5-Aminolevulinic acid is a promising marker for detection of anaplastic foci in diffusely infiltrating gliomas with nonsignificant contrast enhancement

Glioblastoma in the real-world setting: patterns of care and outcome in the Austrian population

PURPOSE

We present results of a retrospective population-based investigation of patterns of care and outcome of glioblastoma patients in Austria.

PATIENTS AND METHODS

In this nation-wide cooperative project, all Austrian glioblastoma patients newly diagnosed between 2014 and 2018 and registered in the ABTR-SANOnet database were included. Histological typing used criteria of the WHO classification of CNS tumors, 4th edition 2016. Patterns of care were assessed, and all patients were followed until the end of 2019.

RESULTS

1,420 adult glioblastoma cases were identified. 813 (57.3%) patients were male and 607 (42.7%) female. Median age at diagnosis was 64 years (range: 18-88). Median overall survival (OS) was 11.6 months in the total cohort and 10.9 months in patients with proven IDH-wildtype. Median OS in the patient group ≤ 65 years receiving postoperative standard of care therapy was 16.1 months. In the patient group > 65 years with postoperative therapy, median OS was 11.2 months. Follow-up ≥ 5 years identified 13/264 (4.9%) long-term survivors. Brain tumor surgery frequently was assisted by 5-aminolevulinic acid (5-ALA) fluorescence (up to 55%). Postoperative treatment was initiated around one month after surgery (median: 31 days) following standardized protocols in 1,041/1,420 (73.3%) cases. In 830 patients (58.5%), concomitant radiochemotherapy was started according to the established standard of care. Treatment in case of progressive disease was considerably variable. 170/1,420 patients (12.0%) underwent a second surgical procedure, 467 (33.0%) received systemic treatment after progression, and 173 (12.2%) were re-irradiated.

CONCLUSION

Our data illustrate and confirm nation-wide translation of effective standard of care to Austrian glioblastoma patients in the recent past. In the case of progressive disease, highly variable therapeutic approaches were used, most frequently accompanied by anti-angiogenic therapy. Long-term survival was observed in a minor proportion of mostly younger patients who typically had gross total tumor resection, a favorable postoperative ECOG score, and standard of care therapy.

Fluorescence-Guided Surgical Techniques in Adult Diffuse Low-Grade Gliomas: State-of-the-Art and Emerging Techniques: A Systematic Review

Diffuse low-grade gliomas are infiltrative tumors whose margins are not distinguishable from the adjacent healthy brain parenchyma. The aim was to precisely examine the results provided by the intraoperative use of macroscopic fluorescence in diffuse low-grade gliomas and to describe the new fluorescence-based techniques capable of guiding the resection of low-grade gliomas. Only about 20% and 50% of low-grade gliomas are macroscopically fluorescent after 5-amino-levulinic acid (5-ALA) or fluorescein sodium intake, respectively. However, 5-ALA is helpful for detecting anaplastic foci, and thus choosing the best biopsy targets in diffuse gliomas. Spectroscopic detection of 5-ALA-induced fluorescence can detect very low and non-macroscopically visible concentrations of protoporphyrin IX, a 5-ALA metabolite, and, consequently, has excellent performances for the detection of low-grade gliomas. Moreover, these tumors have a specific spectroscopic signature with two fluorescence emission peaks, which is useful for distinguishing them not only from healthy brain but also from high-grade gliomas. Confocal laser endomicroscopy can generate intraoperative optic biopsies, but its sensitivity remains limited. In the future, the coupled measurement of autofluorescence and induced fluorescence, and the introduction of fluorescence detection technologies providing a wider field of view could result in the development of operator-friendly tools implementable in the operative routine.

Red light-activated depletion of drug-refractory glioblastoma stem cells and chemosensitization of an acquired-resistant mesenchymal phenotype

Glioblastoma stem cells (GSCs) are potent tumor initiators resistant to radiochemotherapy, and this subpopulation is hypothesized to re-populate the tumor milieu due to selection following conventional therapies. Here, we show that 5-aminolevulinic acid (ALA) treatment-a pro-fluorophore used for fluorescence-guided cancer surgery-leads to elevated levels of fluorophore conversion in patient-derived GSC cultures, and subsequent red light-activation induces apoptosis in both intrinsically temozolomide chemotherapy-sensitive and -resistant GSC phenotypes. Red light irradiation of ALA-treated cultures also exhibits the ability to target mesenchymal GSCs (Mes-GSCs) with induced temozolomide resistance. Furthermore, sub-lethal light doses restore Mes-GSC sensitivity to temozolomide, abrogating GSC-acquired chemoresistance. These results suggest that ALA is not only useful for fluorescence-guided glioblastoma tumor resection, but that it also facilitates a GSC drug-resistance agnostic, red light-activated modality to mop up the surgical margins and prime subsequent chemotherapy.

Localization of protoporphyrin IX during glioma-resection surgery via paired stimulated Raman histology and fluorescence microscopy

The most widely used fluorophore in glioma-resection surgery, 5-aminolevulinic acid (5-ALA), is thought to cause the selective accumulation of fluorescent protoporphyrin IX (PpIX) in tumour cells. Here we show that the clinical detection of PpIX can be improved via a microscope that performs paired stimulated Raman histology and two-photon excitation fluorescence microscopy (TPEF). We validated the technique in fresh tumour specimens from 115 patients with high-grade gliomas across four medical institutions. We found a weak negative correlation between tissue cellularity and the fluorescence intensity of PpIX across all imaged specimens. Semi-supervised clustering of the TPEF images revealed five distinct patterns of PpIX fluorescence, and spatial transcriptomic analyses of the imaged tissue showed that myeloid cells predominate in areas where PpIX accumulates in the intracellular space. Further analysis of external spatially resolved metabolomics, transcriptomics and RNA-sequencing datasets from glioblastoma specimens confirmed that myeloid cells preferentially accumulate and metabolize PpIX. Our findings question 5-ALA-induced fluorescence in glioma cells and show how 5-ALA and TPEF imaging can provide a window into the immune microenvironment of gliomas.

The Application of Sodium Fluorescein in Resection of Medulloblastoma Under YELLOW 560 Filter: Feasibility and Preliminary Results of a Monocentric Cohort and Systematic Review

BACKGROUND

Maximizing surgical resection of medulloblastoma (MB) affects overall survival; nevertheless, surgical resection remains a because of the infiltrative behavior of this tumor. Several dyes have been tested for improving tumor visualization; however, few reports with different protocols of fluorophores use are available and the results are inconsistent. Hence, we report our experience with sodium fluorescein in MB surgery, aiming to assess the role of this technique on the extent of resection. Furthermore, we performed a literature review of this topic.

METHODS

Fluorescence characteristics, extent of resection, and clinical outcome were analyzed in 9 consecutively operated patients with MB. A comprehensive literature search and review for English-language articles concerning fluorescein application in MB was conducted.

RESULTS

In our cohort, no side effect related to fluorescein occurred; all tumors presented with an intense or moderate yellow-green enhancement, and fluorescein was judged fundamental in distinguishing tumors from viable tissue in 7 of 9 cases. Gross total resection or near-total resection (i.e., a residual tumor volume <1.5 cm3) was achieved in 8 patients. The review explored the different techniques and surgical interpretations as well as surgical radicality; we did not find a homogenous protocol for fluorescein injection in the published articles. Fluorescence appeared moderate or intense in almost all cases, with a high percentage of usefulness and consensual achievement of a high rate of gross total resection.

CONCLUSIONS

Based on these results, we can infer that fluorescein-guided surgical resection is a safe and valuable method for patients with MB.

5-ALA induced PpIX fluorescence spectroscopy in neurosurgery: a review

The review begins with an overview of the fundamental principles/physics underlying light, fluorescence, and other light-matter interactions in biological tissues. It then focuses on 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence spectroscopy methods used in neurosurgery (e.g., intensity, time-resolved) and in so doing, describe their specific features (e.g., hardware requirements, main processing methods) as well as their strengths and limitations. Finally, we review current clinical applications and future directions of 5-ALA-induced protoporphyrin IX (PpIX) fluorescence spectroscopy in neurosurgery.

5-aminolevulinic acid-guided endoscopic biopsy with violet light-emitting diode flashlight in malignant glioma: Technical note

Background

5-aminolevulinic acid (5-ALA) photodynamic diagnosis (PDD) has enabled better identification of malignant tumor cells and real-time intraoperative guidance. Here, we report a reasonable procedure for 5-ALA-guided endoscopic biopsy with a violet light-emitting diode (LED) flashlight for deep-seated malignant gliomas.

Methods

A 63-year-old man presented with a headache and left upper homonymous quadrantanopia. Imaging studies showed atypical lesions with non-significant and partial contrast enhancement in the right deep temporo-occipital lobe. An endoscopic biopsy was performed under the guidance of 5-ALA PDD with a violet LED flashlight.

Results

The tumor tissues, which were difficult to distinguish from normal brain parenchyma under white light, were positive for 5-ALA fluorescence. The histopathological diagnosis was astrocytoma (the World Health Organization grade 3). The patient underwent adjuvant chemoradiation therapy. Headache and anopia improved, and no recurrence was observed at 12 months follow-up.

