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Cochlear implantation in the partially ossified cochlea
Operative Techniques in Otolaryngology (2005) 16, 113-116
Cochlear implantation in the partially ossified cochlea Julie Kerr, MD,a Douglas D. Backous, MDb From the aOtolaryngology–Head & Neck Surgery Service, Madigan Army Medical Center, Tacoma, Washington; and the b Listen for Life Center at Virginia Mason, Seattle, Washington. KEYWORDS Partial obstruction; Cochlear implant; Ossification; Techniques
Advances in the understanding of cochlear anatomy, the pathophysiology of labyrinthitis ossificans, and the development of surgical techniques have reduced the number of patients denied candidacy for cochlear implantation due to cochlear duct obstruction. In addition to computed tomography, highresolution magnetic resonance imaging fosters improved surgical planning in cases with soft tissue obstruction without ossification. Specific electrodes for use in the obstructed cochlea maximize insertion and access available ganglion cells. This article addresses the components of the preoperative evaluation, surgical decision-making, and specific techniques for cochlear implant array insertion in the partially ossified cochlea. © 2005 Elsevier Inc. All rights reserved.
Approximately one-fifth of patients being assessed for the placement of a cochlear implant have radiologic evidence of partial or complete obliteration of the basal turn of the cochlea.1-3 Severe-to-profound hearing loss occurs in 10% of children who have bacterial meningitis, and up to 80% have radiologic evidence of partial or complete obstruction of the cochlear duct develop.4,5 Overall, 23% to 37% of patients with cochlear implants are deafened as a result of meningitis.2,6,7 Otosclerosis, trauma, autoimmune processes, occlusion of the labyrinthine artery, leukemia, or other tumors of the temporal bone, viral infections, and Wegener granulomatosis have been reported as less common etiologic factors for basal turn ossification.2,8-10 Advances in the understanding of the anatomy of the cochlea, the subsequent evolution of surgical techniques, and specifically designed electrodes have highly reduced the number of patients excluded from candidacy as a result of cochlear obstruction. This article will address the surgical treatment of the partially ossified cochlea. Please refer to the article by Smullen and Balkany in this issue for a description of surgical techniques for electrode placement in the severely ossified cochlea.
Pathophysiology Ossification in the cochlear duct results from fibroblastic proliferation, followed by the development of granulation tissue and subsequent new bone formation within the perilymphatic spaces. Infectious agents and inflammatory cells enter the inner ear from the subarachnoid space through the internal auditory canal, the cochlear aqueduct, or through the middle ear by traversing the cochlear fenestra.6 The scala tympani is involved much more commonly than the scala vestibuli, and ossification generally progresses from the base, as a result of the entry site of the cochlear aqueduct, to the apex. Paparella and Sugiura8 described 3 pathologic stages leading to ossification. The inflammatory stage is characterized by migration of bacteria and leukocytes into the perilymph. Fibrosis follows as early as 2 weeks after the initial insult. New bone formation secondary to metaplasia of multipotential mesenchymal cells into osteoblasts has been reported up to 30 years after the sentinel episode of meningitis.11-13 Ossification may directly involve spiral ganglion cells, resulting in poorer performance with a cochlear implant.14
Evaluation Address reprint requests and correspondence: Douglas D. Backous, MD, The Listen for Life Center at Virginia Mason, 1100 Ninth Avenue, Seattle, WA 98101. E-mail address: [email protected]. 1043-1810/$ -see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.otot.2005.05.012
Preoperative history should assess for the risk factors of labyrinthitis ossificans. High-resolution computerized tomography (CT), using overlapping 1.50-mm sections with
114
Operative Techniques in Otolaryngology, Vol 16, No 2, June 2005 all patients should be vaccinated against pneumococcus, according to Centers for Disease Control guidelines, before implantation.
Surgical technique
Figure 1 Schematic diagram of the cochlea with limited basal turn ossification extending 8-10 mm. “Drill-through” and complete or partial insertion is possible in this anatomic situation.
