Importance of timing optimization for closed-loop applications of vagus nerve stimulation.

In recent decades, vagus nerve stimulation (VNS) therapy has become widely used for clinical applications including epilepsy, depression, and enhancing the effects of rehabilitation. However, several questions remain regarding optimization of this therapy to maximize clinical outcomes. Although stimulation parameters such as pulse width, amplitude, and frequency are well studied, the timing of stimulation delivery both acutely (with respect to disease events) and chronically (over the timeline of a disease's progression) has generally received less attention. Leveraging such information would provide a framework for the implementation of next generation closed-loop VNS therapies. In this mini-review, we summarize a number of VNS therapies and discuss (1) general timing considerations for these applications and (2) open questions that could lead to further therapy optimization.

Comparison of Responses to DCN vs. VCN Stimulation in a Mouse Model of the Auditory Brainstem Implant (ABI).

The auditory brainstem implant (ABI) is an auditory neuroprosthesis that provides hearing to deaf patients by electrically stimulating the cochlear nucleus (CN) of the brainstem. Whether such stimulation activates one or the other of the CN's two major subdivisions is not known. Here, we demonstrate clear response differences from the stimulation of the dorsal (D) vs. ventral (V) subdivisions of the CN in a mouse model of the ABI with a surface-stimulating electrode array. For the DCN, low levels of stimulation evoked multiunit responses in the inferior colliculus (IC) that were unimodally distributed with early latencies (avg. peak latency of 3.3 ms). However, high levels of stimulation evoked a bimodal distribution with the addition of a late latency response peak (avg. peak latency of 7.1 ms). For the VCN, in contrast, electrical stimulation elicited multiunit responses that were usually unimodal and had a latency similar to the DCN's late response. Local field potentials (LFP) from the IC showed components that correlated with early and late multiunit responses. Surgical cuts to sever the output of the DCN, the dorsal acoustic stria (DAS), gave insight into the origin of these early and late responses. Cuts eliminated early responses but had little-to-no effect on late responses. The early responses thus originate from cells that project through the DAS, such as DCN's pyramidal and giant cells. Late responses likely arise from the spread of stimulation from a DCN-placed electrode array to the VCN and could originate in bushy and/or stellate cells. In human ABI users, the spread of stimulation in the CN may result in abnormal response patterns that could hinder performance.

Three-Dimensional Surface Reconstruction of the Human Cochlear Nucleus: Implications for Auditory Brain Stem Implant Design.

Objective The auditory brain stem implant (ABI) is a neuroprosthesis placed on the surface of the cochlear nucleus (CN) to provide hearing sensations in children and adults who are not candidates for cochlear implantation. Contemporary ABI arrays are stiff and do not conform to the curved brain stem surface. Recent advancements in microfabrication techniques have enabled the development of flexible surface arrays, but these have only been applied in animal models. Herein, we measure the surface curvature of the human CN and adjoining regions to assist in the design and placement of next-generation conformable clinical ABI arrays. Three-dimensional (3D) reconstructions from ultrahigh T1-weighted brain magnetic resonance imaging (MRI) sequences and histologic reconstructions based on postmortem adult human brain stem specimens were used. Design This is a retrospective review of radiologic data and postmortem histologic axial sections. Setting This is set at the tertiary referral center. Participants Data were acquired from healthy adults. Main Outcome Measures The main outcome measures are principal curvature values (Kmin and Kmax) and global radius of curvature. Results The CN was successfully extracted and rendered as a 3D surface in all cases. Significant curvatures of the CN in both histologic and radiographic reconstructions were found with global radius of curvature ranging from 2.08 to 8.5 mm. In addition, local curvature analysis revealed that the surface is highly complex. Conclusion Detailed rendering of the human CN is feasible using histology and 3D MRI reconstruction and highlights complex surface topography that is not recapitulated by contemporary stiff ABI arrays.

Effect of anesthesia on evoked auditory responses in pediatric auditory brainstem implant surgery.

