR -BLOOD SUPPLY
• Arise from both the internal and external carotid system.
• The overlap is extensive and great variability is present.
• Supply is from the anterior tympanic, stylomastoid, maxillary, posterior auricular, middle meningeal, ascending
pharyngeal, artery of pterygoid canal and internal carotid arteries.
• The anterior tympanic and stylomastoid arteries are the biggest.
• Anterior tympanic artery br. of Maxillary Artery supplies ant part of Tympanic membrane; malleus and incus; anterior
part of tympanic cavity.
• Stylomastoid artery br. of Posterior Auricular artery supplies Posterior part of tympanic cavity; stapedius muscle and
Mastoid air cell
42. MASTOID
CONSIST OF 3 PARTS
1 ) ADITUS AD ANTRUM
2)MASTOID ANTRUM
3)MASTOID AIR CELLS
43. MASTOID-ADITUS AD ANTRUM
▪ It is a short canal connecting epitympanum with mastoid antrum.
▪ Short process of incus lies on its floor.
▪ Facial nerve runs in its canal in the floor
▪ Lateral semicircular canal lies in its medial wall.
44. MASTOID ANTRUM
• The mastoid antrum is an air-filled sinus in the petrous part of temporal bone.
• It communicates with the middle ear by the aditus.
• Antrum is well developed at birth.
•
• Volume = 2 ml (adult).
• The roof of the mastoid antrum and mastoid air cell space form the floor of the middle cranial fossa.
• The medial wall relates to the posterior semicircular canal.
• More deeply and inferiorly is the dura of the posterior cranial fossa and the endolymphatic sac
45. MASTOID ANTRUM
• Posterior to the endolymphatic system is the sigmoid sinus, which curves down, pass medial to the facial nerve and
then becomes the dome of the jugular bulb in the middle ear space
• The posterior belly of the digastric muscle forms a groove in the base of the mastoid bone
• The digastric ridge inside the mastoid lies lateral to the sigmoid sinus and the facial nerve and is a useful landmark
for finding the nerve
• The periosteum of the digastric groove continues anteriorly and part of it becomes the endosteum of the
stylomastoid foramen and subsequently of the facial nerve canal.
46. MASTOID ANTRUM
Macewen's triangle is a direct lateral relation to the mastoid
antrum.
In most individuals, the mastoid air cell system is fairly
extensive with air cells
Normally, lining of the mastoid is a flattened, nonciliated
epithelium without goblet cells or mucus glands.
48. MASTOID AIR CELL.
The extent of pneumatization of the temporal bone varies according to heredity, environment, nutrition, infection, and eustachian
tube function.
There are five recognized regions of pneumatization:
• Middle ear,
• Mastoid,
• Perilabyrinthine,
• Petrous apex, and
• Accessory.
There are five recognized air cell tracts.
• The posterosuperior tract
• The posteromedial cell tract
• The subarcuate tract.
• The perilabyrinthine tracts
• Peritubal tract surrounds the eustachian tube.
49. MIDDLE EAR- APPLIED ANATOMY
1.Middle ear transformer mechanism
▪ Divided into 3 stages:
▪ provided by ear drum (catenary lever)..ratio
▪ Provided by ossicles(ossicular lever) provides mechanical advantage is 2.3
▪ Provided by difference in surface area between tympanic membrane and footplate of
stapes(hydraulic lever) depends on areal ratio.transformer ratio is 18:1
▪ Phase difference
▪ Stapedial reflex
50. Functions of Eustachian tube-
▪ Ventilation of middle ear cleft-plays an important role in equalising middle ear pressure with
atmospheric pressure.
▪ Prevents reflux of nasopharygeal secretions
▪ Clearance of middle ear secretions
51. ▪ Impedance audiometry
Important landmarks in middle ear surgeries
▪ Prussacks space- cholestatoma
▪ Sinus tympani-residual cholesteatoma
▪ Oval window , processus cochleariformis and 1st genu-landmark for facial nerve.
▪ Facial recess-residual cholesteatoma and posterior tympanotomy approach.
▪ Trautmann’s triangle- infection reaches cerebellum through posterior cranial fossa.
▪ Korners septum,Spine of Henle, Macewan’s triangle –landmarks to locate mastoid antrum.
▪ Donaldson line-inferior to this line is the endolymphatic sac .
