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Ear study with 64 slices Multidetector CT
María Lourdes Mallo, Cecilia C. Giordanengo, Carlos A. Bertona,
Juan José Bertona, Cecilia Gigena, María Paula Florez
Abstract
The ear is a complex anatomic structure. Its study and understanding represent a constant challenge for the radiologist. As a consequence, the computed tomography becomes an essential tool for its examination.
The conventional tomographic examination with both axial and coronal reconstruction of the image allows a satisfactory visualization of different structures. However, the study requires long periods of time for its acquisition and uncomfortable or intolerable
positions for some patients. Besides, the characterization of some ear’s structures becomes limited.
The 64 slices multidetector computed tomography enables an optimal study of the ear’s small and complex anatomy, performing
volumetric acquisitions with 0.5 mm slices, which leads to accurate multiplanar reconstructions in the three basic planes, in curved
planes and three dimensional reconstructions. These make a detailed visualization of its structures in few seconds, avoiding discomfort in the patients.
Our purpose in this article is to demonstrate the utility of reconstructions particularly in oblique planes, reaching an optimal visualization of the temporal bone.
Key words: Inner ear. Multidetector computed tomography. Temporal bone.
INTRODUCTION
From the advent of Computed Tomography (CT),
the study of temporal bone structures is limited to
axial and coronal (1) orientations, with slices of the lowest thickness (usually of slices between 1 and 3 mm)
(2,3)
. In that way, the identification of smallest and most
complex anatomic ear structures is limited.
Furthermore, it is necessary to consider time exploration in order to avoid movements and uncomfortable position in coronal plane orientations.
The incorporation of 64 slices Multidetector
Computed Tomography (64MDCT), by reconstructing
the image in any space plane, with acquisition in few
seconds and with a tolerable position for all patients,
enables a detailed observation of the ear’s anatomic
repairs and progress in addressing different diseases (3).
64 MDCT PROTOCOL
Data Acquisition: The temporal bone CT SCAN
was performed in our institution using a 64 channels
multidetector scanner Aquilion Toshiba.
The exploration was conducted in the standard
axial plane with helicoidal technique and volumetric
acquisition (120 kv, 200 mA, rotation time of 0,5 seconds, thickness of the section of 0,5mm, matrix 512 l x
512). The head of the patient was located in a neutral
Servicio de Diagnótico por Imágenes - Clínica Privada,
Velez Sarfield, Córdoba - Argentina
Correspondencia: María Lourdes Mallo
[email protected]
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position and the time of study was of 4 to 6 seconds.
Image reconstruction and post-processing: The
data analysis was performed in a Vítrea® work station. The temporal bones were visualized in three
basic planes (axial, sagital and coronal), reconstructed
in isometric way (with the same resolution as the original acquisition) every 0,5, 1 or 2 mm. In addition,
there were performed 3D reconstructions, multiplanar
and oblique curves, and Maximum Intensity
Projections (MIP), according to the structure of clinical
interest or as the findings: ossicular chain, round and
oval windows,the cochlea, vestibular aqueduct, semicircular canals and facial nerve canal.
EXTERNAL EAR
It comprises the pinna and external auditory canal
(EAC). The EAC has an italic S shape on its way to the
tympanic membrane. Its two internal thirds are
osseous and slightly narrower than the lateral third,
which is cartilaginous. The tympanic membrane
shows the intermediate limit of EAC, separating the
external ear from the tympanic cavity (2, 5, 6, 7).
The exploration of these structures with 64 MDCT,
with volumetric and 3D reconstructions allowed a very
detailed view of them (Fig. 1), resulting a valuable help
in the detection of pathological features (Fig. 2).
Recibido: agosto 2010; aceptado: septiembre 2010
Received: august 2010; accepted: september 2010
®SAR-FAARDIT 2010
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Ear study with 64 slices Multidetector CT
MIDDLE EAR
tions, and congenital anomalies of the ossicular chain
and oval window (10-11).
Ossicular chain
Hammer and incus
The handle of the hammer and the incus are not
clearly defined by conventional scan of the temporal
bone, which consists on axial and coronal acquisitions (1).
Oblique coronal planes (Figs. 3-4), oriented along
long axis of these two ossicular structures provide a
better identification of them.
The oblique sagital plane (Fig. 5) also enables its
visualization and provides an alternative to the axial
plane for the examination of incude-maleolar joint (8).
The reconstruction of this plane of hammer and incus,
resemble a molar tooth (9-12) (Fig. 6). These reconstruction planes can be helpful for studying the erosions of
the ossicular chain, colesteatoma, traumatic disloca-
Stapes- oval window
The oval window is located laterally to the
vestibule, above and behind the promontory. It connects the tympanic cavity with the vestibule and it is
occupied by the stapes footplate (2-3). Its longitudinal
diameter is of 3-4 mm and its vertical is of 1,5-2 mm.
Its conventional topographical visualization is optimum on the coronal plane, and it is not satisfactory
visualized on the axial plane (1).
A double-oblique orientation of the reconstruction’s axial plane enables an optimum exhibition of
the stapes and oval window (Fig. 7). An oblique sagital reconstruction is useful to confirm the presence of
both branches of the stapes, next to the oval window.
The combination of sagital, axial and oblique
Fig. 1. 3D reconstruction of external ear with 64 MDCT. (A) skin, (B & C) bone.
Fig. 2. 3D reconstruction of external ear with 64 MDCT. (A & B) Atresia of the external bone of EAC, occupied by compact bone (Arrows). (C)
Skin fold.
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María Lourdes Mallo et al.
Fig. 3. CT with Multiplanar Reconstruction (MPR) double oblique
coronal of the hammer, shows hammer’s head (C), handle (M) and neck
(CU). Also, tensor timpani (TT).