1.0-mm intervals, delineates bony labyrinthine anatomy. Cochlear duct obliteration or the pathognomonic “halo” sign, secondary to demineralization of the labyrinthine bone seen in advanced otosclerosis, can be seen in axial or coronal sections with a reported accuracy of 54% to 92%.6,15 Attenuation of the intracochlear fluid signal seen on highresolution (T2 weighted) magnetic resonance imaging (MRI) is indicative of bony or soft tissue blockage.16-19 Intense enhancement on T1 imaging with gadolinium enhanced T1 imaging can detect early fibrosis and is a useful in high risk patients to clarify the decision for early implantation. Sagittal MRI cuts through the internal auditory canals can document the presence or absence of neural structures. MRI is our imaging modality of choice, with CT being used as a supplement to discern bony anatomy when severe ossification or other malformations are identified. The true degree of obliteration of the cochlear duct is determined during surgical exploration.
In their classic article, Balkany et al20 outlined a systematic approach to cochlear implantation based on the degree of cochlear duct ossification: obliteration of the round window niche, obstruction limited to the inferior segment of the basal turn, and upper segment obstruction. Ossification extending up to 8-10 mm in the distal inferior segment (Figure 1) can typically be “drilled though” and a standard or compressed electrode array inserted into the scala tympani. Drilling should begin anterior and inferior to the round window. In cases with obliteration of the round window niche, drilling is targeted 1.5-mm posterior and inferior to the stapes and pyramidal process (Figure 2). Obstruction can appear gray-white or chalky with a softer consistency. Drilling is continued cautiously to avoid inadvertent entry into the carotid canal anteriorly and into the internal auditory canal medially (Figure 2). Care must be taken to use copious irrigation so not to create thermal injury to the remaining cell bodies and neurons in the scala tympani. Fine picks, delicate 1.2-1.5-mm burrs, or handheld lasers are useful for safe tunneling.21,22 When obstruction involves the upper or ascending segment of the basal turn and a drill-through cannot be completed, a new cochleostomy is created 0.5-1.0-mm superiorly and anteriorly to enter the scala vestibuli (Figure 3). Electrode placement in the scala vestibuli generates similar
Surgical decision making Timing of cochlear implant surgery in the partially obstructed cochlea hinges on several factors. In survivors of bacterial meningitis, we recommend stabilization of concurrent neurologic problems, and implementation of appropriate amplification and auditory rehabilitation. Serial audiometry and serial imaging at 3-6-month intervals will document hearing decline or progressive cochlear duct obstruction, prompting timely cochlear implant placement. Repeated audiometry will identify the rare case of spontaneous hearing recovery.6,13 Degeneration of auditory function and progression of ossification on neuroimaging are indications for moving forward with implantation, even at ages younger than 12 months. Even after having meningitis,
Figure 2 Schematic diagram of basal turn ossification limited to the round window and proximal basal turn. Array insertion into the scala tympani is preferred in this setting. In the drill-through technique, drilling commences anterior and inferior to the round window with insertion of the standard or compressed electrode arrays into the scala tympani.
Kerr and Backous
Cochlear Implantation in the Partially Ossified Cochlea
Figure 3 Schematic diagram of basal turn ossification obliterating the basal turn with preservation of the scala vestibuli. When the ascending segment of the basal turn is obstructed, in addition to the distal inferior segment, a drill-through technique cannot be completed. Scala vestibuli insertion is an option. It requires a cochleostomy 0.5-1.0 mm superior and anterior to the round window. Insertion into the scala vestibuli optimizes electrical stimulation with results similar to scala tympani insertion.
