Wk 1 - ME Anatomy & Development Flashcards
What are the 3 stages of human prenatal development?
Pre-embryonic (0-3 wks)
Embryonic (4-8 wks)
Fetal (9wks - birth)
Pathogens or trauma during which stage of prenatal development is likely to cause spontaneous abortion or miscarriage?
Pre-embryonic
Many developmental auditory disorders begin d/t maldevelopment at which prenatal stage?
Embryonic
High levels of noise exposure can cause cochlear damage during which prenatal stage?
Fetal
What happens during the pre-embryonic stage?
- Fertilization
- Cleavage of the zygote as it passes down the uterine tube
- Implantation into the uterine wall
- Hypoblast formation
- Bilaminar disc formation
- Formation of the primitive streak, notocord, & neural tube
What happens during the embryonic stage?
- Development of the branchial structures
- Initial formation of the external ear, TM, ME cavity and Eustachian Tube
- Initial development of the cochlea duct, otic pit, utricle, saccule, and vestibular and cochlear portions of the membraneous labyrinth
- Initial development of the pinnae
What happens during the fetal stage?
- rapid growth and differentiation of organ systems
- less susceptibility to teratogens
- development of sensory structures of the ear
Newborns have very thin, flaccid pinnae. What are the implications of this?
The spectral transfer function at each location in space is less pronounced (less resonant), and so is less useful in elevation perception
- babies are able to localize in the horizontal plane by about 5 months; vertical localization matures beyond 1 year of age
Which branchial arches do the pinnae develop from?
1st (mandibular) and 2nd (hyoid)
What types of anomalies can we expect from abnormalities of the 1st branchial arch? Give 2 syndromic examples
Mandibular and ME anomalies
- Treacher Collins Syndrome - abnormal outer ear, mandible, and lower eyelid
- Pierre Robin Sequence - deformed mandible, eyes, ears, and cleft palate
Describe stenosis and atresia. What type of hearing loss can atresia cause?
Stenosis = partial closure of the ear canal
Atresia = complete closure of the ear canal; may cause 50-60 dB HL conductive loss
What type of maldevelopment can cause 10 dB of hearing loss at 5 kHz?
Anotia/absent pinna
T/F: Maldevelopment of the pinna often occurs in isolation
False - it will often occur with abnormalities of the ear canal - such as stenosis or atresia - as well
Microtia is due to incomplete development of which branchial arches before which week of gestation?
The 1st and 2nd branchial arches before the 5th week gestation
What syndromes have bilateral microtia?
Treacher Collins
Fraser, Nager, and Goldenhar syndromes
(most are genetic disorders associated with hearing loss)
What is it called when the pinna comes to a sharp point with forward folding (d/t deficiency in the 4th hillock/maldevelopment b/w 6th and 8th week gestation)?
Satyr Ear
Describe Stahl Ear?
- abnormality in superior crus of antihelix
- may have “third” crus
- poorly formed helix; hard, less elastic cartilage
- may be d/t abnormality in uniting of 4th and 5th hillocks
What is the name of the small growth that can occur at the superior part of the helix? What is is d/t?
Darwinian Tubercle
- d/t small growth in the position of the 5th hillock
- autosomal dominant trait
What is Lop Ear?
- down folding of helix and scapha
- problem with the intrinsic musculature or abnormal growth of 3rd hillock
What is the name of the outer ear deformity that causes a cleft b/w the helix and the lobe?
Question Mark Ear
- defects b/w 5th and 6th hillocks
- maldevelopment may occur b/w 6th and 8th week gestation
Name 3 differences in the EAM of infants compared to adults
In infants:
- the TM is nearly parallel to the canal wall
- TM is oval, not round
- TM is thicker
- EAM is ~3-5 mm shorter
- EAM wall is thin cartilage, soft and compliant
What impact does the thinner, more compliant EAM of infants have on resonant frequency?
Infants have a higher resonant frequency (~3.8 kHz vs ~3 kHz)
The pinna forms from which 2 branchial arches?
1st and 2nd
The EAM forms from which branchial cleft?
1st
- plug that degenerates fetally
The TM has an external layer that is continuous with EAM (___-derm), an inner layer continuous with the ME cavity (___- derm) and a middle, fibrous layer
Ectoderm
Endoderm
Cartilaginous derivatives of the 1st and 2nd branchial arch contribute to the development of _________
ME ossicles
What ossicular structures does the 1st branchial arch contribute to?
Head and neck of malleus
Body and short process of incus
The 2nd branchial arch contributes to with ossicular structures?
- manubrium of malleus
- long process of incus
- head, neck, and footplate of stapes (lateral surface)
The medial surface of the stapes footplate comes from which structure?
The Otic Capsule
Ossicular anomalies often do not occur in isolation. If there is a single abnormality, what would we expect it to be?
- Disconnection b/w incus and stapes
- Long process of incus is absent or abnormal and superstructure of the stapes malformed
Malformation of the ossicular chain rarely occurs as a solitary lesion. What is it usually associated with?
Other temporal bone anomalies (atresia of the EAM)
Due to the smaller size of the middle ear, what changes in impedance can we expect in infants?
Increased impedance
The Eustachian tube develops from which structure?
The 1st pharyngeal pouch
What is the purpose of the Eustachian Tube (ET)?
Ventilation and clearance
Why do we see a lot of ear infections in young children?
The ET is short, straight, horizontal and narrow. Infants also only have one muscle (the tensor paliti) to open it (vs 2 in adults - the tensor paliti and levator paliti), and it’s close to the adenoids and can be easily blocked
