4. Ear Development1

In the adult, the ear forms one anatomic unit serving both hearing and

equilibrium. In the embryo, however, it develops from three distinctly different

parts: (1) the external ear, the sound-collecting organ; (2) the middle ear, a sound

conductor from the external to the internal ear; and (3) the internal ear, which

converts sound waves into nerve impulses and registers changes in equilibrium.

a. Internal Ear

The first indication of the developing ear can be found in embryos of

approximately 22 days as a thickening of the surface ectoderm on each side of

the rhombencephalon.

Figure 4.1 A. An embryo at the end of the fourth week of development showing the

otic and optic vesicles. B. Region of the rhombencephalon showing the otic placodes

in a 22-day embryo1

These thickenings, the otic placodes, invaginate rapidly and form the otic

or auditory vesicles (otocysts).

Figure 4.2 A–C. Transverse sections through the region of the rhombencephalon

showing formation of the otic vesicles. A. 24 days. B. 27 days. C. 4.5 weeks. Note

the statoacoustic ganglia1

During later development, each vesicle divides into (1) a ventral

component that gives rise to the saccule and cochlear duct and (2) a dorsal

component that forms the utricle, semicircular canals, and endolymphatic

duct.

Figure 4.3 A,B. Development of the otocyst showing a dorsal utricular portion with

the endolymphatic duct and a ventral saccular portion. C–E. Cochlear duct at 6, 7,

and 8 weeks, respectively. Note formation of the ductus reuniens and the

utriculosaccular duct1

On the development of the scala tympani and scala vestibuli the cochlear

duct is surrounded by a cartilaginous shell. During the 10th week, large

vacuoles appear in the cartilaginous shell. The cochlear duct (scala media) is

separated from the scala tympani and the scala vestibuli by the basilar and

vestibular membranes, respectively. Note the auditory nerve fi bers and the

spiral (cochlear) ganglion.

Figure 4.5 Development of the semicircular canals. A. 5 weeks. B. 6 weeks. C. 8

weeks. D–F. Apposition, fusion, and disappearance, respectively, of the central

portions of the walls of the semicircular outpocketings. Note the ampullae in the

semicircular canals1

Together, these epithelial structures form the membranous labyrinth.

b. Middle Ear

The tympanic cavity, which originates in the endoderm, is derived from

the fi rst pharyngeal pouch. This pouch expands in a lateral direction and

comes in contact with the floor of the first pharyngeal cleft. The distal part of

the pouch, the tubotympanic recess, widens and gives rise to the primitive

tympanic cavity, and the proximal part remains narrow and forms the

auditory tube (eustachian tube, through which the tympanic cavity

communicates with the nasopharynx.

Figure 4.6 A. Transverse section of a 7-week embryo in the region of the

rhombencephalon, showing the tubotympanic recess, the first pharyngeal cleft, and

mesenchymal condensation, foreshadowing development of the ossicles. B. Middle

ear showing the cartilaginous precursors of the auditory ossicles. Thin yellow line in

mesenchyme indicates future expansion of the primitive tympanic cavity. Note the

meatal plug extending from the primitive auditory meatus to the tympanic cavity1

The malleus and incus are derived from cartilage of the fi rst pharyngeal

arch, and the stapes is derived from that of the second arch. Although the

ossicles appear during the first half of fetal life, they remain embedded in

mesenchyme until the eighth month, when the surrounding tissue dissolves.

The endodermal epithelial lining of the primitive tympanic cavity then

extends along the wall of the newly developing space. The tympanic

cavity is now at least twice as large as before. When the

ossicles are entirely free of surrounding mesenchyme, the

endodermal epithelium connects them in a mesentery-like

fashion to the wall of the cavity. The supporting ligaments of

the ossicles develop later within these mesenteries.

Figure 4.7 Ear showing the external auditory meatus, the middle

ear with its ossicles, and the inner ear1

Because the malleus is derived from the fi rst pharyngeal

arch, its muscle, the tensor tympani, is innervated by the

mandibular branch of the trigeminal nerve. The

stapedius muscle, which is attached to the stapes, is

innervated by the facial nerve, the nerve to the second

pharyngeal arch.

Figure 4.8 A. Derivatives of the fi rst three pharyngeal arches. Note the malleus and

incus at the dorsal tip of the first arch and the stapes at that of the second arch. B.

