Transcript Windows to the Acoustic World: A Review of

Windows to the Acoustic World: A
Review of Pathologies Involving the
Oval, Round, and ‘Third’ Windows.
Authors: Rickin Shah, MD
Ashok Srinivasan, MD
University of Michigan
Department of Radiology
Disclosures
None
Special Thanks to
Danielle Dobbs
for illustrations
Objectives
To review physiology of hearing and the importance of
the oval and round windows in this process
To discuss pathologies involving the oval and
round windows
To describe the 'third window' phenomenon and present
illustrated examples of different causative etiologies
Anatomy
CT Anatomy – Axial Sections
A
Courtesy of Dr. Hoeffner
B
•
3 – Apical cochlear turn
•
4 – Middle cochlear turn
•
5 – Basal cochlear turn
CT Anatomy – Axial Sections
C
Courtesy of Dr. Hoeffner
D
•
M – malleus
•
I – incus
•
V – vestibule
•
IAC – internal auditory canal
CT Anatomy – Axial Sections
E
F
•
Mo - Modiolus
Courtesy of Dr. Hoeffner
•
V – vestibule
•
LSSC – lateral semicircular canal
CT Anatomy – Coronal Sections
G
Courtesy of Dr. Hoeffner
H
•
1 – Facial nerve recess
•
2 – Sinus tympani
MR Anatomy
J
I
Axial Section
•
Asterisk - cochlea
Courtesy of Dr. Hoeffner
Coronal Section
•
‘White arrow heads – Internal auditory canal
Sound Transmission
• Outer ear channels sound (pressure
waves) to the tympanic membrane
• The pressure wave is comprised of
alternating high and low pressures
which are converted to mechanical
energy at the tympanic membrane
(TM).
• High pressure causes compression
(inward displacement of TM) while low
pressure causes rarefaction (outward
displacement of TM)
http://www.slideshare.net/schwartzcm/ch-10-senses-part-ii
Sound Transmission
• The ossicular chain is attached to the TM and amplifies and transmits
the mechanical energy to the oval window. Due to mechanical
advantage, the displacement of the stapes is greater than the malleus
which allows ability to hear faint noises
• Oval and round windows have comparatively larger surface area than
length to minimize impedance of fluid and transmit sound (pressure
waves)
• Cochlea is filled with
perilymph (incompressible
fluid)
• Each compression of the
oval window converts the
mechanical energy as bulk
motion of perilymph fluid
http://www.slideshare.net/schwartzcm/ch-10senses-part-ii
Sound
Transmission
• Cochlea is lined by
cells called Organ of
Corti which contain
hair cells.
• The movement of
fluid travels along
the scala vestibula
(upper
compartment) from
the oval window
then along the scala
tympani to the
round window.
http://galleryhip.com/transmission-of-sound-through-the-ear.html
Sound Transmission
Each sound wave bends certain hair
cell projections based on their natural
frequency
Each bend of the hair cells converts
the mechanical energy into electric
energy which is sent to the brain
Semicircular canals do not play a role
in hearing but used to detect
rotational acceleration in their planes
Oval Window Pathology
Diagnosis: Oval Window Atresia
Absent cleavage plane between lateral
semicircular canal above and cochlear
promontory below.
Abnormal fixation of stapes on ossified web
over the oval window which results in
conductive hearing loss
Associated with anomalous stapes and
malpositioned facial nerve.
CT findings:
Ossified web replaced normal oval window
Inferomedial positioned tympanic CN 7
Pearl:
Must locate CN 7 for surgeon to ensure safe
correction
Oval Window Pathology
Diagnosis : Calcified annular ligament
and crura of the stapes
Results in abnormal fixation of stapes
on oval window
Clinically can present with conductive
hearing loss
CT features:
Ossification or calcification at the
insertion of the stapes on the oval
window
Round Window Pathology
• Very rare
• Can have atresia of the round window
Dehiscence
• There is a ‘third’ window to the membranous labyrinth that a
dissipates a fraction the sound toward the semicircular canals
• This sound wave causes deflections of the cupula which
stimulates the sensation of movement.
