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Value of Multislice
Computed Tomography
in the evaluation of
early Otosclerosis
Nicolás López-Galletti, Alberto Surur, Mario Zernotti, Alberto Marangoni, Paula
Tiscornia, Ignacio Simez.
Resumen
Abstract
Introducción: La otoesclerosis (OS) es una enfermedad
Introduction: Otosclerosis (OS) is a disease of unknown
de etiología desconocida, que presenta una transmi-
etiology. It is inherited in an autosomal dominant
sión autosómica dominante. Afecta más frecuente-
pattern. It affects 20-30-year-old women whose main
mente a mujeres entre 20 y 30 años, que consultan
clinical manifestation is conductive hearing loss with
clínicamente por una hipoacusia de conducción. La OS
more frequency. The OS is classified as fenestral (85%)
se clasifica en fenestral (85%) y coclear (15%). La To-
and cochlear (15%). Multislice Computed Tomography
mografía Computada Multicorte (TCMC) es un método
(MSCT) is the method of choice in the evaluation of the
radiológico de elección en la valoración de la cápsula
otic capsule. It can accurately show lesions at an initial
ótica. Ésta puede demostrar con precisión lesiones en
stage, such as millimetric hypodense areas, mainly at
la etapa inicial como focos hipodensos milimétricos,
the fissula ante fenestram (FAF) as a sign of “early or
principalmente a nivel de la Fisula Ante Fenestram
initial” OS, even when the audiometric results show a
(FAF) y pueden corresponderse como un signo “pre-
gap of less than 20 db.
coz o inicial” de OS, aun cuando en la audiometría
Case review: Even though OS is a disease of unknown
aparece un gap menor a 20 db.
etiology, it is known that type II collagen fibers in the
Revisión del tema: La OS es una enfermedad de etio-
cartilage remnant tissue of the petrosal bone can gene-
logía desconocida pero se sugiere una relación con las
rate an autoimmune reaction that could be responsible
Contact information:
Nicolás López-Galletti.
38
Sanatorio Allende – Córdoba capital.
Recibido: 4 de noviembre de 2014 / Aceptado: 6 de mayo de 2015
E-mail: [email protected]
Received: November 4, 2014 / Accepted: May 6, 2015
Revista Argentina de Diagnóstico por Imágenes
Value of MSCT in
early Otosclerosis
López-Galletti N. et al.
fibras de colágeno tipo II, presentes en el tejido carti-
for the resorption of bone tissue. This produces focal
laginoso remanente del peñasco, las cuales generarían
areas of spongy bone at the oval and round window
una reacción autoinmune que sería la responsable
and that is why it is called otospongiosis. Other authors
de la reabsorción del tejido óseo. Esto produce zonas
propose that this cartilaginous remnant tissue would
focales de hueso esponjoso a nivel de la ventana oval
be replaced by an immature and highly vascularized
y redonda, por lo que se denomina otoespongiosis.
bone tissue. Histopathological studies describe three
Otros autores piensan que este remanente cartilagi-
phases of this condition: acute (osteoid tissue), subacute
noso sería remplazado por un tejido óseo inmaduro
(osteoclastic remodeling) and chronic (sclerosis).
y altamente vascularizado. Los estudios histopatoló-
Conclusion: Multislice Computed Tomography may
gicos la dividen en tres fases: aguda (tejido osteoide),
be used as an additional and effective tool for the
subaguda (remodelación osteoclástica) y crónica
diagnosis of early or initial OS (audiometry gap of 20
(esclerosis).
db), showing millimetric hypodense areas that cannot
Conclusión: La TCMC puede ser usada como una
be visualized by means of conventional CT, mainly at
herramienta adicional eficiente en el diagnóstico de
the FAF. The findings are predominantly bilateral and
OS precoz o temprana (audiometría con gap de 20
symmetrical. The thickness of the footplate provides
db), mostrando focos hipodensos milimétricos, que no
valuable data, particularly in patients who will undergo
pueden ser visualizados por la TC convencional, prin-
surgery. MSCT demonstrated a high sensitivity for the
cipalmente a nivel de la FAF. Los hallazgos son pre-
diagnosis of this pathology.
dominantemente bilaterales y simétricos. El espesor
de la platina del estribo aporta datos de valor sobre
todo en pacientes que van a ser sometidos a cirugía.
