Understanding the nervous system: lessons from Frontiers in Neurophotonics.

The Frontiers in Neurophotonics Symposium is a biennial event that brings together neurobiologists and physicists/engineers who share interest in the development of leading-edge photonics-based approaches to understand and manipulate the nervous system, from its individual molecular components to complex networks in the intact brain. In this Community paper, we highlight several topics that have been featured at the symposium that took place in October 2022 in Québec City, Canada.

Evidence-based perioperative opioid-sparing techniques during the United States opioid crisis.

PURPOSE OF REVIEW: The current United States opioid epidemic resulted from the overprescribing of opioids by physicians and surgeons in response to deceptive and unlawful marketing campaigns by pharmaceutical companies seeking to profit from opioid sales. Surgeons have a moral obligation to employ evidence-based opioid-sparing analgesia protocols for management of perioperative pain. RECENT FINDINGS: Recent evidence strongly supports the use of NSAIDs in perioperative pain management, with large studies demonstrating no increased risk of postoperative hemorrhage or renal insult. SUMMARY: We present an evidence-based approach for opioid-sparing perioperative pain management, including multimodal analgesia guidelines used at our center for patients undergoing free flap facial reanimation procedures.

Tutorial: multiphoton microscopy to advance neuroscience research.

Multiphoton microscopy (MPM) employs ultrafast infrared lasers for high-resolution deep three-dimensional imaging of live biological samples. The goal of this tutorial is to provide a practical guide to MPM imaging for novice microscopy developers and life-science users. Principles of MPM, microscope setup, and labeling strategies are discussed. Use of MPM to achieve unprecedented imaging depth of whole mounted explants and intravital imaging via implantable glass windows of the mammalian nervous system is demonstrated.

Effective Strategies to Patent Plastic Surgery Ideas and Intellectual Property.

SUMMARY: Patents are of great importance to plastic surgery, a field fueled by constant innovation. Familiarity with the patent process could promote further innovation by plastic surgeons. By granting proprietary rights to inventors in exchange for publication of their inventions, patents incentivize creativity and innovation while promoting diffusion and transfer of technology. The task of securing patent protection, however, is complex, and begins well before the patent application. Inventors must familiarize themselves with regulations to ensure that their inventions satisfy the criteria for patentability, which can differ among countries. Patents regarding surgical methods should undergo additional ethical deliberation given their potential interference with medical altruism. The patent application must be devised and written thoroughly, as it needs to withstand meticulous examination by patent offices and potential third-party opposition, and professional assistance in doing so should be sought. Filing of the application calls for intricate procedural and timing requirements that bear major benefits if well understood and respected by applicants. Given that patent rights only cover the issuing country's territorial scope, further endeavors must be pursued when seeking patent protection in additional countries. In this regard, two options exist, and the ultimate decision should be tailored to each inventor's personal needs. At every step of the patenting process, financial readiness is key because costs can be unpredictable and escalate quickly. In this article, the authors propose effective strategies directed at plastic surgeons to facilitate patenting of their ideas and protection of their intellectual property.

Health Utility Measures Among Patients with Androgenetic Alopecia After Hair Transplant.

BACKGROUND: Hair loss causes significant psychosocial distress to patients. Health utility measurements offer an objective, quantitative assessment of health-related quality of life (QOL). METHODS: We performed a prospective cohort study on patients with hair loss between January 1, 2018 and December 31, 2020. Patient metrics were compared with layperson perception of alopecia, prospectively collected between August 1 and December 31, 2017. Health utility measures were quantified using the visual analog scale (VAS), standard gamble (SG), and time trade-off (TTO) in quality-adjusted life-years (QALYs) and relative to the minimal clinically important difference (MCID). Bonferroni correction to the significance threshold was performed. RESULTS: Thirty-one patients with alopecia were compared with 237 laypeople. Patient metrics for female hair loss were all significantly lower than laypeople measures (VAS QALYs 0.65 ± 0.21 vs. 0.83 ± 0.18, p = 0.0001). Mean SG QALYs were lower for patients in the male alopecia state (0.86 ± 0.23 vs. 0.96 ± 0.12, p = 0.0278). Post-hair transplant improvement in TTO was significantly greater for patients (+ 0.08 ± 0.12 vs. + 0.02 ± 0.09, p = 0.0070) and significantly more often exceeded the MCID (45.2% vs. 16.9%, p = 0.0006). CONCLUSIONS: Alopecia negatively impacts QOL, and the true patient experience is more taxing than what is perceived by laypeople. Hair transplantation improves QOL more for male patients than common perception. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Lower Eyelid Sling for Primary and Revision Correction of Paralytic Lagophthalmos.

