Revision Cochlear Implant Surgery: Causes and Outcome

OBJECTIVE: To review experience with cochlear implant reimplantations, including effect of reinsertion on audiological performance.

STUDY DESIGN AND SETTING: Retrospective review of cochlear implant reinsertions in patients seen in a private tertiary neurotologic practice. Forty-three patients (8 adults and 35 children) underwent revision cochlear implant surgery for device failure or upgrade. Findings at initial and repeat operations were noted, including number of electrodes inserted, and speech perception performance data were obtained when available.

RESULTS: Five complications occurred in the reinsertion operations, 2 (6%) intraoperative cerebral spinal fluid leaks and 3 (7%) postoperative flap break-downs with implant extrusion. Number of electrodes inserted was unchanged in 40/43 patients. Speech perception abilities remained stable or improved.

CONCLUSION: Cochlear reimplantation is technically feasible and allows for continued auditory stimulation.

SIGNIFICANCE: Patients facing reimplantation must be aware of the possibility of differences in sound quality and speech recognition performance with their replacement device, but speech perception ability will typically remain the same or improve.

Endolymphatic Periductal Channels: Possible Role in Ménière’s Disease

Objectives:

Characterize the osseous periductal channels surrounding the human endolymphatic duct. Endolymphatic hydrops is the fundamental pathophysiology underlying Ménière’s disease. Elucidating the regulation of endolymphatic circulation is central to understanding the cause of Ménière’s disease attacks of vertigo and hearing loss.

Methods:

Formalin-fixed, celloidin-embedded human temporal bones were sectioned to 20 microns, and every section was stained with hematoxylin & eosin. Amira software was used to construct a three dimensional image of the periductal channels. We performed immunohistochemical analysis using antibodies directed against vascular, lymphatic, and neural crest markers. The microanatomy was investigated with electron microscopy of the periductal channel epithelium. Finally, we injected horseradish peroxidase into the scala media of guinea pigs to investigate the flow patterns involving these peri-ductal channels.

Results:

Surrounding the human endolymphatic duct is a group of small channels that originate in the proximal cisternal area of the endolymphatic sac and terminate in the supporting tissue of the saccule, as demonstrated by 3D reconstructions. Endolymphatic hydrops was found in eight bones with blocked ducts and blocked or absent periductal channels. Proliferation of channels was evident in temporal bones when the channels were disrupted on one side. Immunohistochemical analysis results suggest a neuroectodermal origin, similar to the cells of the cochlear spiral ligament. Some contain micro-vessels with single endothelial walls that could represent lymphatics or empty capillaries while others suggest a complex absortive epithelium.

Conclusions:

This temporal bone study suggests a role for the periductal channels in absorption of endolymph.

Round window versus cochleostomy technique in cochlear implantation: histologic findings

HYPOTHESIS

Cochleostomy or round window enlargement techniques for cochlear implant electrode insertion result in more abnormal tissue formation in the basal cochlea and are more apt to produce endolymphatic hydrops than round window electrode insertion.

METHODS

Twelve temporal bones from implanted patients were examined under light microscopy and reconstructed with 3-dimensional reconstruction software to determine cochlear damage and volume of neo-ossification and fibrosis after electrode insertion. Amount of new tissue was compared between 3 groups of bones: insertion through the round window (RW), after enlarging the RW (RWE) and cochleostomy (Cochl). The probable role of the electrode was evaluated in each case with hydrops.

RESULTS

More initial damage occurred in the Cochl and RWE groups than in the RW group, and the difference was significant between RWE and RW in cochlear segment I (p < 0.026). The volume of new bone in Segment I differed significantly between groups (p < 0.012) and was greater in the RWE group than in either the Cochl or RW groups (post hoc p's < 0.035 and 0.019, respectively). Hydrops was seen in 5 cases, all in the Cochl and RWE groups. Blockage of the duct was because of new tissue formation in 4 of the 5 hydrops cases.

CONCLUSION

With the electrodes in this series, implantation through the RW minimized initial intracochlear trauma and subsequent new tissue formation, whereas the RW extension technique used at the time of these implantations produced the greatest damage. Future studies may clarify whether today's techniques and electrodes will produce these same patterns of damage.