Conclusion

This technique of neuroendoscopic biopsy guided by 5-ALA PDD fluorescence with a violet LED flashlight may allow a safe and accurate diagnosis of deep-seated malignant gliomas.

How Reliable Is Fluorescence-Guided Surgery in Low-Grade Gliomas? A Systematic Review Concerning Different Fluorophores

BACKGROUND

Fluorescence-guided surgery has been increasingly used to support glioma surgery with the purpose of obtaining a maximal safe resection, in particular in high-grade gliomas, while its role is less definitely assessed in low-grade gliomas.

METHODS

A systematic review was conducted. 5-aminolevulinic acid, sodium fluorescein, indocyanine green and tozuleristide were taken into account. The main considered outcome was the fluorescence rate, defined as the number of patients in whom positive fluorescence was detected out of the total number of patients. Only low-grade gliomas were considered, and data were grouped according to single fluorophores.

RESULTS

16 papers about 5-aminolevulinic acid, 4 about sodium fluorescein, 2 about indocyanine green and 1 about tozuleristide were included in the systematic review. Regarding 5-aminolevulinic acid, a total of 467 low-grade glioma patients were included, and fluorescence positivity was detected in 34 out of 451 Grade II tumors (7.3%); while in Grade I tumors, fluorescence positivity was detected in 9 out of 16 cases. In 16 sodium fluorescein patients, seven positive fluorescent cases were detected. As far as indocyanine is concerned, two studies accounting for six patients (three positive) were included, while for tozuleristide, a single clinical trial with eight patients (two positive) was retrieved.

CONCLUSIONS

The current evidence does not support the routine use of 5-aminolevulinic acid or sodium fluorescein with a standard operating microscope because of the low fluorescence rates. New molecules, including tozuleristide, and new techniques for fluorescence detection have shown promising results; however, their use still needs to be clinically validated on a large scale.

Resection of the contrast-enhancing tumor in diffuse gliomas bordering eloquent areas using electrophysiology and 5-ALA fluorescence: evaluation of resection rates and neurological outcome-a systematic review and meta-analysis

Independently, both 5-aminolevulinic acid (5-ALA) and intraoperative neuromonitoring (IONM) have been shown to improve outcomes with high-grade gliomas (HGG). The interplay and overlap of both techniques are scarcely reported in the literature. We performed a systematic review and meta-analysis focusing on the concomitant use of 5-ALA and intraoperative mapping for HGG located within eloquent cortex. Using PRISMA guidelines, we reviewed articles published between May 2006 and December 2022 for patients with HGG in eloquent cortex who underwent microsurgical resection using intraoperative mapping and 5-ALA fluorescence guidance. Extent of resection was the primary outcome. The secondary outcome was new neurological deficit at day 1 after surgery and persistent at day 90 after surgery. Overall rate of complete resection of the enhancing tumor (CRET) was 73.3% (range: 61.9-84.8%, p < .001). Complete 5-ALA resection was performed in 62.4% (range: 28.1-96.7%, p < .001). Surgery was stopped due to mapping findings in 20.5% (range: 15.6-25.4%, p < .001). Neurological decline at day 1 after surgery was 29.2% (range: 9.8-48.5%, p = 0.003). Persistent neurological decline at day 90 after surgery was 4.6% (range: 0.4-8.7%, p = 0.03). Maximal safe resection guided by IONM and 5-ALA for high-grade gliomas in eloquent areas is achievable in a high percentage of cases (73.3% CRET and 62.4% complete 5-ALA resection). Persistent neurological decline at postoperative day 90 is as low as 4.6%. A balance between 5-ALA and IONM should be maintained for a better quality of life while maximizing oncological control.

A birefringent spectral demultiplexer enables fast hyper-spectral imaging of protoporphyrin IX during neurosurgery

Hyperspectral imaging and spectral analysis quantifies fluorophore concentration during fluorescence-guided surgery1-6. However, acquisition of the multiple wavelengths required to implement these methods can be time-consuming and hinder surgical workflow. To this end, a snapshot hyperspectral imaging system capable of acquiring 64 channels of spectral data simultaneously was developed for rapid hyperspectral imaging during neurosurgery. The system uses a birefringent spectral demultiplexer to split incoming light and redirect wavelengths to different sections of a large format microscope sensor. Its configuration achieves high optical throughput, accepts unpolarized input light and exceeds channel count of prior image-replicating imaging spectrometers by 4-fold. Tissue-simulating phantoms consisting of serial dilutions of the fluorescent agent characterize system linearity and sensitivity, and comparisons to performance of a liquid crystal tunable filter based hyperspectral imaging device are favorable. The new instrument showed comparable, if not improved, sensitivity at low fluorophore concentrations; yet, acquired wide-field images at more than 70-fold increase in frame rate. Image data acquired in the operating room during human brain tumor resection confirm these findings. The new device is an important advance in achieving real-time quantitative imaging of fluorophore concentration for guiding surgery.

Refining the Intraoperative Identification of Suspected High-Grade Glioma Using a Surgical Fluorescence Biomarker: GALA BIDD Study Report

Background. Improving intraoperative accuracy with a validated surgical biomarker is important because identifying high-grade areas within a glioma will aid neurosurgical decision-making and sampling. Methods. We designed a multicentre, prospective surgical cohort study (GALA-BIDD) to validate the presence of visible fluorescence as a pragmatic intraoperative surgical biomarker of suspected high-grade disease within a tumour mass in patients undergoing 5-aminolevulinic acid (5-ALA) fluorescence-guided cytoreductive surgery. Results. A total of 106 patients with a suspected high-grade glioma or malignant transformation of a low-grade glioma were enrolled. Among the 99 patients who received 5-ALA, 89 patients were eligible to assess the correlation of fluorescence with diagnosis as per protocol. Of these 89, 81 patients had visible fluorescence at surgery, and 8 patients had no fluorescence. A total of 80 out of 81 fluorescent patients were diagnosed as high-grade gliomas on postoperative central review with 1 low-grade glioma case. Among the eight patients given 5-ALA who did not show any visible fluorescence, none were high-grade gliomas, and all were low-grade gliomas. Of the seven patients suspected radiologically of malignant transformation of low-grade gliomas and with visible fluorescence at surgery, six were diagnosed with high-grade gliomas, and one had no tissue collected. Conclusion. In patients where there is clinical suspicion, visible 5-ALA fluorescence has clinical utility as an intraoperative surgical biomarker of high-grade gliomas and can aid surgical decision-making and sampling. Further studies assessing the use of 5-ALA to assess malignant transformation in all diffuse gliomas may be valuable.

Flavin fluorescence lifetime and autofluorescence optical redox ratio for improved visualization and classification of brain tumors

Purpose

Modern techniques for improved tumor visualization have the aim to maximize the extent of resection during brain tumor surgery and thus improve patient prognosis. Optical imaging of autofluorescence is a powerful and non-invasive tool to monitor metabolic changes and transformation in brain tumors. Cellular redox ratios can be retrieved from fluorescence emitted by the coenzymes reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD). Recent studies point out that the influence of flavin mononucleotide (FMN) has been underestimated.

Experimental design

Fluorescence lifetime imaging and fluorescence spectroscopy were performed through a modified surgical microscope. We acquired 361 flavin fluorescence lifetime (500-580 nm) and fluorescence spectra (430-740 nm) data points on freshly excised different brain tumors: low-grade gliomas (N=17), high-grade gliomas (N=42), meningiomas (N=23), metastases (N=26) and specimens from the non-tumorous brain (N=3).

Results

Protein-bound FMN fluorescence in brain tumors did increase with a shift toward a more glycolytic metabolism (R=-0.87). This increased the average flavin fluorescence lifetime in tumor entities with respect to the non-tumorous brain. Further, these metrics were characteristic for the different tumor entities and showed promise for machine learning based brain tumor classification.

Conclusions

Our results shed light on FMN fluorescence in metabolic imaging and outline the potential for supporting the neurosurgeon in visualizing and classifying brain tumor tissue during surgery.

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.

Deep proteome investigation of high-grade gliomas reveals heterogeneity driving differential metabolism of 5-aminolevulinic acid

Background

Fluorescence-guided surgery (FGS) using 5-aminolevulinic acid (5-ALA) as adjunct for high-grade gliomas (HGGs) has been on the rise in recent years. Despite being largely effective, we observed multiple histologically similar sub-regions of the same tumor from a few individuals with varying protoporphyrin IX (PpIX) levels. The current study aims at understanding the proteomic changes driving differential metabolism of 5-ALA in HGGs.

Methods

Biopsies were histologically and biochemically assayed. Following this, a deep proteomics investigation was carried out using high resolution liquid chromatography-mass spectrometry (HR LC-MS) to identify protein expression in differentially fluorescing regions of HGGs.

Results

Our analysis identified 5437 proteins with high confidence. Differential analysis in the subgroup with HGGs carrying IDH mutation (IDH mt.) revealed 93 differentially regulated proteins (raw p-value ≤ 0.05 and absolute FC ≥ 1.5). Similar analysis in the IDH wild type (IDH wt.) subgroup revealed 20 differentially regulated proteins. Gene set enrichment analysis (GSEA) identified key pathways like ion channel transport, trafficking of AMPA receptors, and regulation of heme-oxygenase-1 in the IDH wt. subgroup. Pathways such as scavenging of heme, signaling by NOTCH4, negative regulation of PI3-AKT pathway, and iron uptake and transport were observed to be differentially regulated in the IDH mt. subgroup.

