Download Ear Anatomy

Anatomy
Embryology
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External ear develop from 3 pairs of auricular hillocks from the 1st (mandibular)
and 2nd (hyoid) branchial arches in week 5 around the otic placode
Dorsal parts of these two arches give rise to the auricle, middle ear, inner ear, and
facial nerve, while their ventral parts develop into the mandible, maxilla, and the
majority of the hyoid bone.
The external auditory meatus develops by deepening of the 1st pharyngeal cleft
during week 6
Like in the upper limb, ectoderm stimulates the underlying mesenchyme to
proliferate.
His 1882 thought the hillocks developed into specific auricular elements
 First arch hillocks
1. tragus
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2. helix
3. helical crus
 Second arch hillocks
4. antihelix
5. antihelix/scapha
6. antitragus/lobule
Has been controversial with different authors ascribing different areas
In fact latest research show that hillocks represent temporary foci of intense
mesenchymal proliferation before the rate of their proliferation becomes equal to
that of the surrounding mesenchyme.
This mesenchymal equalization occurs at the start of the seventh week, with
blending of the hillocks resulting in a bland topography
Porter and Tan PRS 2005
A diagrammatic representation (lateral view) of the development of the left auricle in gestational weeks
5 through 9.
Derivatives of the mandibular (Md) and hyoid (H) arches are shown in white and light gray,
respectively, while the first branchial cleft is illustrated in dark gray. III, IV, and VI represent the third,
fourth, and sixth branchial arches, respectively. The fifth branchial arch becomes absorbed into the
adjacent branchial arches. Derivatives of the free ear fold are represented in intermediate gray. (Above,
left)
At gestational day 35, the five branchial arches with the mandibular arch (Md) and hyoid arch (H).
(Above, center) At gestational day 40, the six hillocks of His that derive from the mandibular and hyoid
arches surround the first branchial cleft (represented in dark gray). (Above, right)
At gestational day 44, the hillocks are merging. (Center, left) At day 49, the six transitional hillocks
have merged to form a bland auricle, which enlarges with the first branchial cleft, becoming relatively
small. (Center, center)
At day 52, the developing auricle begins to show auricular definition; the dashed line represents the
boundary between derivatives from the hyoid arch and those from the free ear fold. (Center, right)
At day 56, further increase in auricular definition with the first branchial cleft being obscured by the
developing tragus. (Below, left)
At day 63, the definitive auricle at the end of the embryologic development. (Below, right)
A fully developed auricle. Note that the majority of the auricular components are derived from the
hyoid arch and the free ear fold. The derivatives from the mandibular arch include the tragus,
anterior helix, and root of the helix. The dashed line (passing through the junction between the
anterior and superior helix, along the body and superior crus of the antihelix, and though the junction
between the posterior helix and lobule) represents the boundary between the derivatives from the hyoid
arch and those from the free ear fold.
The derivatives of the free ear fold, which include the superior and posterior helix, scaphoid
fossa, and superior crus of the antihelix, are the structures most prone to deformational forces.
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The furl of the helical rim develops during the sixth week.
Week 8-12, the helix develops rapidly and overhangs the antihelix.
Antihelical furl develops over the subsequent 4 weeks (weeks 12-16), medializing
the helical rim.
Postnatal ear growth
 85% of adult size by age 3
 90% by 9
 95% by 14
Landmarks
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consists of a complex convoluted yellow elastic cartilage framework
covered mainly by hairless skin.
skin on the anterior auricular surface is adherent to the cartilage, in contrast to that
on the posterior surface, which is loosely attached.
lobule contains no cartilage and consists of fibrofatty tissue
Muscles
 Consists of three extrinsic and six intrinsic muscle
 Extrinsic – originate outside of ear
1. Auriculares anterior – a rises from the lateral edge of the galea aponeurotica,
and its fibers converge to be inserted into a projection on the front of the helix
2. Auriculares superior - arise from the galea aponeurotica, and converge to be
inserted by a thin, flattened tendon into the upper part of the cranial surface of
the auricula.
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3. Auriculares posterior. - arise from the mastoid portion of the temporal bone
by short aponeurotic fibers. They are inserted into the lower part of the cranial
surface of the concha.
Intrinsic – arise within ear
1. Helicis major.
2. Helicis minor
3. Antitragicus.
4. Tragicus
5. Transversus auriculæ.
6. Obliquus auriculæ.
Three extrinsic muscles: anterior (A), superior (S), and posterior (P); and six intrinsic
muscles: helical muscles, large (HL) and small (HS), muscle of the tragus (T), muscle
of the antitragus (AT), transverse muscle (TM), oblique muscle (O).
Blood supply
Some correspondence to embryology
1) Superficial temporal artery
2) Posterior auricular artery (posterior branch from facial above posterior belly of
digastric)
 Two arterial networks supply the anterior ear: the triangular fossa-scapha network
and the conchal network. The posterior auricular artery provides the dominant
blood supply for both networks of the anterior ear through perforating vessels that
pierce the cartilage at (first 3 most consistent) :
1) Helical root
2) cavum conchae
3) lobule
4) triangular fossa
5) cymba conchae
 The PAA sends a communicating branch to the superficial temporal artery (STA)
at the cephalic base of the ear, thereby forming a vascular ring around the base of
the ear
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The secondary blood supply is the superficial temporal artery, which provides one
to three branches to the ear. These branches supply the earlobe, tragus, and
ascending helix.
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In addition, the deep auricular artery, a branch of the 1st part of the maxillary
artery coming up through the auditory canal, can supply enough arterial inflow to
be the only vascular supply to a traumatized ear.
The occipital artery supplies a minor contribution to auricular blood flow to the
posterior auricle.
Sensory supply
1) great auricular nerve(C2,C3)
a. supplies inferior two-thirds of both sides of ear
b. 6.5 cm below the EAM, it lies halfway across SCM.
2) lesser occipital (c2 c3)
a. supplies superior one-third of posterior ear.
b. emerges behind the posterior border of the sternocleidomastoid muscle
superior to the great auricular nerve
3) auriculotemporal nerve
a. supplies superior 1/3rd of anterior ear (root and spine of helix)
4) auricular branch of vagus (Arnold’s nerve)
a. supplies cymba and antihelix middle 1/3rd anteriorly and posterior 1/3rd to
mastoid
b. passes behind the internal jugular vein, and enters the mastoid canaliculus
on the lateral wall of the jugular fossa.
c. traversing the substance of the temporal bone, it crosses the facial canal
about 4 mm. above the stylomastoid foramen, and gives off an ascending
branch which joins the facial nerve.
d. reaches the surface by passing through the tympanomastoid fissure
between the mastoid process and the tympanic part of the temporal bone
5) Facial (only sensory branch – intratemporal)
a. Via nerve branches from tympanic plexus to tympanic membrane
6) glossopharyngeal. (Jacobson’s nerve)
a. probably does not supply external ear - middle ear nerve supply
b. enters petrous bone through tympanic canaliculus between jugular and
carotid foramen
Lymphatic supply
 Follows embryology
 On Anterior surface:
1) Superior 1/3rd to parotid nodes
2) Posterior 2/3rd to superficial and deep cervical lymph glands
 On posterior surface
o Mastoid and retroauricular nodes in addition to cervical nodes