Lighting Up the Tumor-Fluorescein-Guided Resection of Gangliogliomas

Synthesis, Preclinical Evaluation, and First-in-Human Assessment of ICG-PSMA-D5: A PSMA-Targeted Probe for Fluorescence-Guided Surgery of Prostate Cancer

Precise surgical resection of prostate cancer (PCa) is a significant clinical challenge due to the impact of positive surgical margins on postoperative outcomes. Fluorescence-guided surgery (FGS) enables real-time tumor visualization using fluorescent probes. In this study, we synthesized and evaluated an indocyanine green (ICG)-based PSMA-targeted near-infrared probe, ICG-PSMA-D5, for intraoperative imaging of PCa lesions. Spectroscopic analysis revealed that ICG-PSMA-D5 retained the optical properties of ICG while improving solubility in PBS due to additional carboxyl groups. In vitro assays demonstrated high binding affinity (Ki = 0.39 nM) and minimal cytotoxicity. In vivo studies in tumor-bearing mice showed strong tumor targeting, extended retention at tumor site, and favorable biodistribution, with significant tumor-to-background ratios. The first-in-human study in a patient with localized PCa indicated the probe's potential for real-time, radiation-free surgical guidance. Overall, ICG-PSMA-D5 displayed excellent performance in tumor detection and margin delineation, making it a promising candidate for intraoperative FGS in PCa.

Pediatric cerebral ganglioglioma epilepsy surgery: enhancing seizure outcomes through optimized resection applying high-field intraoperative magnetic resonance imaging

PURPOSE

Gangliogliomas are rare, slow-growing brain tumors frequently associated with seizures in pediatric patients. This study evaluated the utility of high-field intraoperative magnetic resonance imaging (ioMRI) in the surgical management of ganglioglioma-related drug-resistant epilepsy in children. Specifically, it sought to determine whether ioMRI improves outcomes by optimizing the extent of resection, enhancing seizure control, reducing reoperations, and minimizing complications.

METHODS

This retrospective single-center study included 14 pediatric patients with cerebral ganglioglioma who underwent epilepsy surgery with ioMRI from 2014 to 2022. The median age was 11.5 years (range 3-16 years). Patient demographics, the rate of continued ioMRI-guided surgery, the extent of resection, histology, complications, reoperations, and seizure outcomes at 1 year postoperatively were assessed.

RESULTS

Residual tumor was detected using ioMRI in 9 of 14 patients (64.3%), leading to further resection. Complete tumor resection was achieved in 12 patients (100%) as intended, while two patients underwent planned tumor debulking. Temporary neurological deficits were observed in two patients, with no permanent deficits documented. One patient required reoperation, and another was scheduled for one. The median follow-up duration was 43 months (range 12-65 months). Seizure outcomes were classified as Engel I in 9 of 10 (90%) and Engel III in 1 of 10 patients (10%). Four patients were lost to follow-up.

CONCLUSION

The use of ioMRI in pediatric epilepsy surgery for ganglioglioma facilitated more complete resections, contributing to favorable seizure outcomes and a low complication rate. These findings support ioMRI as a valuable tool in optimizing surgical management for this patient population.

Enlightening the invisible: Applications, limits and perspectives of intraoperative fluorescence in neurosurgery

Introduction

The introduction of intraoperative fluorophores represented a significant advancement in neurosurgical practice. Nowadays they found different applications: in oncology to improve the visualization of tumoral tissue and optimize resection rates and in vascular neurosurgery to assess the exclusion of vascular malformations or the permeability of bypasses, with real-time intraoperative evaluations.

Research question

A comprehensive knowledge of how fluorophores work is crucial to maximize their benefits and to incorporate them into daily neurosurgical practice. We would like to revise here their applications and clinical relevance.

Material and methods

A focused literature review of relevant articles dealing with the versatile applications of fluorophores in neurosurgery was performed.

Results

The fundamental mechanisms of action of intraoperative fluorophores are enlightened, examining their interactions with target tissues and the principles driving fluorescence-guided surgery. The clinical applications of the principal fluorophores, namely fluorescein sodium, 5-ALA and indocyanine green, are detailed, in regards to the management of vascular malformations, brain tumors and pathologies treated through endoscopic endonasal approaches.