hearing results as seen with traditional scala tympani placement (Figure 3).3 Isolated scala tympani obstruction is attributed to the entry of the cochlear aqueduct 2-mm distal ot the round window. In cases with obstruction of the scala tympani and scala vestibuli, partial insertion of standard straight or compressed arrays can produce acceptable performance. Whenever possible, the electrode should be secured with a split-bridge technique. Tight packing of the cochleostomy with fascia or periosteum not only seals the bony opening but also may contribute to stable long-term electrode positioning. In demineralizing conditions, like otosclerosis, care must be taken to avoid penetrating the otic capsule when inserting the electrode array. Forceful insertion should be avoided. Penetration of soft, chalky bone matrix can result in entry into in the hypotympanum, internal auditory canal, or fallopian canal. The use of neural navigation systems and intraoperative radiologic techniques are currently under investigation as possible adjuncts to safe insertion in difficult cases. We recommend an intraoperative, modified Stenvers view plain film to verify electrode positioning and postoperative CT in cases in which final electrode position is in question.
Results Patients with deafness from bacterial meningitis have less predictable performance when compared with the overall cochlear implant population.3,23,24 Decreased ganglion cell
115
populations, difficulty obtaining optimum electrode positioning, damage to neurons in the drilling process, and central sequela from bacterial meningitis all contribute to decreased performance. The majority of reports include dated electrode technology and programming strategies. The role of modiolus approximating electrodes is questionable, and straight arrays continue to provide reasonable performance. Thomas and Cheshire25 documented that meningitis in adults older than 40 years resulted in an increased risk of neurologic and cognitive sequelae in addition to profound deafness. Therefore, patients with a history of meningitis may take several years to gain maximum benefit from their implant. Presurgical counseling is essential to build realistic expectations with patients and their families. Balkany et al reported 75% open set recognition in 15 patients with basal turn ossification treated with complete insertion after a drill-through technique. Although variable, these results compare favorably with patients implanted with nonossified cochleas. Kemink et al26 reported no significant difference in 5 children with partial electrode insertion matched against 5 children with insertion of a full electrode array. Eight patients with partial insertion reported by Cohen and Waltzman27 averaged 12% open set identification. Steenerson et al28 showed 2 patients who presented with scala vestibuli insertion who had lower levels of performance in open set testing when compared with patients with full insertion and no ossification. Reviews of patients with ossification implanted with updated electrodes and modern programming strategies are needed to determine if performance exceeds that from earlier reports. Although insertion of a cochlear implant electrode into the ossified cochlea is nearly uniformly possible with improved microsurgical techniques, the more difficult question to be answered is whether there is a point at which ossification is significant enough to limit patients from obtaining enough benefit to justify the risks and financial costs of surgery.
Pitfalls Bleeding, the risk for early or delayed infection, transient or long-term disequilibrium, tinnitus, taste dysfunction, facial nerve palsy, receiver/stimulator extrusion, delayed wound complications, device failure, and hearing performance below predicted levels are potential complications of cochlear implant surgery. Facial nerve monitoring, although not a standard of care in mastoid surgery, complements the understanding of facial nerve anatomy gleaned from preoperative imaging. Minimal incision techniques preserve blood flow to the skin over the implant, thus reducing the risk of skin flap complications. Electrode placement in an ossified cochlea requires a 3-dimensional understanding of temporal bone anatomy because normal surface landmarks can be obscured, and structures like the carotid artery, jugular bulb, and geniculate ganglion are at more risk with advanced drilling techniques. A stepwise approach to drilling the ossified cochlea and placing active electrodes ensures the best possible outcome for patients. Ensuring electrode stability in the cochlea is critical for preventing device extrusion. Particularly when the incus
116
Operative Techniques in Otolaryngology, Vol 16, No 2, June 2005
buttress has been removed, meticulous packing of the cochleostomy will secure the electrode and seal the cochlear opening to reduce the risk of meningitis. Postoperative CT can be used to establish a baseline for electrode placement, which can be repeated if decrements of performance suggest possible device migration or electrode extrusion.
