CT Evaluation of Prosthetic Ossicular Reconstruction ...

SCIENTIFIC EXHIBIT 593

CT Evaluation of Pros-

thetic Ossicular Recon-

struction Procedures:

What the Otologist

Needs to Know1

Jeffrey A. Stone, MD • Suresh K. Mukherji, MD • Brian S. Jewett, MD
Vincent N. Carrasco, MD • Mauricio Castillo, MD

Postoperative otologic evaluation of patients who have undergone os-
sicular reconstruction is often difficult. However, thin-section com-
puted tomography (CT) can help determine the type of prosthesis
used for reconstruction and adequately assess for complications that
may be causing postoperative conductive hearing loss. A variety of
prostheses may be used in ossicular reconstruction (eg, stapes prosthe-
sis, incus interposition graft, Applebaum prosthesis, Black oval-top
prosthesis, Richards centered prosthesis, Goldenberg prosthesis) and
can usually be identified at CT by their shapes and locations. Several
causes of prosthetic failure are readily demonstrated at CT, including
recurrent cholesteatoma and otitis media, formation of granulation tis-
sue or adhesions, and various mechanical problems (eg, subluxation,
dislocation, extrusion, fracture, bending). Perilymphatic fistula can be
difficult to identify at CT but may be suggested by the presence of
pneumolabyrinth, unexplained middle ear effusion, or fluid accumula-
tion within the mastoid air cells. The presence of soft tissue within the
oval window niche 4–6 weeks following surgery may indicate post-
stapedectomy granuloma or fibrosis. Familiarity with the normal and
abnormal CT appearances of ossicular prostheses will enable the radi-
ologist to assist the otologist in identifying patients in whom revision
surgery is most appropriate.

Abbreviations: AIDS = acquired immunodeficiency syndrome, PORP = partial ossicular replacement prosthesis, TORP = total ossicular re-
placement prosthesis

Index terms: Ear, CT, 212.1211 • Ear, prostheses, 212.42, 212.456 • Stents and prostheses, 212.42, 212.456

RadioGraphics 2000; 20:593–605

1From the Departments of Radiology (J.A.S., S.K.M., M.C.) and Otolaryngology (S.K.M., B.S.J., V.N.C.), University of North Carolina School
of Medicine, Chapel Hill. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received April 13, 1999; revision requested May
5 and received May 28; accepted June 1. Address reprint requests to J.A.S., Department of Radiology, Medical College of Georgia, 1120 15th
St, Augusta, GA 30912-3910 (e-mail: [email protected]).

©RSNA, 2000

594 May-June 2000 RG s Volume 20 • Number 3

Prostheses Most Commonly Used for Ossicular Reconstruction

Type of Prosthesis Type of Graft Used Function

Stapes prosthesis Synthetic (autograft, Replaces diseased stapes
homograft rare)
Incus interposition Extends from the malleus to the stapes or oval window
graft Autograft, homograft
Extends from the long process of the incus to the capitulum
Applebaum prosthesis Synthetic of the stapes

Black oval-top Synthetic Extends from the tympanic membrane to the capitulum of
prosthesis the stapes or oval window
Synthetic
Richards centered Extends from the tympanic membrane to the capitulum of
prosthesis Synthetic the stapes or oval window

Goldenberg prosthesis Extends from the tympanic membrane to the capitulum of
the stapes or oval window

