Metastatic brain tumor surgery using fluorescein sodium: technical note

Fluorescence and Intraoperative Ultrasound as Surgical Adjuncts for Brain Metastases Resection: What Do We Know? A Systematic Review of the Literature

(1) Background: brain metastases (BMs) are the most common neoplasm of the central nervous system; despite the high incidence of this type of tumour, to date there is no universal consensus on the most effective treatment in patients with BMs, even if surgery still plays a primary role. Despite this, the adjunct systems that help to reach the GTR, which are well structured for other tumour forms such as ultrasound and fluorescence systems, are not yet well employed and standardised in surgical practice. The aim of this review is to provide a picture of the current state-of-art of the roles of iOUS and intraoperative fluorescence to better understand their potential roles as surgical tools. (2) Methods: to reach this goal, the PubMed database was searched using the following string as the keyword: (((Brain cerebral metastasis [MeSH Major Topic])OR (brain metastasis, [MeSH Major Topic])) AND ((5-ala, [MeSH Terms]) OR (Aminolevulinicacid [All fields]) OR (fluorescein, [MeSH Terms]) OR (contrast enhanced ultrasound [MeSH Terms])OR ((intraoperative ultrasound. [MeSH Terms]))) AND (english [Filter]) AND ((english [Filter]) AND (2010:2022 [pdat])) AND (english [Filter]). (3) Results: from our research, a total of 661 articles emerged; of these, 57 were selected. 21 of these included BMs generically as a secondary class for comparisons with gliomas, without going deeply into specific details. Therefore, for our purposes, 36 articles were considered. (4) Conclusions: with regard to BMs treatment and their surgical adjuncts, there is still much to be explored. This is mainly related to the heterogeneity of patients, the primary tumour histology and the extent of systemic disease; regardless, surgery plays a paramount role in obtaining a local disease control, and more standardised surgical protocols need to be made, with the aim of optimizing the use of the available surgical adjuncts and in order to increase the rate of GTR.

Creation of Non-Contact Device for Use in Metastatic Melanoma Margin Identification in ex vivo Mouse Brain

Because contemporary intraoperative tumor detection modalities, such as intraoperative MRI, are not ubiquitously available and can disrupt surgical workflow, there is an imperative for an accessible diagnostic device that can meet the surgeon's needs in identifying tissue types. The objective of this paper is to determine the efficacy of a novel non-contact tumor detection device for metastatic melanoma boundary identification in a tissue-mimicking phantom, evaluate the identification of metastatic melanoma boundaries in ex vivo mouse brain tissue, and find the error associated with identifying this boundary. To validate the spatial and fluorescence resolution of the device, tissue-mimicking phantoms were created with modifiable optical properties. Phantom tissue provided ground truth measurements for fluorophore concentration differences with respect to spatial dimensions. Modeling metastatic disease, ex vivo melanoma brain metastases were evaluated to detect differences in fluorescence between healthy and neoplastic tissue. This analysis includes determining required-to-observe fluorescence differences in tissue. H&E staining confirmed tumor presence in mouse tissue samples. The device detected a difference in normalized average fluorescence intensity in all three phantoms. There were differences in fluorescence with the presence and absence of melanin. The estimated tumor boundary of all tissue phantoms was within 0.30 mm of the ground truth tumor boundary for all boundaries. Likewise, when applied to the melanoma-bearing brains from ex vivo mice, a difference in normalized fluorescence intensity was successfully detected. The potential prediction window for the tumor boundary location is less than 1.5 mm for all ex vivo mouse brain tumors boundaries. We present a non-contact, laser-induced fluorescence device that can identify tumor boundaries based on changes in laser-induced fluorescence emission intensity. The device can identify phantom ground truth tumor boundaries within 0.30 mm using instantaneous rate of change of normalized fluorescence emission intensity and can detect endogenous fluorescence differences in melanoma brain metastases in ex vivo mouse tissue.

Robotic-Assisted Digital Exoscope for Resection of Cerebral Metastases: A Case Series

BACKGROUND

Surgical resection is the primary treatment for cerebral metastases with safe complete resection as the goal. The robotically assisted digital surgical exoscope is a novel system with advanced visualization methods with recent applications in neurosurgery.

OBJECTIVE

To evaluate the outcomes for patients with cerebral metastases undergoing resection with the surgical exoscope.