OBJECTIVE: Electrically evoked auditory brainstem responses (EABR) guide placement of the multichannel auditory brainstem implant (ABI) array during surgery. EABRs are also recorded under anesthesia in nontumor pediatric ABI recipients prior to device activation to confirm placement and guide device programming. We examine the influence of anesthesia on evoked response morphology in pediatric ABI users by comparing intraoperative with postoperative EABR recordings. STUDY DESIGN: Retrospective review. METHODS: Seven children underwent ABI surgery by way of retrosigmoid craniotomy. General anesthesia included inhaled sevoflurane induction and propofol maintenance during which EABRs were recorded to confirm accurate positioning of the ABI. A mean of 7.7 ± 2.8 weeks following surgery, the ABI was activated under general anesthesia or sedation (dexmedetomidine) and EABR recordings were made. A qualitative analysis of intraoperative and postoperative waveform morphology was performed. RESULTS: Seven subjects (mean age 20.6 months) underwent nine ABI surgeries (seven primary, two revisions) and nine activations. EABRs were observed in eight of nine postoperative recordings. In three cases, intraoperative EABRs during general anesthesia were similar to postoperative EABRs with sedation. In one case, sevoflurane and propofol were used for intra- and postoperative recordings, and waveforms were also similar. In four cases, amplitude and latency changes were observed for intraoperative versus postoperative EABRs. CONCLUSION: Similarity of EABR morphology in the anesthetized versus sedated condition suggests that anesthesia does not have a large effect on far-field evoked potentials. Changes in EABR waveform morphology observed postoperatively may be influenced by other factors such as movements of the surface array. LEVEL OF EVIDENCE: 4 Laryngoscope, 130:507-513, 2020.

Super-resolution Diffusion Tensor Imaging for Delineating the Facial Nerve in Patients with Vestibular Schwannoma.

Objectives Predicting the course of cranial nerves (CNs) VII and VIII in the cerebellopontine angle on preoperative imaging for vestibular schwannoma (VS) may help guide surgical resection and reduce complications. Diffusion magnetic resonance imaging dMRI is commonly used for this purpose, but is limited by its resolution. We investigate the use of super-resolution reconstruction (SRR), where several different dMRIs are combined into one dataset. We hypothesize that SRR improves the visualization of the CN VII and VIII. Design Retrospective case review. Setting Tertiary referral center. SRR was performed on the basis of axial and parasagittal single-shot epiplanar diffusion tensor imaging on a 3.0-tesla MRI scanner. Participants Seventeen adult patients with suspected neoplasms of the lateral skull base. Main Outcome Measures We assessed separability of the two distinct nerves on fractional anisotropy (FA) maps, the tractography of the nerves through the cerebrospinal fluid (CSF), and FA in the CSF as a measure of noise. Results SRR increases separability of the CN VII and VIII (16/17 vs. 0/17, p = 0.008). Mean FA of CSF surrounding the nerves is significantly lower in SRRs (0.07 ± 0.02 vs. 0.13 ± 0.03 [axial images]/0.14 ± 0.05 [parasagittal images], p = 0.00003/ p = 0.00005). Combined scanning times (parasagittal and axial) used for SRR were shorter (8 minute 25 seconds) than a comparable high-resolution scan (15 minute 17 seconds). Conclusion SRR improves the resolution of CN VII and VIII. The technique can be readily applied in the clinical setting, improving surgical counseling and planning in patients with VS.

Microstructured thin-film electrode technology enables proof of concept of scalable, soft auditory brainstem implants.

Auditory brainstem implants (ABIs) provide sound awareness to deaf individuals who are not candidates for the cochlear implant. The ABI electrode array rests on the surface of the cochlear nucleus (CN) in the brainstem and delivers multichannel electrical stimulation. The complex anatomy and physiology of the CN, together with poor spatial selectivity of electrical stimulation and inherent stiffness of contemporary multichannel arrays, leads to only modest auditory outcomes among ABI users. Here, we hypothesized that a soft ABI could enhance biomechanical compatibility with the curved CN surface. We developed implantable ABIs that are compatible with surgical handling, conform to the curvature of the CN after placement, and deliver efficient electrical stimulation. The soft ABI array design relies on precise microstructuring of plastic-metal-plastic multilayers to enable mechanical compliance, patterning, and electrical function. We fabricated soft ABIs to the scale of mouse and human CN and validated them in vitro. Experiments in mice demonstrated that these implants reliably evoked auditory neural activity over 1 month in vivo. Evaluation in human cadaveric models confirmed compatibility after insertion using an endoscopic-assisted craniotomy surgery, ease of array positioning, and robustness and reliability of the soft electrodes. This neurotechnology offers an opportunity to treat deafness in patients who are not candidates for the cochlear implant, and the design and manufacturing principles are broadly applicable to implantable soft bioelectronics throughout the central and peripheral nervous system.