Background: Lateral tarsal techniques alone for lower eyelid correction in paralytic lagophthalmos may yield suboptimal outcomes. Objective: To describe a lower eyelid sling technique for primary and revision correction of lower eyelid ptosis and ectropion and evaluate outcomes as measured by margin reflex distance 2 (MRD2). Methods: A retrospective review of patients with long-standing unilateral paralytic lagophthalmos who underwent primary or revision lower eyelid ptosis correction by sling suspension between January 2016 and August 2020 at a tertiary medical center was performed. Surgical technique is illustrated with video and technical considerations are discussed. Pre- and postoperative MRD2 values were quantified from databased photographs. Results: Thirty-eight patients were included. Eighteen patients had undergone prior procedures for ptosis correction. Lower eyelid symmetry and paralyzed side MRD2 significantly improved after lower lid sling for primary and revision cases (p < 0.05), and improvement was sustained over the study period (mean follow-up duration 13.3 months, range 1-33 months). No postoperative complications occurred. Conclusion: Lower eyelid sling yielded safe, effective, and durable correction of lower eyelid position in a cohort of patients with paralytic lagophthalmos.

Lower Eyelid Management in Facial Paralysis.

Correction of lower eyelid retraction is necessary to restore adequate blink in paralytic lagophthalmos. A plethora of static and dynamic surgical techniques have been described for lower eyelid repositioning. This article provides an approach to management of the paralytic lower eyelid, including a summary of existing techniques, case examples, and surgical technique for in-office lower eyelid suspension using a palmaris longus tendon graft.

Predictive Outcomes of Deep Learning Measurement of the Anterior Glottic Angle in Bilateral Vocal Fold Immobility.

OBJECTIVE: (1) To compare maximum glottic opening angle (anterior glottic angle, AGA) in patients with bilateral vocal fold immobility (BVFI), unilateral vocal fold immobility (UVFI) and normal larynges (NL), and (2) to correlate maximum AGA with patient-reported outcome measures. METHODS: Patients wisth BVFI, UVFI, and NL were retrospectively studied. An open-source deep learning-based computer vision tool for vocal fold tracking was used to analyze videolaryngoscopy. Minimum and maximum AGA were calculated and correlated with three patient-reported outcomes measures. RESULTS: Two hundred and fourteen patients were included. Mean maximum AGA was 29.91° (14.40° SD), 42.59° (12.37° SD), and 57.08° (11.14° SD) in BVFI (N = 70), UVFI (N = 70), and NL (N = 72) groups, respectively (p < 0.001). Patients requiring operative airway intervention for BVFI had an average maximum AGA of 24.94° (10.66° SD), statistically different from those not requiring intervention (p = 0.0001). There was moderate negative correlation between Dyspnea Index scores and AGA (Spearman r = -0.345, p = 0.0003). Maximum AGA demonstrated high discriminatory ability for BVFI diagnosis (AUC 0.92, 95% CI 0.81-0.97, p < 0.001) and moderate ability to predict need for operative airway intervention (AUC 0.77, 95% CI 0.64-0.89, p < 0.001). CONCLUSIONS: A computer vision tool for quantitative assessment of the AGA from videolaryngoscopy demonstrated ability to discriminate between patients with BVFI, UVFI, and normal controls and predict need for operative airway intervention. This tool may be useful for assessment of other neurological laryngeal conditions and may help guide decision-making in laryngeal surgery. LEVEL OF EVIDENCE: III Laryngoscope, 133:2285-2291, 2023.

Super-resolved fluorescence imaging of peripheral nerve.

