AJR 2000; 174:387-392
© American Roentgen Ray Society
Helical CT Findings in Patients Who Have Undergone Stapes Surgery for Otosclerosis
Marc T. Williams1,
Denis Ayache2,
Monique Elmaleh1,
Françoise Héran1,
Pierre Elbaz2 and
Jean-Daniel Piekarski1
1
Department of Medical Imaging, Fondation Ophtalmologique Adolphe de
Rothschild, 25 rue Manin, 75940 Paris, France.
2
Department of Otorhinolaryngology, Fondation Ophtalmologique Adolphe de
Rothschild, 75940 Paris, France.
Received May 17, 1999;
accepted after revision July 15, 1999.
Address correspondence to M. T. Williams.
Introduction
Progressive conductive hearing loss is the major clinical symptom of
otosclerosis, which causes stapediovestibular ankylosis
(Fig. 1). The aim of stapes
surgery is to restore hearing in patients with otosclerosis. Successful
surgical results are observed in more than 90% of patients with this technique
[1]. However, unsuccessful
outcomes or rare surgical complications are observed and may lead to a
surgical revision. Two major indications of unsuccessful surgery are seen. The
persistence or recurrence of a conductive hearing loss is mainly related to
the following conditions: prosthesis displacement, necrosis of the incus,
postoperative intratympanic fibrosis, obliterative otosclerosis, malleoincudal
dislocation, and ankylosis of the malleus to the tympanic walls. Occurrence of
vertigo or fluctuating sensorineural hearing loss is suggestive of an
intravestibular protrusion of the prosthesis, a perilymph fistula, or a
reparative granuloma in the oval window.
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Fig. 1. —Incremental axial CT scan at level of oval window in 54-year-old
woman with bilateral conductive hearing loss caused by otosclerosis shows
otosclerotic focus as ill-defined hyperdense area (arrow) at anterior
margin of oval window and anterior part of stapes footplate.
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Conventional CT has been used for several years in the exploration of these
symptoms [2,
3,
4]. However, this technique is
limited by the obliquity of the prosthesis relative to the conventional scan
planes. Conversely, helical CT yields high-resolution reformatting in oblique
planes along the main axis of the prosthesis, allowing a more accurate
depiction of the prosthesis status, which is helpful for planning the surgical
revision. In this pictorial essay, we present CT findings in patients with
unsuccessful stapes surgery.
Surgical Procedures
The surgical procedure consists of removal of the stapedial arch followed
by the insertion of a prosthesis
[5]
(Fig. 2A). The lateral end of
the prosthesis is bound to the long process of the incus; its medial end
transmits the sound vibrations to the perilymphatic fluid through an opening
made in the stapes footplate. Two alternative surgical procedures are often
performed: total stapedectomy (removal of the stapes footplate and insertion
of a prosthesis with graft interposition)
(Fig. 2B) and small fenestra
stapedectomy (creation of a fenestration of the footplate) with or without
graft interposition (Figs. 2C
and 2D). Vein, aponeurosis, or
perichondrial grafts are used in the former surgical techniques to close the
footplate opening; in the latter, the calibrated fenestration is directly
sealed by the prosthesis. Several types of stapedial prostheses are available;
we used polytetrafluoroethylene prostheses.
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Fig. 2B. —Drawings show principles of surgical treatment of stapedovestibular
otosclerosis. Stapedectomy with graft interposition. Stapes footplate is
completely removed. Oval window is sealed by a graft. Lateral ring-shaped end
of prosthesis is bound to long process of incus. Medial end of prosthesis is
set against graft and transmits vibrations to perilymphatic fluid.
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Fig. 2C. —Drawings show principles of surgical treatment of stapedovestibular
otosclerosis. Small fenestra stapedectomy with graft interposition.
Fenestration is created in stapes footplate and sealed by graft. Prosthesis is
then inserted as described in B.
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Fig. 2D. —Drawings show principles of surgical treatment of stapedovestibular
otosclerosis. Small fenestra stapedectomy without graft. Small circular
fenestration is performed in footplate. Fenestration is then sealed directly
by medial end of prosthesis.
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Imaging Technique
Helical CT was performed using a Twin Flash system (Elscint, Haifa, Israel)
with the following parameters: single axial helical acquisition (with caudal
angulation of the scan plane 20° below the orbitomeatal plane to prevent
direct lens irradiation); 120 kVp; 440 mAs; pitch: 0.5; slice thickness: 0.6
mm; increment: 0.3 mm; scan length: 25 mm; acquisition duration: 50 sec. A
150-mm acquisition field of view was used with a 512 x 512 matrix and a
spatial reconstruction algorithm. Multiplanar reconstructions were then
performed in oblique axial and coronal planes along the axis of the prosthesis
(Fig. 3). Reformatted images of
both ears, reproducing a conventional examination in axial and coronal planes,
were also obtained.
