Near-infrared stimulation of the auditory nerve: A decade of progress toward an optical cochlear implant

OBJECTIVES

We provide an appraisal of recent research on stimulation of the auditory system with light. In particular, we discuss direct infrared stimulation and ongoing controversies regarding the feasibility of this modality. We also discuss advancements and barriers to the development of an optical cochlear implant.

METHODS

This is a review article that covers relevant animal studies.

RESULTS

The auditory system has been stimulated with infrared light, and in a much more spatially selective manner than with electrical stimulation. However, there are experiments from other labs that have not been able to reproduce these results. This has resulted in an ongoing controversy regarding the feasibility of infrared stimulation, and the reasons for these experimental differences still require explanation. The neural response characteristics also appear to be much different than with electrical stimulation. The electrical stimulation paradigms used for modern cochlear implants do not apply well to optical stimulation and new coding strategies are under development. Stimulation with infrared light brings the risk of heat accumulation in the tissue at high pulse repetition rates, so optimal pulse shapes and combined optical/electrical stimulation are being investigated to mitigate this. Optogenetics is another promising technique, which makes neurons more sensitive to light stimulation by inserting light sensitive ion channels via viral vectors. Challenges of optogenetics include the expression of light sensitive channels in sufficient density in the target neurons, and the risk of damaging neurons by the expression of a foreign protein.

CONCLUSION

Optical stimulation of the nervous system is a promising new field, and there has been progress toward the development of a cochlear implant that takes advantage of the benefits of optical stimulation. There are barriers, and controversies, but so far none that seem intractable.

LEVEL OF EVIDENCE

NA (animal studies and basic research).

A time-sensitive rubric for assessing mastoidectomy proficiency

OBJECTIVE

To develop a time-sensitive, standardized rubric for cadaveric temporal bone dissection for otolaryngology resident education.

METHODS

This is a five-year prospective cohort study that evaluated otolaryngology resident performance during sequential cadaveric temporal bone dissection courses at a single otolaryngology residency training program. A canal-wall-up mastoidectomy with a facial recess approach was performed adhering to a 30-minute time limit and graded according to a standardized rubric. Main outcome measures included: (1) correct structure identification and (2) injuries sustained to structures as compared by resident post-graduate year (PGY) level.

RESULTS

Thirteen residents were evaluated from October 2012 to March 2017. This included 57 individual graded exercises performed over ten dissection courses. The average score for PGY-2 residents was lowest (68.9), and PGY-5 residents achieved the highest average score (87.7). Junior residents correctly identified fewer structures (77.5%) when compared to senior residents (91.3%), p < 0.0001. Correct performance of a facial recess approach was achieved by 100% of senior residents, but only 59.3% of junior residents (p = 0.0003). The percentage of major injuries, which included the facial nerve, tegmen, labyrinth, and ossicular chain, decreased each PGY-level from a maximum of 17% by PGY-2 residents to a minimum of 5% by PGY-5 residents.

CONCLUSION

Senior residents correctly identify more structures and are able to complete a facial recess approach with higher fidelity when subjected to a time-sensitive graded mastoidectomy rubric.

Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing

Objective: We aim to examine the existing literature on, and identify knowledge gaps in, the study of adverse animal and human audiovestibular effects from exposure to acoustic or electromagnetic waves that are outside of conventional human hearing. Design/Setting/Participants: A review was performed, which included searches of relevant MeSH terms using PubMed, Embase, and Scopus. Primary outcomes included documented auditory and/or vestibular signs or symptoms in animals or humans exposed to infrasound, ultrasound, radiofrequency, and magnetic resonance imaging. The references of these articles were then reviewed in order to identify primary sources and literature not captured by electronic search databases. Results: Infrasound and ultrasound acoustic waves have been described in the literature to result in audiovestibular symptomology following exposure. Technology emitting infrasound such as wind turbines and rocket engines have produced isolated reports of vestibular symptoms, including dizziness and nausea and auditory complaints, such as tinnitus following exposure. Occupational exposure to both low frequency and high frequency ultrasound has resulted in reports of wide-ranging audiovestibular symptoms, with less robust evidence of symptomology following modern-day exposure via new technology such as remote controls, automated door openers, and wireless phone chargers. Radiofrequency exposure has been linked to both auditory and vestibular dysfunction in animal models, with additional historical evidence of human audiovestibular disturbance following unquantifiable exposure. While several theories, such as the cavitation theory, have been postulated as a cause for symptomology, there is extremely limited knowledge of the pathophysiology behind the adverse effects that particular exposure frequencies, intensities, and durations have on animals and humans. This has created a knowledge gap in which much of our understanding is derived from retrospective examination of patients who develop symptoms after postulated exposures. Conclusion and Relevance: Evidence for adverse human audiovestibular symptomology following exposure to acoustic waves and electromagnetic energy outside the spectrum of human hearing is largely rooted in case series or small cohort studies. Further research on the pathogenesis of audiovestibular dysfunction following acoustic exposure to these frequencies is critical to understand reported symptoms.