Traditional histopathologic evaluation of peripheral nerve employs brightfield microscopy with diffraction limited resolution of ~ 250 nm. Though electron microscopy yields nanoscale resolution of the nervous system, sample preparation is costly and the technique is incompatible with living samples. Super-resolution microscopy (SRM) comprises a set of imaging techniques that permit nanoscale resolution of fluorescent objects using visible light. The advent of SRM has transformed biomedical science in establishing non-toxic means for investigation of nanoscale cellular structures. Herein, sciatic nerve sections from GFP-variant expressing mice, and regenerating human nerve from cross-facial autografts labelled with a myelin-specific fluorescent dye were imaged by super-resolution radial fluctuation microscopy, stimulated emission depletion microscopy, and structured illumination microscopy. Super-resolution imaging of axial cryosections of murine sciatic nerves yielded robust visualization myelinated and unmyelinated axons. Super-resolution imaging of axial cryosections of human cross-facial nerve grafts demonstrated enhanced resolution of small-caliber thinly-myelinated regenerating motor axons. Resolution and contrast enhancement afforded by super-resolution imaging techniques enables visualization of unmyelinated axons, regenerating axons, cytoskeleton ultrastructure, and neuronal appendages of mammalian peripheral nerves using light microscopes.

The Tinel Sign and Myelinated Axons in the Cross-Face Nerve Graft: Predictors of Smile Reanimation Outcome for Free Gracilis Muscle Transfer?

Introduction: During a two-stage free gracilis muscle transfer (FGMT) to restore smile to patients with facial paralysis, some surgeons assess nerve regeneration through the cross-face nerve graft (CFNG) with the Tinel sign and a nerve biopsy. Objective: To test whether ultimate smile reanimation outcomes are correlated with (1) the Tinel sign or (2) myelinated axons of the biopsied CFNG at the time of FGMT. Methods: Retrospective case series was performed at a tertiary care facial nerve center. Dynamic smile outcomes were quantified with Emotrics analysis of pre- and postoperative photographs. Results: Of the 113 FGMT surgeries by CFNG performed since 2002, 92 patients had pre- and postoperative photo-documentation. Most patients (89%, N = 82) had a positive Tinel sign at the time of FGMT; however, 14 patients with positive Tinel signs were deemed failures. Interestingly, 4 patients with a negative Tinel sign went on to have successful dynamic outcomes and 16 patients lacking myelinated axons in their CFNG biopsy ultimately achieved successful smile outcomes. Conclusion: Although the majority of patients had a positive Tinel sign and myelinated axons in the CFNG at the time of FGMT, the presence or absence of either factor did not predict ultimate smile outcome in this series.

Multiphoton microscopy for label-free multicolor imaging of peripheral nerve.

SIGNIFICANCE: Means for quantitation of myelinated fibers in peripheral nerve may guide diagnosis and clinical decision making in management of peripheral nerve disorders. Multiphoton microscopy techniques such as the third-harmonic generation enable label-free in vivo imaging of peripheral nerves. AIM: Develop a multiphoton microscope based on a custom high-power infrared fiber laser for label-free imaging of peripheral nerve. APPROACH: A cost-effective multiphoton microscope employing a single fiber laser source at 1300 nm was designed and used for stain-free multicolor imaging of murine and human peripheral nerve. RESULTS: Second-harmonic generation signal from collagen centered about 650-nm delineated neural connective tissue, whereas third-harmonic general signal centered about 433-nm delineated myelin and other lipids. In sciatic nerve from transgenic reporter mice expressing yellow fluorescent protein within peripheral neurons, three-photon-excitation with emission peak at 527-nm delineated axoplasm. The signal obtained from unlabeled axially sectioned samples was adequate for segmentation of myelinated fibers using commercial image processing software. In unlabeled whole mount specimens, imaging depths over 100-µm were achieved. CONCLUSIONS: A multiphoton microscope powered by a fiber laser enables stain-free histomorphometry of mammalian peripheral nerve. The simplicity of the microscope design carries potential for clinical translation to inform decision making in peripheral nerve disorders.

Automated Spontaneity Assessment after Smile Reanimation: A Machine Learning Approach.

