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The Laryngoscope Lippincott Williams & Wilkins, Inc. © 2006 The American Laryngological, Rhinological and Otological Society, Inc.
Auditory Brainstem Implant in a Child with Severely Ossified Cochlea Mario Sanna, MD; Tarek Khrais, MD, DHS, FRCS; Maurizio Guida; Maurizio Falcioni, MD
Objective: The hearing outcome after implanting a severely ossified cochlea has always been less satisfactory than implanting a patent one. The aim of our study is to present a case where brainstem implantation was successfully performed as an alternative to cochlear implantation in a child with bilateral severe ossification of the cochlea. Study Design: Case presentation. This study was conducted at Gruppo Otologico, Rome, Italy, a private referral center for neurotology and skull base surgery. Methods: The subject of our study was a 12-year-old female child with postmeningitic deafness and bilaterally ossified cochleae. This case is the first brainstem implantation performed at our center with the indication of severe ossification of the cochlea. Results: Successful brainstem implantation of a device was carried out, and the hearing of the patient was restored to the degree that she can freely use the telephone after 8 months of implantation. Conclusion: Although more cases are needed before establishing the exact outcome of brainstem implantation in cases of deafness in the presence of severe bilateral cochlear ossification, preliminary results show the superiority of brainstem implants to conventional or even customized cochlear implants. Key Words: Ossified cochlea, cochlear implant, brainstem implant, child. Laryngoscope, 116:1700 –1703, 2006
INTRODUCTION Since its introduction, the results of cochlear implantation for the rehabilitation of bilateral sensorineural hearing loss (HL) have improved significantly. Indications for implantation have also been expanded to include patients with severe to profound HL. Unfortunately, however, in cases of severe cochlear ossification, the results have not been as satisfying. Various techniques have been proposed by different surgeons to deal with this problem, examples include electrode insertion in the scala vestibuli,1 insertion of electrodes through the middle cranial fossa,2 the
From Gruppo Otologico Piacenza (M.S., M.G., M.F.), Rome, Italy, and Jordan University of Science and Technology (T.K.), Irbid, Jordan. Editor’s Note: This manuscript was accepted for publication May 26, 2006. Send correspondence to Tarek Khrais, P.O. Box 3710, Irbid 21110, Jordan. E-mail: [email protected] DOI: 10.1097/01.mlg.0000231739.79208.97
Laryngoscope 116: September 2006
1700
drillout circummodiolar technique,3 the use of a double electrode array,4 or even a triple array implant.5 Regardless of the technique used, however, in severe cochlear ossification, the reported results are not satisfactory.6,7 Explanations proposed include an inadequate number of inserted electrodes,8 the distance between the electrodes and the nerve fibers within the modiolus,9 the involvement of the spiral ganglion cells by ossification,10 and peripheral nerve degeneration associated with ossification or even mere fibrosis.11 Recently, there have been a few reports describing the use of auditory brainstem implant (ABI) for management of such cases.9,12,13 In this paper, we report an additional case of ABI use for rehabilitation of a child with complete deafness and severe bilateral cochlear ossification after an attack of meningitis.
CASE REPORT A 12-year-old female patient was referred to us 7 months after the onset of meningitis, which has led to an immediate bilateral deafness. The patient did not have any additional neurologic sequel. Five months after the onset of HL, an attempt at right cochlear implantation was performed at another center. During surgery, however, the cochlea was found to be completely ossified, and implantation was judged impossible by the surgeon. Our assessment of the patient’s condition revealed a normal tympanic membrane bilaterally. Audiologic examination confirmed a total bilateral HL. With lip reading, the patient had 20% word recognition and 18% sentence recognition. She also had good language development. Radiologic examination revealed an ossified cochlea bilaterally with computed tomographic (CT) scanning (Fig. 1), wheras magnetic resonance imaging showed the presence of the 7th and 8th cranial nerves bilaterally. The decision was taken to implant the left side. Because the CT showed severe ossification of the left cochlea and failure of the earlier implant attempt on the right side, an informed consent was also obtained from the family to shift for an ABI if ossification prevented cochlear implantation. We chose a subtotal petrosectomy with blind-sac closure of the external auditory canal to provide a wide surgical field to deal with the ossification. As expected, during surgery, the cochlea was found completely ossified, so we decided to shift to brainstem implantation. The subtotal petrosectomy was transformed into a translabyrinthine approach. Once the posterior fossa dura was opened, adhesions were encountered in the cerebellopontine angle that were a result of the meningitis. The nerves and the vessels within the cerebellopontine angle were matted together, obliterating access to the lateral recess of the 4th ventricle. Dissection proceeded slowly to identify the 8th and 9th cranial
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
Fig. 3. Mapping of electrodes immediately after positioning of array.