La TCMC demostró tener una gran sensibilidad para el
diagnóstico de esta patología.
Palabras clave: Otoesclerosis precoz, Otoespongio-
Key words: Early Otosclerosis, Otospongiosis, Fissula
sis, Fisula Ante Fenestram, Tomografía Computada
ante Fenestram, Multislice Computed Tomography.
Multicorte.
Introduction
Otosclerosis (OS) is a disease of unknown etiology. It
is inherited in an autosomal dominant pattern (1, 2).
Frequently, it affects women aged 20-30, with tinnitus and conductive hearing loss. The presentation
of this condition is bilateral in 80% (3). Cochlear involvement is associated with neurosensory hearing
loss, secondary to the action of protease that affects
nerve cells.
OS is classified as fenestral (85%) and cochlear
(15%), causing hearing loss that can be conductive,
neurosensory or a combination of both. Initially, conVol. 4 / Nº 11 - Agosto 2015
ductive hearing loss, which is the most frequent, has
an air-bone gap equal or greater than 20 db, with a
tympanometric rigid curve (Type A Jerger curve). In
these cases, imaging studies can be useful to reach
an early and accurate diagnosis. They play an important role in the diagnosis and clinical management of
OS. Multislice Computed Tomography (MSCT) is the
radiologic method of choice to assess the labyrinthine windows and the otic capsule. It can show the active or spongiotic lesions of OS at an early stage with
precision. The lesions are millimetric lytic or hypodense areas that cannot be detected with conventio39
Value of MSCT in
early Otosclerosis
nal tomography and that can be seen predominantly
in the otic capsule, mainly at the level of fissula ante
fenestram (FAF) as an “early” sign of OS (1-4). When
we talk about early signs of OS we refer to the radiological findings mentioned above, even when the
audiometry shows a slight loss in hearing, whether
they are conductive, neurosensory or a combination
of both. These lesions can be unique or multiple,
confluent or non-confluent, bilateral or unilateral and
can be the cause of a process of bone demineralization (5, 6) or of a thickening of the footplate to a
size greater than 0.6 mm. MSCT performs narrower
views with a greater spatial definition, which helps
characterize lesions better.
Case review
OS is a disease of unknown etiology and it is inherited in an autosomal dominant or recessive pattern.
This condition is also related to fibrillary collagen
type II present in the cartilage remnant from the petrosal bone, which would generate the autoimmune
reaction of reabsorbing bone tissue. This produces
focal areas of spongy bone at the level of the oval
and rounded window and that is why it receives the
name of otospongiosis (1, 2). Other authors think
that this cartilaginous remnant would be replaced by
an immature and highly vascularized bone tissue (7).
Histopathological studies describe three phases of
this condition: acute (osteoid tissue), subacute (osteoclastic remodeling) and chronic (sclerosis).
An advanced cochlear OS often has hypodense
areas producing an image of a halo around the bony
labyrinth, frequently at the level of the basal cochlear
turn, which is called “double-ring sign”. In addition,
in a chronic stage there are calcification areas in
those regions that appear as “plate-like bones”. The
complete obliteration of the oval window in 2% of
the cases is called obliterative fenestral OS.
Among differential diagnoses there is tympanosclerosis, Paget’s disease, fibrous dysplasia and osteogenesis imperfecta (1).
Paget’s disease: It affects people older than 60 and
it is part of the diseases of bone metabolism. Initially,
it generates a lytic diffuse process affecting the bony
labyrinth, and in an advanced stage it produces an
increase in bone density. It starts in the vertex of the
40
López-Galletti N. et al.
petrosal bone and progresses laterally. It differs from
OS in that Paget’s disease starts in the peripheral region and progresses in a centripetal way affecting the
otic capsule in a later stage, whereas OS progresses
in reverse. Paget’s disease also affects the calvaria.