Multiple Otosclerotic Foci: Impact on Cochlear Function

Objective: Quantify and illustrate the location of otosclerosic foci using morphologic images and 3D reconstruction. Evaluate the impact of multiple otosclerotic foci on hearing loss.

Method: We investigated our histopathological collection to identify all the temporal bones with: 1) oval window otosclerosis (n = 200), 2) oval window and multiple otosclerotic foci (n = 35), 3) oval window plus cochlear otosclerosis (n = 133), and 4) oval window foci with cochlear and multiple other otosclerotic foci (n = 31). Foci were tabulated for each specimen. Cochlear function (hearing) and morphology (otosclerotic foci quantity and location) were compared.

Results: Of 574 temporal bones with evidence of otosclerosis, 67 had multiple foci. Ectopic foci were found in the internal auditory canal, the peri-carotid area, semicircular canals and anterior to the cochlea. There was no influence of the number of foci (not involving the cochlea) on hearing loss and cochlear morphology.

Conclusion: This is the first systematic evaluation of the number and location of ectopic multiple otosclerotic foci. As previously reported, there is a relationship between cochlear otosclerosis and sensorineural hearing loss, however the addition of other foci does not affect hearing.

Evolution in the management of facial nerve schwannoma

OBJECTIVE

To design a treatment algorithm based on experience with facial nerve schwannomas (FNS) over a 30-year period.

STUDY DESIGN

Retrospective chart review.

METHOD

Seventy-nine patients with facial nerve schwannomas seen from 1979 through 2009 at a tertiary referral private otologic practice were categorized by treatment modality. Interventions included surgical resection with grafting, bony decompression, observation, or stereotactic radiation. Outcome measures included House-Brackmann facial nerve grade before and after intervention as well as change in facial nerve grade, tumor size, involved segments of nerve, time to intervention.

RESULTS

Thirty-seven patients (46.8%) ultimately underwent surgical excision with grafting or primary anastomosis, 21 (26.6%) underwent bony decompression alone, 15 (19.0%) were managed with observation only, and 6 (7.6%) had stereotactic radiation. Through 1995, 85% of cases had surgical resection and none had observation only. Of the 52 patients seen after 1995, 27% had surgical resection and grafting, 33% had bony decompression, 29% were managed with observation alone, and 11% had radiotherapy. Facial nerve grade was maintained or improved over the follow-up period (mean time = 3.9 years) in 78.9% of the decompression group and 100% of the observation and radiation groups compared to 54.8% of the resection group (P ≤ .012).

CONCLUSIONS

Surgical resection and grafting, once widely accepted and practiced, has in many cases given way to observation, bony decompression, or stereotactic radiation. A wide armamentarium of options is available to the neurotologist treating facial nerve schwannomas with the ability to preserve facial function for a longer period of time.

Vestibular neuritis

The epidemiology, diagnostic features, differential diagnosis, and treatment of vestibular neuritis are reviewed. The authors present considerations for physical examination, imaging, and management in both the acute and chronic phases of this disease. The authors also present a dizziness questionnaire in the Appendix of this publication.

Treatment of recurrent and residual glomus jugulare tumors

Residual and recurrent glomus jugulare tumors are rare but challenging. Treatment options include microsurgical resection, stereotactic radiotherapy, a combination of modalities, and "observation." Choice of treatment must be made on a case-by-case basis, considering patient age, health status, location and size of tumor, status of the lower cranial nerves, and, of course, patient desire. Surgery is preferred when total resection of the tumor with preservation of function is deemed achievable. When function of the lower cranial nerves has been compromised, total surgical resection may also be possible, provided that the patient's health allows it. Cases where function is still preserved despite presence of a large tumor are more challenging, and a combination modality may be most effective. The goal of treatment is to provide tumor control with low morbidity. Current surgical techniques and the availability of stereotactic radiotherapy make this possible in the majority of cases.