Semicircular Canals
Dehiscence
Sound and/or
pressure
induced
vestibular
symptoms
Increased
sensitivity of
bone
conducted
sound
Decreased
sensitivity of
air conducted
sound
Sound induced vestibular symptoms
Flow of fluid pressure
wave through the
dehiscence and away from
the vestibule and cochlea
There is excitation of
the cupula resulting in
motion sensation
and decrease sound conduction in cochlea
Impact on Bone Conducted Hearing
Normally, there is pressure difference
between the scala vestibula and scala
tympani which allows for perception of bone
conducted sound
A pathologic window on the scala vestibula
side increases the pressure difference
This causes larger fluid movement of the
vestibula side and improves the cochlear
response to bone conducted sound
Impact on Air Conducted Hearing
Mechanical pressure wave
transmitted onto oval window by
stapes
Some perilymph fluid is displaced
away from cochlea
This causes decreased response of
cochlea to air conducted sound
Positive Tullio phenomenon
(noise induced vertigo)
Coronal
Positive Tullio phenomenon
(noise induced vertigo)
Sagittal
Superior Semicircular Canal Dehiscence
• Absence of bony roof of the SSC of unclear etiology
• Thinning of tegmen tympani maybe associated
• Tullio phenomenon is a clinical manifestation with sound
induced vertigo and/or nystagmus
• Should be considered in patients with suspected conductive
hearing loss but intact TM and normal middle ears
• Pearl: asymptomatic thinning of SSC can occur and usually
only seen on one coronal or axial section
Treatment
• Fascia and/or bone chip plugging of
dehiscence
• Resurfacing of the dehiscence with fascia
and bone graft
Poschl and Stenver views are helpful in diagnosis to see > 2 mm of dehiscence.
Stenver
Poschl
Positive Tullio phenomenon
(noise induced vertigo)
Stenver’s view
Other Causes of the
‘Third Window’
Posterior Semicircular Canal (PSCC)
Dehiscence
Axial section demonstrating dehiscence of the
posterior semicircular canal from a high riding jugular bulb.
Vestibular Aqueduct Dehiscence
Axial section demonstrating dehiscence of the
vestibular aqueduct from a high riding jugular bulb
PSCC and Vestibular Aqueduct
Dehiscence
• Reported incidence is lower than superior
semicircular dehiscence
• Frequently due to a high riding jugular bulb
• Diagnosis must be made in conjunction with
clinical exam and tests.
Otosclerosis
• Lytic spongy bone of unclear etiology which
starts just anterior to oval window (fissula
ante fenestram)
• Can progress along medial wall of the
middle ear and may involve the cochlear
bony labyrinth
• It can cross the stapedial annular ligament
and fixate the stapes to the oval window
causing conductive hearing loss
Cavitary otosclerosis
• This can create a connection between the
membranous labyrinth and middle ear
results in a pathologic third window
• Fenestral and cochlear otosclerosis do not
cause a ‘third’ window phenomenon
Bilateral cavitary otosclerosis
Axial sections
Cholesteatoma
• Comprised of squamous
epithelium and keratin
• Appears pearly white or
pale yellow
• CT - Erosion into cochlear
promontory
• Creates pathologic ‘third’
window
Coronal
Summary
• Understanding the complex temporal anatomy is
key for interpretation.
• There are many structural causes for conductive
hearing loss and identifying the oval and round
window pathologies is important.
• There are many causes for the ‘third window’
phenomenon and identifying the various entities is
important for clinical management.
References
•
Bou-Assaly W, Mukherji S, and Srinivasan A. Bilateral Cavitary Otosclerosis: A Rare Presentation of
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doi.org/10.1016/j.clinimag.2013.07.007
•
Merchant S and Rosowski J. Conductive Hearing Loss Caused by Third Window Lesions of the Inner Ear.
Otol Neurotol. April 2008; 29(3):282-289. doi:10.1097/mao.0b013e318161ab24.
•
Alarcon A, Jahrsdoerfer R, and Kesser B. Congenital Absence of the Oval Window: Diagnosis, Surgery,
and Audiometric Outcomes. Otol Neurotol. 2007; 29:23-28.
•
Zeifer B, Sabini P, and Sonne J. Congenital Absence of the Oval Window: Radiologic Diagnosis and
Associated Anomalies. Am J Neurorad. Feb. 2000; 21:322-327.
•
Curtin H. Superior Semicircular Canal Dehiscence Syndrome and Multi-Detector Row CT. Radiol. 2003;
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Minor L, et al. Dehiscence of Bone Overlying the Superior Canal as a Cause of Apparent Conductive
Hearing Loss. Otol Neurotol. 2003; 24:270-278.
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Russo J, et al. Posterior Semicircular Canal Dehiscence: CT Prevalence and Clinical Symptoms. Otol
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