Conclusions

Tumor regions from the same patient exhibiting differential fluorescence following 5-ALA administration were observed to have different proteome profiles. Future studies aimed at a better molecular understanding of 5-ALA metabolism in HGGs hold the potential to increase the efficacy of FGS and the use of 5-ALA as a theragnostic tool.

Review of Intraoperative Adjuncts for Maximal Safe Resection of Gliomas and Its Impact on Outcomes

Maximal safe resection is the mainstay of treatment in the neurosurgical management of gliomas, and preserving functional integrity is linked to favorable outcomes. How these modalities differ in their effectiveness on the extent of resection (EOR), survival, and complications remains unknown. A systematic literature search was performed with the following inclusion criteria: published between 2005 and 2022, involving brain glioma surgery, and including one or a combination of intraoperative modalities: intraoperative magnetic resonance imaging (iMRI), awake/general anesthesia craniotomy mapping (AC/GA), fluorescence-guided imaging, or combined modalities. Of 525 articles, 464 were excluded and 61 articles were included, involving 5221 glioma patients, 7(11.4%) articles used iMRI, 21(36.8%) used cortical mapping, 15(24.5%) used 5-aminolevulinic acid (5-ALA) or fluorescein sodium, and 18(29.5%) used combined modalities. The heterogeneity in reporting the amount of surgical resection prevented further analysis. Progression-free survival/overall survival (PFS/OS) were reported in 18/61(29.5%) articles, while complications and permanent disability were reported in 38/61(62.2%) articles. The reviewed studies demonstrate that intraoperative adjuncts such as iMRI, AC/GA mapping, fluorescence-guided imaging, and a combination of these modalities improve EOR. However, PFS/OS were underreported. Combining multiple intraoperative modalities seems to have the highest effect compared to each adjunct alone.

From white to blue light: evolution of endoscope-assisted intracranial tumor neurosurgery and expansion to intraaxial tumors

OBJECTIVE

Intraoperative use of the endoscope to assist in visualization of intracranial tumor pathology has expanded with increasing surgeon experience and improved instrumentation. The authors aimed to study how advancements in endoscopic technology have affected the evolution of endoscope use, with particular focus on blue light-filter modification allowing for discrimination of fluorescent tumor tissue following 5-ALA administration.

METHODS

A retrospective analysis of patients undergoing craniotomy for tumor resection at a single institution between February 2012 and July 2021 was performed. Patients were included if the endoscope was used for diagnostic tumor cavity inspection or therapeutic assistance with tumor resection following standard craniotomy and microsurgical tumor resection, with emphasis on those cases in which blue light endoscopy was used. Medical records were queried for patient demographics, operative reports describing the use of the endoscope and extent of resection, associations with tumor pathology, and postoperative outcomes. Preoperative and postoperative MR images were reviewed for radiographic extent of resection.

RESULTS

A total of 52 patients who underwent endoscope-assisted craniotomy for tumor were included. Thirty patients (57.7%) were men and the average age was 52.6 ± 16.1 years. Standard white light endoscopes were used for assistance with tumor resection in 28 cases (53.8%) for tumors primarily located in the ventricular system, parasellar region, and cerebellopontine angle. A blue light endoscope for detection of 5-ALA fluorescence was introduced into our practice in 2014 and subsequently used for assistance with tumor resection in 24 cases (46.2%) (intraaxial: n = 22, extraaxial: n = 2). Beyond the use of the surgical microscope as the primary visualization source, the blue light endoscope was used to directly perform additional tumor resection in 19/21 cases as a result of improved fluorescence detection as compared to the surgical microscope. No complications were associated with the use of the endoscope or with additional resection performed under white or blue light visualization.

CONCLUSIONS

Endoscopic assistance to visualize intracranial tumors had previously been limited to white light, assisting mostly in the visualization of extraaxial tumors confined to intraventricular and cisternal compartments. Blue light-equipped endoscopes provide improved versatility and visualization of 5-ALA fluorescing tissue beyond the capability of the surgical microscope, thereby expanding its use into the realm of intraaxial tumor resections.

5-Aminolevulinic acid-enhanced fluorescence-guided treatment of high-grade glioma using angled endoscopic blue light visualization: technical case series with preliminary follow-up

OBJECTIVE

5-Aminolevulinic acid (5-ALA)-enhanced fluorescence-guided resection of high-grade glioma (HGG) using microscopic blue light visualization offers the ability to improve extent of resection (EOR); however, few descriptions of HGG resection performed using endoscopic blue light visualization are currently available. In this report, the authors sought to describe their surgical experience and patient outcomes of 5-ALA-enhanced fluorescence-guided resection of HGG using primary or adjunctive endoscopic blue light visualization.

METHODS

The authors performed a retrospective review of prospectively collected data from 30 consecutive patients who underwent 5-ALA-enhanced fluorescence-guided biopsy or resection of newly diagnosed HGG was performed. Patient demographic data, tumor characteristics, surgical technique, EOR, tumor fluorescence patterns, and progression-free survival were recorded.

RESULTS

In total, 30 newly diagnosed HGG patients were included for analysis. The endoscope was utilized for direct 5-ALA-guided port-based biopsy (n = 9), microscopic to endoscopic (M2E; n = 18) resection, or exoscopic to endoscopic (E2E; n = 3) resection. All endoscopic biopsies of fluorescent tissue were diagnostic. 5-ALA-enhanced tumor fluorescence was visible in all glioblastoma cases, but only in 50% of anaplastic astrocytoma cases and no anaplastic oligodendroglioma cases. Gross-total resection (GTR) was achieved in 10 patients in whom complete resection was considered safe, with 11 patients undergoing subtotal resection. In all cases, endoscopic fluorescence was more avid than microscopic fluorescence. The endoscope offered the ability to diagnose and resect additional tumor not visualized by the microscope in 83.3% (n = 10/12) of glioblastoma cases, driven by angled lenses and increased fluorescence facilitated by light source delivery within the cavity. Mean volumetric EOR was 90.7% in all resection patients and 98.8% in patients undergoing planned GTR. No complications were attributable to 5-ALA or blue light endoscopy.

CONCLUSIONS

The blue light endoscope is a viable primary or adjunctive visualization platform for optimization of 5-ALA-enhanced HGG fluorescence. Implementation of the blue light endoscope to guide resection of HGG glioma is feasible and ergonomically favorable, with a potential advantage of enabling increased detection of tumor fluorescence in deep surgical cavities compared to the microscope.

5-ALA-guided tumor resection during awake speech mapping in gliomas located in eloquent speech areas: Single-center experience

Background

Achieving maximal functionally safe resection of gliomas located within the eloquent speech areas is challenging, and there is a lack of literature on the combined use of 5-aminolevulinic acid (5-ALA) guidance and awake craniotomy.

Objective

The aim of this study was to describe our experience with the simultaneous use of 5-ALA fluorescence and awake speech mapping in patients with left frontal gliomas located within the vicinity of eloquent speech areas.

Materials and methods

A prospectively collected database of patients was reviewed. 5-ALA was administered at a dose of 20 mg/kg 2 h prior to operation, and an operating microscope in BLUE400 mode was used to visualize fluorescence. All patients underwent surgery using the "asleep-awake-asleep" protocol with monopolar and bipolar electrical stimulation to identify the proximity of eloquent cortex and white matter tracts and to guide safe limits of resection along with fluorescence guidance. Speech function was assessed by a trained neuropsychologist before, during, and after surgery.

Results

In 28 patients operated with cortical mapping and 5-ALA guidance (12 Grade 4, 6 Grade 3, and 10 Grade 2 gliomas), Broca's area was identified in 23 cases and Wernicke's area was identified in 5 cases. Fluorescence was present in 14 cases. Six tumors had residual fluorescence due to the positive speech mapping in the tumor bed. Transient aphasia developed in 14 patients, and permanent aphasia developed in 4 patients. In 6 patients operated with cortical and subcortical speech mapping and 5-ALA guidance (4 Grade 4, 1 Grade 3, and 1 Grade 2 gliomas), cortical speech areas were mapped in 5 patients and subcortical tracts were encountered in all cases. In all cases, resection was stopped despite the presence of residual fluorescence due to speech mapping findings. Transient aphasia developed in 6 patients and permanent aphasia developed in 4 patients. In patients with Grade 2-3 gliomas, targeted biopsy of focal fluorescence areas led to upgrading the grade and thus more accurate diagnosis.

Conclusion

5-ALA guidance during awake speech mapping is useful in augmenting the extent of resection for infiltrative high-grade gliomas and identifying foci of anaplasia in non-enhancing gliomas, while maintaining safe limits of functional resection based on speech mapping. Positive 5-ALA fluorescence in diffuse Grade 2 gliomas may be predictive of a more aggressive disease course.

