Insights Imaging (2014) 5:245–252
DOI 10.1007/s13244-014-0313-9
PICTORIAL REVIEW
Imaging in otosclerosis: A pictorial review
Bela Purohit & Robert Hermans & Katya Op de beeck
Received: 11 November 2013 / Revised: 5 January 2014 / Accepted: 13 January 2014 / Published online: 9 February 2014
# The Author(s) 2014. This article is published with open access at Springerlink.com
Abstract Otosclerosis is an otodystrophy of the otic capsule Keywords Otosclerosis . Fenestral . Retrofenestral . HRCT
and is a cause of conductive, mixed or sensorineural hearing temporal bone . Stapedectomy
loss in the 2nd to 4th decades of life. Otosclerosis is
categorised into two types, fenestral and retrofenestral. Imag- Abbreviations
ing plays an important role in the diagnosis and management HRCT high-resolution CT
of otosclerosis. High-resolution CT (HRCT) of the temporal CHL conductive hearing loss
bone using 1-mm (or less) thick sections is the modality of SNHL sensorineural hearing loss
choice for assessment of the labyrinthine windows and co- MHL mixed hearing loss
chlear capsules. MRI has limited application in the evaluation CI cochlear implantation
of the labyrinthine capsules but is useful for assessment of the
cochlear lumen prior to cochlear implantation in patients with
profound hearing loss. The treatment of fenestral otosclerosis
is primarily surgical with stapedectomy and prosthesis inser- Introduction
tion. Patients with retrofenestral otosclerosis and profound
hearing loss are treated medically using fluorides, but may Otosclerosis is a unique autosomal dominant otodystrophy of
derive significant benefit from cochlear implantation. This the otic capsule. It is also called ‘otospongiosis’ as it is
pictorial review aims to acquaint the reader with the pathology characterised by replacement of the normal ivory-like
and clinical features of otosclerosis, the classical imaging enchondral bone by spongy vascular bone. The decalcified
appearances on CT and MRI, a radiological checklist for foci tend to recalcify, becoming less vascular and more solid.
preoperative CT evaluation of otosclerosis, imaging mimics Patients typically present in the 2nd- 4th decades of life with
and a few examples of post-stapedectomy imaging and conductive hearing loss (CHL), sensorineural hearing loss
complications. (SNHL) or mixed hearing loss (MHL) and/or tinnitus. Oto-
Teaching points sclerosis is commoner in Caucasians as compared to blacks,
• Otosclerosis causes conductive, sensorineural and mixed Native Americans and Asians. The disease is more common
hearing loss in adults. in women and commonly bilateral (85 %). Otosclerosis is
• HRCT of the temporal bone is the diagnostic imaging mo- categorised into two types, fenestral and retrofenestral/
dality of choice. cochlear. Retrofenestral otosclerosis rarely occurs without
• Stapedectomy is used to treat fenestral otosclerosis. fenestral involvement; hence these manifestations are consid-
• Fluorides and cochlear implantation are used to treat ered to be a continuum rather than two separate entities [1–4].
retrofenestral otosclerosis.
Fenestral Otosclerosis
Pathology, clinical findings and imaging
B. Purohit (*) : R. Hermans : K. Op de beeck
Department of Radiology, University Hospitals Leuven,
3000 Leuven, Belgium The more common fenestral type of otosclerosis involves the
e-mail: purohitbela@yahoo.co.in lateral wall of the bony labyrinth. Histologically,
246 Insights Imaging (2014) 5:245–252
Fig. 1 Axial (a) and coronal (b)
HRCT images of the right
temporal bone in an adult patient
with right-sided CHL. A
hypodense demineralised plaque
(arrow) is noted in the region of
the fissula ante fenestram in
keeping with fenestral
otosclerosis
demineralised foci of spongy new bone typically occur in the niche and tympanic segment of the facial nerve canal can also
region of the embryonic fissula ante fenestram, which is a cleft be involved [1–3]. The disease gradually extends to involve
of fibrocartilagenous tissue between the inner and middle ear, the entire footplate of the stapes and may subsequently in-
just anterior to the oval window (Fig. 1). Bilateral involve- volve the cochlea. Heaped-up bony plaques formed in the
ment is common (Fig. 2). The promontory, round window healing phase typically cause narrowing of the oval and round
Fig. 2 Axial HRCT images of
the right (a) and left (b) temporal
bone in an adult patient with
bilateral CHL. Hypodense
demineralised plaques (arrows)
are noted in bilateral fissula ante
fenestram regions in keeping with
bilateral fenestral otosclerosis
Fig. 3 Axial (a,b) and coronal
(c,d) HRCT images of the right
and left temporal bone in an adult
patient with bilateral severe CHL.