Conclusion Microsurgical techniques have matured to enable the placement of implant electrodes in obstructed and deformed cochleas. Safe surgical technique requires a full understanding of the 3-dimensional anatomy of the cochlea and temporal bone, including the carotid artery, facial nerve, internal auditory canal, modiolus, and jugular bulb. We recommend a stepwise approach for drilling out the occluded cochlea based on intraoperative findings because even with the best imaging, ossification can be more extensive than predicted. Honest preoperative counseling and diligent programming are crucial to enhancing eventual device use and satisfaction.
References 1. Phelps PD: Basal turn of the cochlea. Br J Radiol 65:370-374, 1992 2. Nair SB, Abou-Elhamd KA, Hawthorne M: A retrospective analysis of high resolution computed tomography in the assessment of cochlear implant patients. Clin Otolaryngol Allied Sci 25:55-61, 2000 3. Steenerson Rl, Gary LB: Multichannel cochlear implantation in obliterated cochleas using the Gantz procedure. Laryngoscope 104:10711073, 1994 4. Shelton MM, Marks WA: Bacterial meningitis: An update. Pediatr Neurol 8:605-617, 1990 5. Eisenberg LS, Luxford WM, Becker TS, et al: Electric stimulation of the auditory system in children deafened by meningitis. Otolaryngol Head Neck Surg 92:700-705, 1984 6. Jackler RK, Luxford WM, Schindler RN, et al: Cochlear patency problems in cochlear implantation. Laryngoscope 97:801-805, 1987 7. Frau GN, Luxford WM, Lo WW, et al: High resolution computed tomography in evaluation of cochlear patency in implant candidates: A comparison with surgical findings. J Laryngol Otol 108:743-748, 1994 8. Paparella MM, Sugiura S: The pathology of suppurative labyrinthitis. Ann Otol Rhinol Laryngol 76:544-586, 1967 9. Rarey KE, Bicknell JM, Davis LE: Intralabyrinthine osteogenesis in Cogan’s syndrome. Am J Otolaryngol 7:387-390, 1986 10. Kimura R, Perlman HB: Arterial obstruction of the labyrinth. Part I. Cochlear changes. Part II. Vestibular changes. Ann Otol Rhinol Laryngol 67:25-40, 1958
11. Sugiura S, Paparella MM: The pathology of labyrinthine ossification. Laryngoscope 77:1974-1989, 1967 12. Green JD, Marion MS, Hinojosa R: Labyrinthitis ossificans: Histopathologic consideration for cochlear implantation. Otolaryngol Head Neck Surg 104:320-326, 1991 13. Novak MA, Fifer RC, Barkmeier JC, et al: Labyrinthine ossification after meningitis: Its implications for cochlear implantation. Otolaryngol Head Neck Surg 103:351-356, 1990 14. Otte J, Schuknecht HF, Kerr AG: Ganglion cell populations in normal and pathological human cochlea. Implications for human cochlear implantation. Laryngoscope 88:1231-1245, 1978 15. Rosenberg RA, Cohen NL, Reed D: Radiographic imaging for the cochlear implant. Ann Otol Rhinol Laryngol 96:300-304, 1987 16. Silberman B, Garabedian EN, Denoyelle F, et al: Role of modern imaging technology in the implementation of pediatric cochlear implants. Ann Otol Rhinol Laryngol 104:42-46, 1995 17. Laszig R, Terwey B, Ratimer RD, et al: Magnetic resonance imaging and high resolution CT in cochlear implant candidates. Scand Audiol 17:197-200, 1988 (suppl) 18. Bath AP, O’Donoghue GM, Holland IM, et al: Pediatric cochlear implantation: How reliable is computed tomography in assessing cochlear patency? Clin Otolaryngol 18:475-479, 1993 19. Jackler RK, Dillon WP: Computed tomography and magnetic resonance imaging of the inner ear. Otolaryngol Head Neck Surg 99:494504, 1988 20. Balkany TJ, Gantz BJ, Steenerson RL, et al: Systematic approach to electrode insertion in the ossified cochlea. Otolaryngol Head Neck Surg 114:4-11, 1996 21. Balkany TJ, Gantz BJ, Nadol JB: Multi-channel cochlear implants in partially ossified