METHODS

Data were retrospectively collected from patients with cerebral metastases where resection was achieved with using the surgical exoscope from 2016 to 2020. Demographics, clinical, imaging, and operative and outcome findings were collected. The relationship between perioperative data and discharge disposition as well as progression-free survival (PFS) and 12 mo overall survival (OS) was assessed.

RESULTS

A total of 31 patients (19 males) with a median patient age 63 yr (range 38-80) were included. Average pre- and postoperative volumes were 18.1 cc and 0.75 cc, respectively. Mean depth of the resected lesions was 0.6 cm (range 0-3.6 cm). Complete resection was achieved in 64.5% of patients. The mean extent of resection was 96.7%, with 71.0% achieving PFS at 6 mo. Overall PFS rate was 58.1% and the OS rate at 12 mo was 83.9%. Neurological complications included motor (35.5%) and sensory (12.9%) deficits, with 12 patients reporting no postoperative symptoms.

CONCLUSION

The surgical exoscope can delineate tumor tissues with high resolution, as shown by a gross total resection achieved for the majority of cases in our series. Postoperative complications and patient outcomes were similar to those reported with use of the operative microscope. Use of the exoscope can provide optimal visualization and delineation of cerebral metastases.

The Management of Brain Metastases-Systematic Review of Neurosurgical Aspects

Simple Summary

In this comprehensive review, we focused on the neurosurgical treatment as an integrative part of the challenging multidisciplinary management of cerebral metastases, a neuro-oncologic entity, which has been observed to have an increased incidence over the last years. In selected cases, the surgical removal of the space-occupying mass reduces the intracranial pressure, normalizes the metabolic environment, reduces the symptom burden, and allows for the intensification of local and systemic adjuvant treatment. In detail, we discuss the incidence of brain metastases, the role of surgical resection, as well as the evolution of current neurosurgical techniques, the surgical morbidity and mortality of single and multiple lesions, and we enlighten the role of surgery for recurrent tumors.

Abstract

The multidisciplinary management of patients with brain metastases (BM) consists of surgical resection, different radiation treatment modalities, cytotoxic chemotherapy, and targeted molecular treatment. This review presents the current state of neurosurgical technology applied to achieve maximal resection with minimal morbidity as a treatment paradigm in patients with BM. In addition, we discuss the contribution of neurosurgical resection on functional outcome, advanced systemic treatment strategies, and enhanced understanding of the tumor biology.

Use of intraoperative fluorescence to enhance robot-assisted radical prostatectomy

Robot-assisted radical prostatectomy has become the standard of care for the removal of localized prostate cancer. Positive outcomes depend upon the precise removal of the prostate and associated tissue without damage to nearby structures. This process can be aided by fluorescence-guided surgery to enhance the visual contrast between different structures. Here the authors have conducted a systematic review using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to identify ten investigations into the use of fluorescence-guided surgery in robot-assisted radical prostatectomy. These studies used fluorescent tracers to identify structures, including the prostate, neurovascular bundle and lymph nodes. These studies demonstrate the safe and effective use of fluorescence-guided surgery in robot-assisted radical prostatectomy and pave the way for further developments in this field.

The impact of fluorescein-guided technique in the surgical removal of CNS tumors in a pediatric population: results from a multicentric observational study

BACKGROUND

Surgery has a fundamental role in central nervous system (CNS) tumors in the pediatric population, as aggressive resection correlates with prognosis. Due to its accumulation in areas with damaged blood brain barrier, sodium fluorescein (SF) could be a valid tool to improve the extent of resection in tumors enhancing at preoperative MRI. This study is aimed to systematically assess the utility of SF in a pediatric population.

METHODS

Patient data were collected in two centers, one in Italy and the other in Germany. At the induction of anesthesia, SF was administered intravenously (5 mg/kg). Surgery was performed using a YELLOW560 filter. Fluorescence intensity was graduated as bright, moderate or absent based on surgeon's opinion; furthermore, SF use was judged as "helpful," "not helpful" or "not essential" in tumor removal.

RESULTS

Twenty-four patients for 27 surgical procedures were identified. In 21 of 27 (77.8%) procedures fluorescence was reported as bright or moderate, in two of 27 (7.4%) absent and in four of 27 (14.8%) data were unavailable. Intraoperative fluorescence was reported in 21 of 25 (84%) surgeries whose corresponding preoperative MRI had shown contrast enhancement. In 14 of 27 (51.8%) surgical procedures SF was considered "helpful"; in two of 27 (7.4%) not "helpful"; in seven of 27 (25.9%) "not essential." In four of 27 (14.8%) data were unavailable. No adverse effect to SF was registered.