Middle ear showing the handle of the malleus in contact with the eardrum. The

stapes will establish contact with the membrane in the oval window. The wall of the

tympanic cavity is lined with endodermal epithelium1

During late fetal life, the tympanic cavity expands dorsally

by vacuolization of surrounding tissue to form the tympanic

antrum. After birth, the epithelium of the tympanic cavity

invades the bone of the developing mastoid process, and

epithelium-lined air sacs are formed (pneumatization).

Later, most of the mastoid air sacs come in contact with the

antrum and tympanic cavity. Expansion of infl ammations of

the middle ear into the antrum and mastoid air cells is a

common complication of middle ear infections.

c. External Ear

The external auditory meatus develops from the dorsal portion of the

first pharyngeal cleft. At the beginning of the third month, epithelial cells at

the bottom of the meatus proliferate, forming a solid epithelial plate, the

meatal plug . In the seventh month, this plug dissolves, and the epithelial

lining of the fl oor of the meatus participates in formation of the defi nitive

eardrum. Occasionally, the meatal plug persists until birth, resulting in

congenital deafness.

The eardrum is made up of (1) an ectodermal epithelial lining at the

bottom of the auditory meatus, (2) an endodermal epithelial lining of the

tympanic cavity, and (3) an intermediate layer of connective tissue that forms

the fibrous stratum. The major part of the eardrum is firmly attached to the

handle of the malleus , and the remaining portion forms the separation

between the external auditory meatus and the tympanic cavity.

Figure 4.9 A. Drawing of a 6-week-old embryo showing a lateral view of the head

and six auricular hillocks surrounding the dorsal end of the fi rst pharyngeal cleft. B.

Six-week-old human embryo showing a stage of external ear development similar to

that depicted in A. Note that hillocks 1, 2, and 3 are part of the mandibular portion of

the fi rst pharyngeal arch and that the ear lies horizontally at the side of the neck. At

this stage, the mandible is small. As the mandible grows anteriorly and posteriorly,

the ears, which are located immediately posterior to the mandible, will be

repositioned into their characteristic location at the side of the head. C–E. Fusion

and progressive development of the hillocks into the adult auricle1

The auricle develops from six mesenchymal proliferations at the dorsal

ends of the first and second pharyngeal arches, surrounding the first

pharyngeal cleft. These swellings (auricular hillocks), three on each side of

the external meatus, later fuse and form the defi nitive auricle . As fusion of

the auricular hillocks is complicated, developmental abnormalities of the

auricle are common. Initially, the external ears are in the lower neck region,

but with development of the mandible, they ascend to the side of the head at

the level of the eyes.

1. Sadier, TW. 2012. Langman’s Medical Embryology 12th Edition. Lippincott

Williams and Wilkins, a Wolter Kluwer Business

7. Virus that can Cause Congenital Defect

a. Varicella virus: skin scaring, limb hypoplasio, musle atrophy, intellectual

disability

b. Rubella virus: cataracts, glaucoma, heart defects, hearing loss, tooth

abnormalities

c. Cytomegalovirus: microcephaly, visual impairement, intellectual disability

d. Herpes simplex virus: microcephthalmia, microcephaly, retina dysplasia

Sadier, TW. 2012. Langman’s Medical Embryology 12th Edition. Lippincott

Williams and Wilkins, a Wolter Kluwer Business

12. Infant Cataract

Congenital cataract cause the lens to become opaque during intra uterine

life. Although this anomaly is usually genetical determined, many children born to

mothers who had Rubella (German measles) between the fourth and seventh

weeks of pregnancy cataracts.

If the mother is infected after the seventh week of pregnancy, the lens

escape damage, but the child may have hering loss as a result of cochleal

abnormalities. Because of the MMR vaccine, CRS has been nearly eradicted in

USA.

Sadier, TW. 2012. Langman’s Medical Embryology 12th Edition. Lippincott

Williams and Wilkins, a Wolter Kluwer Business

16. e. Clinical Features of Rubella Disease

Cataracts & other ocular defect

Heart defects

Intra uterine growth retardation

Failure to thrive

Mortality within the first year

Microcephaly

Mental retardatin

Murray, Patrick R. 2009. Medical Microbiology 6th Edition. Philadelphia :

Churcill Livingstone Elsevier

17. Red Flags

Red flag is an informal term that, in this context, simply implies that some

aspect of the child’s development has been noticed as at risk for falling outside the

range deemed typical. A red flag may be discovered during a standardized

developmental screening or through the ongoing, daily interactions between the

infant/toddler caregiver and child. In essence, a red flag is a signal to pay

increased attention to the aspect of concern in a child’s development, and to be

even more intentional in documenting observations and providing opportunities

for the child to acquire the skill.