BACKGROUND: Recreation of a spontaneous, emotional smile remains a paramount goal of smile reanimation surgery. However, optimal techniques to reliably restore spontaneity remain unknown. Dual automated machine-learning tools were used to develop an objective tool to analyze spontaneous smiling. The feasibility of this tool was tested in a sample of functional free muscle transfers. METHODS: Validated humorous videos were used to elicit spontaneous smiles. Automated facial landmark recognition (Emotrics) and emotion detection software (Affdex) were used to analyze video clips of spontaneous smiling in nine normal subjects and 39 facial reanimation cases. Emotionality quotient was used to quantify the ability of spontaneous smiles to express joy. RESULTS: The software could analyze spontaneous smiling in all subjects. Spontaneous smiles of normal subjects exhibited median 100 percent joy and 0 percent negative emotion (emotional quotient score, +100/0). Spontaneous smiles of facial palsy patients after smile reanimation, using cross-facial nerve graft, masseteric nerve, and dual innervation, yielded median emotional quotient scores of +82/0, 0/-48, and +10/-24 respectively (joy, p = 0.006; negative emotion, p = 0.034). CONCLUSIONS: Computer vision software can objectively quantify spontaneous smiling outcomes. Of the retrospective sample of cases reviewed in this study, cross-facial nerve graft-innervated gracilis functional free muscle transfer achieved a greater degree of emotionality during spontaneous smiling than masseteric or dually innervated transfer. Quantification of spontaneous smiling from standard video clips could facilitate future, blinded, multicenter trials with sufficient long-term follow-up to definitively establish the rates of spontaneity from a range of reanimation procedures. CLINICAL QUESTION/LEVEL OF EVIDENCE: Diagnostic, IV.

Automated stain-free histomorphometry of peripheral nerve by contrast-enhancing techniques and artificial intelligence.

BACKGROUND: Traditional histopathologic evaluation of peripheral nerve using brightfield microscopy is resource-intensive, necessitating complex sample preparation. Label-free imaging techniques paired with artificial intelligence-based image reconstruction and segmentation may facilitate peripheral nerve histomorphometry. NEW METHOD: Herein, the utility of label-free phase contrast techniques paired with artificial intelligence-based image processing for imaging of mammalian peripheral nerve is demonstrated. RESULTS: Fresh frozen murine sciatic nerve sections were imaged in transmission modalities using differential interference and phase contrast microscopy and in epifluorescent modality following staining with myelin-specific dye. Deep learning was employed to predict epifluorescent images from transmitted phase contrast images, and machine learning employed for automated segmentation of myelinated axons for reporting of axons counts and g-ratios. COMPARISON WITH EXISTING METHODS: Conventional peripheral nerve histomorphometry employs resource intensive resin embedding, ultra-microtome sectioning, and staining steps. Herein we demonstrate feasibility of high-throughput nerve histomorphometry via label-free phase contrast imaging of frozen sections. CONCLUSIONS: Clinical applications of label-free phase contrast microscopy paired with deep learning algorithms are discussed.

Facial Palsy, Radiographic and Other Workup Negative: FROWN.

OBJECTIVES: Slow-onset peripheral facial palsy is far less common than acute-onset peripheral facial palsy and necessitates diagnostic evaluation for benign or malignant tumors or other less common etiologies. In the rare scenario in which no clarifying etiology is discovered following long-term evaluation (no radiographic or hematologic abnormalities and an otherwise unremarkable evaluation), a diagnostic and management dilemma occurs. We present a series of patients with this possible new clinical entity: Facial palsy, Radiographic and Other Workup Negative (FROWN) and propose a management strategy for this diagnosis of exclusion. METHODS: A series of 3,849 patients presenting with facial palsy to a tertiary facial nerve center was retrospectively assessed to identify those with progressive loss of facial function over at least 1 month. Exclusion criteria were history, physical or hematologic findings indicative of known diseases associated with facial palsy, and radiographic studies demonstrating a benign or malignant tumor. RESULTS: Patients with slow-onset facial palsy constituted 5% (190 patients) of the cohort and were ultimately diagnosed with either a benign or malignant neoplasm or other facial nerve pathology. Fourteen patients with slow-onset facial palsy remained without a diagnosis following long-term evaluation and serial imaging. Eleven patients underwent dynamic facial reanimation surgery and facial nerve and muscle biopsy, with no clear histopathologic diagnosis. CONCLUSION: Patients with slow-onset facial palsy with negative radiographic and medical evaluations over several years may be characterized as having FROWN, an idiopathic and as yet poorly understood condition, which appears to be amenable to facial reanimation but requires further investigation as to its pathophysiology.