Introduction membrane and stapes (eg, incus interposition
graft). In some cases, however, a synthetic pros-
Ossicular prostheses are commonly placed in pa- thesis (Applebaum prosthesis) is used. This pros-
tients with ossicular destruction or disruption thesis extends from the residual long process of
due to cholesteatoma, chronic otitis media, or the incus to the capitulum of the stapes (3). In
congenital ossicular malformation. Autografts advanced disease, more extensive reconstruction
were initially used for ossicular chain reconstruc- with a partial ossicular replacement prosthesis
tion due to their biocompatibility and good (PORP [Smith & Nephew, Memphis, Tenn]) or
sound conduction. However, autografts require total ossicular replacement prosthesis (TORP
time and skill for sculpting and may harbor re- [Smith & Nephew]) may be required. These
sidual histologic disease such as cholesteatoma prostheses extend from the tympanic membrane
(1). As a result, homografts from cadavers gained to the stapes capitulum and footplate, respec-
acceptance and are available in many presculpted tively (Fig 1) (1). Although the terms PORP and
designs, thereby decreasing the time needed for TORP are registered trademarks, most otologists
surgical reconstruction (1). Synthetic prostheses use the terms to refer to any tack-shaped syn-
were developed in the mid-1980s because of dif- thetic prostheses that are used to reconstruct the
ficulty in obtaining homograft materials, imprac- ossicular chain (1).
tical storage requirements, and the growing risk
of transmitting infectious diseases, particularly Malfunction of an ossicular prosthesis may be
acquired immunodeficiency syndrome (AIDS) clinically suspected in the setting of increased
(1,2). conductive hearing loss and may occur weeks to
years after surgery. Thin-section computed to-
It is important for the radiologist to be familiar mography (CT) with contiguous 1-mm sections
with the types of prostheses most commonly used is an important adjunct to clinical evaluation in
for ossicular reconstruction (Table). If disease is patients with conductive hearing loss who have
isolated to the oval window, stapedectomy or undergone ossicular reconstruction. CT may
stapedotomy is usually performed, and the super- help determine the type of prosthesis used when
structure of the stapes may be replaced with a surgical records are unavailable. It can also be
synthetic prosthesis. In cases of incudostapedial used to evaluate the status of the prosthesis and
joint disease, a piece of autogenous bone may be remaining ossicles (4). CT is particularly useful
used to bridge the gap between the tympanic in cases involving middle ear mucosal thickening
because it is often difficult to determine the in-

RG s Volume 20 • Number 3 Stone et al 595

a. b.

Figure 1. Ossicular replacement prostheses. (a) Drawing illustrates a PORP extending from the tympanic mem-
brane (arrowhead) to the capitulum of the stapes (arrow). (b) Drawing illustrates a TORP extending from the tym-
panic membrane (arrowhead) to the oval window (arrow). The ossicles have been excised in these illustrations.

tegrity of the ossicular chain in this setting. CT Stapes reconstruction is also performed for dis-
may occasionally fail to demonstrate the cause of continuity or fracture resulting from prior basilar
prosthetic failure; however, several causes are skull fracture, binding cicatricial adhesions, or
readily demonstrated at CT, including recurrent tympanosclerosis (6). Stapedectomy involves re-
cholesteatoma and otitis media; formation of section of all or part of the footplate to open the
granulation tissue or adhesions; and subluxation, oval window and allow sound to enter the laby-
dislocation, or extrusion of the prosthesis. rinth as well as reconstruction of a conductive
bridge between the incus and labyrinth (6,7). In
In this article, we discuss and illustrate the 1969, Schuknecht and Applebaum (8) intro-
normal and abnormal CT appearances of a vari- duced a technique in which the stapes super-
ety of prostheses used in ossicular reconstruction. structure is resected but the footplate is pre-
These include stapes prostheses, incus interposi- served. In this procedure, known as stapedotomy,
tion grafts, and synthetic PORPs and TORPs a small hole is drilled in the footplate and a 0.6-
(Applebaum prosthesis, Black oval-top prosthe- mm-diameter Teflon wire piston is advanced
sis, Richards centered prosthesis, and Golden- through the small fenestra. This technique elimi-
berg prosthesis). nates many earlier complications of stapedec-
tomy, including vertigo and reparative granu-
Stapes Prosthesis loma formation (5). The Teflon wire piston can
be identified at CT and should extend from the
Procedure
Stapes reconstruction is most often used to re-
store conductive hearing loss in patients with
otosclerosis or congenital abnormalities (5).