Prosthesis in Correct Position
The prosthesis in correct position has a medial, posterior, and cranial
oblique orientation. In conventional axial and coronal CT, three contiguous
scans are usually needed in each plane to image the prosthesis completely.
Moreover, despite the use of high-resolution slices, the lateral or medial
ends are often not precisely seen. Multiplanar reconstructions provided by
helical CT acquisition greatly improve imaging accuracy by showing the full
length of the prosthesis on single axial or coronal reformatted images (Fig.
4A,
4B,
4C). Nevertheless, the
resolution of reformatted images remains insufficient to determine the type of
surgical procedure (i.e., total or small fenestra stapedectomy) that has been
performed.
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Fig. 4A. —35-year-old woman with correctly positioned polytetrafluoroethylene
prosthesis. Conventional axial CT scan at level of oval window shows only tip
of prosthesis (arrowhead). It is impossible to know whether
prosthesis is in contact with stapes footplate or slightly separated from
it.
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Fig. 4B. —35-year-old woman with correctly positioned polytetrafluoroethylene
prosthesis. Oblique (B) axial and coronal (C) multiplanar
reconstructions show entire prosthesis (arrowhead). Device is
correctly inserted on long process of incus (arrow); no gap is seen
between footplate plane and tip of prosthesis.
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Fig. 4C. —35-year-old woman with correctly positioned polytetrafluoroethylene
prosthesis. Oblique (B) axial and coronal (C) multiplanar
reconstructions show entire prosthesis (arrowhead). Device is
correctly inserted on long process of incus (arrow); no gap is seen
between footplate plane and tip of prosthesis.
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Prosthesis Displacement
Prosthesis displacement is the most common cause of conductive hearing loss
recurrence or persistence after stapes surgery
[1,
6,
7]. The dislocation of the
prosthesis from the stapes footplate is in some cases limited to an
inframillimetric gap between the footplate plane and the tip of the
prosthesis; in such cases, the medial end of the prosthesis may appear to be
in the correct position on conventional CT scans, but oblique multiplanar
reconstructions accurately show the abnormal location of the prosthesis (Fig.
5A,
5B). A separation of the
prosthesis ring from the long process of the incus is usually associated with
a displacement of the tip of the prosthesis, resulting in a complete
dislocation. Sometimes the prosthesis may be displaced far from the oval
window in the posterior or the inferior recesses of the tympanic cavity (Fig.
6A,
6B,
6C).
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Fig. 5A. —67-year-old woman with progressive conductive hearing loss occurring
4 years after stapedectomy for stapediovestibular otosclerosis. Conventional
axial CT scan shows tip of prosthesis (arrowhead) apparently in
contact with stapes footplate.
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Fig. 5B. —67-year-old woman with progressive conductive hearing loss occurring
4 years after stapedectomy for stapediovestibular otosclerosis. Oblique axial
reconstruction shows anterior displacement of prosthesis. Gap
(arrowhead) between tip of prosthesis (arrow) and footplate
is clearly visible.
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Fig. 6A. —59-year-old woman with sudden conductive hearing loss recurrence
after head trauma. Conventional axial CT scan shows prosthesis in incorrect
position; linear dense structure (arrow) oriented in sagittal plane
is seen in front of sinus tympani recess.
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Fig. 6B. —59-year-old woman with sudden conductive hearing loss recurrence
after head trauma. Oblique axial (B) and sagittal (C)
reconstructions show complete luxation of prosthesis from long process of
incus and from stapes footplate. Prosthesis (arrow) is located in
posterior part of tympanic cavity.
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Fig. 6C. —59-year-old woman with sudden conductive hearing loss recurrence
after head trauma. Oblique axial (B) and sagittal (C)
reconstructions show complete luxation of prosthesis from long process of
incus and from stapes footplate. Prosthesis (arrow) is located in
posterior part of tympanic cavity.
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Fixation of the Prosthesis by Postoperative Fibrosis
Fixation of the prosthesis can be caused by the development of
postoperative fibrous adhesions to the prosthesis or to the ossicles or
covering the fenestra. The fibrous scar usually appears as a soft-tissue mass
around the tip of the prosthesis (Fig.
7). Fibrous tracts between the caudal part of the prosthesis and
the walls of the tympanic cavity may also be observed.
