(Radiographics. 2000;20:593-605.)
© RSNA, 2000
CT Evaluation of Prosthetic Ossicular Reconstruction Procedures: What the Otologist Needs to Know1
Jeffrey A. Stone, MD,
Suresh K. Mukherji, MD,
Brian S. Jewett, MD,
Vincent N. Carrasco, MD and
Mauricio Castillo, MD
1 From 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: jstone@mail.mcg.edu).
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Abstract
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Postoperative otologic evaluation of patients who have undergone ossicular reconstruction is often difficult. However, thin-section computed 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 prosthesis, 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 tissue 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 accumulation within the mastoid air cells. The presence of soft tissue within the oval window niche 4–6 weeks following surgery may indicate poststapedectomy granuloma or fibrosis. Familiarity with the normal and abnormal CT appearances of ossicular prostheses will enable the radiologist to assist the otologist in identifying patients in whom revision surgery is most appropriate.
Index Terms: Ear, CT, 212.1211 • Ear, prostheses, 212.42, 212.456 • Stents and prostheses, 212.42, 212.456
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Introduction
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Ossicular prostheses are commonly placed in patients with ossicular destruction or disruption due to cholesteatoma, chronic otitis media, or congenital ossicular malformation. Autografts were initially used for ossicular chain reconstruction due to their biocompatibility and good sound conduction. However, autografts require time and skill for sculpting and may harbor residual histologic disease such as cholesteatoma (1). As a result, homografts from cadavers gained acceptance and are available in many presculpted designs, thereby decreasing the time needed for surgical reconstruction (1). Synthetic prostheses were developed in the mid-1980s because of difficulty in obtaining homograft materials, impractical storage requirements, and the growing risk of transmitting infectious diseases, particularly acquired immunodeficiency syndrome (AIDS) (1,2).
It is important for the radiologist to be familiar with the types of prostheses most commonly used for ossicular reconstruction (Table).
If disease is isolated to the oval window, stapedectomy or stapedotomy is usually performed, and the superstructure of the stapes may be replaced with a synthetic prosthesis. In cases of incudostapedial joint disease, a piece of autogenous bone may be used to bridge the gap between the tympanic membrane and stapes (eg, incus interposition graft). In some cases, however, a synthetic prosthesis (Applebaum prosthesis) is used. This prosthesis extends from the residual long process of the incus to the capitulum of the stapes (3). In advanced disease, more extensive reconstruction with a partial ossicular replacement prosthesis (PORP [Smith & Nephew, Memphis, Tenn]) or total ossicular replacement prosthesis (TORP [Smith & Nephew]) may be required. These prostheses extend from the tympanic membrane to the stapes capitulum and footplate, respectively (Fig 1) (1). Although the terms PORP and TORP are registered trademarks, most otologists use the terms to refer to any tack-shaped synthetic prostheses that are used to reconstruct the ossicular chain (1).
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Figure 1a. Ossicular replacement prostheses. (a) Drawing illustrates a PORP extending from the tympanic membrane (arrowhead) to the capitulum of the stapes (arrow). (b) Drawing illustrates a TORP extending from the tympanic membrane (arrowhead) to the oval window (arrow). The ossicles have been excised in these illustrations.
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Figure 1b. Ossicular replacement prostheses. (a) Drawing illustrates a PORP extending from the tympanic membrane (arrowhead) to the capitulum of the stapes (arrow). (b) Drawing illustrates a TORP extending from the tympanic membrane (arrowhead) to the oval window (arrow). The ossicles have been excised in these illustrations.
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Malfunction of an ossicular prosthesis may be clinically suspected in the setting of increased conductive hearing loss and may occur weeks to years after surgery. Thin-section computed tomography (CT) with contiguous 1-mm sections is an important adjunct to clinical evaluation in patients with conductive hearing loss who have undergone ossicular reconstruction. CT may help determine the type of prosthesis used when surgical records are unavailable. It can also be used to evaluate the status of the prosthesis and remaining ossicles (4). CT is particularly useful in cases involving middle ear mucosal thickening because it is often difficult to determine the integrity of the ossicular chain in this setting. CT may occasionally fail to demonstrate the cause of prosthetic failure; however, several causes are readily demonstrated at CT, including recurrent cholesteatoma and otitis media; formation of granulation tissue or adhesions; and subluxation, dislocation, or extrusion of the prosthesis.