596 May-June 2000 RG s Volume 20 • Number 3

2. 3.

Figures 2, 3. (2) Wire stapes prosthesis. Coronal CT scan shows a thin wire prosthesis (arrowhead) extending
from the long process of the incus (white arrow) to the oval window (straight black arrow). The tympanic segment
of the facial nerve is seen superior to the prosthesis (curved arrow). (3) Piston prosthesis. Axial CT scan shows the
distal medial portion of a piston prosthesis (curved arrow) articulating with the oval window (arrowhead). The pros-
thesis was placed for fenestral otosclerosis as seen at the fissula ante fenestram (straight arrow).

lenticular process of the incus to the footplate Figure 4. Prosthetic subluxation. Axial CT scan
(Fig 2). Other prostheses that may be used in- demonstrates migration of the medial aspect of a Tef-
clude a homograft prosthesis made of prefash- lon wire stapes prosthesis (arrowhead) anteriorly from
ioned labyrinthine bone or cadaveric ossicle, a the oval window (arrow).
stainless steel piston prosthesis, a wire prosthesis,
or a polymeric silicone prosthesis (Silastic; Dow sis need not be positioned centrally within the
Corning, Midland, Mich) (Fig 3) (5). Some oval window to function properly (10).
surgeons use a posterior crus preservation tech-
nique, which is a form of partial stapedectomy Evidence of new bone growth at the oval win-
(6). In this procedure, the footplate and anterior dow may be seen at CT. Abnormal spongiotic
crus of the stapes are resected, leaving the incu- bone may form in patients with progressive oto-
dostapedial joint and the posterior crus. The pos- sclerosis or who have undergone unusually exten-
terior crus is placed over a perichondral graft, sive drilling with subsequent bone repair. Surgery
which covers the oval window and may be diffi-
cult to identify at CT.

Complications
A patient with a history of stapedectomy who
presents with recurrent conductive hearing loss
should undergo thorough preoperative evaluation
including CT of the temporal bone. Revision sta-
pedectomy is associated with a significantly in-
creased risk of sensorineural hearing loss and de-
creased success in restoring conductive hearing
compared with primary surgery (9). Therefore,
it is important to determine which patients will
benefit most from revision surgery. The prosthe-

RG s Volume 20 • Number 3 Stone et al 597

a. b.

Figure 5. Prosthetic subluxation. (a) Coronal CT scan shows subluxation of the medial tip of a stainless steel pis-
ton stapes prosthesis (arrowhead) inferior to the oval window (arrow). (b) Axial CT scan reveals that the medial tip
of the prosthesis is also anteriorly displaced (arrow). Correlation of axial and coronal CT findings is necessary to de-
termine the exact location of a malfunctioning prosthesis.

Figure 6. Prosthetic extrusion. Coronal CT scan CT also helps identify repairable causes of
shows a stainless steel piston stapes prosthesis that has prosthetic failure that may be rectified with revi-
migrated from the middle ear cavity (arrowhead). The sion surgery. The most common repairable cause
prosthesis is seen lateral to the tympanic membrane (ar- of prosthetic failure is subluxation or dislocation,
row) in the external auditory canal. Surgery revealed which is seen in 50%–60% of patients with post-
perforation of the tympanic membrane and adherence operative hearing loss (Figs 4, 5) (9). Migration
of the prosthesis to the wall of the external auditory ca- of the stapes prosthesis is most often directed in-
nal. ferior and posterior to the oval window (10–12).
Displacement at the incudal articulation also oc-
is often contraindicated in these patients due to curs with unstable attachment of the wire loop of
the risk of deafness associated with revision sur- the prosthesis to the long process of the incus
gery. Obliteration of the round window by oto- (5). The wire slips inferiorly due to gravity (loose
sclerosis may also be identified at CT. Attempts wire syndrome), and patients often report tempo-
to drill out the obliterated round window are rary improvement in hearing with middle ear in-
usually unsuccessful and often result in further flation (13). Pressure generated through the eu-
sensorineural hearing loss (11). stachian tube is believed to push the wire superi-
orly into the proper position.

