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Thread: PORP (Partial Ossicular Replacement Prosthesis) pictures - Ear Atlas

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    Default PORP (Partial Ossicular Replacement Prosthesis) pictures - Ear Atlas

    Introduction:
    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 . As a result, homografts from cadavers gained acceptance and are available in many presculpted designs, thereby decreasing the time needed for surgical reconstruction . 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) .

    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 . 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) . 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 .

    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).
    PORP (Partial Ossicular Replacement Prosthesis) attachment.php?s=4aa10c6dcc9a59e586d00ca59215c2e6&attachmentid=1850&d=1441387014

    Procedure
    Stapes reconstruction is most often used to restore conductive hearing loss in patients with otosclerosis or congenital abnormalities . Stapes reconstruction is also performed for discontinuity or fracture resulting from prior basilar skull fracture, binding cicatricial adhesions, or tympanosclerosis . 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 . In 1969, Schuknecht and Applebaum 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 . 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) . Some surgeons use a posterior crus preservation technique, which is a form of partial stapedectomy . 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.

    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 . 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 .

    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 .

    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 . Migration of the stapes prosthesis is most often directed inferior and posterior to the oval window . Displacement at the incudal articulation also occurs with unstable attachment of the wire loop of the prosthesis to the long process of the incus . The wire slips inferiorly due to gravity (loose wire syndrome), and patients often report temporary improvement in hearing with middle ear inflation . Pressure generated through the eustachian tube is believed to push the wire superiorly into the proper position.

    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 . The extruded prosthesis may lie within the dependent portion of the middle ear cavity, migrate extrinsic to the middle ear cavity , or be completely absent, having migrated out of the tympanoplasty and the external auditory canal.

    Increased negative pressure in the middle ear due to eustachian tube dysfunction may force a prosthesis into the vestibule . This is seen in approximately 2% of patients who present with postoperative sensorineural hearing loss . 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.

    Perilymphatic fistula is a potentially serious complication of stapes reconstruction that accounts for approximately 10% of cases of failed stapedectomy . 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 . 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 .
    PORP (Partial Ossicular Replacement Prosthesis) attachment.php?s=4aa10c6dcc9a59e586d00ca59215c2e6&attachmentid=1851&d=1441387030

    No soft tissue should be present within the oval window niche 4–6 weeks following surgery . 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 . This reaction may result from immunologic sensitivity to the surgical materials used or from surgical trauma to the mucoperiosteum

    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

    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 . 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 The notch in the short process is then positioned beneath the manubrium. This is known as the “notched incus with short process” procedure 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 This is known as the “notched incus with long process” procedure . 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 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 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 When a homograft prosthesis is used today, it is most often sculpted from cadaveric rib cartilage The incus interposition graft may still occasionally be seen at CT, and it is important to be familiar with its appearance.

    References:

    RSNA Publications Online











    Last edited by Medical Photos; 09-04-2015 at 05:18 PM.

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