cochleas. Ann Otol Rhinol Laryngol 97:3-7, 1988 (suppl 35) 22. Balkany TJ: Endoscopy of the cochlea during cochlear implantation. Ann Otol Rhinol Laryngol 99:919-922, 1990 23. Battmer RD, Gupta SP, Allum-Mecklenburg DJ, et al: Factors influencing cochlear implant perceptual performance in 132 adults. International Cochlear Implant, Speech and Hearing Symposium–Melbourne (Clark GM, Cowan RSC, eds). Ann Otol Rhinol Laryngol 185-187, 1994 (suppl 166) 24. Waltzman SB, Fisher SG, Niparko JK, et al: Predictors of postoperative performance with cochlear implants. Multicenter comparative study of cochlear implants: Final reports of the department of veterans affairs cooperative studies program (Cohen NL, Waltzman SB, eds). Ann Otol Rhinol Laryngol 15-18, 1995 (suppl 165) 25. Thomas J, Cheshire IM: Evaluation of cochlear implantation in post meningitic adults. J Laryngol Otol 24:27-33, 1999 26. Kemink JL, Zimmermann-Phillips S, Kileny PR, et al: Auditory performance of children with cochlear ossification and a partial implant insertion. Laryngoscope 102:1001-1005, 1992 27. Cohen NC, Waltzman SB: Partial insertion of the nucleus multichannel cochlear implant: Technique and results. Am J Otol 14:357-361, 1993 28. Steenerson Rl, Gary LB, Wynens MS: Scala vestibule cochlear implantation in obstructed and obliterated cochleas. Am J Otol 11:360363, 1990
Cochlear implantation in the partially ossified cochlea Julie Kerr, MD,a Douglas D. Backous, MDb From the aOtolaryngology–Head & Neck Surgery Service, Madigan Army Medical Center, Tacoma, Washington; and the b Listen for Life Center at Virginia Mason, Seattle, Washington. KEYWORDS Partial obstruction; Cochlear implant; Ossification; Techniques
Advances in the understanding of cochlear anatomy, the pathophysiology of labyrinthitis ossificans, and the development of surgical techniques have reduced the number of patients denied candidacy for cochlear implantation due to cochlear duct obstruction. In addition to computed tomography, highresolution magnetic resonance imaging fosters improved surgical planning in cases with soft tissue obstruction without ossification. Specific electrodes for use in the obstructed cochlea maximize insertion and access available ganglion cells. This article addresses the components of the preoperative evaluation, surgical decision-making, and specific techniques for cochlear implant array insertion in the partially ossified cochlea. © 2005 Elsevier Inc. All rights reserved.
Approximately one-fifth of patients being assessed for the placement of a cochlear implant have radiologic evidence of partial or complete obliteration of the basal turn of the cochlea.1-3 Severe-to-profound hearing loss occurs in 10% of children who have bacterial meningitis, and up to 80% have radiologic evidence of partial or complete obstruction of the cochlear duct develop.4,5 Overall, 23% to 37% of patients with cochlear implants are deafened as a result of meningitis.2,6,7 Otosclerosis, trauma, autoimmune processes, occlusion of the labyrinthine artery, leukemia, or other tumors of the temporal bone, viral infections, and Wegener granulomatosis have been reported as less common etiologic factors for basal turn ossification.2,8-10 Advances in the understanding of the anatomy of the cochlea, the subsequent evolution of surgical techniques, and specifically designed electrodes have highly reduced the number of patients excluded from candidacy as a result of cochlear obstruction. This article will address the surgical treatment of the partially ossified cochlea. Please refer to the article by Smullen and Balkany in this issue for a description of surgical techniques for electrode placement in the severely ossified cochlea.