A foreign body reaction or direct pressure ero-
sion results in resorptive osteitis of the long pro-
cess of the incus and displacement or extrusion
of the prosthesis (5). The extruded prosthesis
may lie within the dependent portion of the mid-
dle ear cavity, migrate extrinsic to the middle
ear cavity (Fig 6), or be completely absent, hav-
ing migrated out of the tympanoplasty and the
external auditory canal (9).

598 May-June 2000 RG s Volume 20 • Number 3

8a. 8b.

Figures 7, 8. (7) Deformed stapes prosthesis in a pa-

tient who experienced sudden conductive hearing loss.
Axial CT scan shows a bent stainless steel prosthesis (ar-

rowhead). The medial tip of the prosthesis (arrow) has be-

come detached from the oval window. The prosthesis was
replaced at surgery. (8) Vestibular perforation by a stapes

prosthesis in a patient with chronic eustachian tube dys-

function and otitis media. (a) Axial CT scan shows a
stainless steel prosthesis extending through the oval win-

dow (arrowhead) into the vestibule (black arrow). There

is a resultant air gap between the incus and the lateral as-
pect of the prosthesis (white arrow). (b) Coronal CT scan

shows that the medial tip of the prosthesis is angled supe-

riorly into the vestibule (arrowhead) and away from the 7.
basal turn of the cochlea (arrow).

Fracture or bending of a prosthesis is another symptoms should raise suspicion for perilym-
complication that is easily identified at CT (Fig 7). phatic fistula (10). Perilymphatic fistula may be
difficult to identify at CT but may be suggested
Increased negative pressure in the middle ear by the presence of pneumolabyrinth or a new,
due to eustachian tube dysfunction may force a unexplained middle ear effusion. Fluid may also
prosthesis into the vestibule (Fig 8). This is seen accumulate within the mastoid air cells (10).
in approximately 2% of patients who present
with postoperative sensorineural hearing loss No soft tissue should be present within the
(14). These patients may experience vertigo, tin- oval window niche 4–6 weeks following surgery
nitus, disequilibrium, and decreased bone con- (10). If soft tissue is identified at CT, poststape-
duction thresholds. Steroid treatment and early dectomy granuloma and fibrosis should be con-
active aeration of the middle ear cavity may help sidered. Oval window fibrosis has a prevalence of
correct the problem. 2%–37% and may expand to fill a large portion
of the middle ear cavity (11). This reaction may
Perilymphatic fistula is a potentially serious result from immunologic sensitivity to the surgi-
complication of stapes reconstruction that ac- cal materials used or from surgical trauma to the
counts for approximately 10% of cases of failed mucoperiosteum (10).
stapedectomy (11). By definition, a perilym-
phatic fistula is created surgically when the Incus Interposition Graft
footplate is resected or drilled. Transient vertigo
and sensorineural hearing loss in the immediate Procedure
postoperative period are often the result of serous The incus may be used to reconstruct an ossicular
labyrinthitis. However, persistent or worsening chain that has been destroyed by chronic otitis
media and cholesteatoma. Because of the limita-

RG s Volume 20 • Number 3 Stone et al 599

9. 10.