Discussion and conclusion

Future perspective dealing with the development of new technologies or of new molecules are discussed. By critically assessing the efficacy and applications of the different fluorophores, as well as charting their potential future uses, this paper seeks to guide clinicians in their practice and provide insights for driving innovation and progress in fluorescence-based surgery and research.

Role of sodium fluorescein in pediatric low-grade glioma surgery: an update

PURPOSE

Complete surgical resection is still the mainstay in the treatment of central nervous system low-grade tumors, eventually resulting curative. The complete surgical removal of these lesions, however, may be difficult in some cases because of their infiltrative nature. Intraoperative adjuncts may be a game changer. Sodium fluorescein (SF) is among the ideal candidates as intraoperative tools to favor the actual recognition of the tumor extension, since it accumulates in areas of altered blood-brain barrier, a typical characteristic of pediatric gliomas, and has a low rate of adverse events. This work proposes an update of previous works about the evaluation of the feasibility and usefulness of a systematic use of SF in a low-grade lesion group of pediatric patients.

METHODS

Pediatric patients operated on for a resection or a biopsy of a low-grade glial or glioneuronal lesion (WHO grade I and II) at our Institution between September 2021 and December 2023, with the intraoperative use of sodium fluorescein (SF), were enrolled in the study. We collected pre-operative and postoperative clinical and radiological data, intraoperative findings, and post-operative pathological diagnoses.

RESULTS

No adverse events were registered related to the intraoperative use of SF. SF appeared useful for the localization of boundaries of tumors, especially when characterized by a high degree of infiltration or by a deep-seated location, and for the checking of possible tumor remnants at the end of surgery. A good tumor-to-healthy tissue contrast was registered when tumor visualization was in a range between 1 to 2 h and 30 min after SF injection. Possible "false positives" due to intraoperative vascular wall injury and clearance of SF from both tumor and healthy tissue were observed in some cases and still remain open issues.

CONCLUSIONS

SF is a feasible and safe intraoperative adjunct tool in the surgical removal of pediatric low-grade tumors. SF may show its usefulness especially in selected cases, such as deep-seated lesions and infiltrating tumors. Its safety profile, user-friendly management, and potential utility in both tumor resections and neuronavigated biopsies favor its wider use in the surgical treatment of pediatric low-grade tumors.

Intraoperative Fluorescein Sodium in Pediatric Neurosurgery: A Preliminary Case Series from a Singapore Children's Hospital

(1) Background: Fluorescein sodium (Na-Fl) has been described as a safe and useful neurosurgical adjunct in adult neurooncology. However, its use has yet to be fully established in children. We designed a study to investigate the use of intraoperative Na-Fl in pediatric brain tumor surgery. (2) Methods: This is a single-institution study for pediatric brain tumor patients managed by the Neurosurgical Service, KK Women's and Children's Hospital. Inclusion criteria consists of patients undergoing surgery for suspected brain tumors from 3 to 19 years old. A predefined intravenous dose of 2 mg/kg of 10% Na-Fl is administered per patient. Following craniotomy, surgery is performed under alternating white light and YELLOW-560 nm filter illumination. (3) Results: A total of 21 patients with suspected brain tumours were included. Median age was 12.1 years old. For three patients (14.3%), there was no significant Na-Fl fluorescence detected and their final histologies reported a cavernoma and two radiation-induced high grade gliomas. The remaining patients (85.7%) had adequate intraoperative fluorescence for their lesions. No adverse side effects were encountered with the use of Na-Fl. (4) Conclusions: Preliminary findings demonstrate the safe and efficacious use of intraoperative Na-Fl for brain tumors as a neurosurgical adjunct in our pediatric patients.