The effects of repeated low-level blast exposure on hearing in marines

BACKGROUND

The study evaluates a group of Military Service Members specialized in blast explosive training called "Breachers" who are routinely exposed to multiple low-level blasts while teaching breaching at the U.S. Marine Corps in Quantico Virginia. The objective of this study was to determine if there are any acute or long-term auditory changes due to repeated low-level blast exposures used in training. The performance of the instructor group "Breachers" was compared to a control group, "Engineers".

METHODS

A total of 11 Breachers and four engineers were evaluated in the study. The participants received comprehensive auditory tests, including pure-tone testing, speech-in-noise (SIN) measures, and central auditory behavioral and objective tests using early and late (P300) auditory evoked potentials over a period of 17 months. They also received shorter assessments immediately following the blast-exposure onsite at Quantico.

RESULTS

No acute or longitudinal effects were identified. However, there were some interesting baseline effects found in both groups. Contrary to the expected, the onsite hearing thresholds and distortion product otoacoustic emissions were slightly better at a few frequencies immediately after blast-exposure than measurements obtained with the same equipment weeks to months after each blast-exposure.

CONCLUSIONS

To date, the current study is the most comprehensive study that evaluates the long-term effects of blast-exposure on hearing. Despite extensive testing to assess changes, the findings of this study suggest that the levels of current exposures used in this military training environment do not seem to have an obvious deleterious effect on hearing.

Asymmetric Hearing Loss Prompting MRI Referral in a Military Population: Redefining Audiometric Criteria

Objective

To reevaluate asymmetric sensorineural hearing loss (ASNHL) criteria used to justify magnetic resonance imaging (MRI) in the evaluation of retrocochlear tumors in a military population.

Study Design

Retrospective case-control study.

Setting

Tertiary care military medical center.

Subjects and Methods

Patients with military service and a history of ASNHL prompting referral for MRI, with or without retrocochlear tumors, were compared between 2005 and 2016. Predictor variables included pure tone ASNHL, speech audiometry, and a history of noise exposure. Logistic regression models for hearing asymmetries were performed, and receiver operator curves were used to calculate sensitivity and specificity.

Results

Thirty-eight retrocochlear tumors were identified. The MRI diagnosis rate for patients with ASHNL was 0.85%. Patients with tumors were slightly older (42 vs 37 years, P = .021) and had less noise exposure (47% vs 85%, P < .001). A sensitivity of 0.83 and a specificity of 0.58 were calculated for asymmetries ≥10 dB at 2000 Hz without adjusting for noise exposure. Instituting this imaging threshold would have reduced the number of MRI scans by half while missing 16% of tumors.

Conclusion

The tumor diagnosis rate among those undergoing MRI for ASNHL is low in the military population, likely because service-related noise exposure commonly causes ASNHL. Optimal MRI referral criteria should conserve resources while balancing the risks of over- and underdiagnosis. For those with a history of military service, an asymmetry ≥10 dB at 2000 Hz among patients meeting current ANSHL referral criteria is most predictive of a retrocochlear tumor.

Dizziness, malpractice, and the otolaryngologist

PURPOSE

To assess malpractice claims related to the management of dizziness in otolaryngology in order to improve care and minimize the risk of litigation.

MATERIALS AND METHODS

This is a retrospective review of the LexisNexis "Jury Verdicts and Settlements" database. All lawsuits and out of court adjudications related to the management of dizziness by otolaryngologists were collected. Data including patient demographics, plaintiff allegation, procedure performed, and indemnities were analyzed.

RESULTS

Of 21 cases meeting inclusion criteria, 17 were decided by a trial jury and four were resolved out of court. Jury verdicts favored the plaintiff 53% of the time and a payout was made in 57% of cases overall. Average payments were higher for jury verdicts in favor of the plaintiff ($1.8 million) as compared to out of court settlements ($545,000). Two-thirds of cases involved surgery, most commonly stapes surgery. Legal allegations, including physical injury, negligence, and lack of informed consent failed to predict the legal outcome.