Heaped-up bony otosclerotic
plaques are noted causing severe
bilateral oval window narrowing
(arrows)
Insights Imaging (2014) 5:245–252 247
Fig. 4 Axial HRCT images of
the right (a) and left (b) temporal
bone in a patient with bilateral
fenestral otosclerosis.
Otosclerotic plaques are noted
causing bilateral round window
narrowing (arrows), right more
than left
windows. Involvement of the annular ligament leads to me- The classical clinical findings include progressive CHL up
chanical fixation of the stapedo-vestibular joint, which is to about 50–60 dB, absent stapedial reflexes, a normal tym-
responsible for the typical CHL/audiometric air-bone gap panic membrane and no evidence of middle ear inflammation
(Carhart’s notch) [1–5]. Complete obliteration of the oval [1–5].
window may occur in 2 % cases (Fig. 3). This rarely is Imaging is usually not pursued in patients with un-
associated with secondary torsional subluxation of the incus complicated CHL and characteristic clinical findings.
[2]. Otosclerosis can sometimes present as isolated round The treatment of fenestral otosclerosis is primarily sur-
window involvement without pericochlear or oval window gical with stapedectomy and stapes prosthesis insertion
involvement [6]. [1–5].
Fig. 5 a Axial HRCT image of the right temporal bone in an adult patient the fissula ante fenestram. b Axial HRCT image of the same patient as (a)
with progressive right-sided CHL and remote history of ipsilateral head at a slightly higher level. There is also evidence of malleo-incudal
injury. A hypodense demineralised otosclerotic plaque (arrow) is noted in dislocation (arrow)
Fig. 6 Axial (a) and coronal (b) HRCT images of the left temporal bone blunting of the scutum (arrow) is in favour of a cholesteatoma. In
in an adult patient with left-sided CHL and previous history of left-sided addition, a tiny hypodense fenestral otosclerotic focus (arrowheads) is
otitis media. The soft-tissue density noted in the attic (asterisk) causing noted anterior to the oval window
248 Insights Imaging (2014) 5:245–252
Table 1 Reporting checklist for preoperative HRCT of the temporal bone in otosclerosis
Reporting points Clinical and surgical relevance
1. Size and location of plaques Size and location of plaques may correlate with severity of CHL/air-bone gap
2. Status of oval window Complete obliteration may require surgical drilling prior to prosthesis insertion
3. Status of round window Obliteration may result in a poor result after stapedectomy
4. Facial nerve canal Floppy facial nerve may complicate oval window surgery or render this impossible
5. Concurrent middle ear pathology Inflammatory disease must be treated prior to surgery
6. Ossicular chain integrity Ossicular fixation, fusion and fracture may compound CHL
7. Sinus plate and jugular bulb Dehiscent jugular bulb may complicate surgery
8. Inner ear pathology Congenital cochlear and inner ear anomalies may preclude surgery
9. Opposite ear Disease is bilateral in 80-85 % cases, even in absence of symptoms
Fig. 7 Axial (a) and coronal (b)
HRCT images of the right
temporal bone in a child with
suspected left SNHL. The small
lucency seen around the cochlea
(arrow) on both the axial and
coronal images is in keeping with
a cochlear cleft (normal variant)
Fig. 8 Axial (a) and coronal (b)
HRCT images of the right
temporal bone in a patient with
stapedectomy. The radiodense
stapes prosthesis is well
positioned with its distal end
against the oval window
Fig. 9 Axial (a) and coronal (b)
HRCT images of the left temporal
bone in a patient with persistent
CHL, post stapedectomy. The
stapes prosthesis (arrow) is
dislocated posteriorly in relation
to the oval window (arrowhead)
with complete loss of contact
Insights Imaging (2014) 5:245–252 249
suprastructure. All studies are performed without contrast and
the entire petrous temporal bone is included in the sections.
Demineralised hypodense fenestral otosclerotic foci are best
seen on axial HRCT because of the anteroposterior orientation
of the oval window and stapes crura. Fenestral otosclerotic foci
as small as 1 mm in size can be diagnosed on HRCT [1–5].