Fig. 1. Axial (A) and coronal (B) computed tomography scan showing the ossification of cochlea.
nerves. Following these nerves medially led to the foramen of Luschka and consequently the lateral recess, both of which were free of adhesions. The correct identification of the foramen of
Fig. 2. Electrical auditory brain stem responses elicited at positioning of array.
Laryngoscope 116: September 2006
Luschka was further confirmed by the cerebrospinal fluid exiting from the foramen with Valsalva maneuvers. An ABI24 mol/L implant (Nucleus, Lone Cove, Australia) was easily inserted under direct monitoring of the 7th, 9th, and 11th cranial nerves and indirect monitoring of the 10th cranial nerve through electrocardiographic recording. Intraoperative impedance telemetry and electrical auditory brainstem responses (EABR) were performed to ascertain the correct position and function of the implant. An example of the obtained EABR waves is shown on Figure 2. During surgery, it was not possible to obtain any EABR from the most medial four electrodes, which, on the contrary, produced some stimulation of the 11th cranial nerve (Fig. 3). At the end of the operation, the eustachian tube was obliterated with periosteum and the surgical cavity with long strips of abdominal fat inserted deeply into the cerebellopontine angle through the dural defect. The surgical wound was then sutured in layers. The postoperative period was uneventful. The position of the implant was radiologically confirmed by a postoperative CT (Fig. 4), and the patient was discharged on the fourth postoperative day. Activation of the implant was performed, after 1 month, in the operating room under electrocardiographic monitoring and in the presence of an anesthesiologist. The spectral peak (SPEAK) strategy was adopted. During activation, the number of electrodes stimulating the 11th cranial nerve without eliciting any auditory sensation was reduced to only 2, thus, overall, we had 19 functioning electrodes (Fig. 5). Immediately after activation, the hearing assessment tests resulted in 40% sound identification, whereas recognition of bisyllable words and sentences was 0%. Audiologic rehabilitation
Fig. 4. Correct position as confirmed by soft tissue coronal computed tomography.
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
1701
was instituted, and follow-up was performed at 1, 3, 5 and 8 months after the surgery. There was a marked improvement with each visit (Fig. 6) so that during the last follow-up, the results were very satisfying. The patient scored 100% sound identification, 90% recognition of bisyllable words, and 100% sentences recognition, with 31 words per minute at speech tracking. All the tests reported were performed in open set auditory-only mode. In addition, she is now able to communicate with the telephone.
DISCUSSION The consistency of the tonotopic orientation of the nerve fibers in the modiolus has made it easy to produce good hearing results after cochlear implantation. However, to achieve this aim, one of the important prerequisites is having a cochlea with patent turns. These turns act as a canal that can house the electrode array for the stimulation of the nerve fibers at the modiolus. In cases of severe cochlear ossification, the absence of this canal has led some authors to try to drill a neocanal for accommodation of the array. Although the results were discouraging, various techniques have been developed with the hope of obtaining results similar to those in patent cochlea.1–5 Unfortunately, none of these techniques could markedly improve the outcome in cases of severe ossification, and only a few patients were able to obtain some open set discrimination. Tonotopic organization has also been demonstrated at the level of the cochlear nucleus; however, in most patients with bilateral acoustic neuromas (NF2), hearing results using ABI have been unsatisfactory. In these cases, ABI is used when the cochlear nerve cannot be preserved, and hearing is lost during surgery. This is more frequent with larger schwannomas. In these cases, the tumor usually stretches the cochlear nerve and compresses the area of the brainstem where the cochlear nucleus is located. Distortion of the cochlear nucleus usually results in reduction and disorganization of the auditory fibers and, as a consequence, alteration of the complex three-dimensional tonotopic orientation.14,15 Theoretically, then, if the implant stimulates an undisturbed cochlear nucleus, there would be a better chance of achieving a good result, which is the case if ABI is performed in cases of cochlea ossification. Grayeli et al.9 were the first to report a case of ABI insertion for the bypass of a severely ossified cochlea. Colletti et al.12,13 then reported four similar cases. Four of five patients reached at least 60% sentence recognition in open set, auditory-only mode. Our case, which to the best of our knowledge is the sixth reported in the literature and the first in a child, represents living evidence of the accuracy of the aforementioned theory. In
Fig. 6. Results of audiologic testing according to time.