CD34 microvascularity in low-grade glioma: correlation with 5-aminolevulinic acid fluorescence and patient prognosis in a multicenter study at three specialized centers

OBJECTIVE

Early markers are urgently needed in low-grade glioma (LGG) evaluation to rapidly estimate the individual patient's prognosis and to determine the optimal postoperative management. Generally, visible 5-aminolevulinic acid (5-ALA) fluorescence is present in only a few LGGs. Recently, the authors identified visible 5-ALA fluorescence as a powerful intraoperative marker for unfavorable outcome in LGG treatment. However, its precise histopathological correlate is unclear. Neoangiogenesis represents a crucial event in tumor evolution, and CD34 is an established marker for vascular endothelial progenitors potentially indicating tumor progression. The aim of this study was thus to correlate 5-ALA fluorescence and CD34 microvascularity as well as to investigate the prognostic value of CD34 in a large series of LGGs.

METHODS

In this retrospective study including 3 specialized centers, patients with histopathologically confirmed isocitrate dehydrogenase-mutated LGGs (WHO grade II) receiving 5-ALA prior to resection were included. During surgery, the presence of visible fluorescence was analyzed and one representative tumor sample from the area with the maximum fluorescence effect (tumor with focal fluorescence or nonfluorescing tumor) was selected for each LGG. All fluorescing or nonfluorescing tumor samples were stained for CD34 and semiquantitatively analyzed for microvascular proliferation patterns (physiological vessels, branching capillaries, or microvessel clusters) as well as automatically quantified for CD34 microvessel density (MVD) by standardized histomorphometry software. These semiquantitative/quantitative CD34 data were correlated to the fluorescence status and patient outcome including progression-free survival (PFS), malignant transformation-free survival (MTFS), and overall survival (OS).

RESULTS

In a total of 86 LGGs, visible fluorescence was found during surgery in 13 (15%) cases. First, the semiquantitative CD34 score significantly correlated with intraoperative fluorescence (p = 0.049). Accordingly, the quantitative CD34 MVD was significantly higher in tumors showing fluorescence (p = 0.03). Altogether, the semiquantitative CD34 score showed a strong correlation with quantitative CD34 MVD (p < 0.001). At a mean follow-up of 5.4 ± 2.6 years, microvessel clusters in semiquantitative analysis were a prognostic marker for poor PFS (p = 0.01) and MTFS (p = 0.006), but not OS (p = 0.28). Finally, quantitative CD34 MVD > 10 vessels/mm2 was a prognostic marker for poor PFS (p = 0.01), MTFS (p = 0.008), and OS (p = 0.049).

CONCLUSIONS

The data indicate that CD34 microvascularity is associated with intraoperative 5-ALA fluorescence and outcomes in patients with LGG. Thus, visible fluorescence in LGGs might indicate increased CD34 microvascularity, serving as an early prognostic marker for unfavorable patient outcome that is already available during surgery.

Development and validation of a triple-LED surgical loupe device for fluorescence-guided resections with 5-ALA

OBJECTIVE

Fluorescence-guided resections performed using 5-aminolevulinic acid (5-ALA) have been studied extensively using the BLUE400 system. The authors introduce a triple-light-emitting diode (LED) headlight/loupe device for visualizing fluorescence, and compare this to the BLUE400 gold standard in order to assure similar and not more or less sensitive protoporphyrin-IX visualization.

METHODS

The authors defined the spectral requirements for a triple-LED headlight/loupe device for reproducing the xenon-based BLUE400 module. The system consisted of a white LED (normal surgery), a 409-nm LED for excitation, a 450-nm LED for background illumination, and appropriate observation filters. The prototype's excitation and emission spectra, illumination and detection intensities, and spot homogeneity were determined. The authors further performed a prospectively randomized and blinded study for fluorescence assessments of fresh, marginal, fluorescing and nonfluorescing tumor samples comparing the LED/loupe device with BLUE400 in patients with malignant glioma treated with 20 mg/kg body weight 5-ALA. Tumor samples were immediately assessed in turn, both with a Kinevo and with a novel triple-LED/loupe device by different surgeons.

RESULTS

Seven triple-LED/loupe devices were analyzed. Illumination intensities in the 409- and 450-nm range were comparable to BLUE400, with high spot homogeneity. Fluorescence intensities measured distally to microscope oculars/loupes were 9.9-fold higher with the loupe device. For validation 26 patients with malignant gliomas with 240 biopsies were analyzed. With BLUE400 results as the reference, sensitivity for reproducing fluorescence findings was 100%, specificity was 95%, positive predictive value was 98%, negative predictive value was 100%, and accuracy was 95%. This study reached its primary aim, with agreement in 226 of 240 (94.2%, 95% CI 0.904-0.968).

CONCLUSIONS

The authors observed only minor differences regarding spectra and illumination intensities during evaluation. Fluorescence intensities available to surgeons were 9.9-fold higher with the loupe device. Importantly, the independent perception of fluorescence achieved using the new system and BLUE400 was statistically equivalent. The authors believe the triple-LED/loupe device to be a useful and safe option for surgeons who prefer loupes to the microscope for resections in appropriate patients.

Utility of 5-ALA for resection of CNS tumours other than high-grade gliomas: a protocol for a systematic review

INTRODUCTION

5-aminolevulinic acid (5-ALA) is a proagent developed for fluorescent-guided surgery for high-grade glioma patients associated with a significant increase in resection conferring survival. 5-ALA was shown to penetrate the blood-brain barrier accumulating in malignant glioma cells with high selectivity, sensitivity and positive predictive value. However, those have yet to be explored aiding diagnosis for tumours of the central nervous system (CNS) other than high-grade gliomas (HGG). No up-to-date systematic review exists reporting the major surgical outcomes and diagnostic accuracy. We sought to conduct a systematic review of the literature summarising surgical outcomes, evaluate the quality of diagnostic accuracy reported in the literature and qualitatively assess the evidence to inform future studies.

METHODS AND ANALYSIS

We will search electronic databases (Medline, Embase) with subsequent interrogation of references lists of articles reporting the use of 5-ALA for brain tumours other than high-grade glioma adult patients, which also report the extent of resection and/or survival. Prospective and retrospective cohort and case-control studies with more than five patients will be included. Two independent reviewers will screen the abstracts and full articles, with a third reviewer resolving any conflicts. The data will be extracted in a standardised template and outcomes will be reported using descriptive statists. The quality of non-randomised studies will be appraised.

ETHICS AND DISSEMINATION

The study will summarise the available evidence on the effect of the clinical utility of 5-ALA in achieving resection and improving survival and its diagnostic accuracy for tumours of the CNS other than HGG. The data will be presented nationally and internationally and the manuscript will be published in a peer-reviewed journal. No ethical approvals were needed. The aim is to inform prospective studies minimising reporting bias allowing for more reliable, reproducible and generalisable results. The study has been registered in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.PROSPERO registration numberCRD42021260542.

Evolutionary Trend Analysis of Research on 5-ALA Delivery and Theranostic Applications Based on a Scientometrics Study

5-aminolevulinic acid (5-ALA) has been extensively studied for its sustainability and broad-spectrum applications in medical research and theranostics, as well as other areas. It’s a precursor of protoporphyrin IX (PpIX), a sustainable endogenous and naturally-existing photosensitizer. However, to the best of our knowledge, a scientometrics study based on the scientific knowledge assay of the overall situation on 5-ALA research has not been reported so far, which would be of major importance to the relevant researchers. In this study, we collected all the research articles published in the last two decades from the Web of Science Core Collection database and employed bibliometric methods to comprehensively analyze the dataset from different perspectives using CiteSpace. A total of 1595 articles were identified. The analysis results showed that China published the largest number of articles, and SBI Pharmaceuticals Co., Ltd. was the most productive institution that sponsored several of the most productive authors. The cluster analysis and burst detections indicated that the improvement of photodynamic efficacy theranostics is the up-to-date key direction in 5-ALA research. Furthermore, we emphatically studied nanotechnology involvement in 5-ALA delivery and theranostics research. We envision that our results will be beneficial for researchers to have a panorama of and deep insights into this area, thus inspiring further exploitations, especially of the nanomaterial-based systems for 5-ALA delivery and theranostic applications.

The application of fluorescein sodium for the resection of medulloblastoma

Introduction

Surgical resection of medulloblastoma (MB) remains a challenge. At present, a variety of tracers have been used for intraoperative tumor visualization. However, there are few reports on the intraoperative visualization of MB. Hence, we reported our experience of applying fluorescein sodium (FS) in MB surgery.

Methods

We retrospectively analyzed the clinical information of patients with MB confirmed by surgery and pathology from January 2016 to December 2020 from Sun Yat-sen University Cancer Center. A total of 62 patients were enrolled, of which 27 received intraoperative FS and 35 did not. The intraoperative dose of FS was 3 mg/kg.

Results

Among the 62 patients, 42 were males, and twenty were females. The age of onset in the FS group was 9.588 ± 7.322, which in the non-fluorescein sodium group was 13.469 ± 10.968, p = 0.198. We did not find significant differences in tumor location, tumor size, tumor resection, tumor histology, and preoperative symptoms (hydrocephalus, headache, vomit, balance disorder) between the groups. There was no significant difference in the postoperative symptoms (hydrocephalus, headache, vomiting, balance disorder, and cerebellar mutism). However, patients in the FS group had a relatively low incidence of balance disorder and cerebellar mutism. There was definite fluorescence of tumor in all cases of the FS group, and even the tiny metastatic lesion was visible. No case had side effects related to the use of FS.