Increasing the expression level of ChR2 enhances the optogenetic excitability of cochlear neurons.

Optogenetics comprise a promising alternative to electrical stimulation for characterization of neural circuits and for the next generation of neural prostheses. Optogenetic stimulation relies on expression of photosensitive microbial proteins in animal cells to initiate a flow of ions into the cells in response to visible light. Here, we generated a novel transgenic mouse model in which we studied the optogenetic activation of spiral ganglion neurons, the primary afferent neurons of the auditory system, and showed a strong optogenetic response, with a similar amplitude as the acoustically evoked response. A twofold increase in the level of channelrhodopsin expression significantly increased the photosensitivity at both the single cell and organismal levels but also partially compromised the native electrophysiological properties of the neurons. The importance of channelrhodopsin expression level to optogenetic stimulation, revealed by these quantitative measurements, will be significant for the characterization of neural circuitry and for the use of optogenetics in neural prostheses.NEW & NOTEWORTHY This study reveals a dose-response relationship between channelrhodopsin expression and optogenetic excitation. Both single cell and organismal responses depend on the expression level of the heterologous protein. Expression level of the opsin is thus an important variable in determining the outcome of an optogenetic experiment. These results are key to the implementation of neural prostheses based on optogenetics, such as next generation cochlear implants, which would use light to elicit a neural response to sound.

Semiautomated Motion Tracking for Objective Skills Assessment in Otologic Surgery: A Pilot Study.

Perioperative teaching and feedback of technical performance are essential during surgical training but are limited by competing demands on faculty time, resident work-hour restrictions, and desire for efficient operating room utilization. The increasing use of high-definition video microscopy and endoscopy in otolaryngology offers opportunities for trainees and faculty to evaluate performance outside the operating room but still requires faculty time. Our hypothesis is that automated motion tracking via video analysis offers a way forward to provide more consistent and objective feedback for surgical trainees. In this study, otolaryngology trainees at various levels were recorded performing a cortical mastoidectomy on cadaveric temporal bones using standard surgical instrumentation and high-definition video cameras coupled to an operating microscope. Videos were postprocessed to automatically track the tip of otologic dissection instruments. Data were analyzed for key metrics potentially applicable to the global rating scale used in the Accreditation Council for Graduate Medical Education's Objective Structured Assessments of Technical Skills.

Auditory Brainstem Implants: Recent Progress and Future Perspectives.

The auditory brainstem implant (ABI) was first developed nearly 40 years ago and provides auditory rehabilitation to patients who are deaf and ineligible for cochlear implant surgery due to abnormalities of the cochlea and cochlear nerve. The aims of the following review are to describe the history of the ABI and innovations leading up to the modern ABI system, as well as highlight areas of future development in implant design.

Initial Experience with 3-Dimensional Exoscope-Assisted Transmastoid and Lateral Skull Base Surgery.

Extracorporeal video microscopes, or "exoscopes," provide high-definition views of the operative field and are alternatives to the operating microscope or loupes for large-corridor surgical approaches. In this proof-of-concept study, we aim to determine the feasibility of 3-dimensional exoscopes as alternatives to operating microscopes in otology and neurotology, espeically in conjunction with endoscopes. Eleven consecutive cases were performed using 3-dimensional exoscopes in place of, or as adjuncts to, the operating microscope. The exoscope was the sole visualization tool in 7 cases, with 4 including the use of an endoscope or microscope. There were no perioperative complications. Potential subjective advantages include superior ergonomics, compact size, and an equal visual experience for surgeons and observers. Limitations include low lighting in small surgical corridors and pixilation at high magnification. Exoscopes are potentially viable alternatives to the microscope in otologic and neurotologic surgery.

Utility of intraoral ultrasound in managing oral tongue squamous cell carcinoma: Systematic review.