Figures 9, 10. (9) Incus interposition graft. Coronal CT scan shows a surgically remodeled incus (arrowhead)
used as an interposition graft extending from the manubrium of the malleus (curved arrow) to the capitulum of the
stapes (straight arrow). (10) Normal ossicular anatomy. Coronal CT scan of the ossicular chain shows the relation-
ship between the incus and stapes (cf Fig 9). The long process (open arrow) and lenticular process (solid arrow) of
the incus as well as the incudostapedial joint (arrowhead) are also identified.

tions of autografts described earlier, incus interpo- malleus (2,15). This is known as the “notched
sition homografts evolved and are now available in incus with long process” procedure (2).
a variety of sizes that can easily be sculpted to fit a
patient’s unique middle ear anatomy. The homo- The incus interposition homograft was widely
graft bone becomes living tissue over time as it used from 1972 to 1986 but is rarely used today
is incorporated by the host ear and provides supe- as a result of the AIDS epidemic and the theo-
rior audiologic results compared with autografts retic risk of infectious spread from cadaveric ma-
(15). terials (2). It is occasionally used in cases of
trauma or incudal disarticulation following stape-
Incus interposition grafting involves resection dectomy. Because of poor structural support, the
of the diseased incus. The stapes may also be incus is vulnerable to trauma, and trauma-related
resected depending on its integrity. A notch is incudal disarticulation is responsible for 80% of
created in the upper border of the short process persistent posttraumatic conductive hearing loss
of the incus to fit beneath the manubrium of the (16). Complete incudal disarticulation may also
malleus and stabilize the prosthesis (2). If the occur following stapedectomy as a result of ex-
stapes superstructure is intact, the long process of cessive disarticulation of the incudostapedial
the incus is amputated and a small cup is fash- joint, fibrosis between the incus and tympano-
ioned to fit the stapes head (2,15). The notch in meatal flap, inadvertent malleoincudal trauma,
the short process is then positioned beneath the or torsional stress induced by obliterative otoscle-
manubrium. This is known as the “notched incus rosis at the oval window (17,18). When a ho-
with short process” procedure (Figs 9, 10) (2). mograft prosthesis is used today, it is most often
If the stapes superstructure is absent, a longer sculpted from cadaveric rib cartilage (19). The
bridge is needed to fill the gap. Consequently, incus interposition graft may still occasionally be
the lenticular process of the incus is amputated, seen at CT, and it is important to be familiar
the long process is placed on the stapedial foot- with its appearance.
plate, and the notch created in the short process
is positioned beneath the manubrium of the

600 May-June 2000 RG s Volume 20 • Number 3

a. b.

Figure 11. Incus interposition graft dysfunction due to granulation tissue in a patient who presented with progres-
sive conductive hearing loss. (a) Coronal CT scan obtained at the level of the cochlea shows an incus interposition
graft encased by granulation tissue (arrow). (b) On a coronal CT scan obtained at the level of the vestibule, the in-
cus interposition graft is seen articulating with the head of the stapes (arrow) despite extensive encasement by granu-
lation tissue.

Complications Figure 12. Applebaum prosthesis. Drawing illus-
Complications of incus interposition grafting that trates an Applebaum prosthesis with the characteristic
can be identified at CT and are amenable to sur- L-shaped configuration. A long notch fits over the end
gery include prosthetic subluxation, incudal ne- of the partially amputated long process of the incus
crosis, reparative granuloma formation, and re- (arrowhead). The length of the notch can be varied to
current cholesteatoma. Of these complications, accommodate residual long processes of different
subluxation is the most difficult to identify at lengths. The capitulum of the stapes inserts into a hole
CT. Progressive mucosal thickening in the mid- at the other end of the prosthesis (arrow).
dle ear with ossicle erosion may indicate re-
current cholesteatoma, whereas thickening with- cium phosphate polymer that has the capacity to
out ossicle erosion may indicate granuloma for- form bonds with living bone and efficiently con-
mation (Fig 11). Over time, granuloma forma- ducts vibratory energy (1,20). The biocompat-
tion may cause dislocation or resorption of the ibility of the head permits it to be in direct con-
incus graft. Ankylosis of the incus graft may also tact with the tympanic membrane without requir-
occur, particularly if the prosthesis is too large (1). ing a cartilage or tissue graft to prevent extrusion
(20). If the long process of the malleus is present,
Synthetic PORP and TORP a prosthesis with a notched head is used. This
notch fits over the manubrium and helps prevent
Nowadays, reconstruction of the ossicular chain prosthetic subluxation. If the manubrium is ab-
is typically performed with synthetic prostheses.
The PORP is the most commonly used prosthe-
sis. It attaches to the medial surface of the tym-
panic membrane or occasionally to the long pro-
cess of the incus and extends to the capitulum of
the stapes (Fig 1) (7). The stapes is left intact
during placement of the PORP. If the diseased
stapes is resected, a TORP is used to connect the
medial surface of the tympanic membrane to an
intact stapes footplate or oval window (Fig 1) (7).