Conclusions

FS is safe and effective in MB surgery. Whether the application of FS for surgery can reduce complications remains to be studied in the future.

A Data-Driven Approach to Predicting 5-Aminolevulinic Acid-Induced Fluorescence and World Health Organization Grade in Newly Diagnosed Diffuse Gliomas

BACKGROUND

A growing body of evidence has revealed the potential utility of 5-aminolevulinic acid (5-ALA) as a surgical adjunct in selected lower-grade gliomas. However, a reliable means of identifying which lower-grade gliomas will fluoresce has not been established.

OBJECTIVE

To identify clinical and radiological factors predictive of intraoperative fluorescence in intermediate-grade gliomas. In addition, given that higher-grade gliomas are more likely to fluoresce than lower-grade gliomas, we also sought to develop a means of predicting glioma grade.

METHODS

We investigated a cohort of patients with grade II and grade III gliomas who received 5-ALA before resection at a single institution. Using a logistic regression-based model, we evaluated 14 clinical and molecular variables considered plausible determinants of fluorescence. We then distilled the most predictive features to develop a model for predicting both fluorescence and tumor grade. We also explored the relationship between intraoperative fluorescence and diagnostic molecular markers.

RESULTS

One hundered seventy-nine subjects were eligible for inclusion. Our logistic regression classifier accurately predicted intraoperative fluorescence in our cohort with 91.9% accuracy and revealed enhancement as the singular variable in determining intraoperative fluorescence. There was a direct relationship between enhancement on MRI and the likelihood of observed fluorescence. Observed fluorescence correlated with MIB-1 index but not with isocitrate dehydrogenase (IDH) status, 1p19q codeletion, or methylguanine DNA methyltransferase promoter methylation.

CONCLUSION

We demonstrate a strong correlation between enhancement on preoperative MRI and the likelihood of visible fluorescence during surgery in patients with intermediate-grade glioma. Our analysis provides a robust method for predicting 5-ALA-induced fluorescence in patients with grade II and grade III gliomas.

5-Aminolevulinic acid a biomarker for worse prognosis in IDH-wildtype brain tumors? Evolution of a Fluorescence-Positive Diffuse Astrocytoma: Case Report

Introduction  In 2017, the U.S. Food and Drug Administration (FDA) approved 5-aminolevulinic acid (5-ALA) as an intraoperative optical imaging agent in patients with suspected high-grade gliomas (HGGs). However, the application of 5-ALA for low-grade gliomas is still less accepted. Astrocytoma, isocitrate dehydrogenase (IDH) mutant tumors are diffuse infiltrating astrocytic tumors where there is no identifiable border between the tumor and normal brain tissue, even though the borders may appear relatively well-marginated on imaging. Generally, it is considered that 5-ALA cannot pass through a normal blood–brain barrier (BBB). Thus, 5-ALA fluorescence may mean disruption of BBB in grade II glioma.

Case Report  A 74-year-old male patient was diagnosed with a right parietal lesion suggestive of a low-grade brain tumor in a surgical resection using 5-ALA, which led to the detection of tiny fluorescence spots during the surgery. The frozen section was consistent with diffuse astrocytoma, IDH-wildtype (World Health Organization [WHO] grade II). The patient's postoperative magnetic resonance imaging (MRI) showed complete resection. Eight months after surgery, he began experiencing symptoms again and was admitted with a brain MRI finding consistent with recurrent infiltrating astrocytomas. This required reoperation of the brain tumor resection with 5-ALA. Unlike the first surgery, they observed a high fluorescence intensity; the pathological finding was glioblastoma, IDH-wildtype (WHO grade IV). Postsurgical brain MRI showed total resection of the tumor. The patient was discharged 4 weeks after surgery and continued with specialized clinical follow-up.

Conclusion  The use of 5-ALA continues to be a great contributor to the improvement in complete resection of primary brain tumors, especially HGG. Besides, fluorescence is increasingly approaching its use as a prognostic tool for aggressive clinical course, regardless of the initial grade of the tumor. This case report is an effort to expand knowledge for potentially using 5-ALA to help prognosticate brain tumors. Nevertheless, more clinical prospective studies must be conducted.

Heme Biosynthesis Factors and 5-ALA Induced Fluorescence: Analysis of mRNA and Protein Expression in Fluorescing and Non-fluorescing Gliomas

Objective

The intraoperative visualization of adult-type diffuse gliomas with 5-aminolevulinic acid (5-ALA) induced fluorescence is widely used in the neurosurgical field. While visible 5-ALA induced fluorescence is found in the majority of high-grade gliomas, most low-grade gliomas lack visible fluorescence during surgery. Recently, the heme biosynthesis pathway was identified as crucial influencing factor for presence of visible fluorescence since it metabolizes 5-ALA to fluorescing Protoporphyrin IX (PpIX). However, the exact alterations within the heme biosynthesis pathway resulting in visible 5-ALA induced fluorescence in gliomas are still unclear. The aim of the present study was thus to compare the mRNA and protein expression of promising intramitochondrial heme biosynthesis enzymes/transporters in glioma tissue samples of different fluorescence behavior.

Methods

A total of 19 strongly fluorescing and 21 non-fluorescing tissue samples from neurosurgical adult-type diffuse gliomas (WHO grades II-IV) were included in the current analysis. In these samples, we investigated the mRNA expression by quantitative real time PCR and protein expression using immunohistochemistry of the intramitochondrial heme biosynthesis enzymes Coproporphyrinogen Oxidase (CPOX), Protoporphyrinogen Oxidase (PPOX), Ferrochelatase (FECH), and the transporter ATP-binding Cassette Subfamily B Member 2 (ABCG2).

Results

Regarding mRNA expression analysis, we found a significantly decreased ABCG2 expression in fluorescing specimens compared to non-fluorescing samples (p = 0.001), whereas no difference in CPOX, PPOX and FECH was present. With respect to protein expression, significantly higher levels of CPOX (p = 0.005), PPOX (p < 0.01) and FECH (p = 0.003) were detected in fluorescing samples. Similar to mRNA expression analysis, the protein expression of ABCG2 (p = 0.001) was significantly lower in fluorescing samples.

Conclusion

Distinct alterations of the analyzed heme biosynthesis factors were found primarily on protein level. Our data indicate that heme biosynthesis pathway activity in general is enhanced in fluorescing gliomas with upregulation of PpIX generating enzymes and decreased ABCG2 mediated PpIX efflux outweighing the also increased further metabolization of PpIX to heme. Intramitochondrial heme biosynthesis factors thus constitute promising pharmacological targets to optimize intraoperative 5-ALA fluorescence visualization of usually non-fluorescing tumors such as low-grade gliomas.

Impact of Levetiracetam Treatment on 5-Aminolevulinic Acid Fluorescence Expression in IDH1 Wild-Type Glioblastoma

Simple Summary

The amino acid 5-aminolevulinic acid (5-ALA) is the benchmark regarding intraoperative imaging tools for glioblastoma (GB) surgery, and is known to facilitate the extent of resection, which results in an enhanced 6 month progression-free survival rate. Recent in vitro studies suggest that antiepileptic drugs (AEDs) result in a reduction in the fluorescence quality in gliomas. To date, there is no large clinical series investigating this issue in a homogeneous cohort. Approximately 25% of all GB patients have a symptomatic epilepsy as the initial symptom at presentation. Hence, this potential dilemma is of paramount importance. We found that the preoperative intake of levetiracetam is a significant risk factor for reduced intraoperative fluorescence in IDH1 wild-type GBs. We believe that this issue must be considered in future external validations, and physicians must carefully evaluate the indication of levetiracetam and avoid a prophylactic levetiracetam treatment in terms of the suspected diagnosis of glioblastoma.

Abstract

The amino acid 5-aminolevulinic acid (5-ALA) is the most established neurosurgical fluorescent dye and facilitates the achievement of gross total resection. In vitro studies raised concerns that antiepileptic drugs (AED) reduce the quality of fluorescence. Between 2013 and 2018, 175 IDH1 wild-type glioblastoma (GB) patients underwent 5-ALA guided surgery. Patients’ data were retrospectively reviewed regarding demographics, comorbidities, medications, tumor morphology, neuropathological characteristics, and their association with intraoperative 5-ALA fluorescence. The fluorescence of 5-ALA was graded in a three point scaling system (grade 0 = no; grade 1 = weak; grade 2 = strong). Univariable analysis shows that the intake of dexamethasone or levetiracetam, and larger preoperative tumor area significantly reduce the intraoperative fluorescence activity (fluorescence grade: 0 + 1). Multivariable binary logistic regression analysis demonstrates the preoperative intake of levetiracetam (adjusted odds ratio: 12.05, 95% confidence interval: 3.91–37.16, p = 0.001) as the only independent and significant risk factor for reduced fluorescence quality. Preoperative levetiracetam intake significantly reduced intraoperative fluorescence. The indication for levetiracetam in suspected GB should be carefully reviewed and prophylactic treatment avoided for this tumor entity. Future comparative trials of neurosurgical fluorescent dyes need a special focus on the influence of levetiracetam on fluorescence intensity. Further trials must validate our findings.