In this article, we discuss and illustrate the normal and abnormal CT appearances of a variety of prostheses used in ossicular reconstruction. These include stapes prostheses, incus interposition grafts, and synthetic PORPs and TORPs (Applebaum prosthesis, Black oval-top prosthesis, Richards centered prosthesis, and Goldenberg prosthesis).
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Stapes Prosthesis
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Procedure
Stapes reconstruction is most often used to restore conductive hearing loss in patients with otosclerosis or congenital abnormalities (5). Stapes reconstruction is also performed for discontinuity or fracture resulting from prior basilar skull fracture, binding cicatricial adhesions, or tympanosclerosis (6). Stapedectomy involves resection of all or part of the footplate to open the oval window and allow sound to enter the labyrinth as well as reconstruction of a conductive bridge between the incus and labyrinth (6,7). In 1969, Schuknecht and Applebaum (8) introduced a technique in which the stapes superstructure is resected but the footplate is preserved. In this procedure, known as stapedotomy, a small hole is drilled in the footplate and a 0.6-mm-diameter Teflon wire piston is advanced through the small fenestra. This technique eliminates many earlier complications of stapedectomy, including vertigo and reparative granuloma formation (5). The Teflon wire piston can be identified at CT and should extend from the lenticular process of the incus to the footplate (Fig 2). Other prostheses that may be used include a homograft prosthesis made of prefashioned labyrinthine bone or cadaveric ossicle, a stainless steel piston prosthesis, a wire prosthesis, or a polymeric silicone prosthesis (Silastic; Dow Corning, Midland, Mich) (Fig 3) (5). Some surgeons use a posterior crus preservation technique, which is a form of partial stapedectomy (6). In this procedure, the footplate and anterior crus of the stapes are resected, leaving the incudostapedial joint and the posterior crus. The posterior crus is placed over a perichondral graft, which covers the oval window and may be difficult to identify at CT.
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Figure 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).
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Figure 3. Piston prosthesis. Axial CT scan shows the distal medial portion of a piston prosthesis (curved arrow) articulating with the oval window (arrowhead). The prosthesis was placed for fenestral otosclerosis as seen at the fissula ante fenestram (straight arrow).
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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 stapedectomy is associated with a significantly increased risk of sensorineural hearing loss and decreased 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 prosthesis need not be positioned centrally within the oval window to function properly (10).
Evidence of new bone growth at the oval window may be seen at CT. Abnormal spongiotic bone may form in patients with progressive otosclerosis or who have undergone unusually extensive drilling with subsequent bone repair. Surgery CT is contraindicated in these patients due to the risk of deafness associated with revision surgery. Obliteration of the round window by otosclerosis may also be identified at CT. Attempts to drill out the obliterated round window are usually unsuccessful and often result in further sensorineaural hearing loss (1).
CT also helps identify repairable causes of prosthetic failure that may be rectified with revision surgery. The most common repairable cause of prosthetic failure is subluxation or dislocation, which is seen in 50%–60% of patients with postoperative hearing loss (Figs 4, 5) (9). Migration of the stapes prosthesis is most often directed inferior and posterior to the oval window (10–12). Displacement at the incudal articulation also occurs with unstable attachment of the wire loop of the prosthesis to the long process of the incus (5). The wire slips inferiorly due to gravity (loose wire syndrome), and patients often report temporary improvement in hearing with middle ear inflation (13). Pressure generated through the eustachian tube is believed to push the wire superiorly into the proper position.
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Figure 5a. Prosthetic subluxation. (a) Coronal CT scan shows subluxation of the medial tip of a stainless steel piston 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 determine the exact location of a malfunctioning prosthesis.
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Figure 5b. Prosthetic subluxation. (a) Coronal CT scan shows subluxation of the medial tip of a stainless steel piston 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 determine the exact location of a malfunctioning prosthesis.
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A foreign body reaction or direct pressure erosion results in resorptive osteitis of the long process of the incus and displacement or extrusion of the prosthesis (5). The extruded prosthesis may lie within the dependent portion of the middle ear cavity, migrate extrinsic to the middle ear cavity (Fig 6), or be completely absent, having migrated out of the tympanoplasty and the external auditory canal (9).
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Figure 6. Prosthetic extrusion. Coronal CT scan shows a stainless steel piston stapes prosthesis that has migrated from the middle ear cavity (arrowhead). The prosthesis is seen lateral to the tympanic membrane (arrow) in the external auditory canal. Surgery revealed perforation of the tympanic membrane and adherence of the prosthesis to the wall of the external auditory canal.