CONCLUSIONS

SF could be considered a valid and safe tool to improve visualization of tumors enhancing at preoperative MRI also in pediatric patients. Future prospective studies are needed to confirm these preliminary data.

The utilization of fluorescein in brain tumor surgery: a systematic review

INTRODUCTION

Sodium fluorescein (SF) is a green, water-soluble dye with the capacity to accumulate in cerebral areas as a result of damaged blood-brain barrier (BBB); this property allows SF to concentrate specifically at the tumor site of various types of brain neoplasms, making the tumor tissue more clearly visible.

EVIDENCE ACQUISITION

A literature search (1947-2018) was conducted with the keywords "fluorescein neurosurgery," "YELLOW neurosurgery," "fluorescein brain tumor," "YELLOW brain tumor." We included clinical studies, clinical trials, observational studies, only conducted on humans and concerning surgery; in addition, we have included 3 articles derived from the analysis of the references of other papers. Ultimately, 57 articles were included for further analysis.

EVIDENCE SYNTHESIS

Fluorescein as a fluorescent tracer in neuro-oncology is gaining a wider acceptance in the neurosurgical literature: until February 1st, 2018, at least 1099 neuro-oncological patients have been operated through fluorescein-assistance, mostly only after 2012. The most important application remains the aim to improve tumor visualization and extent of resection for high-grade gliomas (HGG), but the nonspecific mechanism of action is the theoretical base for its use also for tumors different from HGG. Nevertheless, no homogenous protocol of fluorescein utilization in neurosurgical oncology can be found in literature.

CONCLUSIONS

Fluorescein-guided surgery is a safe and effective technique to improve visualization and resection of different CNS tumors and conditions, based on BBB alteration, with a growing evidence-based background.

Fluorescence-Guided Surgery

Surgical resection of cancer remains an important treatment modality. Despite advances in preoperative imaging, surgery itself is primarily guided by the surgeon’s ability to locate pathology with conventional white light imaging. Fluorescence-guided surgery (FGS) can be used to define tumor location and margins during the procedure. Intraoperative visualization of tumors may not only allow more complete resections but also improve safety by avoiding unnecessary damage to normal tissue which can also reduce operative time and decrease the need for second-look surgeries. A number of new FGS imaging probes have recently been developed, complementing a small but useful number of existing probes. In this review, we describe current and new fluorescent probes that may assist FGS.

Sodium Fluorescein Facilitates Guided Sampling of Diagnostic Tumor Tissue in Nonenhancing Gliomas

BACKGROUND

Accurate tissue sampling in nonenhancing (NE) gliomas is a unique surgical challenge due to their intratumoral histological heterogeneity and absence of contrast enhancement as a guide for intraoperative stereotactic guidance. Instead, T2/fluid-attenuated inversion-recovery (FLAIR) hyperintensity on MRI is commonly used as an imaging surrogate for pathological tissue, but sampling from this region can yield nondiagnostic or underdiagnostic brain tissue. Sodium fluorescein is an intraoperative fluorescent dye that has a high predictive value for tumor identification in areas of contrast enhancement and NE in glioblastomas. However, the underlying histopathological alterations in fluorescent regions of NE gliomas remain undefined.

OBJECTIVE

To evaluate whether fluorescein can identify diagnostic tissue and differentiate regions with higher malignant potential during surgery for NE gliomas, thus improving sampling accuracy.

METHODS

Thirteen patients who presented with NE, T2/FLAIR hyperintense lesions suspicious for glioma received fluorescein (10%, 3 mg/kg intravenously) during surgical resection.

RESULTS

Patchy fluorescence was identified within the T2/FLAIR hyperintense area in 10 of 13 (77%) patients. Samples taken from fluorescent regions were more likely to demonstrate diagnostic glioma tissue and cytologic atypia (P < .05). Fluorescein demonstrated a 95% positive predictive value for the presence of diagnostic tissue. Samples from areas of fluorescence also demonstrated greater total cell density and higher Ki-67 labeling than nonfluorescent biopsies (P < .05).

CONCLUSION

Fluorescence in NE gliomas is highly predictive of diagnostic tumor tissue and regions of higher cell density and proliferative activity.