OBJECTIVES/HYPOTHESIS: Adequate surgical resection of early stage oral tongue cancer provides the best chance at preventing locoregional disease recurrence. Determination of tumor dimensions and margin location is challenging and can lead to inadequate resections with close/positive margins. Ultrasonography has proven its utility in determining the thickness and extent of tongue tumors. Preoperative tumor dimension measurements carry increased significance with the addition of depth of invasion (DOI) to the eighth edition of the American Joint Committee on Cancer (AJCC) TNM staging system. We report the results of a systematic review of the literature pertaining to the use of ultrasound in the diagnosis and management of oral tongue carcinoma. METHODS: The Preferred Reporting Items for Systematic Reviews and Meta-analysis statement checklist was used to inform the design of this systematic review. All studies that utilized ultrasound in the diagnosis/management of primary carcinoma of the oral tongue were included. PubMed, Embase, and Cochrane were reviewed to identify eligible studies. RESULTS: Nineteen articles were included in our analysis. Six hundred seventy-eight patients were studied in the articles included. Ultrasound tumor thickness measurements correlate well with those on histopathology and show promise as a predictor of cervical lymph node metastasis. Ultrasound can be safely used intraoperatively for deep margin assessment. CONCLUSIONS: Ultrasound is useful in the evaluation of oral tongue malignancies. More experience is needed to determine if it is reliable in determining preoperative DOI in light of the role this tumor parameter plays in the eighth edition of the AJCC staging manual. Laryngoscope, 129:662-670, 2019.

Ancestral Adeno-Associated Virus Vector Delivery of Opsins to Spiral Ganglion Neurons: Implications for Optogenetic Cochlear Implants.

Optogenetics is a transformative technology based on light-sensitive microbial proteins, known as opsins, that enable precise modulation of neuronal activity with pulsed radiant energy. Optogenetics has been proposed as a means to improve auditory implant outcomes by reducing channel interaction and increasing electrode density, but the introduction of opsins into cochlear spiral ganglion neurons (SGNs) in vivo has been challenging. Here we test opsin delivery using a synthetically developed ancestral adeno-associated virus (AAV) vector called Anc80L65. Wild-type C57BL/6 mouse pups were injected via the round window of cochlea with Anc80L65 carrying opsin Chronos under the control of a CAG promoter. Following an incubation of 6-22 weeks, pulsed blue light was delivered to cochlear SGNs via a cochleosotomy approach and flexible optical fiber. Optically evoked auditory brainstem responses (oABRs) and multiunit activity in inferior colliculus (IC) were observed. Post-experiment cochlear histology demonstrated opsin expression in SGNs (mean = 74%), with an even distribution of opsin along the cochlear basal/apical gradient. This study is the first to describe robust SGN transduction, opsin expression, and optically evoked auditory electrophysiology in neonatal mice. Ultimately, this work may provide the basis for a new generation of cochlear implant based on light.

Diffusion Tensor Imaging of Central Auditory Pathways in Patients with Sensorineural Hearing Loss: A Systematic Review.

Objective The radiologic evaluation of patients with hearing loss includes computed tomography and magnetic resonance imaging (MRI) to highlight temporal bone and cochlear nerve anatomy. The central auditory pathways are often not studied for routine clinical evaluation. Diffusion tensor imaging (DTI) is an emerging MRI-based modality that can reveal microstructural changes in white matter. In this systematic review, we summarize the value of DTI in the detection of structural changes of the central auditory pathways in patients with sensorineural hearing loss. Data Sources PubMed, Embase, and Cochrane. Review Methods We used the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement checklist for study design. All studies that included at least 1 sensorineural hearing loss patient with DTI outcome data were included. Results After inclusion and exclusion criteria were met, 20 articles were analyzed. Patients with bilateral hearing loss comprised 60.8% of all subjects. Patients with unilateral or progressive hearing loss and tinnitus made up the remaining studies. The auditory cortex and inferior colliculus (IC) were the most commonly studied regions using DTI, and most cases were found to have changes in diffusion metrics, such as fractional anisotropy, compared to normal hearing controls. Detectable changes in other auditory regions were reported, but there was a higher degree of variability. Conclusion White matter changes based on DTI metrics can be seen in patients with sensorineural hearing loss, but studies are few in number with modest sample sizes. Further standardization of DTI using a prospective study design with larger sample sizes is needed.