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Fracture or bending of a prosthesis is another complication that is easily identified at CT (Fig 7).
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> Deformed stapes prosthesis in a patient who experienced sudden conductive hearing loss. Axial CT scan shows a bent stainless steel prosthesis (arrowhead). The medial tip of the prosthesis (arrow) has become detached from the oval window. The prosthesis was replaced at surgery.
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Increased negative pressure in the middle ear due to eustachian tube dysfunction may force a prosthesis into the vestibule (Fig 8). This is seen in approximately 2% of patients who present with postoperative sensorineural hearing loss (14). These patients may experience vertigo, tinnitus, disequilibrium, and decreased bone conduction thresholds. Steroid treatment and early active aeration of the middle ear cavity may help correct the problem.
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Figure 8a. Vestibular perforation by a stapes prosthesis in a patient with chronic eustachian tube dysfunction and otitis media. (a) Axial CT scan shows a stainless steel prosthesis extending through the oval window (arrowhead) into the vestibule (black arrow). There is a resultant air gap between the incus and the lateral aspect of the prosthesis (white arrow). (b) Coronal CT scan shows that the medial tip of the prosthesis is angled superiorly into the vestibule (arrowhead) and away from the basal turn of the cochlea (arrow).
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Figure 8b. Vestibular perforation by a stapes prosthesis in a patient with chronic eustachian tube dysfunction and otitis media. (a) Axial CT scan shows a stainless steel prosthesis extending through the oval window (arrowhead) into the vestibule (black arrow). There is a resultant air gap between the incus and the lateral aspect of the prosthesis (white arrow). (b) Coronal CT scan shows that the medial tip of the prosthesis is angled superiorly into the vestibule (arrowhead) and away from the basal turn of the cochlea (arrow).
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Perilymphatic fistula is a potentially serious complication of stapes reconstruction that accounts for approximately 10% of cases of failed stapedectomy (11). By definition, a perilymphatic fistula is created surgically when the footplate is resected or drilled. Transient vertigo and sensorineural hearing loss in the immediate postoperative period are often the result of serous labyrinthitis. However, persistent or worsening symptoms should raise suspicion for perilymphatic fistula (10). Perilymphatic fistula may be difficult to identify at CT but may be suggested by the presence of pneumolabyrinth or a new, unexplained middle ear effusion. Fluid may also accumulate within the mastoid air cells (10).
No soft tissue should be present within the oval window niche 4–6 weeks following surgery (10). If soft tissue is identified at CT, poststapedectomy granuloma and fibrosis should be considered. Oval window fibrosis has a prevalence of 2%–37% and may expand to fill a large portion of the middle ear cavity (11). This reaction may result from immunologic sensitivity to the surgical materials used or from surgical trauma to the mucoperiosteum (10).
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Incus Interposition Graft
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Procedure
The incus may be used to reconstruct an ossicular chain that has been destroyed by chronic otitis media and cholesteatoma. Because of the limitations of autografts described earlier, incus interposition homografts evolved and are now available in a variety of sizes that can easily be sculpted to fit a patient's unique middle ear anatomy. The homograft bone becomes living tissue over time as it is incorporated by the host ear and provides superior audiologic results compared with autografts (15).
Incus interposition grafting involves resection of the diseased incus. The stapes may also be resected depending on its integrity. A notch is created in the upper border of the short process of the incus to fit beneath the manubrium of the malleus and stabilize the prosthesis (2). If the stapes superstructure is intact, the long process of the incus is amputated and a small cup is fashioned to fit the stapes head (2,15). The notch in the short process is then positioned beneath the manubrium. This is known as the "notched incus with short process" procedure (Figs 9, 10) (2). If the stapes superstructure is absent, a longer bridge is needed to fill the gap. Consequently, the lenticular process of the incus is amputated, the long process is placed on the stapedial footplate, and the notch created in the short process is positioned beneath the manubrium of the malleus (2,15). This is known as the "notched incus with long process" procedure (2). The incus interposition homograft was widely used from 1972 to 1986 but is rarely used today as a result of the AIDS epidemic and the theoretic risk of infectious spread from cadaveric materials (2). It is occasionally used in cases of trauma or incudal disarticulation following stapedectomy. Because of poor structural support, the incus is vulnerable to trauma, and trauma-related incudal disarticulation is responsible for 80% of persistent posttraumatic conductive hearing loss (16). Complete incudal disarticulation may also occur following stapedectomy as a result of excessive disarticulation of the incudostapedial joint, fibrosis between the incus and tympanomeatal flap, inadvertent malleoincudal trauma, or torsional stress induced by obliterative otosclerosis at the oval window (17,18). When a homograft prosthesis is used today, it is most often sculpted from cadaveric rib cartilage (19). The incus interposition graft may still occasionally be seen at CT, and it is important to be familiar with its appearance.