our case, access to the cerebellopontine angle was gained through the translabyrinthine approach, which, unlike the retrosigmoid approach, provides a more direct approach to the foramen of Luschka, without any cerebellar retraction. In addition, in this specific case, the translabyrinthine approach offered the possibility of performing the ABI insertion during the same stage as the cochlear exploration, with a simple extension of the approach. The results obtained in this case after 8 months of rehabilitation were 100% sound recognition, 90% bisyllable word recognition, and 100% sentence recognition, with 31 words per minute speech tracking (open set, auditory-only mode). In addition, the patient is now able to conduct regular telephone conversations. In evaluating our results and those reported in literature, one can notice a general trend toward better hearing results with the increase of the number of active electrodes.
CONCLUSIONS The preliminary results of ABI in bilateral ossified cochlea appear promising when compared with those obtained with cochlear implantation in similar cases. We need a large number of cases to prove the effectiveness of ABI. We should also take into consideration that the surgery is more difficult and risky when compared with cochlear implantation and, as a consequence, must be reserved for selected referral centers. In every case, our policy has been to first attempt a cochleostomy to evaluate the possibility of cochlear implantation and reserve the ABI for situations in which there is no practical possibility to obtain satisfactory results from cochlear implantation.
BIBLIOGRAPHY
Fig. 5. Mapping of electrodes at follow-up.
Laryngoscope 116: September 2006
1702
1. Steenerson RL, Gary LB, Wynens MS. Scala vestibuli cochlear implantation for labyrinthine ossification. Am J Otol 1990;11:360 –363. 2. Colletti V, Fiorino FG, Carner M, et al. New approach for cochlear implantation: cochleostomy through the middle fossa. Otolaryngol Head Neck Surg 2000;123:467– 474. 3. Balkany T, Gantz B, Nadol JB Jr. Multichannel cochlear implants in partially ossified cochleas. Ann Otol Rhinol Laryngol Suppl 1988;135:3–7. 4. Lenarz T, Buchner A, Tasche C, et al. The results in patients implanted with the nucleus double array cochlear implant:
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
5. 6. 7. 8. 9. 10.
pitch discrimination and auditory performance. Ear Hear 2002;23(1 Suppl):90S–101S. Richardson HC, Beliaeff M, Clarke G, Hawthorne M. A three-array cochlear implant: a new approach for the ossified cochlea. J Laryngol Otol 1999;113:811– 814. El-Kashlan HK, Ashbaugh C, Zwolan T, Telian SA. Cochlear implantation in perlingually deaf children with ossified cochleae. Am J Otol 1999;20:442– 444. Steenerson RL, Gary LB. Multichannel cochlear implantation in children with cochlear ossification. Laryngoscope 1994; 104:1071–1073. Cohen NL, Waltzman SB. Partial insertion of the nucleus multichannel cochlear implant: technique and results. Am J Otol 1993;14:357–361. Grayeli AB, Bouccara D, Kalamarides M, et al. Auditory brainstem implant in bilateral and completely ossified cochleae. Otol Neurotol 2003;24:79 – 82. Otte J, Schunknecht HF, Kerr AG. Ganglion cell populations
Laryngoscope 116: September 2006
11. 12. 13. 14. 15.
in normal and pathological human cochleae. Implications for cochlear implantation. Laryngoscope 1978;88: 1231–1246. Green JD Jr, Marion MS, Hinojosa R. Labyrinthitis ossificans: histopathologic consideration for cochlear implantation. Otolaryngol Head Neck Surg 1991;104:320 –326. Colletti V, Fiorino FG, Carner M, et al. Auditory brainstem implant as a salvage treatment after unsuccessful cochlear implantation. Otol Neurotol 2004;25:485– 496. Colletti V, Carner M, Miorelli V, et al. Auditory brainstem implant (ABI): new frontiers in adults and children. Otolaryngol Head Neck Surg 2005;133:126 –138. Lenarz T, Moshrefi M, Matthies C, et al. Auditory brainstem implant. Part I. Auditory performance and its evolution over time. Otol Neurotol 2001;22:823– 833. Shannon RV, Fayad J, Moore J, et al. Auditory brainstem implant. Part II. Postsurgical issues and performance. Otolaryngol Head Neck Surg 1993;108:634 – 642.