Extralabyrinthine manifestations of DFNA9

DFNA9 is an autosomal dominant cause of non-syndromic adult-onset sensorineural hearing loss with associated variable vestibular dysfunction caused by mutations in the COCH gene. DFNA9 has previously been characterized by the presence of unique histopathologic features limited to the cochlear and vestibular labyrinth. This report describes newly discovered extralabyrinthine findings within the middle ear in DFNA9 and discusses their implications. The histopathologic anatomy of extralabyrinthine structures was reviewed in 12 temporal bones from seven individuals with DFNA9 and compared with age-matched controls. All temporal bones with DFNA9 had abnormal deposits within the tympanic membrane, incudomalleal joint, and incudostapedial joint. Hematoxylin and eosin stain and Movat's pentachrome stain both revealed different staining patterns of the extralabyrinthine deposits compared with the intralabyrinthine deposits suggesting that the composition of the deposits varies with location. The deposits within the tympanic membrane resembled cartilage morphologically and stained positively for aggrecan, an extracellular matrix protein found in cartilage. However, the cellular component of the tympanic membrane deposits did not stain with immunomarkers for chondrocytes (s100 and connective tissue growth factor). These novel findings in DFNA9 have implications for the phenotypic expression of the disorder and the clinical workup of adult-onset sensorineural hearing loss.

Endolymphatic pseudohydrops of the cochlear apex

OBJECTIVE

To demonstrate that what appears to be endolymphatic hydrops of the apical scala media is normal anatomy.

STUDY DESIGN

Computer-generated three-dimensional reconstruction of the cochlear apex and tabulation of the number of cases with arched Reissner's membranes (pseudohydrops) versus flat membranes.

SETTING

Temporal bone laboratory consisting of 809 documented pairs of temporal bones.

SUBJECTS AND METHODS

Archival temporal bone sections from 107 bones (65 patients) were used to determine the percentage of arched (pseudohydrops) versus flat Reissner's membranes. Two bones, one of each membrane shape, were randomly selected for computer-generated three-dimensional reconstructions showing the cochlear apical anatomy.

RESULTS

An arched Reissner's membrane was found in 48.6 percent of bones. In the cochlear apex, Reissner's membrane appears to be distended, simulating hydrops, due to its transition from a conical structure to a triangle bounded by the basilar membrane with the organ of Corti, the stria vascularis, and Reissner's membrane. Membrane findings were similar in both ears in 73.8 percent of the bilateral cases studied. There were no significant relationships between membrane type and clinical characteristics.

CONCLUSION

What appears to be endolymphatic hydrops of the cochlear apex is the transition area of the cochlear duct from a conical shape at the extreme apex to the triangular shape found in the rest of the cochlea. The appearance of distension is dependent upon the cochlear length and the level of the microscopic section.

The Medial wall of the Jugular Foramen

OBJECTIVE: To better understand the variable and complex anatomy of the jugular foramen (JF) and the relationship between the neurovascular structures in the medial wall of the jugular bulb (JB).

STUDY DESIGN: A temporal bone anatomic study.

SETTING: A temporal bone laboratory within a hearing research facility.

SUBJECTS AND METHODS: Twenty-two temporal bones were dissected under the operating microscope. The JF anatomy was exposed by using the modified infratemporal fossa approach (no rerouting of the facial nerve). Pictures were taken at various intervals during the dissection. Distances between important structures were measured with two-point calipers and transferred to a millimetric scale.

RESULTS: The right JF was found to be larger than the left side in 72.7 percent of the dissected temporal bones. A fibrous septum separated the glossopharyngeal (CN IX) from the vagus (CN X) and accessory (CN XI) nerves in 19 specimens (86.4%), and a complete bony septum was present in three specimens (13.6%). The CNs IX, X, and XI traveled anteromedially to the JB within the JF. The inferior petrosal sinus (IPS) drained into the medial wall of the JB at various locations by two or more channels. In most of the specimens (86.4%), the IPS separated CNs IX and X.

CONCLUSION: The lower cranial nerves have an intimate relationship to the medial wall of the JB. Within the JF, the neurovascular structures vary in size, shape, and location. To minimize surgical morbidity, the surgeon should be familiar with the complex anatomy of the JB and its variations.