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Figure 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).
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Figure 10. Normal ossicular anatomy. Coronal CT scan of the ossicular chain shows the relationship 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.
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Complications
Complications of incus interposition grafting that can be identified at CT and are amenable to surgery include prosthetic subluxation, incudal necrosis, reparative granuloma formation, and recurrent cholesteatoma. Of these complications, subluxation is the most difficult to identify at CT. Progressive mucosal thickening in the middle ear with ossicle erosion may indicate recurrent cholesteatoma, whereas thickening without ossicle erosion may indicate granuloma formation (Fig 11). Over time, granuloma formation may cause dislocation or resorption of the incus graft. Ankylosis of the incus graft may also occur, particularly if the prosthesis is too large (1).
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Figure 11a. Incus interposition graft dysfunction due to granulation tissue in a patient who presented with progressive 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 incus interposition graft is seen articulating with the head of the stapes (arrow) despite extensive encasement by granulation tissue.
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Figure 11b. Incus interposition graft dysfunction due to granulation tissue in a patient who presented with progressive 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 incus interposition graft is seen articulating with the head of the stapes (arrow) despite extensive encasement by granulation tissue.
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Synthetic PORP and TORP
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Nowadays, reconstruction of the ossicular chain is typically performed with synthetic prostheses. The PORP is the most commonly used prosthesis. It attaches to the medial surface of the tympanic membrane or occasionally to the long process 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 prostheses consisting of a head and a shaft. The head is made of hydroxyapatite, a biocompatible calcium phosphate polymer that has the capacity to form bonds with living bone and efficiently conducts vibratory energy (1,20). The biocompatibility of the head permits it to be in direct contact with the tympanic membrane without requiring a cartilage or tissue graft to prevent extrusion (20). If the long process of the malleus is present, a prosthesis with a notched head is used. This notch fits over the manubrium and helps prevent prosthetic subluxation. If the manubrium is absent, a prosthesis with a flat or egg-shaped head is used to maximize contact with the tympanic membrane. The shaft of the prosthesis is made of high-density polyethylene sponge (Plasti-Pore, Smith & Nephew), fluoroplastic, or a polymer of hydroxyapatite and polyethylene (Hapex, Smith & Nephew) (7,20,21). These materials are easy to cut and permit the shaft to be trimmed to within a 0.5-mm variance based on intraoperative measurement (20). Familiarity with the different configurations of PORPs and TORPs enables the radiologist to identify the type of prosthesis that was used for reconstruction and adequately assess for complications that may have caused postoperative conductive hearing loss.
Applebaum Prosthesis
Trauma and chronic otitis media often result in defects of the incudostapedial joint and of the distal end of the long process of the incus (3). The Applebaum prosthesis forms a bridge between the residual long process of the incus and the capitulum of the stapes. This prosthesis is L-shaped with a hole in one end to accommodate the stapes head and a trough at the other end to receive the truncated long process of the incus (Fig 12). Because of its location and shape, the Applebaum prosthesis is easily identified at CT (Fig 13).
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Figure 12. Applebaum prosthesis. Drawing illustrates an Applebaum prosthesis with the characteristic L-shaped configuration. A long notch fits over the end of the partially amputated long process of the incus (arrowhead). The length of the notch can be varied to accommodate residual long processes of different lengths. The capitulum of the stapes inserts into a hole at the other end of the prosthesis (arrow).
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Figure 13a. 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).
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Figure 13b. 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).
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Black Oval-Top Prosthesis
The Black oval-top prosthesis was originally designed for use in cases of severe atelectasis resulting from chronic dysfunction of the eustachian tube (22). This prosthesis has an egg-shaped hydroxyapatite head that is off center relative to the shaft, giving it a characteristic "horseshoe" appearance at CT (Figs 14 –16). Because the malleus is not engaged with the Black oval-top prosthesis, its presence and orientation to the stapes are unimportant. This design results in decreased stability of the prosthesis at its articulation with the tympanic membrane and obstruction of the surgeon's view of the shaft in relation to the stapes or oval window. It is also associated with a slightly increased risk of tympanic membrane perforation.
