Download Imaging conductive hearing loss

Imaging conductive hearing loss
Poster No.:
C-1556
Congress:
ECR 2012
Type:
Educational Exhibit
Authors:
R. Swamy , P. Khatri , S. Ghosh-Ray , R. K. Lingam ; Harrow/
1
1
1
2 1
2
UK, HA13UJ/UK
Keywords:
CT-High Resolution, CT, Head and neck, Ear / Nose / Throat,
Anatomy, History, Congenital
DOI:
10.1594/ecr2012/C-1556
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Learning objectives
1. To outline the essential CT anatomy of the conductive hearing pathway
2. To review the common causes of conductive hearing loss in adults and to illustrate
their radiological features on high resolution CT of the temporal bones.
3. To highlight the important CT features which guide surgical management.
4. To note the limitations of CT in the imaging of conductive hearing loss.
Background
There are many causes of conductive hearing loss. High resolution CT, due to its
excellent depiction of the anatomy of the conductive hearing pathway, can aid in the
detection and management of the various causes.
Sound passes down the external auditory canal (EAC) to the tympanic membrane. This
energy is then amplified due to the relative size of the tympanic membrane to the oval
window and lever action of the connecting ossicles. Fig. 1 on page 2
Conductive hearing loss (CHL) disrupts this normal passage of sound between the
external ear and the cochlea.
The clinical evaluation of CHL includes a history of hearing loss associated with ear
discharge/fullness/pain, trauma, tinnitus and vertigo. The examination involves otoscopy,
tuning fork tests and a complete head and neck examination (as needed).
A Tympanogram is performed which measures mobility of tympanic membrane.
Acoustic reflex can be performed to detect the presence of a stapedial reflex which can
be diminished in otosclerosis.
Pure Tone Audiogram (PTA): measures hearing thresholds via air and bone conduction.
An air-bone gap suggests CHL. Fig. 2 on page 3
Images for this section:
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Fig. 1: Image of the normal conductive hearing pathway. Sound travels through the
external auditory canal, through the tympanic membrane via the middle ear ossicles into
the inner ear.
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Fig. 2: Figure 2: demonstrating the investigation of hearing loss with (a)normal
tympanogram,(b)Ossicular discontinuity - hypermobile TM, (c)Normal Audiogram,
(d)Audiogram showing an air-bone gap typical of otosclerosis (double arrow)
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Imaging findings OR Procedure details
There are many causes of conductive hearing loss. High resolution CT, due to its
excellent depiction of the anatomy of the conductive hearing pathway, can aid in the
diagnosis and management of the various causes.
Conductive deafness, can be secondary to causes from the external auditory canal, the
middle ear or bony labyrinth Table 1 on page 8 . Below is a brief description of the
various causes and their appearances on high resolution CT of the temporal bones.
External auditory canal(EAC):
1. Wax: Luminal low density material filling the EAC. No bony erosion or expansion of
the EAC Fig. 3 on page 9
2. EAC atresia: Hearing loss caused by inefficient conduction of sound to the inner ear.
Essentially, children with aural atresia have hearing loss because the sound cannot travel
into the (usually) healthy inner ear-there is no ear canal, no eardrum, and the ossicles
are underdeveloped. Fig. 4 on page 11 Fig. 5 on page 10. A CT is perfomed to
evaluate the middle and inner ear structures
3. Keratosis obturans: Is caused by abnormal accumulation and obstruction of the bony
external auditory canal from desquamated keratin without erosive bony changes. Imaging
demonstrates homgenous soft tissue within EAC with bony expansion but no destruction.
CT is performed to evaluate for any bony erosion or suspicious features. Fig. 6 on page
12 Treatment would need excision of keratin plug which may require anaethesia.
4. Otitis externa: Presents with otorrhoea and otalgia, usually occurs in elderly diabetic
patients. On CT destructive, osteomyelitic appearance of the bony EAC affecting the
inferior portion with spread of infection/ abscess formation in the parotid space/ mastoid/
TM joint.
5. EAC cholesteatoma: Erosive soft tissue mass +/- bony flecks in matrix with scalloping
of margins. Fig. 17 on page 23
5. Medial canal fibrosis: Band of soft tissue filling the medial EAC, abutting the tympanic
membrane. Surgical intervention corrects the hearing loss. Fig. 19 on page 25
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6. EAC osteoma: Rare benign focal, pedunculated bony overgrowth of osseous EAC with
normal overlying soft tissues. Usually asymptomatic and an incidental finding. Clinically
difficult to differentiate from EAC exostoses. Fig. 7 on page 14 Fig. 8 on page 13
7. Eac exostoses: Also called "surfers ear" is a benign overgrowth of the bony EAC,
lesions are usually located medial to isthmus of EAC. Patients are usually young males
with chronic history of prolonged cold water exposure( swimmers, surfers, divers).