Fibrous dysplasia: It affects people younger than
30 years of age. It produces a ground-glass density
that expands the bone preserving the cortex. Commonly, it affects the mastoid and presents slight involvement of the bony labyrinth, facial nerve canal
and internal auditory canal. Lytic lesions are less
common.
Osteogenesis imperfecta: It affects children with
brittle bones and blue sclerae. It can be hard to differentiate it from advanced cochlear OS.
Tympanosclerosis: It is a post-inflammatory deposit of new bone tissue that is not limited to the oval
window and can affect all of the middle ear structures, tympanic membrane and mastoid. The bone
tissue deposit has an irregular morphology (8-10).
The primary objective of MSCT in this type of pathology is to prove the existence and distribution of
the early focal area of otosclerosis (FAOS) since these findings were not visible through conventional or
basic helical tomography. According to international
literature, the sensitivity of MSCT or computed conventional tomography for the diagnosis of OS ranges from 34% to 90%. However, recent studies have
shown that MSCT has a positivity of 90% to detect
fenestral focal areas in an early stage of the disease
(5, 6, 11). It is not possible to detect these early little
changes with conventional computed tomography.
Figure 1 shows one of the most relevant tomographic views that require a detailed analysis of the anatomy to obtain as much information as possible.
Marx et al. identified a sensitivity of 95% and a
specificity of 99,1% in the diagnosis of OS (12). Our
samples consisted of 58 MSCT performed on patients
with a clinical auditory diagnosis of OS, i. e., they
had an air gap of 20 db to 25 db in low and middle
pitch frequencies and a tympanometry with a rigid
Type A Jerger curve. Some of the patients had absent
stapedial reflex. MSCT demonstrated a sensitivity of
95% in the detection of focal areas of otospongiosis.
Oliveira et al. (4) identified focal areas of OS in 47
patients (87%). Shin et al. (5) observed that 84.7% of
patients with focal areas of OS in MSCT had positive
Revista Argentina de Diagnóstico por Imágenes
Value of MSCT in
early Otosclerosis
López-Galletti N. et al.
clinical results.
In 70% to 95% of cases, otodystrophic lesions of
otospongiosis are located at the fenestral level in the
FAF. This topography must be considered as the most
important in the radiologic diagnosis of this entity
(3, 4). In our study there were 55% to 60% cases of
focal areas of OS at the level of the FAF, in both the
right ear and the left ear. Oliveira et al. (4) identified
focal areas of OS at the same level in 83.3% of patients. Shin et al. (5) in 69.8%, and Veillon et al. (13)
in 68.2%. Wycherly et al. (7) identified lesions at the
level of FAF in 21 out of 24 patients (87.5%). This is
an area with great radiologic relevance for the early diagnosis of patients suspected of having OS that
should be analyzed in detail during a tomographic
examination.
Shin et al. (5) identified bilateral focal areas of OS
in 78.7% and bilateral and symmetrical focal areas
in 38% of patients. Oliveira et al. (4) identified these
findings in 70% and 48.38% of the cases, respectively.
In patients studied for this research paper, 70.68%
presented bilateral focal areas of OS, and 68.96% presented symmetrical focal areas. In 1.72% of the cases
the presentation was symmetrical.
A study conducted by Wycherly et al. (7) showed
that 10 patients (56%) had bilateral OS, 4 (22%) had
unilateral OS, and 4 (22%) did not present focal
areas of OS. 8 out of 10 patients presented bilateral
and symmetrical OS (80%). In our cases, 14 patients
(24.13%) had unilateral focal areas of OS.
Based on histopathological findings of patients
who underwent surgery reported in literature, the
round window is the second most commonly affected region with an incidence that ranges from 20%
to 50% (14).
Evidence of the involvement of the footplate provides valuable information, especially in cases of
patients selected to undergo stapedectomy. Veillon
et al. (10) defined an abnormal thickening of the
footplate greater than 0.6 mm, which was found in
12.7% of their patients. Shin et al. (5) observed this
in 23% of the cases.