Analysis of corticosteroid and antiepileptic drug treatment effects on heme biosynthesis mRNA expression in lower-grade gliomas: potential implications for 5-ALA metabolization

OBJECTIVES

Intraoperative visualization of gliomas with 5-aminolevulinic acid (5-ALA) induced fluorescence constitutes a powerful technique. While visible fluorescence is typically observed in high-grade gliomas, fluorescence is considerably less common in lower-grade gliomas (LGGs) WHO grade II&III. Whereas the exact mechanisms determining fluorescence in LGGs are not fully understood, metabolization of non-fluorescent 5-ALA to fluorescent Protoporphyrin IX by specific heme biosynthesis enzymes/transporters has been identified as relevant mechanism influencing fluorescence behavior. Furthermore, recent in-vitro studies have suggested preoperative treatment with corticosteroids and anti-epileptic drugs (AED) as potential factors influencing 5-ALA induced fluorescence.

METHODS

The goal of this study was thus to investigate the effect of preoperative corticosteroid/AED treatment on heme biosynthesis mRNA expression in a clinically relevant patient population. For this purpose, we analyzed the mRNA expression levels of specific heme biosynthesis factors including ALAD, HMBS, UROS, UROD, CPOX, PPOX, FECH, ABCB6, ACG2, SLC15A1 and SLC15A2, ABCB1, ABCB10 in a cohort of LGGs from "The Cancer Genome Atlas".

RESULTS

Altogether, 403 patients with available data on preoperative corticosteroid/AED treatment and heme biosynthesis mRNA expression were identified. Regarding corticosteroid treatment, no significant differences in expression of any of the 11 investigated heme biosynthesis factors were found. In contrast, a marginal yet statistically significant increase in SLC15A1 levels and decrease in ABCB6 levels were observed in patients with preoperative AED treatment.

CONCLUSION

While no significant differences in heme biosynthesis mRNA expression were observed according to preoperative corticosteroid treatment, changes in SLC15A1 as well as ABCB6 expression were detected in patients treated with AED. However, since these alterations were minor and have opposing effects on 5-ALA metabolization, our findings do not support a distinct effect of AED and corticosteroid treatment on heme biosynthesis regulation in LGGs.

Improved Protoporphyrin IX-Guided Neurosurgical Tumor Detection with Frequency-Domain Fluorescence Lifetime Imaging

Precise intraoperative brain tumor visualization supports surgeons in achieving maximal safe resection. In this sense, improved prognosis in patients with high-grade gliomas undergoing protoporphyrin IX fluorescence-guided surgery has been demonstrated. Phase fluorescence lifetime imaging in the frequency-domain has shown promise to distinguish weak protoporphyrin IX fluorescence from competing endogenous tissue fluorophores, thus allowing for brain tumor detection with high sensitivity. In this work, we show that this technique can be further improved by minimizing the crosstalk of autofluorescence signal contributions when only detecting the fluorescence emission above 615 nm. Combining fluorescence lifetime and spectroscopic measurements on a set of 130 ex vivo brain tumor specimens (14 low- and 56 high-grade gliomas, 39 meningiomas and 21 metastases) coherently substantiated the resulting increase of the fluorescence lifetime with respect to the detection band employed in previous work. This is of major interest for obtaining a clear-cut distinction from the autofluorescence background of the physiological brain. In particular, the median fluorescence lifetime of low- and high-grade glioma specimens lacking visual fluorescence during surgical resection was increased from 4.7 ns to 5.4 ns and 2.9 ns to 3.3 ns, respectively. While more data are needed to create statistical evidence, the coherence of what was observed throughout all tumor groups emphasized that this optimization should be taken into account for future studies.

Analysis of Factors Affecting 5-ALA Fluorescence Intensity in Visualizing Glial Tumor Cells-Literature Review

Glial tumors are one of the most common lesions of the central nervous system. Despite the implementation of appropriate treatment, the prognosis is not successful. As shown in the literature, maximal tumor resection is a key element in improving therapeutic outcome. One of the methods to achieve it is the use of fluorescent intraoperative navigation with 5-aminolevulinic acid. Unfortunately, often the level of fluorescence emitted is not satisfactory, resulting in difficulties in the course of surgery. This article summarizes currently available knowledge regarding differences in the level of emitted fluorescence. It may depend on both the histological type and the genetic profile of the tumor, which is reflected in the activity and expression of enzymes involved in the intracellular metabolism of fluorescent dyes, such as PBGD, FECH, UROS, and ALAS. The transport of 5-aminolevulinic acid and its metabolites across the blood–brain barrier and cell membranes mediated by transporters, such as ABCB6 and ABCG2, is also important. Accompanying therapies, such as antiepileptic drugs or steroids, also have an impact on light emission by tumor cells. Accurate determination of the factors influencing the fluorescence of 5-aminolevulinic acid-treated cells may contribute to the improvement of fluorescence navigation in patients with highly malignant gliomas.

Efficacy, Outcome, and Safety of Elderly Patients with Glioblastoma in the 5-ALA Era: Single Center Experience of More Than 10 Years

Simple Summary

In the next decades, the incidence of patients with glioblastoma (GBM) will markedly increase due to the growth of the elderly population. Despite the increasing incidence of GBM, elderly patients are frequently excluded from clinical studies and thus, only few data are available specifically focusing on the elderly population. In the current study, we aimed to investigate the efficacy, outcome, and safety of surgically-treated GBM including resections and biopsies in the 5-ALA era in a large elderly cohort of altogether 272 patients. Our data of this large elderly cohort demonstrate for the first time the clinical utility and safety of 5-ALA fluorescence in GBM for improved tumor visualization in both resections as well as biopsies. Therefore, we recommend the use of 5-ALA not only in resections, but also in open/stereotactic biopsies to optimize the neurosurgical management of elderly GBM patients.

Abstract

Background: In the next decades, the incidence of patients with glioblastoma (GBM) will increase due to the growth of the elderly population. Fluorescence-guided resection using 5-aminolevulinic acid (5-ALA) is widely applied to achieve maximal safe resection of GBM and is identified as a novel intraoperative marker for diagnostic tissue during biopsies. However, detailed analyses of the use of 5-ALA in resections as well as biopsies in a large elderly cohort are still missing. The aim of this study was thus to investigate the efficacy, outcome, and safety of surgically- treated GBM in the 5-ALA era in a large elderly cohort. Methods: All GBM patients aged 65 years or older who underwent neurosurgical intervention between 2007 and 2019 were included. Data on 5-ALA application, intraoperative fluorescence status, and 5-ALA-related side effects were derived from our databank. In the case of resection, the tumor resectability and the extent of resection were determined. Potential prognostic parameters relevant for overall survival were analyzed. Results: 272 GBM patients with a median age of 71 years were included. Intraoperative 5-ALA fluorescence was applied in most neurosurgical procedures (n = 255/272, 88%) and visible fluorescence was detected in most cases (n = 252/255, 99%). In biopsies, 5-ALA was capable of visualizing tumor tissue by visible fluorescence in all but one case (n = 91/92, 99%). 5-ALA administration did not result in any severe side effects. Regarding patient outcome, smaller preoperative tumor volume (<22.75 cm³), gross total resection, single lesions, improved postoperative neurological status, and concomitant radio-chemotherapy showed a significantly longer overall survival. Conclusions: Our data of this large elderly cohort demonstrate the clinical utility and safety of 5-ALA fluorescence in GBM for improved tumor visualization in both resections as well as biopsies. Therefore, we recommend the use of 5-ALA not only in resections, but also in open/stereotactic biopsies to optimize the neurosurgical management of elderly GBM patients.

Preliminary Report: Rapid Intraoperative Detection of Residual Glioma Cell in Resection Cavity Walls Using a Compact Fluorescence Microscope

Objective: The surgical eradication of malignant glioma cells is theoretically impossible. Therefore, reducing the number of remaining tumor cells around the brain–tumor interface (BTI) is crucial for achieving satisfactory clinical results. The usefulness of fluorescence–guided resection for the treatment of malignant glioma was recently reported, but the detection of infiltrating tumor cells in the BTI using a surgical microscope is not realistic. Therefore, we have developed an intraoperative rapid fluorescence cytology system, and exploratorily evaluated its clinical feasibility for the management of malignant glioma. Materials and methods: A total of 25 selected patients with malignant glioma (newly diagnosed: 17; recurrent: 8) underwent surgical resection under photodiagnosis using photosensitizer Talaporfin sodium and a semiconductor laser. Intraoperatively, a crush smear preparation was made from a tiny amount of tumor tissue, and the fluorescence emitted upon 620/660 nm excitation was evaluated rapidly using a compact fluorescence microscope in the operating theater. Results: Fluorescence intensities of tumor tissues measured using a surgical microscope correlated with the tumor cell densities of tissues evaluated by measuring the red fluorescence emitted from the cytoplasm of tumor cells using a fluorescence microscope. A “weak fluorescence” indicated a reduction in the tumor cell density, whereas “no fluorescence” did not indicate the complete eradication of the tumor cells, but indicated that few tumor cells were emitting fluorescence. Conclusion: The rapid intraoperative detection of fluorescence from glioma cells using a compact fluorescence microscope was probably useful to evaluate the presence of tumor cells in the resection cavity walls, and could provide surgical implications for the more complete resection of malignant gliomas.