Single vertical incision for Baha implant surgery: Preliminary results

Objectives: A single vertical skin incision with subcutaneous tissue removal is a cosmetic alternative for Baha implant placement. We aimed to determine the preliminary complication rate using a 4-cm vertical skin incision.

Study Design: Retrospective review.

Subjects and Methods: Vertical incision Baha implant placements from January 2006 to August 2007 were reviewed. Complications including skin irritation, skin overgrowth, and implant extrusion were tallied. A total of 71 patients underwent surgery, with a mean follow-up time of 7 months.

Results: There were five minor complications (three cases of skin irritation, one wound infection requiring oral antibiotics, one postoperative hematoma) and seven major complications (one case of irritation requiring abutment removal, six cases of skin overgrowth or infection requiring flap revision), for a total complication rate of 16.9 percent.

Conclusions: A single vertical incision for Baha implant placement has a complication rate similar to that of traditional dermatome use in this preliminary study. Patients with thick scalps or risk factors for hypertrophic scarring may require longer abutments.

GRM7 variants confer susceptibility to age-related hearing impairment

Age-related hearing impairment (ARHI), or presbycusis, is the most prevalent sensory impairment in the elderly. ARHI is a complex disease caused by an interaction between environmental and genetic factors. Here we describe the results of the first whole genome association study for ARHI. The study was performed using 846 cases and 846 controls selected from 3434 individuals collected by eight centers in six European countries. DNA pools for cases and controls were allelotyped on the Affymetrix 500K GeneChip for each center separately. The 252 top-ranked single nucleotide polymorphisms (SNPs) identified in a non-Finnish European sample group (1332 samples) and the 177 top-ranked SNPs from a Finnish sample group (360 samples) were confirmed using individual genotyping. Subsequently, the 23 most interesting SNPs were individually genotyped in an independent European replication group (138 samples). This resulted in the identification of a highly significant and replicated SNP located in GRM7, the gene encoding metabotropic glutamate receptor type 7. Also in the Finnish sample group, two GRM7 SNPs were significant, albeit in a different region of the gene. As the Finnish are genetically distinct from the rest of the European population, this may be due to allelic heterogeneity. We performed histochemical studies in human and mouse and showed that mGluR7 is expressed in hair cells and in spiral ganglion cells of the inner ear. Together these data indicate that common alleles of GRM7 contribute to an individual's risk of developing ARHI, possibly through a mechanism of altered susceptibility to glutamate excitotoxicity.

Single Vertical Incision for BAHA: Preliminary Results

Objective

A single vertical skin incision with subcutaneous tissue undermining is a cosmetic alternative to standard dermatome skin graft elevation for bone anchored hearing aid (BAHA) placement. A vertical incision minimizes alopecia and simplifies wound closure, while maintaining thin skin flaps. We aimed to determine the preliminary complication rate using a 4cm skin inicsion with 4⋉4 cm of subcutaneous tissue removal.

Methods

A retrospective chart review of patients undergoing BAHA placement from January 2006 to August 2007 was performed. This search was filtered to include only vertical incision BAHA patients. Complications including skin irritation or infection, skin overgrowth, and implant extrusion were tallied. Pertinent patient risk factors were identified. 71 patients underwent vertical incision surgery, with a mean followup time of 6.8 months. 50 patients had sensorineural hearing losses and 21 had conductive hearing losses.

Results

No patient had spontaneous extrusion of the titanium abutment. There were 5 minor complications (skin irritation 3, wound infection requiring oral antibiotics 1, postoperative hematoma 1) and 7 major complications (irritation requiring abutment removal 1, skin overgrowth or infection requiring flap revision 6). Total complication rate was 16% and major complication rate was 9.8%.

Conclusions

A single vertical incision for BAHA placement has a similar complication rate to traditional dermatome use in this preliminary study, though more follow-up is necessary to identify cases of late skin overgrowth. Patients with thick scalps or risk factors for hypertrophic scarring may require placement of longer abutments.

Distribution of low-frequency nerve fibers in the auditory nerve: Temporal bone findings and clinical implications

HYPOTHESIS

Low-frequency cochlear fibers are on the outer surface of the auditory nerve adjacent to the vestibular nerve in the distal part of the internal auditory canal.