CONCLUSIONS

Appropriate examination, testing, and referrals within a timely manner are crucial in the management of dizzy patients to avoid misdiagnoses. It is imperative that patients undergoing ear surgery are appropriately counseled that dizziness is a potential complication. The analysis of malpractice literature is complementary to clinical studies, with the potential to educate practitioners, improve patient care, and mitigate risk.

Ceruminous adenocarcinoma: An analysis of the Surveillance Epidemiology and End Results (SEER) database

OBJECTIVES

Ceruminous adenocarcinoma is a rare malignancy. However, due to the paucity of cases, this has been difficult to study. Using a population-based national database, patient demographics and survival trends were analyzed to further elucidate the management of this malignancy.

METHODS

The SEER database was queried for patients diagnosed with ceruminous adenocarcinoma between 1973 and 2010.

RESULTS

Twenty-two patients were identified in the database. The average age of diagnosis was between 60 and 64 years. All of the patients underwent surgical resection of the primary malignancy. Eight patients (36%) also had postoperative radiation.

CONCLUSIONS

Ceruminous adenocarcinoma is uncommon but may not have as poor a prognosis as previously thought. Surgical resection alone appears to be a reasonable treatment option. Larger prospective studies are needed, but database analysis like this may provide clarity on the management of uncommon diseases.

The Vestibular Effects of Repeated Low-Level Blasts

The objective of this study was to use a prospective cohort of United States Marine Corps (USMC) instructors to identify any acute or long-term vestibular dysfunction following repeated blast exposures during explosive breaching training. They were assessed in clinic and on location during training at the USMC Methods of Entry School, Quantico, VA. Subjects received comprehensive baseline vestibular assessments and these were repeated in order to identify longitudinal changes. They also received shorter assessments immediately following blast exposure in order to identify acute findings. The main outcome measures were the Neurobehavioral Symptom Inventory, vestibular Visual Analog Scale (VAS) of subjective vestibular function, videonystagmography (VNG), vestibular evoked myogenic potentials (VEMP), rotary chair (including the unilateral centrifugation test), computerized dynamic posturography, and computerized dynamic visual acuity. A total of 11 breachers and 4 engineers were followed for up to 17 months. No acute effects or longitudinal deteriorations were identified, but there were some interesting baseline group differences. Upbeat positional nystagmus was common, and correlated (p<0.005) with a history of mild traumatic brain injury (mTBI). Several instructors had abnormally short low-frequency phase leads on rotary chair testing. This study evaluated breaching instructors over a longer test period than any other study, and the results suggest that this population appears to be safe from a vestibular standpoint at the current exposure levels. Upbeat positional nystagmus correlated with a history of mTBI in this population, and this has not been described elsewhere. The data trends also suggest that this nystagmus could be an acute blast effect. However, the reasons for the abnormally short phase leads seen in rotary chair testing are unclear at this time. Further investigation seems warranted.

Total Auricular Rehabilitation: Combined Cosmetic and Functional Lateral Temporal Bone Reconstruction

OBJECTIVE

The aim of the study was to describe 3 cases of total auricular rehabilitation, including the novel use of iliac crest bone grafts to support bone-anchored auricular prostheses.

STUDY DESIGN

This study is a retrospective case series from a single institution.

RESULTS

Three cases with large lateral temporal bone and soft tissue defects were successfully treated with total auricular rehabilitation. Rehabilitation included the following: soft tissue coverage with an anterolateral thigh microvascular free flap, iliac crest-free bone graft with staged placement of a bone-anchored auricular prosthesis into the bone graft, and audiologic rehabilitation with a bone-anchored hearing aid (BAHA). All of the cases with grafts and flaps survived and were without significant donor site morbidity. Bone-anchored hearing aid abutment skin overgrowth was seen in 2 cases and was revised under local anesthesia. All of the patients had expected functional recovery on postoperative audiologic testing. Each patient continues to consistently wear his/her auricular prosthesis and BAHA during 3 years of follow-up.

CONCLUSIONS

Total auricular rehabilitation is a complex task involving reconstruction of extensive soft tissue defects, bony defects, and the hearing apparatus. Acceptable cosmetic and functional outcomes and high patient satisfaction is possible in committed patients.