8. Tumours: Occur in elderly patients., secondary involement from regional tumours is
commoner than primary. CT demonstrates osseous destructive changes which is crucial
as bony invasion predicts treatment outcome. The parotid nodes are 1st order drainage
nodal group.
9. Bony dystrophies: Pagets disease, Fibrous dysplasia, osteopetrosis
These are rare and cause hearing loss either by narrowing of the EAC or middle ear or
involve the otic capsule.Fig. 16 on page 22
Wet middle ear:
1. Chronic serous otitis media: Commonest cause of CHL in children. Imaging shows non
dependant opacification of the middle ear +/- mastoid with or without ossicular erosion.
Improves with grommet insertion. Fig. 20 on page 26
2. Cholesteatoma: Accumulation of desquamated keratin epithelium in the middle ear
cleft or any other pneumatized portion of the temporal bone. Imaging demonstrates
non dependant soft tissue in the Prussack's space with scutum, ossicle or lateral
epitympanic wall erosion. CT is performed to look for extent and complications of
cholestatoma( labyrinthine fistula, tegmen erosion etc). Surgery is treatment of choice
with follow up to look for recurrance. Fig. 10 on page 16
Dry middle ear:
1. Ossicular disclocation:
(a) Traumatic: Longitudinal fractures are caused by tempro-parietal trauma, associated
with high incidence conductive deafness secondary to ossicular disruption/injury. These
fractures typically spare the otic capsule and sensorineural hearing loss is unsual
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In contrast, transverse fractures are secondary to fronto occipital trauma, often involve the
inner ear and cause sensorineural hearing loss. A conductive hearing loss can present
at a later stage due to ossicular disruption.
Imaging: Best identified on axial high resolution CT images. CT or MR angiogram may
be performed if surrounding structues are involved.
Ice cream(head of the Malleus) off the cone( incus) Fig. 14 on page 20
(b) Post surgical: Ossicular disruption may be a consequence of middle ear surgery or
dislodgement of an ossicular prosthesis. Fig. 11 on page 17
2. Tympanosclerosis/ myringosclerosis: Calcific, bony or fibrous middle ear foci form
secondary to chronic otitis media. Involvement of the tympanic membrane only is referred
to as myringosclerosis. Fig. 9 on page 15. CT is useful to exclude a cholesteatoma
and ossicular disruption.
3. Otosclerosis: Presents as uni/bi lateral hearing loss(conductive or mixed) in a young
patient. Absent stapedial reflex and Carhart's notch ( air-bone gap on audiogram)is not
always seen. Can be of fenestral or cochlear types.Fig. 13 on page 19
On CT Fenestral otosclerosis(FOto) is seen as a radiolucent focusat the anterior margin
of oval window in the early phase. Late phase shows heaped up new bone formation
around oval and round windows.
Cochlear otosclerosis(COto) is seen as focal lytic plaques in pericochlear labyrinth.
Checklist:
"If COto is present, FOto is also present- must always look at anterior margin of oval
window for FOto"
Check involevement of round window- narrowing of it makes cochlear implantation
difficult.
Rare causes
4. Semicircular canal dehiscence(SSCD) :
Rare cause of conductive hearing loss with few reported cases.
SSCD introduces a 'third' window into the inner ear which produces the airbone gap by
(1) shunting air-conducted sound away from the cochlea, thus elevating air conduction
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thresholds, and (2) increasing the difference in impedance between the scala tympani
2
and scala vestibuli, thus improving thresholds for bone-conducted sound . Fig. 12 on
page 18
5. Oval window atresia:
Ossific membrane seen overlying the oval window with superior migration of the facial
nerve recess where the oval window should be.
Fig. 15 on page 21
Overall CT is extremely good at demonstrating most causes of conductive hearing loss,
however not all patients with conductive hearing loss require a CT:
1.
2.
3.
4.
If an abnormality is confidently diagnosed clinically, is non-cancerous and
is of known anatomical extent - CT does not aid clinical management.
However where there is diagnostic uncertainty, and to stage cancerous
lesions or define anatomical extent of non-cancerous lesions, such as
infections or benign tumours - CT is a valuable investigation.
CT imaging is also helpful in planning surgical approaches to best target
lesions, allows identification anatomical abnormalities/variations as well as
disease complications (such as vestibular fistulae and tegmen defects).
Being able to show patients their disease and its proximity to vital structures
is also valuable during the consenting process for a surgical procedure.
The limitations of CT should also be recognised, it does not necessarily pick
up all causes of a conductive hearing loss( for eg- only 70% of otosclerosis
3
is confidently diagnosed on CT ) and is at the cost of radiation to the patient
Images for this section:
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Table 1: Table summarising the known causes of conductive hearing loss.
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Fig. 3: Luminal soft tissue filling the external auditory canal(arrow) is seen on the left in
keeping with wax.