Influence of dexamethasone on visible 5-ALA fluorescence and quantitative protoporphyrin IX accumulation measured by fluorescence lifetime imaging in glioblastomas: is pretreatment obligatory before fluorescence-guided surgery?

OBJECTIVE

Fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA) is nowadays widely applied for improved resection of glioblastomas (GBMs). Initially, pretreatment with dexamethasone was considered to be essential for optimal fluorescence effect. However, recent studies reported comparably high rates of visible fluorescence in GBMs despite absence of dexamethasone pretreatment. Recently, the authors proposed fluorescence lifetime imaging (FLIM) for the quantitative analysis of 5-ALA-induced protoporphyrin IX (PpIX) accumulation. The aim of this study was thus to investigate the influence of dexamethasone on visible fluorescence and quantitative PpIX accumulation.

METHODS

The authors prospectively analyzed the presence of visible fluorescence during surgery in a cohort of patients with GBMs. In this study, patients received dexamethasone preoperatively only if clinically indicated. One representative tumor sample was collected from each GBM, and PpIX accumulation was analyzed ex vivo by FLIM. The visible fluorescence status and mean FLIM values were correlated with preoperative intake of dexamethasone.

RESULTS

In total, two subgroups with (n = 27) and without (n = 20) pretreatment with dexamethasone were analyzed. All patients showed visible fluorescence independent from preoperative dexamethasone intake. Furthermore, the authors did not find a statistically significant difference in the mean FLIM values between patients with and without dexamethasone pretreatment (p = 0.097).

CONCLUSIONS

In this first study to date, the authors found no significant influence of dexamethasone pretreatment on either visible 5-ALA fluorescence during GBM surgery or PpIX accumulation based on FLIM. According to these preliminary data, the authors recommend administering dexamethasone prior to fluorescence-guided surgery of GBMs only when clinically indicated.

Fluorescence Lifetime Imaging and Spectroscopic Co-Validation for Protoporphyrin IX-Guided Tumor Visualization in Neurosurgery

Maximal safe resection is a key strategy for improving patient prognosis in the management of brain tumors. Intraoperative fluorescence guidance has emerged as a standard in the surgery of high-grade gliomas. The administration of 5-aminolevulinic acid prior to surgery induces tumor-specific accumulation of protoporphyrin IX, which emits red fluorescence under blue-light illumination. The technology, however, is substantially limited for low-grade gliomas and weakly tumor-infiltrated brain, where low protoporphyrin IX concentrations are outweighed by tissue autofluorescence. In this context, fluorescence lifetime imaging has shown promise to distinguish spectrally overlapping fluorophores. We integrated frequency-domain fluorescence lifetime imaging in a surgical microscope and combined it with spatially registered fluorescence spectroscopy, which can be considered a research benchmark for sensitive protoporphyrin IX detection. Fluorescence lifetime maps and spectra were acquired for a representative set of fresh ex-vivo brain tumor specimens (low-grade gliomas n = 15, high-grade gliomas n = 80, meningiomas n = 41, and metastases n = 35). Combining the fluorescence lifetime with fluorescence spectra unveiled how weak protoporphyrin IX accumulations increased the lifetime respective to tissue autofluorescence. Infiltration zones (4.1ns ± 1.8ns, p = 0.017) and core tumor areas (4.8ns ± 1.3ns, p = 0.040) of low-grade gliomas were significantly distinguishable from non-pathologic tissue (1.6ns ± 0.5ns). Similarly, fluorescence lifetimes for infiltrated and reactive tissue as well as necrotic and core tumor areas were increased for high-grade gliomas and metastasis. Meningioma tumor specimens showed strongly increased lifetimes (12.2ns ± 2.5ns, p = 0.005). Our results emphasize the potential of fluorescence lifetime imaging to optimize maximal safe resection in brain tumors in future and highlight its potential toward clinical translation.

Limited utility of 5-ALA optical fluorescence in endoscopic endonasal skull base surgery: a multicenter retrospective study

OBJECTIVE

Incomplete resection of skull base pathology may result in local tumor recurrence. This study investigates the utility of 5-aminolevulinic acid (5-ALA) fluorescence during endoscopic endonasal approaches (EEAs) to increase visibility of pathologic tissue.

METHODS

This retrospective multicenter series comprises patients with planned resection of an anterior skull base lesion who received preoperative 5-ALA at two tertiary care centers. Diagnostic use of a blue light endoscope was performed during EEA for all cases. Demographic and tumor characteristics as well as fluorescence status, quality, and homogeneity were assessed for each skull base pathology.

RESULTS

Twenty-eight skull base pathologies underwent blue-light EEA with preoperative 5-ALA, including 15 pituitary adenomas (54%), 4 meningiomas (14%), 3 craniopharyngiomas (11%), 2 Rathke's cleft cysts (7%), as well as plasmacytoma, esthesioneuroblastoma, and sinonasal squamous cell carcinoma. Of these, 6 (21%) of 28 showed invasive growth into surrounding structures such as dura, bone, or compartments of the cavernous sinus. Tumor fluorescence was detected in 2 cases (7%), with strong fluorescence in 1 tuberculum sellae meningioma and vague fluorescence in 1 pituicytoma. In all other cases fluorescence was absent. Faint fluorescence of the normal pituitary gland was seen in 1 (7%) of 15 cases. A comparison between the particular tumor entities as well as a correlation between invasiveness, WHO grade, Ki-67, and positive fluorescence did not show any significant association.

CONCLUSIONS

With the possible exception of meningiomas, 5-ALA fluorescence has limited utility in the majority of endonasal skull base surgeries, although other pathology may be worth investigating.

5-ALA in Suspected Low-Grade Gliomas: Current Role, Limitations, and New Approaches

Radiologically suspected low-grade gliomas (LGG) represent a special challenge for the neurosurgeon during surgery due to their histopathological heterogeneity and indefinite tumor margin. Therefore, new techniques are required to overcome these current surgical drawbacks. Intraoperative visualization of brain tumors with assistance of 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PpIX) fluorescence is one of the major advancements in the neurosurgical field in the last decades. Initially, this technique was exclusively applied for fluorescence-guided surgery of high-grade glioma (HGG). In the last years, the use of 5-ALA was also extended to other indications such as radiologically suspected LGG. Here, we discuss the current role of 5-ALA for intraoperative visualization of focal malignant transformation within suspected LGG. Furthermore, we discuss the current limitations of the 5-ALA technology in pure LGG which usually cannot be visualized by visible fluorescence. Finally, we introduce new approaches based on fluorescence technology for improved detection of pure LGG tissue such as spectroscopic PpIX quantification fluorescence lifetime imaging of PpIX and confocal microscopy to optimize surgery.

Fluorescence-Guided Surgery: A Review on Timing and Use in Brain Tumor Surgery

Fluorescence-guided surgery (FGS) allows surgeons to have improved visualization of tumor tissue in the operating room, enabling maximal safe resection of malignant brain tumors. Over the past two decades, multiple fluorescent agents have been studied for FGS, including 5-aminolevulinic acid (5-ALA), fluorescein sodium, and indocyanine green (ICG). Both non-targeted and targeted fluorescent agents are currently being used in clinical practice, as well as under investigation, for glioma visualization and resection. While the efficacy of intraoperative fluorescence in studied fluorophores has been well established in the literature, the effect of timing on fluorophore administration in glioma surgery has not been as well depicted. In the past year, recent studies of 5-ALA use have shown that intraoperative fluorescence may persist beyond the previously studied window used in prior multicenter trials. Additionally, the use of fluorophores for different brain tumor types is discussed in detail, including a discussion of choosing the right fluorophore based on tumor etiology. In the following review, the authors will describe the temporal nature of the various fluorophores used in glioma surgery, what remains uncertain in FGS, and provide a guide for using fluorescence as a surgical adjunct in brain tumor surgery.

5-ALA Fluorescence Is a Powerful Prognostic Marker during Surgery of Low-Grade Gliomas (WHO Grade II)-Experience at Two Specialized Centers

The prediction of the individual prognosis of low-grade glioma (LGG) patients is limited in routine clinical practice. Nowadays, 5-aminolevulinic acid (5-ALA) fluorescence is primarily applied for improved intraoperative visualization of high-grade gliomas. However, visible fluorescence is also observed in rare cases despite LGG histopathology and might be an indicator for aggressive tumor behavior. The aim of this study was thus to investigate the value of intraoperative 5-ALA fluorescence for prognosis in LGG patients. We performed a retrospective analysis of patients with newly diagnosed histopathologically confirmed LGG and preoperative 5-ALA administration at two independent specialized centers. In this cohort, we correlated the visible intraoperative fluorescence status with progression-free survival (PFS), malignant transformation-free survival (MTFS) and overall survival (OS). Altogether, visible fluorescence was detected in 7 (12%) of 59 included patients in focal intratumoral areas. At a mean follow-up time of 5.3 ± 2.9 years, patients with fluorescing LGG had significantly shorter PFS (2.3 ± 0.7 vs. 5.0 ± 0.4 years; p = 0.01), MTFS (3.9 ± 0.7 vs. 8.0 ± 0.6 years; p = 0.03), and OS (5.4 ± 1.0 vs. 10.3 ± 0.5 years; p = 0.01) than non-fluorescing tumors. Our data indicate that visible 5-ALA fluorescence during surgery of pure LGG might be an already intraoperatively available marker of unfavorable patient outcome and thus close imaging follow-up might be considered.