Fluorescein sodium-guided resection of cerebral metastases-an update

BACKGROUND

Cerebral metastasis (CM) is the most common malignancy affecting the brain. In patients eligible for surgery, complete tumor removal is the most important predictor of overall survival and neurological outcome. The emergence of surgical microscopes fitted with a fluorescein-specific filter have facilitated fluorescein-guided microsurgery and identification of tumor tissue. In 2012, we started evaluating fluorescein (FL) with the dedicated microscope filter in cerebral metastases (CM). After describing the treatment results of our first 30 patients, we now retrospectively report on 95 patients.

METHODS

Ninety-five patients with CM of different primary cancers were included (47 women, 48 men, mean age, 60 years, range, 25-85 years); 5 mg/kg bodyweight of FL was intravenously injected at induction of anesthesia. A YELLOW 560-nm filter (Pentero 900, ZEISS Meditec, Germany) was used for microsurgical tumor resection and resection control. The extent of resection (EOR) was assessed by means of early postoperative contrast-enhanced MRI and the grade of fluorescent staining as described in the surgical reports. Furthermore, we evaluated information on neurological outcome and surgical complications as well as any adverse events.

RESULTS

Ninety patients (95%) showed bright fluorescent staining that markedly enhanced tumor visibility. Five patients (5%); three with adenocarcinoma of the lung, one with melanoma of the skin, and one with renal cell carcinoma) showed insufficient FL staining. Thirteen patients (14%) showed residual tumor tissue on the postoperative MRI. Additionally, the MRI of three patients did not confirm complete resection beyond doubt. Thus, gross-total resection had been achieved in 83% (n = 79) of patients. No adverse events were registered during the postoperative course.

CONCLUSIONS

FL and the YELLOW 560-nm filter are safe and feasible tools for increasing the EOR in patients with CM. Further prospective evaluation of the FL-guided technique in CM-surgery is in planning.

Optical technologies for intraoperative neurosurgical guidance

Biomedical optics is a broadly interdisciplinary field at the interface of optical engineering, biophysics, computer science, medicine, biology, and chemistry, helping us understand light-tissue interactions to create applications with diagnostic and therapeutic value in medicine. Implementation of biomedical optics tools and principles has had a notable scientific and clinical resurgence in recent years in the neurosurgical community. This is in great part due to work in fluorescence-guided surgery of brain tumors leading to reports of significant improvement in maximizing the rates of gross-total resection. Multiple additional optical technologies have been implemented clinically, including diffuse reflectance spectroscopy and imaging, optical coherence tomography, Raman spectroscopy and imaging, and advanced quantitative methods, including quantitative fluorescence and lifetime imaging. Here we present a clinically relevant and technologically informed overview and discussion of some of the major clinical implementations of optical technologies as intraoperative guidance tools in neurosurgery.

Intraoperative fluorescein staining for benign brain tumors

OBJECTIVE

Successful use of high-dose fluorescein-sodium (20mg/kg) with a standard light microscope for resection of high-grade gliomas, meningiomas, hemangioblastoma and metastases was reported. The principle of brain tumor staining by fluorescein-sodium (Fl-Na) consists in the accumulation of fluorescein in brain tumors with impaired blood-brain barrier. The aim of our study was to investigate for the first time the usefulness of high-dose fluorescein in patients operated on for benign neuroepithelial brain tumors (grade I WHO tumors) with contrast enhancement on magnetic resonance imaging.

METHODS

Our study included 11 patients operated on for benign neuroepithelial primary brain tumors with contrast enhancement on magnetic resonance imaging (MRI): pilocytic astrocytomas (5 patients), dysembrioplastic neuroepithelial tumors (4) and gangliogliomas grade I (2). In all cases, Fl-Na was injected intravenously (20mg/kg) just after the craniotomy using a peripheral venous line. The dural opening was performed 10min later. Microsurgical tumor resection using conventional neurosurgical microscope guided by the fluorescein staining was performed.

RESULTS

Complete resection of the yellow-green stained tissue was achieved in 10 patients confirmed by postoperative control MRI study. Subtotal resection of the colored tissue was achieved in one case with fourth ventricle pilocytic astrocytoma because of the involvement of the medial eminence and functional constraints discovered during intraoperative neuromonitoring. Three patients have had a postoperative volume of resection greater than the tumor volume because of the planed perilesionectomy by our epilepsy surgery team. Surrounding tissue not stained by Fl-Na was obtained in these 3 cases. The histopathological examination did not find tumor tissue in the perilesional Fl-Na negative tissue. On the other hand, all 11 Fl-Na positive specimens presented signs of tumor involvement. We did not observe complications related to the use of high dose Fl-Na.

