Chapter 31 - Otology anatomy, embryology, radiology Flashcards
Where outer, middle and inner ear structures come from embryologically
Outer and middle: 1/2 arches, 1 pouch/groove
Inner ear: bilateral otic placodes
Detection of angular and linear acceleration
Semicircular canals- angular
Utricle, saccule- linear (horiz, vert, respectively)
Pathway of auditory information to brain
Hair cells Auditory nerve Cochlear nucleus Superior olivary complex (crossover here) lateral lemniscus inferior colliculi medial geniculate body auditory cortex (Upper Temporal Lobe/Heschl)
Cochlea basilar membrane vs apex
BM: thick, stiff, narrow, for high frequencies
Apex: thin, flexible, wide for low frequencies
Anatomy of ear canal
Lateral third cartilaginous, hair follicles, cerumen/sebaceous
Medial 2/3 osseus
Length and resonance frequency of EAC
2.5cm adults
3-4kHz
6 Hillocks of His
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
Function of auricle
Collect, direct sound toward TM
Shape creates small high-pitched frequency resonances helping you localize sound vertically
From which branchial structure does the EAC develop?
1st branchial groove
Treacher-Collins
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
Goldenhar syndrome (Oculo-Auriculo-Verteral Synd)
1/2 arch malformation
Unilateral craniofracial malf
hemifacial microsomia, eye, strabismus, anotia, tags, atresia
Scoliosis
Branchio-oto-renal syndrome
AD Hypoplastic/absent kidneys pit/tag middle ear malformation branchial cleft cyst/fistula
CHARGE
Coloboma Heart Atresia choana Retard growth/develop Genital (hypogonad) ear (low set, lop ears, asymmetric pinnae)
DiGeorge sequence
22q11 deletion
Hypoplasia thymus/parathyroid
Cardiovascular
Low ears, micrognathia, hypertelorism, short philtrum, cleft palate, choanal atresia
Crouzon syndrome
AD
Craniosynostosis
exophthalmos, hypotelorism, strabismus, beak-shaped nose, hypoplastic maxilla, low ears, atresia/stenosis canal
Middle ear anatomy: what it contains, and is continuous with
1-2cm^3
ossciles, stapedius, tensor tympani, chorda
continuous with mastoid air cells via antrum, nasopharynx via ET
1st branchial arch: ossicles
head/neck malleus
body incus
2nd arch: ossicles
long process malleus, incus
stapes
Where does stapes footplate derive from
2nd arch and otic capsule
Embryology of annulus
NCC-origin, mesenchyme, ossifies during 3rd month gestation
Embyrology of TM
outer ectoderm
middle mesoderm
inner endoderm
Stapedius and tensor tympani
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
Four sections of temporal bone
squamous
petrous
tympanic
mastoid
Describe course of CN VII through T bone
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
Imaging necessary to evaluate facial nerve
CT - see osseus facial nerve canal integrity
MRI - nerve itself
Need both!
Endolymph vs perilymph
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
What maintains the endocochlear potential?
Stria Vascularis, which is in outer wall of membranous labyrinth
Inner vs outer hair cells
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)
How hair cells are stimulated
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
Embryology of inner ear
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
How much of congenital deafness can be attributed to membranous dysplasia? How would you test for this?
90%
Can only detect histopathologically
Only 5-15% congen deaf have otic capsule anl (would show on IMG)
Describe SCC dehiscense
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
Cochlear Aplasia: location, age of arrest, appearance
osseus and membranous labyrinth
5th wk
Only see a vestibule and SCCs
Cochlear hypolasia: location, age of arrest, appearance
Osseus and membranous
6th wk
Single turn or less
Incomplete partition - Mondini: location, age of arrest, appearance
Osseus/Memb
7th wk
1.5 turns, partial or complete lack of interscalar septum
Common cavity: location, age of arrest, appearance
Entire osseus and membranous labyrinth
4th week
Cochlea and vestibule are confluent, forming ovoid cystic space, no internal architecture
Complete labyrinthine aplasia (Michel): location, age of arrest, appearance
Entire osseus and membranous lab
Prior to 4th wk
complete absence inner ear structures
Which vestibular organ also responds to auditory stimuli?
Saccule
Because of this the vestibular-evoked myogenic potential EP test works, to evaluate balance function
Where is the auditory info processed in brain?
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