Red flags guidliness (6-24 months):

1) 6 month of age

a. Fine motor: Infant is unable to hold or grasp an adult finger or a toy/object

for a short period of time, persistence of grasp reflex, and consistently

ignores or has difficulty using one side of body; or uses one hand

exclusively

b. Gross motor: Does not pull up to sit or does not roll over, baby is unable to

hold head in the middle to turn and look left and right and asymmetry (i.e.

a difference between two sides of body or body too stiff or too floppy)

c. Vision: Turning or tilting head to use only one eye to look at things,

Holding toys close to eyes, or no interest in small objects and constant

jiggling or moving of eyes side-to-side

d. Speech and language: Early babbling stops, Does not respond when called

and a lot of colds and ear infections

e. Cognitive : Unable to follow moving objects with his/her eyes and will not

reach out to explore/touch objects

f. Social : Unresponsive to a familiar voice, no eye contact, unresponsive to

social situations (i.e., flat affect), not smiling socially

g. Emotional: Unresponsive to familiar caregivers, Extreme irritability and

unresponsive to social situations

2) 12 month of age

a. Fine motor: Consistently ignores or has difficulty using one side of body

or uses one hand exclusively

b. Gross motor: Baby is unable to hold head in the middle to turn and look

left and right and asymmetry (i.e. a difference between two sides of body

or body too stiff or too floppy)

c. Vision: Unusually short attention span; will only look at you if he or she

hears you, turning or tilting head to use only one eye to look at things,

eyes that cross, turn in or out, move independently, no interest in small

objects and pictures, and constant jiggling or moving of eyes side-to-side

(roving)

d. Speech and language: Lost vocalization

e. Cognitive : Does not make sounds to get attention, does not search for

dropped or hidden objects and child does not respond to caregiver

interactions

f. Social : Will not show interest or participate in social situations,not

laughing in playful situations,hard to console, stiffens when approached

g. Emotional: Will not seek comfort when upset

3) 18 month of age

a. Fine motor: Infant is unable to hold or grasp an adult finger or a toy/object

for a short period of time, unable to use hands in a variety of ways,

turning, twisting, throwing, etc and unconsistently ignores or has difficulty

using one side of body, or uses one hand exclusively

a. Gross motor: Baby is unable to hold head in the middle to turn and look

left and right and asymmetry (i.e. a difference between two sides of body

or body too stiff or too floppy)

b. Vision: Eyes that itch or burn; sensitivity to bright light and sun, unusually

short attention span; will only look at you if he or she hears you,

avoidance of tasks with small objects, turning or tilting head to use only

one eye to look at things, eyes that cross, turn in or out, move

independently, and constant jiggling or moving of eyes side-to-side

c. Speech and language: Failure to do what they may to do

d. Cognitive : Does not imitate simple actions, does not show any

understanding of cause and effect. does not search for objects when moved

from within sight to out of sight

e. Social : Does not explore the environment, very passive responses, does

not show preferences and dislikes, child ignores, avoids or is hostile with

caregiver after separation, and shows little fear towards a new room or

stranger

f. Emotional: Facial expression shows little variation, child shows few

emotions, does not seek comfort in a person or object when distressed

4) 12 month of age

a. Fine motor: Unable to use hands in a variety of ways, turning, twisting,

throwing, etc

b. Gross motor: Unable to walk with heels down

c. Vision: Eyes that itch or burn; sensitive to bright light and sun, avoidance

of tasks with small objects, turning or tilting head to use only one eye to

look at things

d. Speech and language: Lack of face to face or eye contact and loss of

speech

e. Cognitive : Misses small objects when reaching for them and does not use

trial and error to solve problems

f. Social : Does not make face to face contact during play or any interactions,

does not show affection for familiar people or objects, child kicks, bites

and scream easily and without provocation, and rocks back and forth

g. Emotional: Failure to talk about feelings, show preferences of likes and

dislikes, show pride and pleasure at new accomplishments and xpress

negative feelings

Department of Maternal and Child Health. 2010. Infant/Toddler Development, Screening, and Assessment. Chapel Hill : The University of North Carolina