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
1703
Auditory Brainstem Implant in a Child with Severely Ossified Cochlea Mario Sanna, MD; Tarek Khrais, MD, DHS, FRCS; Maurizio Guida; Maurizio Falcioni, MD
Objective: The hearing outcome after implanting a severely ossified cochlea has always been less satisfactory than implanting a patent one. The aim of our study is to present a case where brainstem implantation was successfully performed as an alternative to cochlear implantation in a child with bilateral severe ossification of the cochlea. Study Design: Case presentation. This study was conducted at Gruppo Otologico, Rome, Italy, a private referral center for neurotology and skull base surgery. Methods: The subject of our study was a 12-year-old female child with postmeningitic deafness and bilaterally ossified cochleae. This case is the first brainstem implantation performed at our center with the indication of severe ossification of the cochlea. Results: Successful brainstem implantation of a device was carried out, and the hearing of the patient was restored to the degree that she can freely use the telephone after 8 months of implantation. Conclusion: Although more cases are needed before establishing the exact outcome of brainstem implantation in cases of deafness in the presence of severe bilateral cochlear ossification, preliminary results show the superiority of brainstem implants to conventional or even customized cochlear implants. Key Words: Ossified cochlea, cochlear implant, brainstem implant, child. Laryngoscope, 116:1700 –1703, 2006
INTRODUCTION Since its introduction, the results of cochlear implantation for the rehabilitation of bilateral sensorineural hearing loss (HL) have improved significantly. Indications for implantation have also been expanded to include patients with severe to profound HL. Unfortunately, however, in cases of severe cochlear ossification, the results have not been as satisfying. Various techniques have been proposed by different surgeons to deal with this problem, examples include electrode insertion in the scala vestibuli,1 insertion of electrodes through the middle cranial fossa,2 the
From Gruppo Otologico Piacenza (M.S., M.G., M.F.), Rome, Italy, and Jordan University of Science and Technology (T.K.), Irbid, Jordan. Editor’s Note: This manuscript was accepted for publication May 26, 2006. Send correspondence to Tarek Khrais, P.O. Box 3710, Irbid 21110, Jordan. E-mail: [email protected] DOI: 10.1097/01.mlg.0000231739.79208.97
Laryngoscope 116: September 2006
1700
drillout circummodiolar technique,3 the use of a double electrode array,4 or even a triple array implant.5 Regardless of the technique used, however, in severe cochlear ossification, the reported results are not satisfactory.6,7 Explanations proposed include an inadequate number of inserted electrodes,8 the distance between the electrodes and the nerve fibers within the modiolus,9 the involvement of the spiral ganglion cells by ossification,10 and peripheral nerve degeneration associated with ossification or even mere fibrosis.11 Recently, there have been a few reports describing the use of auditory brainstem implant (ABI) for management of such cases.9,12,13 In this paper, we report an additional case of ABI use for rehabilitation of a child with complete deafness and severe bilateral cochlear ossification after an attack of meningitis.
CASE REPORT A 12-year-old female patient was referred to us 7 months after the onset of meningitis, which has led to an immediate bilateral deafness. The patient did not have any additional neurologic sequel. Five months after the onset of HL, an attempt at right cochlear implantation was performed at another center. During surgery, however, the cochlea was found to be completely ossified, and implantation was judged impossible by the surgeon. Our assessment of the patient’s condition revealed a normal tympanic membrane bilaterally. Audiologic examination confirmed a total bilateral HL. With lip reading, the patient had 20% word recognition and 18% sentence recognition. She also had good language development. Radiologic examination revealed an ossified cochlea bilaterally with computed tomographic (CT) scanning (Fig. 1), wheras magnetic resonance imaging showed the presence of the 7th and 8th cranial nerves bilaterally. The decision was taken to implant the left side. Because the CT showed severe ossification of the left cochlea and failure of the earlier implant attempt on the right side, an informed consent was also obtained from the family to shift for an ABI if ossification prevented cochlear implantation. We chose a subtotal petrosectomy with blind-sac closure of the external auditory canal to provide a wide surgical field to deal with the ossification. As expected, during surgery, the cochlea was found completely ossified, so we decided to shift to brainstem implantation. The subtotal petrosectomy was transformed into a translabyrinthine approach. Once the posterior fossa dura was opened, adhesions were encountered in the cerebellopontine angle that were a result of the meningitis. The nerves and the vessels within the cerebellopontine angle were matted together, obliterating access to the lateral recess of the 4th ventricle. Dissection proceeded slowly to identify the 8th and 9th cranial
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
Fig. 3. Mapping of electrodes immediately after positioning of array.