Pathophysiology Ossification in the cochlear duct results from fibroblastic proliferation, followed by the development of granulation tissue and subsequent new bone formation within the perilymphatic spaces. Infectious agents and inflammatory cells enter the inner ear from the subarachnoid space through the internal auditory canal, the cochlear aqueduct, or through the middle ear by traversing the cochlear fenestra.6 The scala tympani is involved much more commonly than the scala vestibuli, and ossification generally progresses from the base, as a result of the entry site of the cochlear aqueduct, to the apex. Paparella and Sugiura8 described 3 pathologic stages leading to ossification. The inflammatory stage is characterized by migration of bacteria and leukocytes into the perilymph. Fibrosis follows as early as 2 weeks after the initial insult. New bone formation secondary to metaplasia of multipotential mesenchymal cells into osteoblasts has been reported up to 30 years after the sentinel episode of meningitis.11-13 Ossification may directly involve spiral ganglion cells, resulting in poorer performance with a cochlear implant.14
Evaluation Address reprint requests and correspondence: Douglas D. Backous, MD, The Listen for Life Center at Virginia Mason, 1100 Ninth Avenue, Seattle, WA 98101. E-mail address: [email protected]. 1043-1810/$ -see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.otot.2005.05.012
Preoperative history should assess for the risk factors of labyrinthitis ossificans. High-resolution computerized tomography (CT), using overlapping 1.50-mm sections with
114
Operative Techniques in Otolaryngology, Vol 16, No 2, June 2005 all patients should be vaccinated against pneumococcus, according to Centers for Disease Control guidelines, before implantation.
Surgical technique
Figure 1 Schematic diagram of the cochlea with limited basal turn ossification extending 8-10 mm. “Drill-through” and complete or partial insertion is possible in this anatomic situation.
1.0-mm intervals, delineates bony labyrinthine anatomy. Cochlear duct obliteration or the pathognomonic “halo” sign, secondary to demineralization of the labyrinthine bone seen in advanced otosclerosis, can be seen in axial or coronal sections with a reported accuracy of 54% to 92%.6,15 Attenuation of the intracochlear fluid signal seen on highresolution (T2 weighted) magnetic resonance imaging (MRI) is indicative of bony or soft tissue blockage.16-19 Intense enhancement on T1 imaging with gadolinium enhanced T1 imaging can detect early fibrosis and is a useful in high risk patients to clarify the decision for early implantation. Sagittal MRI cuts through the internal auditory canals can document the presence or absence of neural structures. MRI is our imaging modality of choice, with CT being used as a supplement to discern bony anatomy when severe ossification or other malformations are identified. The true degree of obliteration of the cochlear duct is determined during surgical exploration.
In their classic article, Balkany et al20 outlined a systematic approach to cochlear implantation based on the degree of cochlear duct ossification: obliteration of the round window niche, obstruction limited to the inferior segment of the basal turn, and upper segment obstruction. Ossification extending up to 8-10 mm in the distal inferior segment (Figure 1) can typically be “drilled though” and a standard or compressed electrode array inserted into the scala tympani. Drilling should begin anterior and inferior to the round window. In cases with obliteration of the round window niche, drilling is targeted 1.5-mm posterior and inferior to the stapes and pyramidal process (Figure 2). Obstruction can appear gray-white or chalky with a softer consistency. Drilling is continued cautiously to avoid inadvertent entry into the carotid canal anteriorly and into the internal auditory canal medially (Figure 2). Care must be taken to use copious irrigation so not to create thermal injury to the remaining cell bodies and neurons in the scala tympani. Fine picks, delicate 1.2-1.5-mm burrs, or handheld lasers are useful for safe tunneling.21,22 When obstruction involves the upper or ascending segment of the basal turn and a drill-through cannot be completed, a new cochleostomy is created 0.5-1.0-mm superiorly and anteriorly to enter the scala vestibuli (Figure 3). Electrode placement in the scala vestibuli generates similar
Surgical decision making Timing of cochlear implant surgery in the partially obstructed cochlea hinges on several factors. In survivors of bacterial meningitis, we recommend stabilization of concurrent neurologic problems, and implementation of appropriate amplification and auditory rehabilitation. Serial audiometry and serial imaging at 3-6-month intervals will document hearing decline or progressive cochlear duct obstruction, prompting timely cochlear implant placement. Repeated audiometry will identify the rare case of spontaneous hearing recovery.6,13 Degeneration of auditory function and progression of ossification on neuroimaging are indications for moving forward with implantation, even at ages younger than 12 months. Even after having meningitis,
Figure 2 Schematic diagram of basal turn ossification limited to the round window and proximal basal turn. Array insertion into the scala tympani is preferred in this setting. In the drill-through technique, drilling commences anterior and inferior to the round window with insertion of the standard or compressed electrode arrays into the scala tympani.
