Nerve spectroscopy: understanding peripheral nerve autofluorescence through photodynamics

High-Precision Identification of Sensory and Motor Branches of the Recurrent Laryngeal Nerve Via Autofluorescence System in Thyroid Surgery

Recurrent laryngeal nerve (RLN) injury is a critical complication in thyroidectomy, with the severe sequelae of operation-related vocal cord palsies. The primary therapy following RLN injury includes voice therapy and surgical reintervention, both of which render subpar results paired with a long road to recovery. Despite the development of technical measures to prevent inadvertent operational injury of the RLN, its occurrence is still a concern. A newly developed handheld device with nerve autofluorescence technology has emerged as a visual aid tool for the intraoperative identification of nervous anatomical landmarks in thyroid surgery, showcasing promising initial findings. This study evaluates the efficacy of the aforementioned device in the intraoperative identification and differentiation of sensory and motor branches of the RLN. Sixteen patients undergoing thyroid surgery were included in this study, of which 16 RLNs and its branches were examined. Basic demographics, indication for thyroid surgery, and postoperative outcomes were identified. Multiple intraoperative images were analyzed through image processing software programs for the total number of nerves and branches, type of branch (e.g., sensory versus motor branches), near-ultraviolet (NUV) light intensity emitted by the nerve structures, and length and angular aperture of branches. The ability to prevent operation-related RLN injury was clinically evaluated at postoperative follow-up. Following analyses, no significant difference was observed between NUV light intensity (p=0.70) or structural length (p=0.18) between sensory and motor nerve branches of the RLN. This was further confirmed by fast Fourier transform (FFT) analyses and three-dimensional surface plots. No partial or total vocal cord palsies were recorded in the perioperative period, thus confirming the accuracy for intraoperative identification of the RLN and the preservation of structural integrity irrespective of surgical technique or type of branch (sensory or motor). Altogether, these findings highlight the potential of autofluorescence technology to enhance surgical precision, improve nerve preservation, and reduce the risk of nerve injury via safe surgical navigation in comparison to current intraoperative neuromonitoring systems limited to motor branch detection.

Multiphoton Microscopy to Visualize Live Renal Nerves in Reanimated Kidney Blocks

Renal denervation to treat arterial hypertension is growing in adoption but still shows inconsistent results. Device improvement is difficult, as there is currently no way to study the immediate success of renal denervation devices in living tissue. In an effort to visualize live renal nerves surrounding their arteries using multiphoton microscopy, kidney pairs were explanted from Yorkshire pigs. They were maintained viable with a pulsatile perfusion apparatus using Visible Kidney™ methodologies, in which blood is replaced by a modified, oxygenated, and warmed (37 °C) Krebs-Henseleit buffer. The block resection allows catheter placement for nerve ablation treatment. Subsequently, the kidney block was disconnected from the perfusion system and underwent multiphoton microscopy (Nikon A1R 1024 MP). A total of three renal blocks were imaged using this model. Using 780 nm excitation for autofluorescence, we were able to selectively image peri-arterial nerves (2.5-23 μm diameter) alongside arteriolar elastin fibers (1.96 ± 0.87 μm; range: 0.3-4.27) at 25× magnification at a pixel size of 1.02 µm). Autofluoresecence was not strong enough to identify nerves at 4× magnification. There was a high but variable signal-to-noise ratio of 52.3 (median, IQR 159). This model may be useful for improving future physician training and innovations in renal denervation technologies.

Fluorescence-guided inguinal hernia repair with heightened nerve visualization to prevent chronic post-operative inguinal pain: Case report

INTRODUCTION

Iatrogenic injury to the ilioinguinal nerve and its branches during anterior inguinal hernia repair is a cause of chronic inguinal pain in up to 12 % of patients undergoing this operation. The risk of nerve injury is high, given the nerves' relatively small caliber and strictly-confined space through which they pass. In the current report, we describe using a novel fluorescence imaging system developed to detect nerve autofluorescence in a 66-year-old man who presented with a left-sided Type II inguinal hernia and underwent inguinal hernioplasty.

CASE PRESENTATION

Under general anesthesia, a left inguinal hernioplasty with mesh was performed using the Lichtenstein technique through an anterior approach. During surgery, a Dendrite® Imaging camera (Dendrite® Imaging, Germany) was employed to allow the surgical team to alternate freely between standard operating room (white) light and near-ultraviolet light (NUVL), specifically to enhance visualization of the ilioinguinal nerve and its branches. Under white light, neither the ilioinguinal nerve nor any of its branches were clearly visible. However, under NUVL, all fluoresced brightly and were easily avoided throughout the course of the hernia repair. The operation proceeded with no intraoperative or postoperative complications.