CONCLUSIONS

High doses intravenous Fl-Na seems to be a useful intraoperative technique for delineation of benign neuroepithelial brain tumors with contrast enhancement. Further larger studies may reveal the real value of high doses Fl-Na as intraoperative method for increasing the extent of resection in these particular indications.

A prospective study of microscope-integrated intraoperative fluorescein videoangiography during arteriovenous malformation surgery: preliminary results

OBJECT

The authors report on the use of a recently developed microscope-integrated fluorescent module using low-dose intravenous fluorescein for videoangiography during arteriovenous malformation (AVM) surgery.

METHODS

The authors analyzed the application of a low-dose intraoperative fluorescein in 4 consecutive patients undergoing AVM surgery. The ability to distinguish the associated vessels of the AVM from normal vessels and to assess the degree of AVM obliteration based on videoangiography of venous drainage was specifically analyzed.

RESULTS

All 4 patients underwent fluorescein angiography without complication. In each case, videoangiography confirmed recognition of feeding arteries and draining veins through the operating oculars under the fluorescent mode. In one case involving a large frontal AVM, videoangiography demonstrated mainly cortical veins on the surface of the AVM and alerted the senior author to first tackle the feeding arteries in the interhemispheric space. While evaluating the flow within the different draining veins after most of the AVM was disconnected, videoangiography also prioritized the order for disconnection of large draining veins to allow mobilization the AVM and exposure of the remaining deep arterial feeders. In the other 3 cases, videoangiography allowed easy recognition of the angioarchitecture of the AVMs, estimated its cortical boundaries, and most importantly, assessed the flow within the draining veins before their disconnection.

CONCLUSIONS

The authors found fluorescein videoangiography to be a useful adjunct in resection of AVMs. This technology offers the unique ability to visualize fluorescent vessels and nonfluorescent tissues in near-natural colors simultaneously and permits microsurgical manipulation of relevant structures under the fluorescent mode. Larger-scale studies are needed to establish its efficacy and wider applicability.

Neurosurgical confocal endomicroscopy: A review of contrast agents, confocal systems, and future imaging modalities

Background:

The clinical application of fluorescent contrast agents (fluorescein, indocyanine green, and aminolevulinic acid) with intraoperative microscopy has led to advances in intraoperative brain tumor imaging. Their properties, mechanism of action, history of use, and safety are analyzed in this report along with a review of current laser scanning confocal endomicroscopy systems. Additional imaging modalities with potential neurosurgical utility are also analyzed.

Methods:

A comprehensive literature search was performed utilizing PubMed and key words: In vivo confocal microscopy, confocal endomicroscopy, fluorescence imaging, in vivo diagnostics/neoplasm, in vivo molecular imaging, and optical imaging. Articles were reviewed that discussed clinically available fluorophores in neurosurgery, confocal endomicroscopy instrumentation, confocal microscopy systems, and intraoperative cancer diagnostics.

Results:

Current clinically available fluorescent contrast agents have specific properties that provide microscopic delineation of tumors when imaged with laser scanning confocal endomicroscopes. Other imaging modalities such as coherent anti-Stokes Raman scattering (CARS) microscopy, confocal reflectance microscopy, fluorescent lifetime imaging (FLIM), two-photon microscopy, and second harmonic generation may also have potential in neurosurgical applications.

Conclusion:

In addition to guiding tumor resection, intraoperative fluorescence and microscopy have the potential to facilitate tumor identification and complement frozen section analysis during surgery by providing real-time histological assessment. Further research, including clinical trials, is necessary to test the efficacy of fluorescent contrast agents and optical imaging instrumentation in order to establish their role in neurosurgery.

Skull Base Meningiomas and Cranial Nerves Contrast Using Sodium Fluorescein: A New Application of an Old Tool

Objective The identification of cranial nerves is one of the most challenging goals in the dissection of skull base meningiomas. The authors present an application of sodium fluorescein (SF) in skull base meningiomas with the purpose of improving the identification of cranial nerves. Design A prospective study within-subjects design. Setting Hospital Ernesto Dornelles, Porto Alegre, Brazil. Participants Patients with skull base meningiomas. Main Outcomes Measures Cranial nerve identification. Results The group of nine meningiomas was composed of one cavernous sinus, three petroclival, one tuberculum sellae, two sphenoid wing, one olfactory groove, and one temporal floor meningioma. The SF enhancement in all tumors was strong, and the contrast with cranial nerves clearly evident. There were one definite olfactory nerve deficit, one transient abducens deficit, and one definite hemiparesis. All lesions were resected (Simpson grades 1 and 2). The analysis of the difference of the delta SF wavelength between the meningiomas and cranial nerve contrast was performed by the Wilcoxon signed rank test and showed p = 0.011. Conclusions The contrast between the enhanced meningiomas and cranial nerves was evident and assisted in the visualization and microsurgical dissection of these structures. The anatomical preservation of these structures was improved using the contrast.