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Fig. 7. —43-year-old man presenting with conductive hearing loss caused by
postoperative intratympanic fibrosis 18 months after stapedectomy. Prosthesis
is correctly inserted. Oval window recess is filled by soft-tissue mass
(arrow) around medial end of prosthesis, causing hearing
impairment.
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Obliterative Otosclerosis with Prosthesis in Correct Position
Proliferation of the otosclerotic focus may cause the impairment of a
correctly located prosthesis. The proliferative focus presents as a slightly
hyperdense calcified space-occupying mass in the oval window niche. This mass
surrounds the medial end of the prosthesis, which remains in contact with the
plane of the footplate (Fig.
8A,
8B). The location of the
prosthesis in the hyperdense mass may be difficult to detect on conventional
CT images because of the oblique orientation of the oval fossa and the
volume-averaging artifacts of the facial canal located just above the oval
window. Oblique axial multiplanar reconstructions provide images that are
exactly in the plane of the oval window, improving the conspicuity of the
prosthesis.
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Fig. 8A. —66-year-old woman with progressive conductive hearing loss 11 years
after stapedectomy and prosthesis placement performed because of obliterative
otosclerosis. Oblique axial (A) and coronal (B) reconstructions
show correct location of prosthesis (curved arrow). Oval window
recess is filled by proliferative otosclerotic focus (straight arrow)
that surrounds medial end of prosthesis.
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Fig. 8B. —66-year-old woman with progressive conductive hearing loss 11 years
after stapedectomy and prosthesis placement performed because of obliterative
otosclerosis. Oblique axial (A) and coronal (B) reconstructions
show correct location of prosthesis (curved arrow). Oval window
recess is filled by proliferative otosclerotic focus (straight arrow)
that surrounds medial end of prosthesis.
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Other Causes of Recurrent Conductive Hearing Loss
Other conditions can lead to a conductive hearing loss. For instance, a
postoperative malleoincudal dislocation
[8] appears on axial CT scans
as an enlargement of the incudomalleal articular space, possibly associated
with malposition of the ossicles (Fig.
9A,
9B). In these cases, the role
of reformatted CT images is to evaluate the status of the prosthesis.
Osteonecrosis of the long process of the incus has been reported as a frequent
postoperative complication of stapes surgery
[6,
7]. However, such a
complication was not observed in our study.
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Fig. 9A. —60-year-old man with persistent conductive hearing loss 6 months
after stapes surgery. Oblique axial reconstruction shows luxation of
prosthesis (straight arrow) posterior to handle of malleus
(curved arrow).
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Fig. 9B. —60-year-old man with persistent conductive hearing loss 6 months
after stapes surgery. Conventional axial CT scan shows incudomalleal
dislocation with enlargment of articular space (arrow).
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Postoperative Granuloma
Labyrinthic symptoms (vertigo, sensorineural hearing loss, tinnitus) may
indicate the development of a postoperative reparative granuloma in the oval
fossa. The symptoms are related to a perilymph leak or to the extension of the
granuloma into the labyrinth. CT shows a nonspecific soft-tissue mass in the
oval window recess (Fig. 10).
However, the extension of the granuloma within the vestibule cannot be
detected on CT because the granuloma and the labyrinthic fluid have the same
density.
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Fig. 10. —32-year-old woman with severe vertigo caused by postoperative
granuloma with resulting displacement of prosthesis. Granuloma presents as
soft-tissue mass (large arrow) in front of posterior part of oval
window. Prosthesis tip (small arrow) is displaced forward by
granuloma.
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Intravestibular Protrusion of the Prosthesis
An intravestibular protrusion of the prosthesis may be observed immediately
after the surgical procedure but may also have a delayed appearance. The
protrusion is usually indicated by vertigo or sensorineural hearing loss. One
millimeter is the generally accepted limit for normal vestibular penetration.
Multiplanar reconstructions show the abnormal protrusion of the shaft of the
prosthesis within the vestibular cavity (Fig.
11A,
11B).
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Fig. 11A. —35-year-old woman with sensorineural hearing loss and vertigo caused
by intravestibular prostrusion of prosthesis 10 days after stapedectomy.
Oblique axial (A) and coronal (B) reconstructions show
protrusion of prosthesis shaft (arrow) in vestibule.
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Fig. 11B. —35-year-old woman with sensorineural hearing loss and vertigo caused
by intravestibular prostrusion of prosthesis 10 days after stapedectomy.
Oblique axial (A) and coronal (B) reconstructions show
protrusion of prosthesis shaft (arrow) in vestibule.
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Yanagisawa E, Lee KJ. Noninfectious diseases of the ear:
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Derlacki EL. Revision stapes surgery: problems with some solutions. Laryngoscope
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Introduction
Surgical Procedures