DISCUSSION

In this case, autofluorescence of the ilioinguinal nerve and its branches under NUVL utilizing a novel, hand-held fluorescent camera during hernia repair aided in their visualization and appeared to help prevent nerve injury.

CONCLUSION

New intraoperative technology that allows nerves to auto-fluoresce intra-operatively under NUVL warrants larger series and comparative trials to evaluate its efficacy at reducing iatrogenic nerve injury during inguinal hernioplasties.

Thyroid surgery under nerve auto-fluorescence & artificial intelligence tissue identification software guidance

Thyroid cancer is a common malignancy that requires comprehensive clinical evaluation prior to adequate surgical management. Over the last three decades thyroid surgery has tripled and is considered one of the most commonly performed procedures in general surgery. These procedures are associated with potential postoperative complications with significant deterioration in the patient's quality of life. While the current rates of recurrent laryngeal nerve injury following thyroidectomy have decreased secondary to intraoperative neuromonitoring, thyroid surgery remains the leading cause of iatrogenic injury. The authors herein present a case of a thyroid nodule with cervical lymph node involvement undergoing total thyroidectomy guided by near-ultraviolet (NUV) imaging nerve auto-fluorescent technology to visualize, identify and protect vital structures.

Nerve-Sparing Parotidectomy Guided by Nerve Auto-Fluorescence Technology

Parotidectomy is a commonly performed surgery for various indications, including inflammatory conditions, infection, congenital symptomatic malformations, and neoplasm resection. Irrespective of its indication, the performance requires meticulous surgical navigation by highly experienced surgeons because of its proximity to the facial nerve. While the surgical technique continues to evolve, nerve paralysis and nerve-related complications remain a significant concern following an intervention. Due to the high learning curve required to reduce the incidence of surgical iatrogenic events, a novel device has been developed to emit real-time nerve auto-fluorescence in parallel to artificial intelligence (AI) surgical navigation software (SNS) feedback to isolate and accurately identify nerve structures during surgery. The authors herein present one of the first cases of a benign parotid tumor excision implementing dual AI and nerve auto-fluorescence technology for a minimally invasive, nerve-sparing parotidectomy. This report underscores the potential of nerve auto-fluorescence-guided surgery to improve surgical precision and patient outcomes.

Nerve autofluorescence to enhance nerve visualization during axillary lymph node dissection in three breast cancer patients: Case series

INTRODUCTION AND IMPORTANCE

Iatrogenic nerve injury is a possible complication of axillary lymph node dissection (ALND), which remains standard-of-care for some breast cancer patients. Recently, several studies have demonstrated that nerves auto-fluoresce in near-ultraviolet light (NUVL). We describe three women with BC in whom a recently-developed NUVL camera was used to facilitate visualization of and prevent iatrogenic injury to the intercostobrachial, long thoracic, and thoracodorsal nerves during ALND.

CASE PRESENTATION

In all three women, ALND was deemed necessary per current guidelines for the treatment of locally-advanced breast cancer following neoadjuvant chemotherapy. The surgery was performed using standard-of-care surgical techniques, except that a Dendrite® Imaging System was employed to visualize the surgical field both in white light and NUVL. In all patients, all nerves fluoresced brightly throughout their course in the surgical field. Such visualization was crucial during resection of lymph nodes close to nerves. No peri-operative complications occurred and no evidence of neurological injury was evident at one-month follow-up.

CLINICAL DISCUSSION

The Dendrite® Imaging System employs a NUVL light source and filter system to detect fluorescent signals emitted by neural tissue. These signals then pass through a filter system within the camera head, are captured by a chip, and are transmitted to a dedicated software platform for real-time analysis, processing, and relay to a display screen, allowing the surgical team to observe neural structures with clarity.

CONCLUSION

In three breast cancer patients undergoing ALND, nerve autofluorescence under NUVL aided in visualizing and preventing injury to all nerves within the surgical field.

Case report: Fluorescence-guided laparotomic radical prostatectomy with heightened nerve visualization

INTRODUCTION AND IMPORTANCE

Iatrogenic injury to the cavernous nerve and its branches results in post-operative erectile dysfunction in up to 85 % of men undergoing a radical prostatectomy. Here, we describe using a novel fluorescence-imaging system developed to detect nerve autofluorescence in a 66-year-old gentleman with prostate adenocarcinoma (Gleason Score 8 [4 + 4], prognostic group 4, indicating a highly-aggressive prostate cancer) who underwent laparotomic radical prostatectomy.