Fig. 4. CT with double oblique coronal MPR of incus, is visualized the
body of the incus (C), short process (SP) and long process (LP).
Fig. 6. Incude-malleolar joint, 3D bone reconstruction.
INTERNAL EAR
Fig. 5. CT with oblique double sagital MPR of incude-malleolar joint
(AIM). The incus body (CY), long process (LP); handle of hammer (MM).
reconstructions can assist in the evaluation of congenital anomalies, in traumatic dislocations and in fixation of the stapes in patients with hearing loss (10).
Round Window
The round window is located behind and below
the oval window, in a shallow pit. It corresponds to
the tympanic orifice of the cochlea’s tympanic scale
and its diameter is 2 mm (2). It can be clearly represented on axial images (Fig. 8), while it is not possible to
do it on the coronal plane, due to its orientation (1). It is
more convenient to use oblique sagital reconstructions (Fig. 9). The radiological study of both windows
is important in several pathologies, such as otosclerosis and malformations (13).
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The internal ear is the bone labyrinth which contains the membranous labyrinth (2).
Cochlea
It is a spiral-shape structure with two and a half
turns. It is located anterolateral to the IAC and contains the organ of Corti. Its long axis can be represented in axial or coronal standard images. The 64 MDCT,
by oblique reconstructions (Fig. 10), enables the evaluation of superior, middle and inferior turns, as well
as the evaluation of the opening of the cochlear nerve.
Curve reconstructions enable to ‘unroll’ the cochlea,
getting insight into its morphology and dimensions.
Finally, volumetric imaging provides morphological
and anatomical detail, which allows to visualize the
total of its turns (3-4).
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Ear study with 64 slices Multidetector CT
Semicircular Canals
They are constituted by three conducts (superior,
posterior and lateral), situated behind and above the
vestibule. The superior semicircular canal is orientated in an approximately 90° angle to the long axis of
the temporal bone. Coronary images are enough to
determine its integrity (1-2-14).
Vestibule and vestibular aqueduct
The vestibule is part of the internal ear’s labyrinth,
situated between the semicircular conducts and the
cochlea. It contains the utriculus and saculus, which
are part of the membranous labyrinth.
The aqueduct or vestibular conduct contains the
endolymphatic conduct and communicates the vestbiule’s saculus with the endolymphatic saculus (2). It is
not usually visualized in coronary images and it is
hard to see it in axial images (1) (Fig. 11). The vestibu-
lar conduct’s course is better identified in the sagital
plane (Fig. 12), which is useful in the diagnosis of
dilated vestibular aqueduct syndrome, an anomaly
more common of the osseous labyrinth observed in
patients with a deep sensorineural hearing loss (15).
Facial nerve canal
It is a bony channel where the facial nerve is located in
its intratemporal course. It starts at the back of the internal
auditory canal. Its first portion, of 4 mm in length, is
between the cochlea (front) and the semicircular canals
(back). It is often injured in longitudinal bone fractures.
The second portion or tympanic portion starts
when it bends back, almost at right angle, to follow a
parallel path to the lateral semicircular canal. It measures 10 mm long and may be dehiscent.
The third portion or descending portion, is 15 mm
long and continues to the stylomastoid foramen (2-16).
With the image reconstruction in an oblique sagi-
Fig. 7. CT with oblique double axial MPR of stapes (E) in the oval window (VO).
Fig. 8. axial MPR of round window.
Fig. 9. CT with sagital oblique MPR of round window (VR), carotid
canal (CC), labyrinthic segment of facial nerve canal (NFL).
Fig. 10. cochlea’s short axis (Arrow), CT with oblique MPR, where the
inferior turn can be observed.
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María Lourdes Mallo et al.
tal plane (Figs. 14-15) and curve reconstructions, the
whole longitude between the tympanic and mastoid
segments of the facial nerve can be represented in just
one image (8-9). The use of this reconstruction plane can
help in the diagnosis of the nerve anomalies and fractures in the path of the facial nerve canal.
Carotid conduct
The intrapetrosal path of the internal carotid
artery (ICA) is perfectly visible with a tomography
regarding its bone repairs . With 64 MDCT it is also
possible to perform angiographic reconstructions for
suspected arterial injuries. This requires iodinated
contrast injection (Figs. 16, 17 and 18).
Fig. 11. CT, standard axial image. Vestibule (V) Posterior semicircular
canal (CSP) and lateral (CSL).
Cochlear implant
64 MDCT in presurgical study for cochlear
implant is an excellent method for anatomical and
pathological detail of the temporal bone region (Fig.
18). Volumetric images provide information about the
anatomy of the ossicular chain, the inner ear and its
relationship to vascular structures, the carotid artery
and the internal jugular vein. Curve reconstructions
enable to ‘unroll’ the cochlea, getting insight into its
morphology and dimensions. This information is very
useful for the i surgeon.
In the postsurgical study, 64 MDCT is an excellent
method to control the correct positioning of the electrodes of the implant, since it avoids image artifices
Fig. 12. CT with MPR, oblique sagital image, where the vestibular conduct is visualized (CV) in its origin, common area of CSS and CSP (ZC).
Fig. 14. CT with MRP, oblique sagital image where superior semicircular conducts (CSS) and lateral (CSL) and facial nerve canal (NF) are
visualized.
Fig.13. 3D reconstruction: semicircular canals CCS: superior CCL: lateral CCP: posterior.
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Ear study with 64 slices Multidetector CT
with an acquisition of submillimetrical slices and optimum resolution (17) in just a few seconds.
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CONCLUSION
64 Channels MDCT is an excellent imaging method
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