Other series presented similar percentages of pericochlear region involvement of around 19.4% and
24.13% of the cases.
Wycherly et al. (7) visualized focal areas at the post
fenestram level in 10% of the tomographic exams
Vol. 4 / Nº 11 - Agosto 2015
analyzed.
Children usually present hypodense areas in the
otic capsule that suggest the differential diagnosis of
early OS and are attributed to an incomplete bone
mineralization or to the presence of cartilage at the
level of the FAF. These areas represent a normal pattern of growth of the anterior otic capsule and they
should not be confused with pathological conditions.
However, in older patients, these hypodense areas in
the FAF can be considered as potential signs of early
OS (2).
Not all patients undergo surgery and, therefore,
histopathological confirmation of these alterations is
not always possible. That is why MSCT is actually
used to confirm clinical findings and findings from
the most precise results of otorhinolaryngological
examinations and tests available.
Findings in MSCT
MSCT can show active or spongiotic lesions of OS in
an early stage with precision. They appear as small
hypodense o millimetric lytic areas at the level of the
FAF or at a pericochlear level. In addition, a thickening of the footplate greater than 0.6 mm is considered an early sign of OS.
In relation to the location, focal areas of OS have a
bilateral and symmetrical distribution in around 70%
of the cases (Figure 2 and 3), a unilateral and symmetrical location in 2% of the cases, and a unilateral
location in 25% of the patients (Figure 4). In 5% of
the cases, they can be negative.
Based on our observations and in relation to other
series of patients, focal areas of OS are located most
commonly at the level of FAF (around 65% of the cases) (Figure 5) followed by a cochlear location, with
an approximate percentage of 35%, both in the right
and left ears (Table 1).
The sensitivity of MSCT to detect the presence
of focal areas in patients with OS was 95%, which
means that every 100 patients with a clinical and
auditory suspicion of OS, MSCT could detect focal
areas in 95 patients.
41
Value of MSCT in
early Otosclerosis
López-Galletti N. et al.
Figure 1. Ear MSCT with high-definition axial
view.
Normal anatomy. COC: Cochlea, FAF: Fissula ante
fenestram, VES: Vestibule, CSP: Posterior semicircular
canal, PLE: Footplate, CPE: Posterior crura of stape, CAE:
Anterior crura of stape, YUN: Incus, MAR: Hammer.
Figure 2. Ear MSCT with high-definition axial view.
Millimetric hypodense areas at the level of the
FAF bilateral and symmetrically (white arrows).
Figure 3. Ear MSCT with high-definition coronal view.
Presence of bilateral and symmetrical focal OS
at the level of the FAF (arrowheads).
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Revista Argentina de Diagnóstico por Imágenes
Value of MSCT in
early Otosclerosis
López-Galletti N. et al.
Figure 4. MSCT with high-definition
axial view of right and left ear.
Patient with unilateral focal OS at the level
of the FAF on the left side (black box).
Figure 5. MSCT with high-definition axial
view of the left ear at the level of the petrosal bone.
Hypodense area of OS (white circle) between the vestibule and the cochlea in the topography of the fissula
ante fenestram (FAF).
Graphic 1. Location of the focal area. Common spots of early focal areas of OS.
Black: FAF; Dark gray: Pericochlear; Light gray: Fissula Post Fenestram; Gray line: Thickening of the footplate.
Vol. 4 / Nº 11 - Agosto 2015
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Value of MSCT in
early Otosclerosis
López-Galletti N. et al.
Table 1.
Conclusion
MSCT may be used as an additional and effective
tool to diagnose early OS even when auditory findings present a small gap ranging from 20 to 25 db
and millimetric hypodense areas that cannot be visualized by conventional CT, mainly at the FAF. The
findings are predominantly bilateral and symmetrical.
The thickness of the footplate provides valuable data
44
particularly in patients who will undergo surgery.
MSCT demonstrated a high sensitivity for the early
diagnosis of this pathology.
Revista Argentina de Diagnóstico por Imágenes
López-Galletti N. et al.
Value of MSCT in
early Otosclerosis
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