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Figure 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.
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Postoperative conductive hearing loss may be the result of subluxation of the prosthesis, particularly at its articulation with the stapes in a PORP or with the oval window in a TORP (Figs 17, 18). Encasement of a prosthesis by granulation tissue or recurrent cholesteatoma may result in subluxation (Figs 19, 20). Prosthetic extrusion occurs in 7% of cases, most often in patients with associated infection, graft breakdown, or eustachian tube dysfunction (22). In patients with normal middle ear ventilation, the rate of extrusion is approximately 3%–4% (22).
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Figure 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).
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Figure 18. Black PORP with subluxation and rotation. Axial CT scan shows the head of a Black PORP (arrowhead) that has become dislocated and has rotated posteriorly to face the tympanic sinus (arrow).
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Figure 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.
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Figure 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 residual ossicles or the tegmen tympani may suggest the diagnosis.
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Richards Centered Prosthesis
Unlike the Black prosthesis, the Richards centered prosthesis has a flat head that is centered on the shaft. Modified versions of the Richards PORP and TORP that have an off-center head with a groove for the malleus are also available and provide increased stability (Fig 21). The shaft of the Richards prosthesis is hollow and can be identified at CT. Recurrent cholesteatoma or reactive granulation tissue may encase a PORP or TORP without causing displacement of the prosthesis (Fig 22). In such cases, conductive hearing loss results from dampening of the pistonlike action of the prosthesis during sound transmission.
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Figure 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.
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Figure 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 (arrowhead) and manifests as a linear area of low attenuation (straight arrow).
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Goldenberg Prosthesis
Like the Richards prosthesis, the Goldenberg prosthesis has a flat head. The major difference between the two prostheses is that the shaft of the Goldenberg prosthesis is off center relative to the head (Figs 23, 24). This design gives the surgeon a clear medial view of the articulation of the prosthesis with the stapes or oval window and increases accuracy in placement. However, the off-center shaft results in poor balance with an increased risk of subluxation (1). The extrusion rate for the Goldenberg prosthesis has been reported to be 2.6%; the rate of subluxation is unknown (23). Because the tympanic membrane often retracts over time due to chronic eustachian tube dysfunction, there is a tendency for the prosthesis to angle and migrate rather than extrude. An air gap between the prosthesis and the oval window suggests subluxation that may result in conductive hearing loss (Fig 25). A correctly positioned prosthesis may also malfunction due to encasement by granulation tissue or recurrent cholesteatoma.
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Figure 23. Goldenberg prosthesis. Photograph shows various Goldenberg PORPs (short, thick shafts) and TORPs (long, thin shafts). The heads of the prostheses are off center relative to the shafts. A prosthesis with a notched head (arrows) is used when the malleus is present. The notch fits over the manubrium of the malleus for added stability.
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Figure 24. Goldenberg TORP. Axial CT scan shows the flat head of a Goldenberg TORP articulating with the tympanic membrane (arrowhead). The shaft (arrow) is off center relative to the head. The articulation of the medial tip of the shaft with the oval window is not seen.
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Figure 25a. 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 noncommunication 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 Goldenberg TORP in its entirety. The air gap is again seen (arrowhead) (cf a), and slight superior subluxation of the medial shaft relative to the oval window can be identified (arrow).
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Figure 25b. 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 noncommunication 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 Goldenberg TORP in its entirety. The air gap is again seen (arrowhead) (cf a), and slight superior subluxation of the medial shaft relative to the oval window can be identified (arrow).
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The modified versions of the Richards prosthesis mentioned earlier may be difficult to distinguish from the Goldenberg prosthesis.
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Conclusions
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The use of ossicular prostheses for middle ear reconstruction continues to expand with advances in microsurgical techniques for the repair of diseased ossicles. The cause of postoperative dysfunction may not be readily apparent at otologic examination, and CT is useful in the diagnostic work-up in affected patients. The type of procedure performed and the prosthesis used can often be determined with CT, which can also help identify many causes of prosthetic dysfunction. Secondary signs of perilymphatic fistula such as pneumolabyrinth and middle ear effusion can also be identified at CT. Familiarity with the normal and abnormal CT appearances of ossicular prostheses will enable the radiologist to assist the otologist in identifying those patients in whom revision surgery is most appropriate.