Case report: 'Photodynamics of Subependymal Giant Cell Astrocytoma with 5-Aminolevulinic acid'

Subependymal Giant Cell Astrocytoma (SEGA) is a common diagnosis in patients with Tuberous Sclerosis. Although surgical treatment is often required, resection may entail a significant risk for cognitive function given the anatomical relation with critical structures such as the fornices and subgenual area. Therefore, target subtotal resections using minimal invasive approaches focused in the higher metabolic areas are valuable options to preserve quality of life while addressing specific problems caused by the tumor, such as hydrocephalus or progressive growth of a specific component of the tumor. In this report, the authors explore the potential role of 5-ALA in the identification of highly metabolic areas during SEGA resection in the context of minimal invasive approaches.

Towards an Established Intraoperative Oncological Favorable Tool: Results of Fluorescein-Guided Resection from a Monocentric, Prospective Series of 93 Primary Glioblastoma Patients

It is commonly reported that maximizing surgical resection of contrast-enhancing regions in patients with glioblastoma improves overall survival. Efforts to achieve an improved rate of resection have included several tools: among those, the recent widespread of fluorophores. Sodium fluorescein is an unspecific, vascular dye which tends to accumulate in areas with an altered blood-brain barrier. In this retrospective analysis of patients prospectively enrolled in the FLUOCERTUM study, we aimed to assess the role of fluorescein-guided surgery on surgical radicality, survival, and morbidity. A retrospective review based on 93 consecutively and prospectively enrolled IDH wild-type glioblastoma patients (2016-2022) was performed; fluorescence characteristics, rate of resection, clinical outcome, and survival were analyzed. No side effect related to fluorescein occurred; all of the tumors presented a strong yellow-green enhancement and fluorescein was judged fundamental in distinguishing tumors from viable tissue in all cases. Gross total resection was achieved in 77 cases out of 93 patients (82.8%). After a mean follow-up time of 17.4 months (3-78 months), the median progression-free survival was 12 months, with a PFS-6 and PFS-12 of 94.2% and 50%, respectively, whereas median overall survival was estimated to be 16 months; survival at 6, 12, and 24 months was 91.8%, 72.3%, and 30.1%, respectively. Based on these results, we can assert that the fluorescein-guided technique is a safe and valuable method for patients harboring a newly diagnosed, untreated glioblastoma.

The use of the sodium fluorescein and YELLOW 560 nm filter for the resection of pediatric posterior fossa lesions

PURPOSE

This study aimed to verify the feasibility, safety, and benefit of using fluorescein sodium (FL) and a YELLOW 560 nm filter in posterior fossa tumors in children.

METHODS

All cases of pediatric posterior fossa tumors that have undergone surgery using fluorescein (2018-2022) have been included and were examined retrospectively. In those cases where resection of the tumor was planned, a blinded neuroradiologist distinguished gross total resection and subtotal resection according to the postoperative MRI findings. The surgical report and medical files were reviewed regarding the intraoperative staining grade and adverse events. The grade of fluorescent staining of the targeted lesion was assessed as described in the surgical reports. The screening was conducted for any reference to the degree of fluorescent staining: "intense," "medium," "slight," and "no staining."

RESULTS

19 cases have been included. In 14 cases, a complete resection was initially intended. In 11 of these cases, a gross total resection could be achieved (78.6%). Staining was described as intense in most cases (58.8%). Except for yellow-colored urine, no side effects obviously related to FL were found throughout the observation period.

CONCLUSION

In combination with a specific filter, FL is a reliable, safe, and feasible tool in posterior fossa surgery in children.

The role of sodium fluorescein in pediatric supratentorial intra-axial tumor resection: new insights from a monocentric series of 33 consecutive patients

INTRODUCTION

Surgical resection represents the mainstay of treatment, in pediatric central nervous system (CNS) tumors, and aggressive resection correlates with prognosis for several histotypes. Sodium fluorescein (SF), a green, water-soluble dye, is used as neurosurgical fluorescent tracer thanks to its property to accumulate in cerebral regions of blood-brain barrier disruption, acting as a valid tool to improve the extent of resection in tumors enhancing at preoperative MRI. Brain neoplasms represent a heterogeneous group of tumors in the pediatric age, constituting the most common solid cancers; they typically show a varying degree of contrast enhancement on MRI.