Late presentation of subcutaneous emphysema and pneumomediastinum following elective tonsillectomy

Subcutaneous emphysema and pneumomediastinum are rare complications following elective tonsillectomy. Although the mechanism of injury is unclear, air is thought to enter through either the buccopharyngeal mucosa during surgery or via alveolar rupture during positive pressure ventilation. Patients typically present immediately after surgery or upon anesthesia emergence. We describe a case of delayed pneumomediastinum in a 30year-old female who presented 4days after surgery. With only one other case described, we review the literature and remind the reader to be cognizant of this late complication.

Practical Otologic Considerations in Head Injury

Program Description:

After our nation’s longest period of conflict, it is important to look for experience and medical advances that might improve our care of the injured patient. Targeting general otolaryngologists, we will present an overview for otologic care of the trauma patient presenting to your office. Emphasis will include an update on surgical management of facial nerve injury, manifestations and treatment of balance disorders after concussion and head trauma, repair of traumatic tympanic membrane perforations, and hearing loss.

Educational Objectives:

1) Articulate timing and indications for surgical treatment of facial nerve injury. 2) Describe treatment principles and best practice for post–head trauma balance disorders. 3) Recognize treatment of traumatic perforations and hearing injury.

Laser stimulation of single auditory nerve fibers

OBJECTIVES/HYPOTHESIS

One limitation with cochlear implants is the difficulty stimulating spatially discrete spiral ganglion cell groups because of electrode interactions. Multipolar electrodes have improved on this some, but also at the cost of much higher device power consumption. Recently, it has been shown that spatially selective stimulation of the auditory nerve is possible with a mid-infrared laser aimed at the spiral ganglion via the round window. However, these neurons must be driven at adequate rates for optical radiation to be useful in cochlear implants. We herein use single-fiber recordings to characterize the responses of auditory neurons to optical radiation.

STUDY DESIGN

In vivo study using normal-hearing adult gerbils.

METHODS

Two diode lasers were used for stimulation of the auditory nerve. They operated between 1.844 μm and 1.873 μm, with pulse durations of 35 μs to 1,000 μs, and at repetition rates up to 1,000 pulses per second (pps). The laser outputs were coupled to a 200-μm-diameter optical fiber placed against the round window membrane and oriented toward the spiral ganglion. The auditory nerve was exposed through a craniotomy, and recordings were taken from single fibers during acoustic and laser stimulation.

RESULTS

Action potentials occurred 2.5 ms to 4.0 ms after the laser pulse. The latency jitter was up to 3 ms. Maximum rates of discharge averaged 97 ± 52.5 action potentials per second. The neurons did not strictly respond to the laser at stimulation rates over 100 pps.

CONCLUSIONS

Auditory neurons can be stimulated by a laser beam passing through the round window membrane and driven at rates sufficient for useful auditory information. Optical stimulation and electrical stimulation have different characteristics; which could be selectively exploited in future cochlear implants.

Acoustic Neuroma (Vestibular Schwannoma) Revision

The authors present their experience of more than 25 years, now in excess of 1200 patients, with cerebellopontine angle tumors. This article focuses on the management of planned subtotal resection of acoustic tumors in five subjects, and unexpected "residual" discovered by MRI scanning in 10 cases, which represents, to the best of the authors' knowledge, a residual rate of 1% of operated patients. The rate of residual tumor is as high as 19% in some series and, in part, depends on the surgical approach. For the purpose of this article, the authors did not include their cases of neurofibromatosis, because these tumors behave differently than unilateral sporadic schwannomas.

Revision BAHA Surgery

The osseointegrated auditory implant (BAHA) is a system used for hearing rehabilitation through direct bone conduction. Although BAHA surgery is not difficult, the surgeon must observe meticulous technique to prevent complications. Indications for revision BAHA surgery can be divided into (1) failure of fixture osseointegration; (2) bone overgrowth; or (3) skin reaction or skin loss. This article discusses the conditions that might predispose a patient to require BAHA revision, and the steps, if any, that can be taken to prevent these complications. Specific surgical steps for revision of each of these three conditions are also addressed.

Radiofrequency excision versus monopolar electrosurgical excision for tonsillectomy

OBJECTIVE

We previously compared radiofrequency (Evac) tonsillotomy with monopolar electrosurgical (Bovie) tonsillectomy and showed significantly less pain with the Evac. Tonsillotomy leaves a cuff of tonsil behind, the significance of which is unknown. We hypothesize that Evac tonsillectomy also is less painful than Bovie tonsillectomy.