Kerr and Backous
Cochlear Implantation in the Partially Ossified Cochlea
Figure 3 Schematic diagram of basal turn ossification obliterating the basal turn with preservation of the scala vestibuli. When the ascending segment of the basal turn is obstructed, in addition to the distal inferior segment, a drill-through technique cannot be completed. Scala vestibuli insertion is an option. It requires a cochleostomy 0.5-1.0 mm superior and anterior to the round window. Insertion into the scala vestibuli optimizes electrical stimulation with results similar to scala tympani insertion.
hearing results as seen with traditional scala tympani placement (Figure 3).3 Isolated scala tympani obstruction is attributed to the entry of the cochlear aqueduct 2-mm distal ot the round window. In cases with obstruction of the scala tympani and scala vestibuli, partial insertion of standard straight or compressed arrays can produce acceptable performance. Whenever possible, the electrode should be secured with a split-bridge technique. Tight packing of the cochleostomy with fascia or periosteum not only seals the bony opening but also may contribute to stable long-term electrode positioning. In demineralizing conditions, like otosclerosis, care must be taken to avoid penetrating the otic capsule when inserting the electrode array. Forceful insertion should be avoided. Penetration of soft, chalky bone matrix can result in entry into in the hypotympanum, internal auditory canal, or fallopian canal. The use of neural navigation systems and intraoperative radiologic techniques are currently under investigation as possible adjuncts to safe insertion in difficult cases. We recommend an intraoperative, modified Stenvers view plain film to verify electrode positioning and postoperative CT in cases in which final electrode position is in question.
Results Patients with deafness from bacterial meningitis have less predictable performance when compared with the overall cochlear implant population.3,23,24 Decreased ganglion cell
115
populations, difficulty obtaining optimum electrode positioning, damage to neurons in the drilling process, and central sequela from bacterial meningitis all contribute to decreased performance. The majority of reports include dated electrode technology and programming strategies. The role of modiolus approximating electrodes is questionable, and straight arrays continue to provide reasonable performance. Thomas and Cheshire25 documented that meningitis in adults older than 40 years resulted in an increased risk of neurologic and cognitive sequelae in addition to profound deafness. Therefore, patients with a history of meningitis may take several years to gain maximum benefit from their implant. Presurgical counseling is essential to build realistic expectations with patients and their families. Balkany et al reported 75% open set recognition in 15 patients with basal turn ossification treated with complete insertion after a drill-through technique. Although variable, these results compare favorably with patients implanted with nonossified cochleas. Kemink et al26 reported no significant difference in 5 children with partial electrode insertion matched against 5 children with insertion of a full electrode array. Eight patients with partial insertion reported by Cohen and Waltzman27 averaged 12% open set identification. Steenerson et al28 showed 2 patients who presented with scala vestibuli insertion who had lower levels of performance in open set testing when compared with patients with full insertion and no ossification. Reviews of patients with ossification implanted with updated electrodes and modern programming strategies are needed to determine if performance exceeds that from earlier reports. Although insertion of a cochlear implant electrode into the ossified cochlea is nearly uniformly possible with improved microsurgical techniques, the more difficult question to be answered is whether there is a point at which ossification is significant enough to limit patients from obtaining enough benefit to justify the risks and financial costs of surgery.