Fig. 1. Axial (A) and coronal (B) computed tomography scan showing the ossification of cochlea.
nerves. Following these nerves medially led to the foramen of Luschka and consequently the lateral recess, both of which were free of adhesions. The correct identification of the foramen of
Fig. 2. Electrical auditory brain stem responses elicited at positioning of array.
Laryngoscope 116: September 2006
Luschka was further confirmed by the cerebrospinal fluid exiting from the foramen with Valsalva maneuvers. An ABI24 mol/L implant (Nucleus, Lone Cove, Australia) was easily inserted under direct monitoring of the 7th, 9th, and 11th cranial nerves and indirect monitoring of the 10th cranial nerve through electrocardiographic recording. Intraoperative impedance telemetry and electrical auditory brainstem responses (EABR) were performed to ascertain the correct position and function of the implant. An example of the obtained EABR waves is shown on Figure 2. During surgery, it was not possible to obtain any EABR from the most medial four electrodes, which, on the contrary, produced some stimulation of the 11th cranial nerve (Fig. 3). At the end of the operation, the eustachian tube was obliterated with periosteum and the surgical cavity with long strips of abdominal fat inserted deeply into the cerebellopontine angle through the dural defect. The surgical wound was then sutured in layers. The postoperative period was uneventful. The position of the implant was radiologically confirmed by a postoperative CT (Fig. 4), and the patient was discharged on the fourth postoperative day. Activation of the implant was performed, after 1 month, in the operating room under electrocardiographic monitoring and in the presence of an anesthesiologist. The spectral peak (SPEAK) strategy was adopted. During activation, the number of electrodes stimulating the 11th cranial nerve without eliciting any auditory sensation was reduced to only 2, thus, overall, we had 19 functioning electrodes (Fig. 5). Immediately after activation, the hearing assessment tests resulted in 40% sound identification, whereas recognition of bisyllable words and sentences was 0%. Audiologic rehabilitation
Fig. 4. Correct position as confirmed by soft tissue coronal computed tomography.
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
1701
was instituted, and follow-up was performed at 1, 3, 5 and 8 months after the surgery. There was a marked improvement with each visit (Fig. 6) so that during the last follow-up, the results were very satisfying. The patient scored 100% sound identification, 90% recognition of bisyllable words, and 100% sentences recognition, with 31 words per minute at speech tracking. All the tests reported were performed in open set auditory-only mode. In addition, she is now able to communicate with the telephone.
DISCUSSION The consistency of the tonotopic orientation of the nerve fibers in the modiolus has made it easy to produce good hearing results after cochlear implantation. However, to achieve this aim, one of the important prerequisites is having a cochlea with patent turns. These turns act as a canal that can house the electrode array for the stimulation of the nerve fibers at the modiolus. In cases of severe cochlear ossification, the absence of this canal has led some authors to try to drill a neocanal for accommodation of the array. Although the results were discouraging, various techniques have been developed with the hope of obtaining results similar to those in patent cochlea.1–5 Unfortunately, none of these techniques could markedly improve the outcome in cases of severe ossification, and only a few patients were able to obtain some open set discrimination. Tonotopic organization has also been demonstrated at the level of the cochlear nucleus; however, in most patients with bilateral acoustic neuromas (NF2), hearing results using ABI have been unsatisfactory. In these cases, ABI is used when the cochlear nerve cannot be preserved, and hearing is lost during surgery. This is more frequent with larger schwannomas. In these cases, the tumor usually stretches the cochlear nerve and compresses the area of the brainstem where the cochlear nucleus is located. Distortion of the cochlear nucleus usually results in reduction and disorganization of the auditory fibers and, as a consequence, alteration of the complex three-dimensional tonotopic orientation.14,15 Theoretically, then, if the implant stimulates an undisturbed cochlear nucleus, there would be a better chance of achieving a good result, which is the case if ABI is performed in cases of cochlea ossification. Grayeli et al.9 were the first to report a case of ABI insertion for the bypass of a severely ossified cochlea. Colletti et al.12,13 then reported four similar cases. Four of five patients reached at least 60% sentence recognition in open set, auditory-only mode. Our case, which to the best of our knowledge is the sixth reported in the literature and the first in a child, represents living evidence of the accuracy of the aforementioned theory. In
Fig. 6. Results of audiologic testing according to time.