Some authors have mentioned a correlation between the size of
the fenestral otosclerotic focus and the air-bone gap [5].
Apart from assessing the size and location of plaques and
the narrowing of the oval window, the radiologist must eval-
uate the status of the round window, facial nerve canal, jugular
bulb, middle ear cavity, ossicular chain and inner ear. Oblit-
eration of the round window by the otosclerotic process may
Fig. 10 Para-axial HRCT image of the left temporal bone in a patient reduce the efficacy of stapedectomy and must be mentioned in
with severe vertigo, post stapedectomy. The stapes prosthesis is the report (Fig. 4) [1–3]. Other or associated causes of CHL
dislocated and lies partly within the vestibule (arrow)
and SNHL must be ruled out prior to surgery. These include
congenital ossicular fusion, ossicular discontinuity (Fig. 5),
High-resolution CT (HRCT) of the temporal bone is the inflammatory middle ear disease (Fig. 6) and inner ear pathol-
modality of choice for the preoperative evaluation of otoscle- ogy such as acoustic neuroma and labyrinthitis ossificans [2].
rosis. Typically, very thin axial sections are obtained on a Table 1 describes a recommended checklist for reporting
multidetector CT scanner, followed by axial and coronal preoperative HRCT of the temporal bone with clinical and
reformats, respectively in the plane of and perpendicular to surgical relevance of each of the points.
the lateral semicircular canal. If needed, additional reformats False-negative CT findings may occur in some cases of
can be made, for example along the plane of the stapedial fenestral otosclerosis in the sclerotic phase when there are no
Fig. 11 Para-coronal (a) and para-axial (b) HRCT images of the left However a small sclerotic focus is seen within the vestibule (arrowheads)
temporal bone in a patient with persistent vertigo and left-sided SNHL in keeping with labyrinthitis ossificans. A small fenestral otosclerotic
after left stapedectomy. The stapes prosthesis (arrow) is well positioned. focus (dashed arrow) is seen in the para-axial view
Fig. 12 Axial HRCT images of
the right (a) and left (b) temporal
bone in an adult patient with
severe bilateral SNHL. The
bilateral pericochlear hypodense
‘double ring’ (arrow) is in
keeping with bilateral cochlear
otosclerosis
250 Insights Imaging (2014) 5:245–252
Table 2 CT grading of otosclerosis (Symons/Fanning 2005) (Fig. 7) [2, 3, 7]. Tympanosclerois with post-inflammatory
CT grading of otosclerosis Location of plaques fixation of the stapes footplate may present clinically with
identical CHL, especially with a healed tympanic membrane.
Grade 1 Solely fenestral This may cause a diagnostic dilemma in certain cases, al-
Grade 2 Patchy localised cochlear disease though, this can be differentiated on CT by observing signs
(+/− fenestral involvement) of inflammation in the middle ear and an underpneumatised
• To basal turn (grade 2A)
• To middle turn (grade 2B)
mastoid [2, 3].
• Around lateral aspect of basal,
middle, apical turns (grade 2C) Post stapedectomy imaging and complications
Grade 3 Diffuse confluent cochlear involvement
(+/− fenestral involvement)
Stapedectomy is commonly combined with insertion of a sta-
pes prosthesis in order to restore ossicular chain continuity. The
use of a radiodense stapes prosthesis helps radiological evalu-
irregularities of the bone contour [5]. The imaging differen- ation on HRCT (Fig. 8). Stapedectomy with prosthesis inser-
tials of fenestral otosclerosis are few. The cochlear cleft is a tion is associated with some inherent complications. The com-
small non-osseous space in the otic capsule in the region of the mon causes for recurrent CHL, vertigo and SNHL after stapes
fissula ante fenestram. It is a normal variant, commonly seen surgery include complete displacement of the prosthesis
in children, and its incidence decreases with age. An inexpe- (Fig. 9), prosthesis displacement into the vestibule (Fig. 10),
rienced reader may mistake a cochlear cleft for a perilymphatic fistula, and development of reparative granulo-
demineralised focus in the region of the fissula ante fenestram mas and labyrinthitis (Fig. 11) HRCT helps to evaluate the
position of the prosthesis and rule out common complications.