MATERIALS AND METHODS

In March 2016, the authors started a prospective, observational trial to evaluate intraoperative fluorescence's characteristics of CNS tumors, the percentage of extent of resection, thanks to fluorescein aid, and side effects related to fluorescein administration. This report is based on a retrospective analysis of a group of 33 consecutive pediatric patients harboring a supratentorial lesion.

RESULTS

In 17 of 33 (51.5%) procedures, fluorescence was reported as intense; in 14 of 33 (42.4%), moderate; and in 2 of 33 (6.1%), slight. Intraoperative fluorescence corresponds to preoperative-MRI-documented contrast enhancement. In 28 of 33 (84.8%) surgical procedures, SF was considered useful; in 2 of 33 (6.1%), partial useful; and in 3 of 33 (9.1%), not essential because the tumor was already recognizable. No adverse effect to SF administration was registered.

CONCLUSION

Fluorescein-guided surgery with a dedicated filter on the microscope is a safe and effective technique to improve visualization and resection of different pediatric brain tumors.

Sodium fluorescein in pediatric neurosurgery: a systematic review with technical considerations and future perspectives

BACKGROUND

Sodium fluorescein (SF) is routinely used in several centers as a valid intraoperative adjunct in adult oncological neurosurgery. Its use in pediatric neurosurgery is increasing, although its role is not yet well-defined in children. We reviewed the current literature in order to evaluate the use of SF in children with CNS and PNS lesions.

METHODS

For this systematic review, we searched PubMed, Scopus, and Embase databases, and forward and backward citations for studies published between database inception and July 31st, 2022. We included any article type or congress abstract adding at least a new case, without restrictions of language or publication status, concerning the use of SF in neurosurgical procedures in patients under 18 years of age. We excluded studies concerning purely vascular cases and cerebrospinal fluid leaks.

RESULTS

Of 4094 records identified, 19 articles were eligible and included for further analysis. As per July 31st, 2022, at least 119 patients aged from 11 months to 17.9 years underwent surgery with SF. No serious adverse events were reported. A large variety of tumor types was operated, in most cases resected under the specific YELLOW 560 nm filter after a low-dose SF injection (2-5 mg/kg) at the end of anesthesia induction. SF was reported particularly useful in gangliogliomas and pilocytic astrocytomas.

DISCUSSION/CONCLUSION

Given its easy-to-use profile, low cost, and safety, SF seems to be a feasible and valid adjunct in the pediatric population when aiming at individuating a biopsy target or maximizing extent of resection, particularly in some tumor types. Further studies are required to strengthen the evidence on its impact on outcomes.

Sodium fluorescein in pediatric oncological neurosurgery: a pilot study on 50 children

BACKGROUND

Sodium fluorescein (SF) is currently considered a valid intraoperative adjunct in the resection of high-grade brain lesions in adults. Experiences in pediatric groups and in low-grade gliomas and other low-grade lesions are still limited in literature, and subjective evaluation of fluorescence is still a limitation.

MATERIAL AND METHODS

This study retrospectively reviewed all patients with brain or spine lesions operated on from September 2021 to July 2022 in the Pediatric Neurosurgery Unit of Hôpital Femme Mère Enfant, Lyon, who had received 5 mg/kg of 10%. Surgery was performed using a YELLOW560 filter at crucial times. At the end of surgery, the first operator completed a questionnaire, including his opinion on whether SF had been useful in tumor resection, recorded as a binary variable. Post hoc, surgical images were reviewed using ImageJ, an open-source Java image processing platform. In order to compare independent discrete variables, we applied the Student's t test, and we applied the Chi-square or Fisher exact test for binary variables. A threshold of p < 0.05 was set for statistical significance.

RESULTS

We included 50 pediatric patients (0.2-17.6 years old). Forty/50 lesions showed SF uptake (80%). The differentiation between healthy and affected tissue, thanks to SF, subjectively evaluated by the surgeon, had as objective counterpart the statistically significant higher brightness of green in lesions, registered by the software (p < 0.001). SF overall allowed a good differentiation in 33/50 lesions, and overall utility of SF has been noted in 67% of them. When specifically considering gliomas, overall utility reached 75%.