our case, access to the cerebellopontine angle was gained through the translabyrinthine approach, which, unlike the retrosigmoid approach, provides a more direct approach to the foramen of Luschka, without any cerebellar retraction. In addition, in this specific case, the translabyrinthine approach offered the possibility of performing the ABI insertion during the same stage as the cochlear exploration, with a simple extension of the approach. The results obtained in this case after 8 months of rehabilitation were 100% sound recognition, 90% bisyllable word recognition, and 100% sentence recognition, with 31 words per minute speech tracking (open set, auditory-only mode). In addition, the patient is now able to conduct regular telephone conversations. In evaluating our results and those reported in literature, one can notice a general trend toward better hearing results with the increase of the number of active electrodes.
CONCLUSIONS The preliminary results of ABI in bilateral ossified cochlea appear promising when compared with those obtained with cochlear implantation in similar cases. We need a large number of cases to prove the effectiveness of ABI. We should also take into consideration that the surgery is more difficult and risky when compared with cochlear implantation and, as a consequence, must be reserved for selected referral centers. In every case, our policy has been to first attempt a cochleostomy to evaluate the possibility of cochlear implantation and reserve the ABI for situations in which there is no practical possibility to obtain satisfactory results from cochlear implantation.
BIBLIOGRAPHY
Fig. 5. Mapping of electrodes at follow-up.
Laryngoscope 116: September 2006
1702
1. Steenerson RL, Gary LB, Wynens MS. Scala vestibuli cochlear implantation for labyrinthine ossification. Am J Otol 1990;11:360 –363. 2. Colletti V, Fiorino FG, Carner M, et al. New approach for cochlear implantation: cochleostomy through the middle fossa. Otolaryngol Head Neck Surg 2000;123:467– 474. 3. Balkany T, Gantz B, Nadol JB Jr. Multichannel cochlear implants in partially ossified cochleas. Ann Otol Rhinol Laryngol Suppl 1988;135:3–7. 4. Lenarz T, Buchner A, Tasche C, et al. The results in patients implanted with the nucleus double array cochlear implant:
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
5. 6. 7. 8. 9. 10.
pitch discrimination and auditory performance. Ear Hear 2002;23(1 Suppl):90S–101S. Richardson HC, Beliaeff M, Clarke G, Hawthorne M. A three-array cochlear implant: a new approach for the ossified cochlea. J Laryngol Otol 1999;113:811– 814. El-Kashlan HK, Ashbaugh C, Zwolan T, Telian SA. Cochlear implantation in perlingually deaf children with ossified cochleae. Am J Otol 1999;20:442– 444. Steenerson RL, Gary LB. Multichannel cochlear implantation in children with cochlear ossification. Laryngoscope 1994; 104:1071–1073. Cohen NL, Waltzman SB. Partial insertion of the nucleus multichannel cochlear implant: technique and results. Am J Otol 1993;14:357–361. Grayeli AB, Bouccara D, Kalamarides M, et al. Auditory brainstem implant in bilateral and completely ossified cochleae. Otol Neurotol 2003;24:79 – 82. Otte J, Schunknecht HF, Kerr AG. Ganglion cell populations
Laryngoscope 116: September 2006
11. 12. 13. 14. 15.
in normal and pathological human cochleae. Implications for cochlear implantation. Laryngoscope 1978;88: 1231–1246. Green JD Jr, Marion MS, Hinojosa R. Labyrinthitis ossificans: histopathologic consideration for cochlear implantation. Otolaryngol Head Neck Surg 1991;104:320 –326. Colletti V, Fiorino FG, Carner M, et al. Auditory brainstem implant as a salvage treatment after unsuccessful cochlear implantation. Otol Neurotol 2004;25:485– 496. Colletti V, Carner M, Miorelli V, et al. Auditory brainstem implant (ABI): new frontiers in adults and children. Otolaryngol Head Neck Surg 2005;133:126 –138. Lenarz T, Moshrefi M, Matthies C, et al. Auditory brainstem implant. Part I. Auditory performance and its evolution over time. Otol Neurotol 2001;22:823– 833. Shannon RV, Fayad J, Moore J, et al. Auditory brainstem implant. Part II. Postsurgical issues and performance. Otolaryngol Head Neck Surg 1993;108:634 – 642.
www.medicsindex.com
Sanna et al.: ABI in Ossified Cochlea
1703