BACKGROUND

There is a misconception that low-frequency cochlear fibers are in the core of the cochlear nerve and are surrounded by high-frequency fibers.

METHODS

We analyzed temporal bones with a loss of upper spiral ganglion cells caused by different etiologies (n = 6) and traced the corresponding fibers into the distal internal auditory canal. Spiral ganglion cells for each segment (I-IV) of the cochlea were counted, and we defined the location of nerve fibers from the various segments.

RESULTS

There was total or near-total degeneration of the upper spiral ganglion cells in these bones. Corresponding low-frequency fibers were on the outer surface of the cochlear nerve adjacent to the vestibular nerve in the distal segment of the internal auditory canal.

CONCLUSION

Low-frequency fibers seem to be located at the periphery of the cochlear nerve. These findings provide one possible explanation for the low-frequency sensorineural hearing loss found in 10% of patients with vestibular nerve schwannomas and may have clinical relevance in the diagnosis of these lesions.

Prevention and Treatment of Cerebrospinal Fluid Leak After Translabyrinthine Acoustic Tumor Removal

OBJECTIVE

To determine the incidence rate of cerebrospinal fluid (CSF) leak after translabyrinthine acoustic tumor removal using titanium mesh cranioplasty and to compare with previous series and historical controls.

STUDY DESIGN

Database analysis with historical controls.

SETTING

Tertiary referral neurotologic private practice.

PATIENTS

The series of 389 patients who underwent titanium mesh cranioplasty after translabyrinthine tumor removal between March 2003 and July 2005. The results were compared with those in a group of 1,195 translabyrinthine tumor removal patients from our previously published series and with those in a group of 324 patients from the immediately preceding two-year period.

INTERVENTION

Cranioplasty using titanium mesh after acoustic tumor removal.

MAIN OUTCOME MEASURES

Rates of CSF leak for this method and previous methods of closure.

RESULTS

Thirteen patients (3.3%) had CSF leaks when using the new method of titanium mesh closure. This compares with rates of 10.9% and 8.7% in series in which other methods of closure were used (p < 0.001 and 0.003). The rates of CSF leak requiring reoperation were 0.5%, 2.5%, and 1.9% for the new and the two older series, respectively.

CONCLUSION

In our hands, titanium mesh cranioplasty seems to reduce the rate of CSF leaks after the translabyrinthine removal of acoustic tumors.

Auditory brainstem implants: surgical aspects

Patients with neurofibromatosis type 2 often develop bilateral life-threatening vestibular schwannoma necessitating tumor removal, which results in deafness. We developed the auditory brainstem implant (ABI) in order to be able to electrically stimulate the cochlear nucleus complex in patients with bilateral cochlear nerve injury from bilateral schwannoma. After tumor removal, the electrode array of the ABI is inserted into the lateral recess of the fourth ventricle and placed over the surface of the ventral and dorsal cochlear nuclei. The ABI is designed to stimulate auditory neural structures within the cochlear nucleus in order to convey salient cues about the frequency, amplitude, and temporal characteristics of sounds. To date, more than 200 patients have received an ABI device at our institution. Recently, penetrating ABIs were introduced, and preliminary results of penetrating ABIs are discussed in this paper. The surgical anatomy of the nucleus and surgical placement of the ABI in patients with neurofibromatosis type 2 are described, and surgical considerations in this group of challenging patients are detailed.

Multichannel cochlear implants: relation of histopathology to performance

OBJECTIVES

To determine the relationship of surviving neural elements to auditory function in multichannel cochlear implant temporal bones.

STUDY DESIGN

Case series of all 14 existing multichannel cochlear implants in our temporal bone collection.

METHODS

Devices included Nucleus 22 (n = 11), Nucleus 24 (n = 1), Ineraid (n = 1), and Clarion (n = 1). Morphologic evaluation of structural elements including spiral ligament, stria vascularis, hair cells, peripheral processes, and spiral ganglion cells was performed. Clinical performance data were obtained from patient charts. For eight patients, nonimplanted contralateral temporal bones were available and paired comparisons were made.