CONCLUSION

SF is a feasible, safe, and useful intraoperative adjunct in pediatric neurosurgery. In particular, it seems to have a promising role in some low-grade infiltrating glial tumors. The subjective evaluation of fluorescence seems to be reliable with respect to image analyses software.

Suprasellar Ganglioglioma Arising from the Third Ventricle Floor: A Case Report and Review of the Literature

Gangliogliomas are uncommon intracranial tumors that include neoplastic and abnormal ganglion cells, and show positive immunohistochemical staining for GFAP and syn. This type of lesion occurs more frequently in the temporal lobe than in other areas; they are extremely rare in the suprasellar region. To the best of our knowledge, including our case, 19 cases of GGs have been found in the suprasellar region. Among them, five tumors invaded the optic nerve, nine tumors invaded the optic chiasm, one tumor invaded the optic tract, and two tumors invaded the entire optic chiasmal hypothalamic pathway. In the present study, we describe the first case of suprasellar GGs arising from the third ventricle floor that was removed through the endoscopic endonasal approach. In addition, we summarize the clinical characteristics of GGs, such as age of onset, gender distribution, MRI signs, main clinical symptoms, and treatment methods for GG cases.

Pediatric Low-Grade Glioma Surgery with Sodium Fluorescein: Efficient Localization for Removal and Association with Intraoperative Pathological Sampling

Low-grade gliomas are among the most common CNS lesions in pediatrics and surgery is often the first-line treatment. Intraoperative tools have been developed to maximize the results of surgery, and in particular dyes such as sodium fluorescein (SF) have been investigated in high-grade adult lesions. The use of SF in pediatric low-grade gliomas is still unclear. We retrospectively reviewed 22 pediatric CNS low-grade gliomas operated on with SF from September 2021 to October 2022. A total of 86% of lesions showed SF uptake, which was helpful intraoperatively (confirmation of initial localization of the tumor, or identification of tumor remnants) in 74% of them. The intraoperative fluorescence seems associated with gadolinium enhancement at the preoperative MRI. Interestingly, the extemporaneous pathological sampling (EPS) was informative in every case showing SF uptake, whereas in cases without SF uptake, the EPS was non-informative, although the tissue was later confirmed as pathological. These findings highlight the interest of SF for perioperative diagnosis of tumor tissue and may suggest in which cases the differentiation of tumor-healthy tissue could be especially blurred, posing difficulties for the pathologist.

Fluorescein sodium in the surgical treatment of pleomorphic xanthoastrocytomas: Results from a retrospective study

OBJECTIVE

Pleomorphic xanthoastrocytoma (PXA) is a rare brain tumor, most commonly affecting children and young adults. Surgical resection represents the mainstay of treatment, and extent of resection is associated with improved survival. In this study, we analyzed the role of sodium fluorescein (SF) in improving intraoperative visualization easing resection.

METHODS

Surgical database of FLUOCERTUM study (Besta Institute, Milan, Italy) was retrospectively reviewed to find pleomorphic xanthoastrocytomas and anaplastic xanthoastrocytomas, according to WHO-2016/2021 classification, surgically removed by a fluorescein-guided technique from March 2016 to February 2022. SF was intravenously injected (5mg/kg) immediately after induction of general anesthesia. Tumors were removed using a microsurgical technique with the YELLOW 560 filter (Carl Zeiss Meditec, Oberkochen, Germany).

RESULTS

Twelve patients (7 males and 5 females; 3 pediatric patients, mean age 10 years, range 5 to 13 years and 9 adult patients, mean age 50.6 years, range 35 to 63 years) underwent fluorescein-guided surgery. No side effects related to SF occurred. In all tumors, contrast enhancement on preoperative MRI correlated with intense, heterogeneous yellow fluorescence with bright fluorescent cystic fluid. Fluorescein was considered helpful in distinguishing tumors from viable tissue in all cases. Gross total resection was achieved in 8 cases (66.7%); in 4 cases, otherwise, the resection was subtotal with fluorescent residual spots to avoid neurological worsening (33.3%).

