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ENT Secrets > Chapter 31 - Otology anatomy, embryology, radiology > Flashcards

Chapter 31 - Otology anatomy, embryology, radiology Flashcards

1
Q

Where outer, middle and inner ear structures come from embryologically

A

Outer and middle: 1/2 arches, 1 pouch/groove

Inner ear: bilateral otic placodes

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2
Q

Detection of angular and linear acceleration

A

Semicircular canals- angular

Utricle, saccule- linear (horiz, vert, respectively)

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3
Q

Pathway of auditory information to brain

A 
Hair cells
Auditory nerve
Cochlear nucleus
Superior olivary complex (crossover here)
lateral lemniscus
inferior colliculi
medial geniculate body
auditory cortex (Upper Temporal Lobe/Heschl)
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4
Q

Cochlea basilar membrane vs apex

A

BM: thick, stiff, narrow, for high frequencies
Apex: thin, flexible, wide for low frequencies

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5
Q

Anatomy of ear canal

A

Lateral third cartilaginous, hair follicles, cerumen/sebaceous
Medial 2/3 osseus

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6
Q

Length and resonance frequency of EAC

A

2.5cm adults

3-4kHz

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7
Q

6 Hillocks of His

A

Mesenchyme buds surrounding dorsal end of 1st branchial cleft. 1-3 mandibular (1st) arch, 4-6 from hyoid (2nd) arch

1- tragus
2-3- helix
4-5- antihelix
6- antitragus

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8
Q

Function of auricle

A

Collect, direct sound toward TM

Shape creates small high-pitched frequency resonances helping you localize sound vertically

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9
Q

From which branchial structure does the EAC develop?

A

1st branchial groove

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10
Q

Treacher-Collins

A 
ALso called mandibulofacial dysostosis
AD, complete penetrance, variable expression
down-slanting palperal fissures
auricular malformations (tag, stenosis, atresia)
ossicular abnormalities
malar hypoplasia, mandibular hypoplasia
flat nasal bridge
cleft palate
dental
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11
Q

Goldenhar syndrome (Oculo-Auriculo-Verteral Synd)

A

1/2 arch malformation
Unilateral craniofracial malf
hemifacial microsomia, eye, strabismus, anotia, tags, atresia
Scoliosis

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12
Q

Branchio-oto-renal syndrome

A 
AD
Hypoplastic/absent kidneys
pit/tag
middle ear malformation
branchial cleft cyst/fistula
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13
Q

CHARGE

A 
Coloboma
Heart
Atresia choana
Retard growth/develop
Genital (hypogonad)
ear (low set, lop ears, asymmetric pinnae)
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14
Q

DiGeorge sequence

A

22q11 deletion
Hypoplasia thymus/parathyroid
Cardiovascular
Low ears, micrognathia, hypertelorism, short philtrum, cleft palate, choanal atresia

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15
Q

Crouzon syndrome

A

AD
Craniosynostosis
exophthalmos, hypotelorism, strabismus, beak-shaped nose, hypoplastic maxilla, low ears, atresia/stenosis canal

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16
Q

Middle ear anatomy: what it contains, and is continuous with

A

1-2cm^3
ossciles, stapedius, tensor tympani, chorda
continuous with mastoid air cells via antrum, nasopharynx via ET

17
Q

1st branchial arch: ossicles

A

head/neck malleus

body incus

18
Q

2nd arch: ossicles

A

long process malleus, incus

stapes

19
Q

Where does stapes footplate derive from

A

2nd arch and otic capsule

20
Q

Embryology of annulus

A

NCC-origin, mesenchyme, ossifies during 3rd month gestation

21
Q

Embyrology of TM

A

outer ectoderm
middle mesoderm
inner endoderm

22
Q

Stapedius and tensor tympani

A

CN VII, V3
contracts with high intensity sound, especially low frequency
Stiffen ossicular chain to decrease sound transmission
Protect cochlea from damage
reduce intensity of low-frequency background noise to preserve higher frequency speech info

23
Q

Four sections of temporal bone

A

squamous
petrous
tympanic
mastoid

24
Q

Describe course of CN VII through T bone

A

Exit IAC
Labyrinthine- superior to cochlea, angle forward just sup/lat to cochlea to reach geniculate ganglion, then posterior/inferior turn (first genu)
Tympanic- extend down from genu posteriorly, laterally along medial wall of tympanic cavity, above oval window, below lateral SCC, reach pyramidal eminence, then drop sharp inferior for second genu
Mastoid- after genu, downward in posterior wall of tympanic cavity, anterior wall of mastoid, exit SMF

25
Q

Imaging necessary to evaluate facial nerve

A

CT - see osseus facial nerve canal integrity
MRI - nerve itself
Need both!

26
Q

Endolymph vs perilymph

A

Perilymph- within osseus labyrinth (surrounds membranous labyrinth aka cochlea/vestibular organs), similar to ECF (high Na, low K)

Endolymph- within cochlea/vestibular organs, High K, low Na, like ICF

Difference in ions –> gradient of 80-100 mV allowing transduction of acoustic energy into neural impulse

27
Q

What maintains the endocochlear potential?

A

Stria Vascularis, which is in outer wall of membranous labyrinth

28
Q

Inner vs outer hair cells

A

Both within the organ of corti (which is within the cochlea), overlaid by tectorial membrane
Inner are afferent
Outer are efferent (from brain to hair cells)

29
Q

How hair cells are stimulated

A

Stereocilia (evaginations of apical surface, look like hair)
Sound moves tectorial and basilar membranes differentially –> shear force –> bends stereocilia –> opens/closes ion channels –> receptor potential –> neurotransmitters onto afferent fibers

30
Q

Embryology of inner ear

A

Otic placodes (ectoderm lateral to neural tube rim)
Invagine to otic pits…enveloped by mesenchyme (otocysts)
Ossify labyrnthine between 16-24 wk
Hair cell, auditory neural development complete by 26-28 wk, so fetus can hear 2-3 months prior to birth

31
Q

How much of congenital deafness can be attributed to membranous dysplasia? How would you test for this?

A

90%
Can only detect histopathologically
Only 5-15% congen deaf have otic capsule anl (would show on IMG)

32
Q

Describe SCC dehiscense

A 
CHL
Sound/pressure induced vertigo
autophony
Absence of bone over superior SCC
May be due to incomplete ossification of otic capsule
IMG with High Res CT
33
Q

Cochlear Aplasia: location, age of arrest, appearance

A

osseus and membranous labyrinth
5th wk
Only see a vestibule and SCCs

34
Q

Cochlear hypolasia: location, age of arrest, appearance

A

Osseus and membranous
6th wk
Single turn or less

35
Q

Incomplete partition - Mondini: location, age of arrest, appearance

A

Osseus/Memb
7th wk
1.5 turns, partial or complete lack of interscalar septum

36
Q

Common cavity: location, age of arrest, appearance

A

Entire osseus and membranous labyrinth
4th week
Cochlea and vestibule are confluent, forming ovoid cystic space, no internal architecture

37
Q

Complete labyrinthine aplasia (Michel): location, age of arrest, appearance

A

Entire osseus and membranous lab
Prior to 4th wk
complete absence inner ear structures

38
Q

Which vestibular organ also responds to auditory stimuli?

A

Saccule

Because of this the vestibular-evoked myogenic potential EP test works, to evaluate balance function

39
Q

Where is the auditory info processed in brain?

A

Heschl’s gyrus, on superior surface of temporal lobe, close to sylvian fissure
High frequency medially, low laterally

Auditory association cortex is lateral to this, part of Wernicke’s area

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