Toward Optimizing Cervical Vestibular Evoked Myogenic Potentials (cVEMP): Combining Air-Bone Gap and cVEMP Thresholds to Improve Diagnosis of Superior Canal Dehiscence.

OBJECTIVE: To develop a novel approach combining low-frequency air-bone gap (ABG) and cervical vestibular evoked myogenic potential (cVEMP) thresholds to improve screening for superior canal dehiscence (SCD) syndrome. STUDY DESIGN: Retrospective study. SETTING: Tertiary care center. PATIENTS: One hundred forty patients with SCD and 21 healthy age-matched controls were included. Ears for each patient were divided into three groups based on computed tomography (CT) findings: 1) dehiscent, 2) thin, or 3) unaffected. MAIN OUTCOME MEASURES: cVEMP and audiometric thresholds were analyzed and differences among groups were evaluated. RESULTS: We define the third window indicator (TWI) as the cVEMP thresholds at 500, 750, and 1000 Hz adjusted for the ABG at 250 Hz (i.e., subtracting ABG from cVEMP threshold). The TWI differentiates between dehiscent and nondehiscent control ears with a sensitivity of 82% and specificity of 100%, corresponding to a positive predictive value of 100%. ABGs and cVEMP thresholds were similar for healthy controls and patients with thin bone over the superior canal. CONCLUSION: This is the largest study to date examining the usefulness of cVEMPs in the diagnosis of SCD. Our "third window indicator" (TWI) combines cVEMP thresholds with the ABG at 250 Hz to improve the ability to screen patients with SCD symptoms.

Quantitative imaging analysis of transcanal endoscopic Infracochlear approach to the internal auditory canal.

PURPOSE: A transcanal endoscopic infracochlear surgical approach to the internal auditory canal (IAC) in a human temporal bone model has previously been described. However, the proportion of patients with favorable anatomy for this novel surgical technique remains unknown. Herein, we perform a quantitative analysis of the transcanal endoscopic infracochlear corridor to the IAC based on computed tomography. MATERIALS AND METHODS: High resolution computed tomography scans of adult temporal bones were measured to determine the accessibility of the IAC when using an endoscopic transcanal, cochlear-sparing surgical corridor. RESULTS: This approach to the IAC was feasible in 92% (35 of 38) specimens based on a minimum distance of 3mm between the basilar turn of the cochlear and the great vessels (jugular bulb and carotid artery). CONCLUSIONS: Infracochlear access to the IAC is feasible in the majority of adult temporal bones and has implications for future hearing preservation drug delivery approaches to the IAC.

Improvement in word recognition following treatment failure for sudden sensorineural hearing loss.

OBJECTIVES: Patients with sudden sensorineural hearing loss (SSNHL) may have word recognition scores (WRS) that correlate with pure tone average (PTA). We hypothesize that there is a subset of patients with SSNHL who have improved WRS despite stable PTA. METHODS: Retrospective case review at a tertiary otolaryngology practice. RESULTS: We identified 13 of 113 patients with SSNHL whose WRS increased despite overall stable pure tone averages. There was an observed average improvement in WRS by 23.8 points in this patient cohort at follow-up, with mean initial PTA in the affected ear at 48.7 dB. CONCLUSIONS: We identify a novel cohort of SSNHL patients that have failed treatment as measured by PTA, but who have increased WRS over time. These data have implications for patient counseling and lend insight into the pathophysiology of SSNHL.

Endoscopic transsphenoidal surgery of Rathke's cleft cyst.

Rathke's cleft cysts (RCC) are benign lesions that originate from remnants of Rathke's pouch. They can compress adjacent structures causing visual loss and endocrine dysfunction. The endoscopic endonasal transsphenoidal approach (EETA) has gained popularity in the surgical management of pituitary and parasellar tumors. However, postoperative cyst recurrence and endocrine dysfunction are still major concerns. A retrospective chart review was performed on 11 patients who underwent a purely EETA. Subtotal resection of the cyst wall with drainage of the intracystic contents followed by obliteration of the cyst with a fat graft was performed in all patients. Two patients underwent repeated surgeries for symptomatic cyst recurrence. One patient ultimately underwent extracapsular removal of the entire cyst wall because of multiple recurrences after simple drainage. There were no incidences of new permanent hypopituitarism, visual deficits, or postoperative cerebrospinal fluid leaks. All patients reported an improvement of initial preoperative symptoms. A non-aggressive strategy of partial cyst wall removal and simple drainage of cyst contents via EETA is a viable approach for surgical treatment of RCC with a low rate of postoperative endocrine and visual complications. A more aggressive strategy of extracapsular removal of the cyst wall may be indicated in patients with repeated recurrence.