CASE PRESENTATION

Under general anesthesia, a laparotomic radical prostatectomy was performed using standard operative techniques. During surgery, a Dendrite imaging camera (Dendrite® Imaging, Germany) was employed to permit the surgical team to toggle freely between standard operating room (white) light and near-ultraviolet light (NUVL), with the specific purpose of enhancing visualization of the periprostatic nerve plexus, including the cavernous nerve and all its branches. Under white light, neither the cavernous nerve nor any of its branches were clearly visible. However, under NUVL, all fluoresced brightly and were easily avoided during prostate resection. Prostate resection proceeded with no intra-operative or post-operative complications. Moreover, upon one-month follow-up in the surgery clinic, the patient reported no erectile dysfunction, difficulties voiding, or other neurological or non-neurological complaints.

CLINICAL DISCUSSION

In this case, autofluorescence of the cavernous nerve and its branches during radical prostatectomy aided in their visualization and appeared to help prevent post-operative erectile dysfunction and all other potential neurological deficits.

CONCLUSION

Novel intra-operative technology enabling nerves to auto-fluoresce warrants larger series and comparative trials to assess its effectiveness reducing iatrogenic nerve injury during radical prostatectomies.

Fluorescence imaging to visualize the recurrent laryngeal nerve during thyroidectomy procedures: analysis of 65 cases and 81 nerves

BACKGROUND

Recurrent laryngeal nerve (RLN) injury after thyroidectomy is relatively common. Locating the RLN prior to thyroid dissection is paramount to avoid injury. We developed a fluorescence imaging system that permits nerve autofluorescence. We aimed to determine the sensitivity and specificity of fluorescence imaging at detecting the RLN relative to thyroid and other background tissue and compared it to white light.

METHODS

In this prospective study, 65 patients underwent thyroidectomy from January to April 2022 (16 bilateral thyroid resections) using white and fluorescent light. Fluorescence intensity [relative fluorescence units (RFU)] was recorded for RLN, thyroid, and background. RFU mean, minimum, and maximum values were calculated using Image J software. Thirty randomly selected pairs of white and fluorescent light images were independently reviewed by two examiners to compare RLN detection rate, number of branches, and length and minimum width of nerves visualized. Parametric and nonparametric statistical analysis was performed.

RESULTS

All 81 RNLs observed were visualized more clearly under fluorescence (mean intensity, µ = 134.3 RFU) than either thyroid (µ = 33.7, p < 0.001) or background (µ = 14.4, p < 0.001). Forest plots revealed no overlap between RLN intensity and that of either other tissue. Sensitivity and specificity for RLN were 100%. All 30 RLNs and all 45 nerve branches were clearly visualized under fluorescence, versus 17 and 22, respectively, with white light (both p < 0.001). Visible nerve length was 2.5 × as great with fluorescence as with white light (µ = 1.90 vs. 0.76 cm, p < 0.001).

CONCLUSIONS

In 65 patients and 81 nerves, RLN detection was markedly and consistently enhanced with autofluorescence neuro-imaging during thyroidectomy, with 100% sensitivity and specificity.

Fluorescence Imaging to Identify and Preserve Fifth Intercostal Sensory Nerves during Bilateral Nipple-sparing Mastectomies

The use of nipple-sparing mastectomies has increased steadily over the past 10-15 years. However, one major source of patient dissatisfaction with both skin- and nipple-sparing mastectomies is lost skin and/or nipple sensation postoperatively due to intraoperative, iatrogenic sensory nerve injury. We summarize the case of a 41-year-old woman with BRCA(+) breast cancer who underwent bilateral, risk-reducing nipple-sparing mastectomies, immediately followed by bilateral, direct-to-implant breast reconstruction, in whom a prototype fluorescent imaging camera was used to facilitate sensory nerve identification and preservation. Preoperatively, tactile and thermal quantitative sensory testing were performed using a 30-gauge needle to determine baseline sensory function over both breasts. Then, nipple-sparing mastectomies and direct-to-implant reconstruction were performed. Using a laterally-displaced submammary approach, the anterior intercostal artery perforator neurovascular pedicle was preserved. Then a prototype camera, which emits near-ultraviolet light, was used to detect nerve autofluorescence. Intraoperatively under near-ultraviolet light, both the fifth intercostal nerve and its sensory branches auto-fluoresced clearly, so that surgery was completed without apparent injury to the fifth intercostal nerve or any of its branches. Postoperatively, the patient reported full sensory function throughout both breasts and both nipple-areolar complexes, which was confirmed on both tactile and thermal sensory testing at 3-month follow-up. The patient experienced no complications and rated her overall satisfaction with surgery on both breasts as 10 out of 10. To our knowledge, this is the first time sensory nerve auto-fluorescence has been reported to reduce the likelihood of intraoperative, iatrogenic nerve injury and preserve sensory function.