Convexity meningiomas enhanced by sodium fluorescein

Background:

The resection of the meningiomas surrounding the dura is an important goal during the removal of a convexity meningioma. The authors present the first application of sodium fluorescein (SF) as a tool for tumor and dural tail identification in convexity meningiomas.

Methods:

Five frontal convexity meningiomas operated on between December 2012 and April 2013 were included. After initial dissection a dose of 1 g of the SF, 20% was injected into a peripheral vein. Tumor and dural tail were removed using the correlation between magnetic resonance imaging (MRI) findings and transoperative SF enhancement.

Results:

Simpson Grade 1 removal was obtained in three cases, grade 2 in one atypical meningioma and grade zero in one case. SF dural tail enhancement was positive in all cases and histologic analysis evidenced involvement of the dura by tumors.

Conclusion:

SF enhancement was evident in meningiomas and dura surrounding the lesions. Histologic analysis confirmed dural involvement. SF could represent an universally available fluorescent tool for meningioma surgery.

Intraoperative fluorescence-guided resection of high-grade gliomas: a comparison of the present techniques and evolution of future strategies

OBJECTIVE

Fluorescence guidance has a demonstrated potential in maximizing the extent of high-grade glioma resection. Different fluorophores (fluorescent biomarkers), including 5-aminolevulinic acid (5-ALA) and fluorescein, have been examined with the use of several imaging techniques. Our goal was to review the state of this technology and discuss strategies for more widespread adoption.

METHODS

We performed a Medline search using the key words "fluorescence," "intraoperative fluorescence-guided resection," "intraoperative image-guided resection," and "brain glioma" for articles from 1960 until the present. This initial search revealed 267 articles. Each abstract and article was reviewed and the reference lists from select articles were further evaluated for relevance. A total of 64 articles included information about the role of fluorescence in resection of high-grade gliomas and therefore were selectively included for our analysis.

RESULTS

5-ALA and fluorescein sodium have shown promise as fluorescent markers in detecting residual tumor intraoperatively. These techniques have demonstrated a significant increase in the extent of tumor resection. Regulatory barriers have limited the use of 5-ALA and technological challenges have restricted the use of fluorescein and its derivatives in the United States. Limitations to this technology currently exist, such as the fact that fluorescence at tumor margins is not always reliable for identification of tumor-brain interface.

CONCLUSIONS

These techniques are safe and effective for increasing gross total resection. The development of more tumor-specific fluorophores is needed to resolve problems with subjective interpretation of fluorescent signal at tumor margins. Techniques such as quantum dots and polymer or iron oxide-based nanoparticles have shown promise as potential future tools.

Image-guided resection of malignant gliomas using fluorescent nanoparticles

Intraoperative fluorescence imaging especially near-infrared fluorescence (NIRF) imaging has the potential to revolutionize neurosurgery by providing high sensitivity and real-time image guidance to surgeons for defining gliomas margins. Fluorescence probes including targeted nanoprobes are expected to improve the specificity and selectivity for intraoperative fluorescence or NIRF tumor imaging. The main focus of this article is to provide a brief overview of intraoperative fluorescence imaging systems and probes including fluorescein sodium, 5-aminolevulinic acid, dye-containing nanoparticles, and targeted NIRF nanoprobes for their applications in image-guided resection of malignant gliomas. Moreover, photoacoustic imaging is a promising molecular imaging modality, and its potential applications for brain tumor imaging are also briefly discussed.

Fluorescence-guided surgery for glioblastoma multiforme using high-dose fluorescein sodium with excitation and barrier filters

We have developed a technique of fluorescence-guided surgery using high-dose fluorescein sodium (20mg/kg) with excitation and barrier filters for glioblastoma multiforme surgery. This technique was used in 10 patients, with surgery proceeding as expected in all patients. There were no complications or permanent side effects. This method uses filters to help distinguish between the usually invisible tumor and the brain surface, as well as allowing a detailed assessment of the positional relationships with tumor vessels and the surrounding normal vessels. As sufficient yellow staining was present even without filters, delicate microsurgery was also possible under a normal white-light microscope. Both environments could be used as necessary during surgery according to the requirements of resection, thereby improving the reliability and safety of surgery.