Transillumination-guided endoscopic endonasal dacryocystorhinostomy: approach to revision cases and challenging anatomy.

Dacryocystorhinostomy (DCR) is a surgical procedure in which a connection is established between the lacrimal sac and the nasal cavity in an effort to bypass an obstruction of the distal lacrimal apparatus. Endoscopic endonasal DCR (EEDCR) is a minimally invasive technique used to achieve this goal. In patients with altered anatomy, EEDCR can be challenging. Here, we describe the use of canalicular transillumination with EEDCR in three cases, and discuss the benefits of this technique.

Do AAO-HNSF CORE Grants Predict Future NIH Funding Success?

OBJECTIVE: To determine (1) whether academic otolaryngologists who have received an American Academy of Otolaryngology- Head and Neck Surgery Foundation (AAO-HNSF) Centralized Otolaryngology Research Efforts (CORE) grant are more likely to procure future National Institutes of Health (NIH) funding; (2) whether CORE grants or NIH Career Development (K) awards have a stronger association with scholarly impact. STUDY DESIGN AND SETTING: Historical cohort. METHODS: Scholarly impact, as measured by the h-index, publication experience, and prior grant history, were determined for CORE-funded and non-CORE-funded academic otolaryngologists. All individuals were assessed for NIH funding history. RESULTS: Of 192 academic otolaryngologists with a CORE funding history, 39.6% had active or prior NIH awards versus 15.1% of 1002 non-CORE-funded faculty (P < .0001). Higher proportions of CORE-funded otolaryngologists have received K-series and R-series grants from the NIH (P-values < .05). K-grant recipients had higher h-indices than CORE recipients (12.6 vs 7.1, P < .01). Upon controlling for rank and experience, this difference remained significant among junior faculty. CONCLUSIONS: A higher proportion of academic otolaryngologists with prior AAO-HNSF CORE funding have received NIH funding relative to their non-CORE-funded peers, suggesting that the CORE program may be successful in its stated goals of preparing individuals for the NIH peer review process, although further prospective study is needed to evaluate a "cause and effect" relationship. Individuals with current or prior NIH K-grants had greater research productivity than those with CORE funding history. Both cohorts had higher scholarly impact values than previously published figures among academic otolaryngologists, highlighting that both CORE grants and NIH K-grants awards are effective career development resources.

Demographics and survival trends of sinonasal adenocarcinoma from 1973 to 2009.

BACKGROUND: The purpose of this work was to study the demographics and survival of patients diagnosed with sinonasal adenocarcinoma (SNAC) within the time period of 1973 to 2009 using the Surveillance, Epidemiology, and End Result (SEER) database. METHODS: A retrospective cohort study using the U.S. National Cancer Institute's SEER registry was performed to study the demographics and survival for SNAC from 1973 to 2009. Analysis was conducted based on race, gender, and stage. RESULTS: In total, 1270 cases of SNAC were analyzed for demographics and survival. Males accounted for 51.6% of cases, while females accounted for 48.4% of cases, amounting to a male to female ratio of 1.06:1.00. Disease specific survival at 5, 10, 15, and 20 years was 65.2%, 50.9%, 40.9%, and 36.5%, respectively. When analyzed by gender, females had higher survival than males, although this difference was not statistically significant. When analyzed by race, the category of other, which encompasses American Indian, Asian, Hispanic, and unknown or unspecified race, was shown to have the best survival, followed by whites and blacks, respectively. CONCLUSION: SNAC is a rare tumor classically associated with occupational exposure and carries a variable prognosis. This is the first dedicated large-scale, retrospective analysis of a North American SNAC population. SNAC appears to affect both males and females equally and predominantly affects whites. Patients categorized as other had significantly better survival outcomes, while gender appeared to have no significant effect on survival.