Most PORPs and TORPs are composite pros-
theses consisting of a head and a shaft. The head
is made of hydroxyapatite, a biocompatible cal-

RG s Volume 20 • Number 3 Stone et al 601

a. b.

Figure 13. Applebaum prosthesis. (a) Axial CT scan shows an Applebaum prosthesis with the notch (arrowhead)
medial to the long process of the incus (straight arrow), which fits into the notch. The crura of the stapes are also
identified (curved arrows). (b) Coronal CT scan shows the medial aspect of the prosthesis (arrowhead) fitted over
the capitulum of the stapes (arrow).

Figure 14. Black oval-top prosthesis. Photograph Applebaum Prosthesis
shows several Black oval-top PORPs (short, thick Trauma and chronic otitis media often result in
shafts) and TORPs (long, thin shafts). defects of the incudostapedial joint and of the
distal end of the long process of the incus (3).
sent, a prosthesis with a flat or egg-shaped head The Applebaum prosthesis forms a bridge be-
is used to maximize contact with the tympanic tween the residual long process of the incus and
membrane. The shaft of the prosthesis is made of the capitulum of the stapes. This prosthesis is L-
high-density polyethylene sponge (Plasti-Pore, shaped with a hole in one end to accommodate
Smith & Nephew), fluoroplastic, or a polymer of the stapes head and a trough at the other end to
hydroxyapatite and polyethylene (Hapex, Smith receive the truncated long process of the incus
& Nephew) (7,20,21). These materials are easy (Fig 12). Because of its location and shape, the
to cut and permit the shaft to be trimmed to Applebaum prosthesis is easily identified at CT
within a 0.5-mm variance based on intraoperative (Fig 13).
measurement (20). Familiarity with the different
configurations of PORPs and TORPs enables the Black Oval-Top Prosthesis
radiologist to identify the type of prosthesis that The Black oval-top prosthesis was originally de-
was used for reconstruction and adequately as- signed for use in cases of severe atelectasis result-
sess for complications that may have caused post- ing from chronic dysfunction of the eustachian
operative conductive hearing loss. tube (22). This prosthesis has an egg-shaped hy-
droxyapatite head that is off center relative to the
shaft, giving it a characteristic “horseshoe” ap-
pearance at CT (Figs 14–16). Because the mal-
leus is not engaged with the Black oval-top pros-
thesis, its presence and orientation to the stapes
are unimportant. This design results in decreased
stability of the prosthesis at its articulation with

602 May-June 2000 RG s Volume 20 • Number 3

15. 16.

Figures 15, 16. (15) Black TORP. Coronal CT scan shows a Black TORP that has been sectioned through its
midportion with the characteristic “horseshoe” appearance (arrow). (16) Black PORP. Axial CT scan shows the
head (arrowhead) and shaft (arrow) of a Black PORP. The shaft is made of Plasti-Pore (Smith & Nephew) and has
significantly lower attenuation than the head. The medial articulation of the prosthesis with the capitulum of the
stapes is not seen.

17. 18.