Additional MRI may act as an adjunct to rule out labyrinthitis
ossicificans. MRI can rule out fibrotic changes in the labyrinth
while ossifications are diagnosed exclusively by CT [2, 3,
8–10]. Repeat surgery may be mandatory for treatment of a
dislocated prosthesis or closure of a perilymph fistula [8–10].
Retrofenestral or cochlear otosclerosis
Pathology, clinical findings and imaging
Retrofenestral or cochlear otosclerosis is much less common;
Fig. 13 Coronal contrast-enhanced MR image in a patient with left-sided
SNHL. Bilateral pericochlear ring-like enhancement (arrow) is sugges- however, it is nearly always associated with fenestral otoscle-
tive of bilateral cochlear otosclerosis, which was further proven by HRCT rosis. Patients typically present with bilaterally symmetrical
Fig. 14 a Axial CISS MR image of the skull base in an adult patient with the left internal auditory canal shows post-contrast enhancement, which
left-sided SNHL. A small hypointense filling defect is seen in the left indicates a small acoustic neuroma (arrowhead). There is also a sugges-
internal auditory canal (arrowhead), which may be suggestive of an tion of enhancement in the left pericochlear region and in the region of the
acoustic neuroma. b Axial contrast-enhanced MR image of the same left fissula ante fenestram (arrow), which suggests associated otosclerosis
patient as (a), at the same level. The previously noted filling defect in is present
Insights Imaging (2014) 5:245–252 251
Fig. 15 Axial HRCT images of
the right (a) and left (b) temporal
bone in a young adult with known
osteogenesis imperfecta tarda and
bilateral SNHL. Bilateral
pericochlear ring-like
hypodensity (arrows) closely
mimics cochlear otosclerosis
ligament due to the lytic process or release of proteolytic
enzymes is implicated as a possible cause for the SNHL [1–4].
HRCT adequately demonstrates the demineralised foci in
the otic capsule. The classical imaging appearance of cochlear
otosclerosis on HRCT is a distinctive pericochlear hypodense
double ring (which is also known as the 4th ring of Valvassori)
(Fig. 12). Bilateral symmetry is common [1–4]. A CT grading
of otosclerosis has been proposed by Symons/Fanning and is
described in Table 2 [4]. Some authors mention that the
severity of cochlear disease correlates with early onset as well
as increasing severity of SNHL [4]. At times, MRI is per-
Fig. 16 Axial HRCT of the skull base in an adult patient with known formed prior to CT for assessing the cause of SNHL. A ring of
Paget’s disease. The hypodense appearance of bilateral otic capsules
pericochlear and perilabyrinthine intermediate signal on T1-
(arrows) may mimic otosclerosis; however the diffuse skull base involve-
ment indicates the true pathology weighted images and mild-moderate post-gadolinium en-
hancement has been reported in cochlear otosclerosis, more
SNHL or MHL. Pulsatile tinnitus is also known to occur. so in the active phase (Fig. 13) [2, 3, 11, 12]. MRI may also
Cochlear otosclerosis represents a continuum of the fenestral pick up other unassociated inner ear pathologies (Fig. 14). The
otosclerotic process. Histologically, foci of demineralised HRCT appearance of cochlear otosclerosis is rarely mimicked
spongy vascular bone are seen in the cochlear capsule, which by various diseases that demineralise the otic capsule, includ-
may extend around the vestibule, semicircular canals and ing osteogenesis imperfecta (Fig. 15) and Paget’s disease
internal auditory canal. The promontory may show a pink (Fig. 16). However the clinical manifestations and involve-
hue when seen through the tympanic membrane, called the ment of other bones suffice to differentiate these pathological
Schwartze sign. Direct injury to the cochlea and spiral conditions from cochlear otosclerosis [2–4, 11, 13].
Fig. 17 a Axial HRCT of the right temporal bone in a patient with known of the cochlea. There is significant obliteration of the fluid space in the
bilateral cochlear otosclerosis. There is almost complete obliteration of basal turn of the right cochlea (arrow). The normal fluid space in the basal
the basal turn of the right cochlea (arrow) by the otosclerotic process. b turn of the left cochlea (arrowhead) is shown for comparison
Axial MRI of the temporal bones in the same patient as (17a) at the level
252 Insights Imaging (2014) 5:245–252
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Open Access This article is distributed under the terms of the Creative
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Bela Purohit
• Study concept and design
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• Literature search
• Manuscript revisions
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