CONCLUSIONS

The use of SF is a valuable method for safe fluorescence-guided tumor resection. Our data documented a positive effect of fluorescein-guided surgery on intraoperative visualization, suggesting a probable role in improving the extent of resection during yellow surgery of PXA.

Fluorescein-guided surgery for the resection of pilocytic astrocytomas: A multicentric retrospective study

Objective

Pilocytic astrocytomas (PAs) are relatively benign tumors, usually enhancing on post-contrast MRI and often characterized by a mural nodule within a cystic component. Surgical resection represents the mainstay of treatment, and extent of resection (EOR) is associated with improved survival. In this study, we analyzed the effect of sodium fluorescein (SF) on the visualization and resection of these circumscribed astrocytic gliomas.

Methods

Surgical databases at two neurosurgical departments (Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy and Department of Neurosurgery, University Medical Center Regensburg, Regensburg, Germany) were retrospectively reviewed to identify the cohort of patients with pilocytic astrocytoma who had undergone fluorescein-guided tumor resection at any of the centers between March 2016 and February 2022. SF was intravenously injected (5 mg/kg) immediately after the induction of general anesthesia. Tumors were removed using a microsurgical technique with the YELLOW 560 filter (Carl Zeiss Meditec, Oberkochen, Germany).

Results

Forty-four patients (25 males and 19 females; 26 pediatric patients, mean age of 9.77 years, range 2 to 17 years; and 18 adult patients, mean age of 34.39 years, range 18 to 58 years) underwent fluorescein-guided surgery. No side effects related to SF occurred. In all tumors, contrast enhancement on preoperative MRI was correlated with intense, heterogeneous yellow fluorescence with bright fluorescent cystic fluid. Fluorescein was considered helpful in distinguishing tumors from viable tissue in all cases except three patients due to faint fluorescein enhancement. Biopsy was intended in two operations, and partial resection was intended in three operations. Gross total resection was achieved in 24 cases out of 39 patients scheduled for tumor removal (61.54%), in five cases a minimal residual volume was highlighted by postoperative MRI despite the intraoperative subjective evaluation of complete tumor removal (12.82%); in the other 10 cases, the resection was subtotal with fluorescent residual spots to avoid neurological worsening (25.64%).

Conclusions

The use of SF is a valuable method for safe fluorescence-guided tumor resection. Our data showed a positive effect of fluorescein-guided surgery on intraoperative visualization during resection of Pas, suggesting a possible role in improving the extent of resection of these lesions.

Combined Application of Sodium Fluorescein and Neuronavigation Techniques in the Resection of Brain Gliomas

Objectives: To explore the effectiveness and safety of the combined application of sodium fluorescein and neuronavigation techniques in the resection of brain gliomas in different locations and patients of different ages.

Methods: Fifty clinical cases of brain gliomas treated at the Department of Neurosurgery of Beijing Tiantan Hospital were collected from March 2014 to March 2019. These cases were divided into a supratentorial group (24 cases) and a brainstem group (26 cases) based on location and an adult group (28 cases) and a pediatric group (22 cases) based on age. Fluorescein-guided surgery was performed: the adult group received 5 mg/kg sodium fluorescein before opening the dura, while the pediatric group received 2.5 mg/kg during resection. Tumor visualization was evaluated by the enhancement of yellow fluorescein and considered “satisfactory” if the illumination demarcated the tumor boundary. Additionally, the consistency between fluorescein and neuronavigation was analyzed. The Karnofsky performance score (KPS) of all patients was recorded and assessed at admission, discharge, and the 6-month follow-up.

Results: In the 28 adult cases, 4 were unsatisfactory, while in the 22 pediatric cases, 2 were unsatisfactory; in 7 cases, there was an inconsistency between yellow fluorescein enhancement and neuronavigation, 6 were in the supratentorial group, and 1 was in the brainstem group. Statistical analysis showed no significant differences in the satisfactory rate between the adult and pediatric groups (P = 0.575), whereas there were significant differences inconsistency between the supratentorial group and brainstem group (P = 0.031). The mean KPS at admission was between 70 and 100, which was not significantly different from that at discharge (P = 0.839), but the KPS at the 6-month follow-up was significantly higher than that at admission (P = 0.041).