Two-photon excitation fluorescent spectral and decay properties of retrograde neuronal tracer Fluoro-Gold.

Fluoro-Gold is a fluorescent neuronal tracer suitable for targeted deep imaging of the nervous system. Widefield fluorescence microscopy enables visualization of Fluoro-Gold, but lacks depth discrimination. Though scanning laser confocal microscopy yields volumetric data, imaging depth is limited, and optimal single-photon excitation of Fluoro-Gold requires an unconventional ultraviolet excitation line. Two-photon excitation microscopy employs ultrafast pulsed infrared lasers to image fluorophores at high-resolution at unparalleled depths in opaque tissue. Deep imaging of Fluoro-Gold-labeled neurons carries potential to advance understanding of the central and peripheral nervous systems, yet its two-photon spectral and temporal properties remain uncharacterized. Herein, we report the two-photon excitation spectrum of Fluoro-Gold between 720 and 990 nm, and its fluorescence decay rate in aqueous solution and murine brainstem tissue. We demonstrate unprecedented imaging depth of whole-mounted murine brainstem via two-photon excitation microscopy of Fluoro-Gold labeled facial motor nuclei. Optimal two-photon excitation of Fluoro-Gold within microscope tuning range occurred at 720 nm, while maximum lifetime contrast was observed at 760 nm with mean fluorescence lifetime of 1.4 ns. Whole-mount brainstem explants were readily imaged to depths in excess of 450 µm via immersion in refractive-index matching solution.

Neurotization Preferences in Smile Reanimation: A Discrete Choice Experiment.

BACKGROUND: Common donor nerve options in smile reanimation include ipsilateral trigeminal motor or contralateral facial nerve branches. Neurotization preference may be influenced by multiple factors, whose relative importance remains poorly understood. In this article, decision-making in smile reanimation is assessed using a stated preference model. METHODS: Qualitative interviews with facial palsy patients identified five relevant attributes for study: smile type ("smile when biting" versus "smile spontaneously" as proxies for trigeminal versus cross-facial neurotization), number of operations, success rates, complication rates, and side effects. Community volunteers (n = 250) completed a discrete-choice experiment relevant to free muscle transfer for smile reanimation. Preoperative and postoperative states were demonstrated through video vignettes, together with explanation of surgical risks, consequences, and benefits. Attribute importance was modeled using hierarchical Bayes estimation. RESULTS: Two hundred forty-one responses met quality controls. Attribute importance ranked as follows: chance of success, 37.3 percent; smile type, 21.4 percent; side effects, 13.9 percent; complication rates, 13.8; and number of operations, 13.6 percent. All attributes significantly correlated with decision making (p < 0.0001). An aggregate response model revealed most participants (67.6 percent; standard error, 3.0 percent) preferred smile reanimation by cross-facial (assuming a success rate of 80 percent) as opposed to ipsilateral trigeminal motor branch neurotization. When the success rate for cross-facial neurotization was reduced below 67 percent, trigeminal neurotization was preferred. CONCLUSIONS: Despite a higher risk of failure, most respondents preferred a cross-facial as opposed to trigeminal neurotization strategy for smile reanimation. These findings highlight the complexity of decision-making and need for individualized risk tolerance assessment in the field of facial reanimation.

Corneal and Facial Sensory Neurotization in Trigeminal Anesthesia.

Trigeminal anesthesia may yield blindness and facial disfigurement, secondary to neurotrophic keratopathy and trigeminal trophic syndrome. This article summarizes contemporary medical and emerging surgical approaches for the therapeutic management of this rare and devastating disease state.

Seeing through the evidence for corneal neurotization.

PURPOSE OF REVIEW: Trigeminal anesthesia causes neurotrophic keratopathy, which may yield facial disfigurement and corneal blindness. RECENT FINDINGS: We summarize approaches and evidence for corneal neurotization. SUMMARY: Regional sensory nerve transfer appears safe and effective for therapeutic management of neurotrophic keratopathy. Prospective randomized clinical trials are necessary to confirm the utility of corneal neurotization.