8.11\ Ossicular Prosthesis

Complications

8.11.1\ Discussion

CT imaging may be obtained after ossicular chain reconstruction if a poorer-than-expected hearing outcome results in order to determine if the prosthesis has slipped or if there is another potential cause of hearing loss such as middle ear effusion, fixation of prosthesis or ossicular remnant by scar tympanosclerosis (especially involving the malleus or incus head in the epitympanum), or recurrent cholesteatoma. Encasement of a prosthesis by granulation tissue or cholesteatoma can cause conductive hearing loss whether or not the ossicular prosthesis is displaced.

Complications of ossicular prostheses depend on the particular type of prosthesis, but generally include migration into the vestibule (TORP or stapes prosthesis) (Fig. 8.37), perilymphatic fistula (Fig. 8.38), subluxation, dislocation, extrusion or other form of malposition (Figs. 8.39, 8.40, 8.41, 8.42, 8.43, 8.44, 8.45, and 8.46), encasement/displacement by granulation tissue or recurrent cholesteatoma (Figs. 8.47 and 8.48), tympanic membrane dehiscence (Fig. 8.49), and bending or

fracture of the prostheses (Fig. 8.50). Prosthesis subluxation or dislocation is the most common complication responsible for up to 60% of postoperative hearing loss and occurs most commonly in the first 6–8 weeks before fibrosis occurs. Stapes prostheses most commonly displace posterior and inferior to the oval window. Alternatively, these prostheses can migrate into the vestibule, which can cause vertigo and possibly a concurrent perilymphatic fistula. Vestibular penetration is a serious complication that represents 10% of stapes prosthesis complications. Signs of perilymphatic fistula include the presence of air in the labyrinth (pneumolabyrinth) and rarely middle ear effusion. The portion of the prosthesis at the stapes footplate can reliably penetrate the vestibule without causing symptoms is 0.25 mm, but slightly deeper penetration may be asymptomatic in some cases. Prosthesis extrusion through the tympanic membrane occurs in 2.6–7% of cases depending on the type of prosthesis and method of tympanoplasty. The main risk factor for prosthesis extrusion is ongoing Eustachian tube dysfunction. CT is the modality of choice for evaluating most of these complications, especially in the late postoperative period. However, MRI is generally better for characterizing granulation tissue and cholesteatoma.

Fig. 8.39  Stapes prosthesis separation from the incus. Axial CT image shows an empty prosthesis wire loop (arrow) adjacent to the incus (Courtesy of Mary Elizabeth Cunnane, M.D.)

Fig. 8.41  Stapes prosthesis detachment from the incus. Coronal CT image shows an air gap (arrow) between the lenticular process of the incus and McGee stapes prosthesis

Fig. 8.40  Lateralized TORP. Coronal CT image shows an air gap (arrow) between the shaft of the hydroxyapatite prosthesis and the oval window. There is also extensive nonspecific opacification of the widened external auditory canal

Fig. 8.42  Stapes bucket prosthesis dislocation. Axial CT image shows the distal end of the prosthesis (arrow) projecting far anterior to the region of the oval widow

Fig. 8.47  Dislocated TORP encased in soft tissue. Poschl plane CT image shows a hydroxyapatite TORP orientated upside down and encased by nonspecific soft tissue

Fig. 8.48  Recurrent cholesteatoma with TORP displacement. Axial CT image shows a cholesteatoma (*) that displaces the ossicular prosthesis

Fig. 8.49  Ossicular prosthesis tympanic membrane detachment. Coronal CT image shows separation of the tympanic membrane graft (arrow) from the head of the prosthesis

Fig. 8.50  Prosthesis fracture. Axial CT image shows an air gap (arrow) between the head and shaft of the prosthesis