STUDY DESIGN AND SETTING

We compared Evac (ENTec Evac 70; ArthroCare, Sunnyvale, CA) and Bovie tonsillectomy in a prospective, blinded fashion. Each participant had 1 tonsil removed by each device. We recorded, by side, the surgical time, blood loss, operative difficulty, pain (postoperative days 1, 3, 5, 7, 10, and 14), and the side that each patient preferred.

RESULTS

Data were analyzed for 17 patients. They reported significantly less pain with the Evac (P < 0.036, F = 5.87). The Evac was preferred by 12 of 14 patients.

CONCLUSION

Evac tonsillectomy is significantly less painful than Bovie tonsillectomy. Patients blinded to treatment preferred the Evac technique.

SIGNIFICANCE

The Evac device decreases postoperative pain.

Radiofrequency ablation versus electrocautery in tonsillectomy

OBJECTIVES

The objective of this study was to compare the safety, difficulty of removal, and postoperative pain profile of radiofrequency ablation versus standard electrocautery removal of tonsils.

STUDY DESIGN AND SETTING

A prospective, blinded study was designed to remove 1 tonsil with each of the 2 methods. Time of operation, estimated blood loss, difficulty of operation, postoperative pain, rate of postoperative hemorrhage, and the patient's preferred technique were evaluated.

RESULTS

The operating time was significantly longer (P < 0.007) and the patients reported significantly less pain (P < 0.001) with radiofrequency ablation. There were no differences in blood loss, difficulty of operation, or postoperative hemorrhage rates. The patients preferred the radiofrequency ablation technique (P < 0.001).

CONCLUSION

Radiofrequency ablation is a viable method to remove tonsillar tissue. Operating time for this procedure will likely decrease with experience. There was significantly less pain reported with radiofrequency ablation compared with standard electrocautery.

Snoring Surgery: Which One is Best for You?

Excessive snoring is a common problem that is frequently treated surgically. In the early 1980s, uvulopalatopharyngoplasty was introduced to the United States as the first surgical treatment for excessive snoring. It remains in common use, but its limitations created an incentive to develop a procedure that is as effective, but safer and more economical. Several other surgical procedures for snoring were developed, including laser-assisted uvulopalatoplasty, palatal stiffening operations, and radiofrequency ablation. Each of these procedures has its own advantages and limitations; which procedure is the best treatment for excessive snoring is controversial. We present our experience with each of these procedures, along with a thorough review of the literature, to help the otolaryngologist determine which is the best snoring surgery for the individual patient.

Snoring surgery: which one is best for you?

Excessive snoring is a common problem that is frequently treated surgically. In the early 1980s, uvulopalatopharyngoplasty was introduced to the United States as the first surgical treatment for excessive snoring. It remains in common use, but its limitations created an incentive to develop a procedure that is as effective, but safer and more economical. Several other surgical procedures for snoring were developed, including laser-assisted uvulopalatoplasty, palatal stiffening operations, and radiofrequency ablation. Each of these procedures has its own advantages and limitations; which procedure is the best treatment for excessive snoring is controversial. We present our experience with each of these procedures, along with a thorough review of the literature, to help the otolaryngologist determine which is the best snoring surgery for the individual patient.

Knodt rod distraction instrumentation in lumbosacral arthrodesis

Review of 40 patients undergoing lumbosacral fusions over a 4-year period was done to determine the value, efficiency, and safety of Knodt rod distraction instrumentation. The age range was 30-80 years. Mean age was 51 years. Follow-up was 1-4 years. Twenty patients underwent decompression and fusion for spinal stenosis, nine underwent spinal arthrodesis for instability, six underwent the same for spondylolisthesis, and five underwent fusions for other diagnoses. A posterior midline approach was used. Laminal hook sites were prepared, and care was taken to prevent dural compression or tenting. Balanced distraction was done to restore soft tissue tension and stability. No attempt was made to reduce deformity. A posterior and lateral mass fusion augmented with allograft bone was performed on all but three patients, in whom autogenous bone was used. The majority of patients were placed in a custom-molded lumbosacral orthosis for 3-6 months after operation. There were no neurologic complications, dural tears, or pseudomeningoceles. The first sacral laminas were instrumented in 22 patients. Nine of the 40 patients underwent rod removal. Reasons for removal were pain due to loosening in five patients and failure of fusion in two. On rod removal in two patients, no abnormality was found. Insertion within the sacral laminas did not lead to neurologic complications. The major problem appeared to be loosening, which necessitated rod removal in 12% of the patients. Knodt rod distraction instrumentation is a safe and effective method of internal fixation for lumbosacral fusions.