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Footnotes
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Abbreviations: AIDS = acquired immunodeficiency syndrome
PORP = partial ossicular replacement prosthesis
TORP = total ossicular replacement prosthesis
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References
|
|---|
-
Kartush JM. Ossicular chain reconstruction: capitulum to malleus. Otolaryngol Clin North Am 1994; 27:689-715.[Medline]
-
Wehrs RE. Incus interposition and ossiculoplasty with hydroxyapatite prostheses. Otolaryngol Clin North Am 1994; 27:677-688.[Medline]
-
Applebaum EL. An hydroxylapatite prosthesis for defects of the incus long process. Laryngoscope 1993; 103:330-332.[Medline]
-
Lemmerling MM, Stambuck HE, Mancuso AA, Antonelli PJ, Kubilis PS. Normal and opacified middle ears: CT appearance of the stapes and incudostapedial joint. Radiology 1997; 203:251-256.[Abstract/Free Full Text]
-
Schuknecht HF. Otosclerosis surgery. In: Nadol JB, Jr, Schuknecht HF, eds. Surgery of the ear and temporal bone. New York, NY: Raven, 1993; 223-244.
-
Hough JVD, Dyer RK, Jr. Stapedectomy: causes of failure and revision surgery in otosclerosis. Otolaryngol Clin North Am 1993; 26:453-470.[Medline]
-
Mukherji SK, Mancusso AA, Kotzur IM, et al. CT of the temporal bone: findings after mastoidectomy, ossicular reconstruction, and cochlear implantation. AJR Am J Roentgenol 1994; 163:1467-1471.[Abstract/Free Full Text]
-
Schuknecht HF, Applebaum EL. Surgery for hearing loss. N Engl J Med 1969; 280:1154-1160.
-
Han WW, Incesulu A, McKenna MJ, Rauch SD, Nadol JB, Jr, Glynn RJ. Revision stapedectomy: intraoperative findings, results, and review of the literature. Laryngoscope 1997; 107:1185-1192.[Medline]
-
Swartz JD, Lansman AK, Berger AS, et al. Stapes prosthesis: evaluation with CT. Radiology 1986; 158:179-182.[Abstract/Free Full Text]
-
Wiet RJ, Harvey SA, Bauer GP. Complications in stapes surgery: options for prevention and management. Otolaryngol Clin North Am 1993; 26:471-490.[Medline]
-
Langman AW, Lindeman RC. Revision stapedectomy. Laryngoscope 1993; 103:954-958.[Medline]
-
McGee TM. The loose wire syndrome. Laryngoscope 1981; 91:1478-1483.[Medline]
-
Causse JB. Etiology and therapy of cochlear hydrops following stapedectomy. Am J Otol 1980; 1:221-224.[Medline]
-
Wehrs RE. Homograft ossicles in tympanoplasty. Laryngoscope 1982; 92:540-546.[Medline]
-
Hough JVD. Fractures of the temporal bone and associated middle and inner ear trauma. Proc R Soc Med 1970; 63:245-262.[Medline]
-
Swartz JD, Laucks RL, Berger AS, Ardito JM, Wolfson RJ, Popky GL. Computed tomography of the disarticulated incus. Laryngoscope 1986; 96:1207-1210.[Medline]
-
Wanamaker HH. Management of unsuccessful stapedectomy. Otolaryngol Clin North Am 1979; 7:13-22.
-
Chole RA. Ossiculoplasty with presculpted banked cartilage. Otolaryngol Clin North Am 1994; 27:717-726.[Medline]
-
Goldenberg RA. Ossiculoplasty with composite prostheses: PORP and TORP. Otolaryngol Clin North Am 1994; 27:727-745.[Medline]
-
Dornhoffer JL. Hearing results with the Dornhoffer ossicular replacement prosthesis. Laryngoscope 1998; 108:531-536.[Medline]
-
Black B. Design and development of a contoured ossicular replacement prosthesis: clinical trials of 125 cases. J Otolaryngol Soc Aust 1971; 94:525-535.
-
Goldenberg RA. Hydroxylapatite ossicular replacement prostheses: a four-year experience. Otolaryngol Head Neck Surg 1992; 106:261-269.[Medline]
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Abstract
Introduction