RESULTS

Despite frequent absence of hair cells and peripheral processes, all bones had at least some remaining spiral ganglion cells. Percent of normal remaining structures were unrelated to auditory performance with the implant for any of the structural elements. Ganglion cell count in segment III showed significant negative correlations to speech discrimination scores for words and sentences (Rhos = -.687 and -.661, P < or = .03 and .04) as did segment IV and total ganglion cell count with word score (Rhos = -.632 and -.638; P < or = .05). Spiral ganglion cell survival did not differ between implanted and nonimplanted ears, with the exception of segment I, which had fewer cells in the implanted ear (P < or = .028).

CONCLUSIONS

Performance variability of cochlear implants cannot be explained on the basis of cochlear neuronal survival. Although hair cells and peripheral processes were frequently absent or greatly diminished from normal, all subjects had at least some spiral ganglion cells. And, in this series, there was an inverse relationship between survival of ganglion cells and performance.

Multichannel cochlear implants: relation of histopathology to performance

OBJECTIVES

To determine the relationship of surviving neural elements to auditory function in multichannel cochlear implant temporal bones.

STUDY DESIGN

Case series of all 14 existing multichannel cochlear implants in our temporal bone collection.

METHODS

Devices included Nucleus 22 (n = 11), Nucleus 24 (n = 1), Ineraid (n = 1), and Clarion (n = 1). Morphologic evaluation of structural elements including spiral ligament, stria vascularis, hair cells, peripheral processes, and spiral ganglion cells was performed. Clinical performance data were obtained from patient charts. For eight patients, nonimplanted contralateral temporal bones were available and paired comparisons were made.

RESULTS

Despite frequent absence of hair cells and peripheral processes, all bones had at least some remaining spiral ganglion cells. Percent of normal remaining structures were unrelated to auditory performance with the implant for any of the structural elements. Ganglion cell count in segment III showed significant negative correlations to speech discrimination scores for words and sentences (Rhos = -.687 and -.661, P < or = .03 and .04) as did segment IV and total ganglion cell count with word score (Rhos = -.632 and -.638; P < or = .05). Spiral ganglion cell survival did not differ between implanted and nonimplanted ears, with the exception of segment I, which had fewer cells in the implanted ear (P < or = .028).

CONCLUSIONS

Performance variability of cochlear implants cannot be explained on the basis of cochlear neuronal survival. Although hair cells and peripheral processes were frequently absent or greatly diminished from normal, all subjects had at least some spiral ganglion cells. And, in this series, there was an inverse relationship between survival of ganglion cells and performance.

Human Cochleae With Three Turns: An Unreported Malformation

OBJECTIVE

The objective of this histologic study of archival temporal bone sections was to describe the morphology of human cochleae found with three turns, a previously unreported anomaly, found in three pairs of temporal bones.

METHODS

The authors conducted histopathologic processing and measurement of basilar membrane length. Basilar membrane length was compared with that found in six normal control bones.

RESULTS

Cochleae with three complete turns, rather than the usual two and a half turns, are described for the first time. All had longer than normal basilar membranes, with a mean length of 40.6 mm compared with a mean of 33.8 mm in the normal bones.

CONCLUSIONS

Human cochleae with three turns exist as an unreported anomaly. This is a new category of anomaly, not likely based on interruption of development.

Understanding drug ototoxicity: molecular insights for prevention and clinical management

Ototoxicity is a trait shared by aminoglycoside and macrolide antibiotics, loop diuretics, platinum-based chemotherapeutic agents, some NSAIDs and antimalarial medications. Because their benefits in combating certain life-threatening diseases often outweigh the risks, the use of these ototoxic drugs cannot simply be avoided. In this review, the authors discuss some of the most frequently used ototoxic drugs and what is currently known about the cell and molecular mechanisms underlying their noxious effects. The authors also provide suggestions for the clinical management of ototoxic medications, including ototoxic detection and drug monitoring. Understanding the mechanisms of drug ototoxicity may lead to new strategies for preventing and curing drug-induced hearing loss, as well as developing new pharmacological drugs with less toxic side effects.