Gross total resection of glioma with the intraoperative fluorescence-guidance of fluorescein sodium

OBJECTIVE

High dose fluorescein sodium has been utilized for fluorescence-guided tumor resection with conflicting reports on the efficacy of this procedure. The aim of this study was to reevaluate the utility and clinical limitations of using fluorescein sodium for the treatment and resection of glioma brain tumors.

METHODS

Patients diagnosed with glioma were divided into two groups with a total of 22 patients enrolled in the study: 1) the study group (n=10), patients that received intravenous injection of fluorescein sodium and 2) the control group (n=12), patients that did not receive injections during surgical resection. Quality of life was evaluated according to Karnofsky Performance Scale (KPS) score and neurological status. Fluorescein sodium was intravenously injected at a dose of 15-20mg/kg of body weight. Glioma resection was evaluated preoperative and postoperatively with enhanced Magnetic Resonance Imaging (MRI).

RESULTS

Significant differences in the gross total resection (GTR) rates were observed between the two patient groups (Fisher's Exact Test p=0.047). Progressive free survival was significantly longer in the study group (Student's T-Test p=0.033) as well as in the GTR group (Student's T-Test p=0.0001) compared to the control and non-GTR groups, respectively. Three patients in the study group and four patients in the control group had transient neurological deterioration. One patient in the control group had permanent hemiplegia.

CONCLUSION

The intraoperative utility of using fluorescein sodium can significantly increase the GTR rate without obvious deterioration. In addition, we find that it is better to apply the fluorescein sodium in the cases with BBB (blood-brain barrier) disruption, which had been enhanced in preoperative MRI.

Anaphylactic reaction after fluorescein sodium administration during intracranial surgery

We present a male patient who underwent a fluorescein sodium-guided brain tumor excision and experienced an anaphylactic reaction with severe hypotension and bradycardia. A 54-year-old, 70 kg man of American Society of Anesthesiologists status II was seen with a history of glioma. In the 80th minute of the operation, 20 mg/kg intravenous (i.v.) fluorescein sodium was injected after dural opening. A few minutes later, the anaphylactic reaction was diagnosed. Surgery was ended and the patient was delivered to the intensive care unit with intubation. Laboratory values were: immunoglobulin E, 332 U (upper limit 100 U); and elevated tryptase, 3.12 mg/dL. In view of the expanding use of fluorescein sodium in clinical procedures, physicians should be alerted to this rare but life-threatening adverse event.

Review of Neurosurgical Fluorescence Imaging Methodologies

Fluorescence imaging in neurosurgery has a long historical development, with several different biomarkers and biochemical agents being used, and several technological approaches. This review focuses on the different contrast agents, summarizing endogenous fluorescence, exogenously stimulated fluorescence and exogenous contrast agents, and then on tools used for imaging. It ends with a summary of key clinical trials that lead to consensus studies. The practical utility of protoporphyrin IX (PpIX) as stimulated by administration of δ-aminolevulinic acid (ALA) has had substantial pilot clinical studies and basic science research completed. Recently multi-center clinical trials using PpIx fluorescence to guide resection have shown efficacy for improved short term survival. Exogenous agents are being developed and tested pre-clinically, and hopefully hold the potential for long term survival benefit if they provide additional capabilities for resection of micro-invasive disease or certain tumor sub-types that do not produce PpIX or help delineate low grade tumors. The range of technologies used for measurement and imaging ranges widely, with most clinical trials being carried out with either point probes or modified surgical microscopes. At this point in time, optimized probe approaches are showing efficacy in clinical trials, and fully commercialized imaging systems are emerging, which will clearly help lead to adoption into neurosurgical practice.

Coregistered fluorescence-enhanced tumor resection of malignant glioma: relationships between δ-aminolevulinic acid-induced protoporphyrin IX fluorescence, magnetic resonance imaging enhancement, and neuropathological parameters. Clinical article

OBJECT

The aim of this study was to investigate the relationships between intraoperative fluorescence, features on MR imaging, and neuropathological parameters in 11 cases of newly diagnosed glioblastoma multiforme (GBM) treated using protoporphyrin IX (PpIX) fluorescence-guided resection.