Use of fluorescence imaging and indocyanine green during thyroid and parathyroid surgery: Results of an intercontinental, multidisciplinary Delphi survey

BACKGROUND

In recent years, fluorescence imaging-relying both on parathyroid gland autofluorescence under near-infrared light and angiography using the fluorescent dye indocyanine green-has been used to reduce risk of iatrogenic parathyroid injury during thyroid and parathyroid resections, but no published guidelines exist regarding its use. In this study, orchestrated by the International Society for Fluorescence Guided Surgery, areas of consensus and nonconsensus were examined among international experts to facilitate future drafting of such guidelines.

METHODS

A 2-round, online Delphi survey was conducted of 10 international experts in fluorescence imaging use during endocrine surgery, asking them to vote on 75 statements divided into 5 modules: 1 = patient preparation and contraindications to fluorescence imaging (n = 11 statements); 2 = technical logistics (n = 16); 3 = indications (n = 21); 4 = potential advantages and disadvantages of fluorescence imaging (n = 20); and 5 = training and research (n = 7). Several methodological steps were taken to minimize voter bias.

RESULTS

Overall, parathyroid autofluorescence was considered better than indocyanine green angiography for localizing parathyroid glands, whereas indocyanine green angiography was deemed superior assessing parathyroid perfusion. Additional surgical scenarios where indocyanine green angiography was thought to facilitate surgery are (1) when >1 parathyroid gland requires resection; (2) during redo surgeries, (3) facilitating parathyroid autoimplantation; and (4) for the predissection visualization of abnormal glands. Both parathyroid autofluorescence and indocyanine green angiography can be used during the same procedure and employing the same imaging equipment. However, further research is needed to optimize the dose and timing of indocyanine green administration.

CONCLUSION

Though further research remains necessary, using fluorescence imaging appears to have uses during thyroid and parathyroid surgery.

Nerve autofluorescence under near-ultraviolet light: cutting-edge technology for intra-operative neural tissue visualization in 17 patients

BACKGROUND

Nerve visualization and the identification of other neural tissues during surgery is crucial for numerous reasons, including the prevention of iatrogenic nerve and neural structure injury and facilitation of nerve repair. However, current methods of intra-operative nerve detection are generally expensive, unproven, and/or technically challenging. Recently, we have documented, in both in vivo animal models and ex vivo human tissue, that nerves autofluorescence when viewed in near-ultraviolet light (NUV). In this paper, we describe our use of nerve autofluorescence to facilitate the visualization of nerves and other neural tissues intra-operatively in 17 patients undergoing a range of surgical procedures.

METHODS

Employing the same prototype axon imaging system previously documented to markedly enhance nerve visualization in both in vivo animal and ex vivo human models, surgical fields were observed in 17 patients under both white and NUV light during parotid tumor resection (n = 3), thyroid tumor resection (n = 7), and surgery for peripheral nerve and spinal tumors and injury (n = 7).

RESULTS

In all 17 patients, the intra-operative use of the imaging system both was feasible and markedly enhanced the localization of all neural tissues throughout their course within the surgical field. All 17 procedures were successful and devoid of any peri-operative complications or post-operative neurological deficits.

CONCLUSIONS

Intra-operatively visualizing auto-fluorescent peripheral nerves and other neural tissues under NUV light is feasible in human patients across a range of clinical scenarios and appears to appreciably enhance nerve and other neural tissue visualization. Controlled studies to explore this technology further are needed.

Nerve autofluorescence in near-ultraviolet light markedly enhances nerve visualization in vivo

BACKGROUND

During surgery, surgeons must accurately localize nerves to avoid injuring them. Recently, we have discovered that nerves fluoresce in near-ultraviolet light (NUV) light. The aims of the current study were to determine the extent to which nerves fluoresce more brightly than background and vascular structures in NUV light, and identify the NUV intensity at which nerves are most distinguishable from other tissues.