Conclusions: The consistency between sodium fluorescein and the neuronavigation system was higher in the brainstem group than in the supratentorial group; a half dose of sodium fluorescein (2.5 mg/kg) was sufficient for pediatric patients. The combined utilization of sodium fluorescein and neuronavigation techniques may confer glioma patients the opportunity to obtain better clinical outcomes after surgery.

Optical Characterization of Sodium Fluorescein In Vitro and Ex Vivo

Objective

The utilization of fluorescein-guided biopsies and resection has been recently discussed as a suitable strategy to improve and expedite operative techniques for the resection of central nervous system (CNS) tumors. However, little is known about the optical properties of sodium fluorescein (NaFl) in human tumor tissue and their potential impact on ex vivo analyses involving fluorescence-based methods.

Methods

Tumor tissue was obtained from a study cohort of an observational study on the utilization of fluorescein-guided biopsy and resection (n=5). The optical properties of fluorescein-stained tissue were compared to the optical features of the dye in vitro and in control samples consisting of tumor tissue of high-grade glioma patients (n=3) without intravenous (i.v.) application of NaFl. The dye-exposed tumor tissues were used for optical measurements to confirm the detectability of NaFl emission ex vivo. The tissue samples were fixed in 4%PFA, immersed in 30% sucrose, embedded in Tissue-Tek OCT compound, and cut to 10 μm cryosections. Spatially resolved emission spectra from tumor samples were recorded on representative slides with a Confocal Laser Scanning Microscope FV1000 (Olympus GmbH, Hamburg, Germany) upon excitation with λ_exc = 488 nm.

Results

Optical measurements of fluorescein in 0.9% sodium chloride (NaCl) under in vitro conditions showed an absorption maximum of λ_{max abs} = 479 nm as detected with spectrophotometer Specord 200 and an emission peak at λ_{max em} = 538 nm recorded with the emCCD detection system of a custom-made microscope-based single particle setup using a 500 nm long-pass filter. Further measurements revealed pH- and concentration-dependent emission spectra of NaFl. Under ex vivo conditions, confocal laser scanning microscopy of fluorescein tumor samples revealed a slight bathochromic shift and a broadening of the emission band.

Conclusion

Tumor uptake of NaFl leads to changes in the optical properties – a bathochromic shift and broadening of the emission band – possibly caused by the dye’s high pH sensitivity and concentration-dependent reabsorption acting as an inner filter of the dye’s emission, particularly in the short wavelength region of the emission spectrum where absorption and fluorescence overlap. Understanding the ex vivo optical properties of fluorescein is crucial for testing and validating its further applicability as an optical probe for intravital microscopy, immunofluorescence localization studies, and flow cytometry analysis.

Intraoperative imaging of brain tumors with fluorescein: confocal laser endomicroscopy in neurosurgery. Clinical and user experience

OBJECTIVE

Confocal laser endomicroscopy (CLE) is an established tool in basic research for tissue imaging at the level of microstructures. Miniaturization and refinement of the technology have made this modality available for operative imaging with a handheld device. Sufficient image contrast is provided by the preoperative application of fluorescein sodium. The authors report their first experiences in a clinical case series using the new confocal laser endomicroscope.

METHODS

Handling, operative workflow, and visualization of the CLE were critically evaluated in 12 cases of different CNS tumors. Three different imaging positions in relation to the tumor were chosen: the tumor border (I), tumor center (II), and perilesional zone (III). Respective diagnostic sampling with H & E staining and matching intraoperative neuronavigation and microscope images are provided.

RESULTS

CLE was found to be beneficial in terms of high-quality visualization of fine structures and for displaying hidden anatomical details. The handling of the device was good, and the workflow was easy.

CONCLUSIONS

Handling ergonomics and image acquisition are intuitive. The endomicroscope allows excellent additional visualization of microstructures in the surgical field with a minimally invasive technique and could improve safety and clinical outcomes. The new confocal laser endomicroscope is an advanced tool with the potential to change intracranial tumor surgery. Imaging of these microstructures is novel, and research with comparative validation with traditional neuropathological assessments is needed.