Figures 17, 18. (17) Black PORP with subluxation. Coronal CT scan obtained at the level of the vestibule and
oval window shows the head of a Black PORP (arrowhead) with subluxation inferior to the capitulum of the stapes
(arrow). (18) Black PORP with subluxation and rotation. Axial CT scan shows the head of a Black PORP (arrow-
head) that has become dislocated and has rotated posteriorly to face the tympanic sinus (arrow).

the tympanic membrane and obstruction of the tion tissue or recurrent cholesteatoma may result
surgeon’s view of the shaft in relation to the in subluxation (Figs 19, 20). Prosthetic extrusion
stapes or oval window. It is also associated with occurs in 7% of cases, most often in patients with
a slightly increased risk of tympanic membrane associated infection, graft breakdown, or eusta-
perforation. chian tube dysfunction (22). In patients with
normal middle ear ventilation, the rate of extru-
Postoperative conductive hearing loss may be sion is approximately 3%–4% (22).
the result of subluxation of the prosthesis, par-
ticularly at its articulation with the stapes in a Richards Centered Prosthesis
PORP or with the oval window in a TORP (Figs Unlike the Black prosthesis, the Richards centered
17, 18). Encasement of a prosthesis by granula- prosthesis has a flat head that is centered on the
shaft. Modified versions of the Richards PORP

RG s Volume 20 • Number 3 Stone et al 603

19. 20.

Figures 19, 20. (19) Black PORP with subluxation due to granulation tissue. Coronal CT scan shows the head
of a Black PORP encased in granulation tissue (arrow). The PORP is dislocated and superiorly rotated. (20) Black
TORP with subluxation due to recurrent cholesteatoma in a patient with a history of mastoidectomy. Axial CT scan
shows the head of a Black TORP that has become dislocated and has rotated posteriorly to face the tympanic sinus
(arrow). The diagnosis of recurrent cholesteatoma may be difficult in this setting, although new erosion of any re-
sidual ossicles or the tegmen tympani may suggest the diagnosis.

21. 22.

Figures 21, 22. (21) Richards centered prostheses. Photograph shows various Richards PORPs (short, thick
shafts) and TORPs (long, thin shafts). A modified Richards PORP (arrowhead) and TORP (arrow) with an off-
center head and a groove for the malleus are included. (22) Richards PORP. Coronal CT scan shows a Richards
PORP. The PORP is encased in granulation tissue but is in normal position with the distal tip in the expected region
of the capitulum of the stapes (curved arrow). The hollow shaft is centered on a flat hydroxyapatite head (arrow-
head) and manifests as a linear area of low attenuation (straight arrow).

and TORP that have an off-center head with a out causing displacement of the prosthesis (Fig
groove for the malleus are also available and pro- 22). In such cases, conductive hearing loss results
vide increased stability (Fig 21). The shaft of the from dampening of the pistonlike action of the
Richards prosthesis is hollow and can be identified prosthesis during sound transmission.
at CT. Recurrent cholesteatoma or reactive granu-
lation tissue may encase a PORP or TORP with-



RG s Volume 20 • Number 3 Stone et al 605

a. b.

Figure 25. Goldenberg TORP with subluxation. (a) Axial CT scan shows the distal shaft of a
Goldenberg prosthesis with an attached hydroxyapatite cap (arrowhead). An air gap (arrow) is
seen between the cap and the oval window, a finding that indicates subluxation and noncom-
munication of the TORP with the oval window. On occasion, a hydroxyapatite cap is attached to
the end of a TORP to decrease trauma to the oval window. (b) Coronal CT scan shows the Gold-
enberg TORP in its entirety. The air gap is again seen (arrowhead) (cf a), and slight superior sub-
luxation of the medial shaft relative to the oval window can be identified (arrow).

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failure and revision surgery in otosclerosis. Otolar- 17. Swartz JD, Laucks RL, Berger AS, Ardito JM,
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7. Mukherji SK, Mancusso AA, Kotzur IM, et al. CT the disarticulated incus. Laryngoscope 1986; 96:
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