Pitfalls Bleeding, the risk for early or delayed infection, transient or long-term disequilibrium, tinnitus, taste dysfunction, facial nerve palsy, receiver/stimulator extrusion, delayed wound complications, device failure, and hearing performance below predicted levels are potential complications of cochlear implant surgery. Facial nerve monitoring, although not a standard of care in mastoid surgery, complements the understanding of facial nerve anatomy gleaned from preoperative imaging. Minimal incision techniques preserve blood flow to the skin over the implant, thus reducing the risk of skin flap complications. Electrode placement in an ossified cochlea requires a 3-dimensional understanding of temporal bone anatomy because normal surface landmarks can be obscured, and structures like the carotid artery, jugular bulb, and geniculate ganglion are at more risk with advanced drilling techniques. A stepwise approach to drilling the ossified cochlea and placing active electrodes ensures the best possible outcome for patients. Ensuring electrode stability in the cochlea is critical for preventing device extrusion. Particularly when the incus
116
Operative Techniques in Otolaryngology, Vol 16, No 2, June 2005
buttress has been removed, meticulous packing of the cochleostomy will secure the electrode and seal the cochlear opening to reduce the risk of meningitis. Postoperative CT can be used to establish a baseline for electrode placement, which can be repeated if decrements of performance suggest possible device migration or electrode extrusion.
Conclusion Microsurgical techniques have matured to enable the placement of implant electrodes in obstructed and deformed cochleas. Safe surgical technique requires a full understanding of the 3-dimensional anatomy of the cochlea and temporal bone, including the carotid artery, facial nerve, internal auditory canal, modiolus, and jugular bulb. We recommend a stepwise approach for drilling out the occluded cochlea based on intraoperative findings because even with the best imaging, ossification can be more extensive than predicted. Honest preoperative counseling and diligent programming are crucial to enhancing eventual device use and satisfaction.
References 1. Phelps PD: Basal turn of the cochlea. Br J Radiol 65:370-374, 1992 2. Nair SB, Abou-Elhamd KA, Hawthorne M: A retrospective analysis of high resolution computed tomography in the assessment of cochlear implant patients. Clin Otolaryngol Allied Sci 25:55-61, 2000 3. Steenerson Rl, Gary LB: Multichannel cochlear implantation in obliterated cochleas using the Gantz procedure. Laryngoscope 104:10711073, 1994 4. Shelton MM, Marks WA: Bacterial meningitis: An update. Pediatr Neurol 8:605-617, 1990 5. Eisenberg LS, Luxford WM, Becker TS, et al: Electric stimulation of the auditory system in children deafened by meningitis. Otolaryngol Head Neck Surg 92:700-705, 1984 6. Jackler RK, Luxford WM, Schindler RN, et al: Cochlear patency problems in cochlear implantation. Laryngoscope 97:801-805, 1987 7. Frau GN, Luxford WM, Lo WW, et al: High resolution computed tomography in evaluation of cochlear patency in implant candidates: A comparison with surgical findings. J Laryngol Otol 108:743-748, 1994 8. Paparella MM, Sugiura S: The pathology of suppurative labyrinthitis. Ann Otol Rhinol Laryngol 76:544-586, 1967 9. Rarey KE, Bicknell JM, Davis LE: Intralabyrinthine osteogenesis in Cogan’s syndrome. Am J Otolaryngol 7:387-390, 1986 10. Kimura R, Perlman HB: Arterial obstruction of the labyrinth. Part I. Cochlear changes. Part II. Vestibular changes. Ann Otol Rhinol Laryngol 67:25-40, 1958
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