METHODS

In 11 patients with a newly diagnosed GBM, δ-aminolevulinic acid (ALA) was administered to enhance endogenous synthesis of the fluorophore PpIX. The patients then underwent fluorescence-guided resection, coregistered with conventional neuronavigational image guidance. Biopsy specimens were collected at different times during surgery and assigned a fluorescence level of 0-3 (0, no fluorescence; 1, low fluorescence; 2, moderate fluorescence; or 3, high fluorescence). Contrast enhancement on MR imaging was quantified using two image metrics: 1) Gd-enhanced signal intensity (GdE) on T1-weighted subtraction MR image volumes, and 2) normalized contrast ratios (nCRs) in T1-weighted, postGd-injection MR image volumes for each biopsy specimen, using the biopsy-specific image-space coordinate transformation provided by the navigation system. Subsequently, each GdE and nCR value was grouped into one of two fluorescence categories, defined by its corresponding biopsy specimen fluorescence assessment as negative fluorescence (fluorescence level 0) or positive fluorescence (fluorescence level 1, 2, or 3). A single neuropathologist analyzed the H & E-stained tissue slides of each biopsy specimen and measured three neuropathological parameters: 1) histopathological score (0-IV); 2) tumor burden score (0-III); and 3) necrotic burden score (0-III).

RESULTS

Mixed-model analyses with random effects for individuals show a highly statistically significant difference between fluorescing and nonfluorescing tissue in GdE (mean difference 8.33, p = 0.018) and nCRs (mean difference 5.15, p < 0.001). An analysis of association demonstrated a significant relationship between the levels of intraoperative fluorescence and histopathological score (χ(2) = 58.8, p < 0.001), between fluorescence levels and tumor burden (χ(2) = 42.7, p < 0.001), and between fluorescence levels and necrotic burden (χ(2) = 30.9, p < 0.001). The corresponding Spearman rank correlation coefficients were 0.51 (p < 0.001) for fluorescence and histopathological score, and 0.49 (p < 0.001) for fluorescence and tumor burden, suggesting a strongly positive relationship for each of these variables.

CONCLUSIONS

These results demonstrate a significant relationship between contrast enhancement on preoperative MR imaging and observable intraoperative PpIX fluorescence. The finding that preoperative MR image signatures are predictive of intraoperative PpIX fluorescence is of practical importance for identifying candidates for the procedure. Furthermore, this study provides evidence that a strong relationship exists between tumor aggressiveness and the degree of tissue fluorescence that is observable intraoperatively, and that observable fluorescence has an excellent positive predictive value but a low negative predictive value.

Fluorescence-guided surgery of metastatic brain tumors using fluorescein sodium

We aimed to demonstrate the effectiveness of fluorescence-guided surgery of metastatic brain tumors using fluorescein sodium. The study comprised 38 patients with metastatic brain tumors who underwent tumor resection after intravenous injection of fluorescein sodium. The local recurrence rate was investigated in 36 of the 38 patients, and compared for patients who had undergone surgery only and surgery plus whole-brain radiotherapy (WBRT). In 31 of 36 patients, the tumors had been completely resected using fluorescence-guided surgery. Postoperative WBRT was not performed in 20 of the 31 patients who underwent gross total resection. Although the recurrence rate for these 20 patients was 20%, compared to 9.1% for the 11 patients who also underwent postoperative WBRT, the difference was not statistically significant. Use of fluorescein sodium in metastatic brain tumor surgery may reduce the rate of local recurrence, and thus help improve the quality of life for these patients.

A low molecular weight PSMA-based fluorescent imaging agent for cancer

We synthesized YC-27 3 to provide a fluorescent imaging agent for the prostate-specific membrane antigen (PSMA), a marker for hormone-independent prostate cancer and tumor neovasculature, with suitable pharmacokinetics for use in vivo. Immediate precursor trifluoroacetate salt of 2-(3-{5-[7-(5-amino-1-carboxy-pentylcarbamoyl)-heptanoylamino]-1-carboxy-pentyl}-ureido)-pentanedioic acid 2 was conjugated with a commercially available near-infrared light-emitting dye (IRDye 800CW) to provide 3 in 72% yield. YC-27 3 demonstrated a PSMA inhibitory activity of 0.37nM and was capable of generating target-to-nontarget ratios of at least 10 in PSMA-expressing PC3-PIP vs. PSMA-negative PC3-flu tumors in vivo. YC-27 3 may be useful for study of PSMA-expressing tissue in preclinical models or for intraoperative guidance.