METHODS

We exposed sciatic nerves within the posterior thigh in five 250-300 gm Wistar rats, then observed them at four different NUV intensity levels: 20%, 35%, 50%, and 100%. Brightness of fluorescence was measured by fluorescence spectroscopy, quantified as a fluorescence score using Image-J software, and statistically compared between nerves, background, and both an artery and vein by unpaired Student's t tests with Bonferroni adjustment to accommodate multiple comparisons. Sensitivity, specificity, and accuracy were calculated for each NUV intensity.

RESULTS

At 20, 35, 50, and 100% NUV intensity, fluorescence scores for nerves versus background tissues were 117.4 versus 40.0, 225.8 versus 88.0, 250.6 versus 121.4, and 252.8 versus 169.4, respectively (all p < 0.001). Fluorescence scores plateaued at 50% NUV intensity for nerves, but continued to rise for background. At 35%, 50%, and 100% NUV intensity, a fluorescence score of 200 was 100% sensitive, specific, and accurate identifying nerves. At 100 NUV intensity, artery and vein scores were 61.8 and 60.0, both dramatically lower than for nerves (p < 0.001).

CONCLUSIONS

At all NUV intensities ≥ 35%, a fluorescence score of 200 is 100% accurate distinguishing nerves from other anatomical structures in vivo.

Endoscopic confocal laser-microscopy for the intraoperative nerve recognition: is it feasible?

Surgeons lose most of their tactile tissue information during minimal invasive surgery and need an additional tool of intraoperative tissue recognition. Confocal laser microscopy (CLM) is a well-established method of tissue investigation. The objective of this study was to analyze the feasibility and diagnostic accuracy of CLM nervous tissue recognition. Images taken with an endoscopic CLM system of sympathetic ganglions, nerve fibers and pleural tissue were characterized in terms of specific signal-patterns ex-vivo. No fluorescent dye was used. Diagnostic accuracy of tissue classification was evaluated by newly trained observers (sensitivity, specificity, PPV, NPV and interobserver variability). Although CLM images showed low CLM image contrast, assessment of nerve tissue was feasible without any fluorescent dye. Sensitivity and specificity ranged between 0.73 and 0.9 and 0.55-1.0, respectively. PPVs were 0.71-1.0 and the NPV range was between 0.58 and 0.86. The overall interobserver variability was 0.36. The eCLM enables to evaluate nervous tissue and to distinguish between nerve fibers, ganglions and pleural tissue based on backscattered light. However, the low image contrast and the heterogeneity in correct tissue diagnosis and a fair interobserver variability indicate the limit of CLM imaging without any fluorescent dye.

Nerve autofluorescence in near-ultraviolet light markedly enhances nerve visualization in vivo

BACKGROUND

During surgery, surgeons must accurately localize nerves to avoid injuring them. Recently, we have discovered that nerves fluoresce in near-ultraviolet light (NUV) light. The aims of the current study were to determine the extent to which nerves fluoresce more brightly than background and vascular structures in NUV light, and identify the NUV intensity at which nerves are most distinguishable from other tissues.

METHODS

We exposed sciatic nerves within the posterior thigh in five 250-300 gm Wistar rats, then observed them at four different NUV intensity levels: 20%, 35%, 50%, and 100%. Brightness of fluorescence was measured by fluorescence spectroscopy, quantified as a fluorescence score using Image-J software, and statistically compared between nerves, background, and both an artery and vein by unpaired Student's t tests with Bonferroni adjustment to accommodate multiple comparisons. Sensitivity, specificity, and accuracy were calculated for each NUV intensity.

RESULTS

At 20, 35, 50, and 100% NUV intensity, fluorescence scores for nerves versus background tissues were 117.4 versus 40.0, 225.8 versus 88.0, 250.6 versus 121.4, and 252.8 versus 169.4, respectively (all p < 0.001). Fluorescence scores plateaued at 50% NUV intensity for nerves, but continued to rise for background. At 35%, 50%, and 100% NUV intensity, a fluorescence score of 200 was 100% sensitive, specific, and accurate identifying nerves. At 100 NUV intensity, artery and vein scores were 61.8 and 60.0, both dramatically lower than for nerves (p < 0.001).

CONCLUSIONS

At all NUV intensities ≥ 35%, a fluorescence score of 200 is 100% accurate distinguishing nerves from other anatomical structures in vivo.