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Fig. 5: Congenital atresia of the left external auditory canal: there is complete atresia of
the inner two thirds of the external auditory canal( straight arrow). The pinna is visualised
but not well formed(curved arrow). CT was performed for reconstruction surgery
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Fig. 4: Congenital left external auditory canal( EAC)atresia (arrow), normal EAC is seen
on the right side
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Fig. 6: Keratosis obturans: Middle aged male presented with 2-month history of right
hearing loss and auditory canal polyp protruding from the ear. On coronal high resolution
CT of the temporal bones, extensive soft tissue (block arrow) is seen in the external
auditor canal (EAC) with complete opacification of its inner 2/3rds abutting the tympanic
membrane (star). The EAC is expanded with scalloping of the bony margins(curved
arrow).
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Fig. 8: EAC osteoma: Another patient, large bony outgrowth right EAC, on close
inspection it is seen attached to the anterior wall of the EAC by a peduncle ( curved arrow)
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Fig. 7: Right EAC osteoma: bony outgrowth in EAC, peduncle is again seen( curved
arrow)
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Fig. 9: Myringosclerosis: Middle aged woman presented with bilateral chronic
serous otitis media. On clinical examination the right tympanic membrane had
a central perforation with inferior white keratin and possible new bone formation
within the hypotympanum. High resolution CT of the temporal bones revealed
extensive calcification of the tympanic membrane on the right(arrow)in keeping with
myringosclerosis. In addition on the right, there are abnormal ectopic calcifications within
the middle ear cavity around the ossicles (starred)in keeping with tympanosclerosis
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Fig. 10: Congenital cholesteatoma: Coronal High resolution CT shows middle ear soft
tissue with ossicular destruction:figures a and b( arrows), and soft tissue in mastoid with
erosion of bony septae : figure c( arrow)
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Fig. 11: Patient with bilateral ossicular prostheses presented with right sided conductive
hearing loss. MIP images from high resolution CT of the temporal bones revealed
an incudo-stapedial( prosthetic) dislocation( block arrow). Normal alignment of the
osscicular prosthesis is shown on the left( curved arrow). Appearance of a normal in-situ
stapedial prosthesis is shown ( inset picture, double arrow)
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Fig. 12: High -resolution Coronal CT of the temporal bones demonstrates bilateral
superior semicircular canal dehiscence( arrows), reformatted sagittal- oblique CT image
through the left semicircular canal shows full size of the dehiscence
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Fig. 13: Bilateral fenestral and retrofenestral otosclerosis: Patient presented with rightsided conductive hearing loss with a history of left-sided surgery: On the high resolution
CT of the temporal bones, focal bony lucencies are seen bilaterally at the fissula
antefenestram(curved arrows) in keeping with fenestral otosclerosis. In addition, in the
same patient, bony lucencies(arrows) are also seen bilaterally around the cochlea in
keeping with cochlear (retrofenestral) otosclerosis
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Fig. 14: Right temporal bone fracture with disclocation of the Incudo-malleal joint:
icecream off cone(curved arrow). Normal incudomalleal( cone and cream of the ice cream
cone respectively)joint is shown separately on the right( double arrow)
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Fig. 15: Patient with left sided congenital hearing loss.CT demonstrates ossification of the
oval window( block arrow) with posterior migration of the stapes(double arrow). Normal
oval window is shown on the left( curved arrow)
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Fig. 16: Patient with known fibrous dysplasia in long bones present with conductive
hearing loss: High resolution CT of the temporal bones demostrated demineralised/
fibrous appearing ossicles( arrows)thought to be secondary to fibrous dysplasia. Normally
mineralised ossicles are shown on the right(double arrow).
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Fig. 17: EAC Cholesteatoma: Large soft tissue seen in the left EAC (arrow) with erosion
of the posterior wall of EAC( chevron), this extends into the mastoid with bony destruction.
Differential diagnosis would include Squamous cell cancer and malignant otitis externa
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Fig. 18: Agressive soft tissue mass in the post surgical (canal wall down mastoidectomy)
right EAC . Biopsy confirmed inflammatory tissue only in keeping with otitis externa.
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Fig. 19: Medial canal fibrosis: Note the presence of concentric soft tissue in the medial
aspect of the left EAC with opacification along the tympanic membrane( arrow)
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Fig. 20: Child with bilateral chronic serous otitis media. Note the opacification of both
middle ears with no ossicular destruction( arrows)
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Conclusion
CT can aid in the diagnosis of a variety of causes of conductive hearing loss.
CT also provides other information which is important in the management of the various
causes, in particular the multiplanar advantage of CT with axial and coronal imaging is
a valuable tool as a roadmap for surgical planning
.
Personal Information
Subspeciality Head and Neck Rdaiology SpR at North-West London hospitals NHS trust.
ESOR Head and neck radiology subspeciality fellowship training centre. London
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