Current Limitations of Intraoperative Ultrasound in Brain Tumor Surgery

While benefits of intraoperative ultrasound (IOUS) have been frequently described, data on IOUS limitations are relatively sparse. Suboptimal ultrasound imaging of some pathologies, various types of ultrasound artifacts, challenging patient positioning during some IOUS-guided surgeries, and absence of an optimal IOUS probe depicting the entire sellar region during transsphenoidal pituitary surgery are some of the most important pitfalls. This review aims to summarize prominent limitations of current IOUS systems, and to present possibilities to reduce them by using ultrasound technology suitable for a specific procedure and by proper scanning techniques. In addition, future trends of IOUS imaging optimization are described in this article.

5-ALA fluorescence for intraoperative visualization of spinal ependymal tumors and identification of unexpected residual tumor tissue: experience in 31 patients

OBJECTIVE

Gross-total resection (GTR) is the treatment of choice in the majority of patients suffering from spinal ependymal tumors. In such tumors, the extent of resection (EOR) is considered the key factor for tumor recurrence and thus patient prognosis. However, incomplete resection is not uncommon and leads to increased risk of tumor recurrence. One important cause of incomplete resection is insufficient intraoperative visualization of tumor tissue as well as residual tumor tissue. Therefore, the authors investigated the value of 5-aminolevulinic acid (5-ALA)-induced fluorescence in a series of spinal ependymal tumors for improved tumor visualization.

METHODS

Adult patients who underwent preoperative 5-ALA administration and surgery for a spinal ependymal tumor were included in this study. For each tumor, a conventional white-light microsurgical resection was performed. Additionally, the fluorescence status (strong, vague, or no fluorescence) and fluorescence homogeneity (homogenous or inhomogeneous) of the spinal ependymal tumors were evaluated during surgery using a modified neurosurgical microscope. In intramedullary tumor cases with assumed GTR, the resection cavity was investigated for potential residual fluorescing foci under white-light microscopy. In cases with residual fluorescing foci, these areas were safely resected and the corresponding samples were histopathologically screened for the presence of tumor tissue.

RESULTS

In total, 31 spinal ependymal tumors, including 27 intramedullary tumors and 4 intradural extramedullary tumors, were included in this study. Visible fluorescence was observed in the majority of spinal ependymal tumors (n = 25, 81%). Of those, strong fluorescence was noted in 23 of these cases (92%), whereas vague fluorescence was present in 2 cases (8%). In contrast, no fluorescence was observed in the remaining 6 tumors (19%). Most ependymal tumors demonstrated an inhomogeneous fluorescence effect (17 of 25 cases, 68%). After assumed GTR in intramedullary tumors (n = 15), unexpected residual fluorescing foci within the resection cavity could be detected in 5 tumors (33%). These residual fluorescing foci histopathologically corresponded to residual tumor tissue in all cases.

CONCLUSIONS

This study indicates that 5-ALA fluorescence makes it possible to visualize the majority of spinal ependymal tumors during surgery. Unexpected residual tumor tissue could be detected with the assistance of 5-ALA fluorescence in approximately one-third of analyzed intramedullary tumors. Thus, 5-ALA fluorescence might be useful to increase the EOR, particularly in intramedullary ependymal tumors, in order to reduce the risk of tumor recurrence.

Improving the Usability of 5-Aminolevulinic Acid Fluorescence-Guided Surgery by Adding an Optimized Secondary Light Source

BACKGROUND

Tumors that take up and metabolize 5-aminolevulinic acid emit bright pink fluorescence when illuminated with blue light, aiding surgeons in identifying the margin of resection. The adoption of this method is hindered by the blue light illumination, which is too dim to safely operate under and therefore necessitates switching back and forth from white-light mode. The aim of this study was to examine the addition of an optimized secondary illuminant adapter to improve usability of blue-light mode without degrading tumor contrast.

METHODS

Color science methods were used to evaluate the color of the secondary illuminant and its impact on color rendering index as well as the tumor-to-background color contrast in data collected from 7 patients with high-grade gliomas (World Health Organization grade III and IV). A secondary illuminant adapter was built to provide 475-600 nm light the intensity of which can be controlled by the surgeon and was evaluated in 2 additional patients.

RESULTS

Secondary illuminant color had opposing effects on color rendering index and tumor-to-background color contrast; providing surgeon control of intensity allows this trade-off to be balanced in real time. Demonstration in 2 high-grade glioma cases confirms this, showing that additional visibility adds value when intensity can be controlled by the surgeon.

CONCLUSIONS

Addition of a secondary illuminant may mitigate surgeon complaints that the operative field is too dark under the blue light illumination required for 5-aminolevulinic acid fluorescence guidance by providing improved color rendering index without completely sacrificing tumor-to-background color contrast.

Macroscopic fluorescence-lifetime imaging of NADH and protoporphyrin IX improves the detection and grading of 5-aminolevulinic acid-stained brain tumors

Maximal safe tumor resection remains the key prognostic factor for improved prognosis in brain tumor patients. Despite 5-aminolevulinic acid-based fluorescence guidance the neurosurgeon is, however, not able to visualize most low-grade gliomas (LGG) and infiltration zone of high-grade gliomas (HGG). To overcome the need for a more sensitive visualization, we investigated the potential of macroscopic, wide-field fluorescence lifetime imaging of nicotinamide adenine dinucleotide (NADH) and protoporphyrin IX (PPIX) in selected human brain tumors. For future intraoperative use, the imaging system offered a square field of view of 11 mm at 250 mm free working distance. We performed imaging of tumor tissue ex vivo, including LGG and HGG as well as brain metastases obtained from 21 patients undergoing fluorescence-guided surgery. Half of all samples showed visible fluorescence during surgery, which was associated with significant increase in PPIX fluorescence lifetime. While the PPIX lifetime was significantly different between specific tumor tissue types, the NADH lifetimes did not differ significantly among them. However, mainly necrotic areas exhibited significantly lower NADH lifetimes compared to compact tumor in HGG. Our pilot study indicates that combined fluorescence lifetime imaging of NADH/PPIX represents a sensitive tool to visualize brain tumor tissue not detectable with conventional 5-ALA fluorescence.

Detailed analysis of 5-aminolevulinic acid induced fluorescence in different brain metastases at two specialized neurosurgical centers: experience in 157 cases

OBJECTIVE

Incomplete neurosurgical resection of brain metastases (BM) due to insufficient intraoperative visualization of tumor tissue is a major clinical challenge and might result in local recurrence. Recently, visible 5-aminolevulinic acid (5-ALA) induced fluorescence was first reported in patients with BM. The aim of this study was thus to investigate, for the first time systematically, the value of 5-ALA fluorescence for intraoperative visualization of BM in a large patient cohort.

METHODS

Adult patients (≥ 18 years) with resection of suspected BM after preoperative 5-ALA administration were prospectively recruited at two specialized neurosurgical centers. During surgery, the fluorescence status (visible or no fluorescence); fluorescence quality (strong, vague, or none); and fluorescence homogeneity (homogeneous or heterogeneous) of each BM was investigated. Additionally, these specific fluorescence characteristics of BM were correlated with the primary tumor type and the histopathological subtype. Tumor diagnosis was established according to the current WHO 2016 criteria.

RESULTS

Altogether, 157 BM were surgically treated in 154 patients. Visible fluorescence was observed in 104 BM (66%), whereas fluorescence was absent in the remaining 53 cases (34%). In detail, 53 tumors (34%) showed strong fluorescence, 51 tumors (32%) showed vague fluorescence, and 53 tumors (34%) had no fluorescence. The majority of BM (84% of cases) demonstrated a heterogeneous fluorescence pattern. According to primary tumor, visible fluorescence was less frequent in BM of melanomas compared to all other tumors (p = 0.037). According to histopathological subtype, visible fluorescence was more common in BM of ductal breast cancer than all other subtypes (p = 0.008). It is of note that visible fluorescence was observed in the surrounding brain tissue after the resection of BM in 74 (67%) of 111 investigated cases as well.

CONCLUSIONS

In this largest series to date, visible 5-ALA fluorescence was detected in two-thirds of BM. However, the characteristic heterogeneous fluorescence pattern and frequent lack of strong fluorescence limits the use of 5-ALA in BM and thus this technique needs further improvements.

Is Intraoperative Pathology Needed if 5-Aminolevulinic-Acid-Induced Tissue Fluorescence Is Found in Stereotactic Brain Tumor Biopsy?

BACKGROUND

Intraoperative histopathology and acquisition of multiple tissue samples in stereotactic biopsies results in a prolonged length of surgery and potentially increased complication rate.

OBJECTIVE

To investigate the clinical benefits of a novel strategy for stereotactic brain tumor biopsies with the assistance of 5-aminolevulinic acid (5-ALA) induced fluorescence.

METHODS

Patients that received 5-ALA prior to stereotactic biopsy of a suspected brain tumor were included. According to our strategy, the procedure was terminated in the case of strong fluorescence of the biopsy samples. In contrast, intraoperative histology was demanded in the case of vague/no fluorescence. Length of surgery, number of biopsy samples, diagnostic rate, and periprocedural complications were compared between these 2 groups.

RESULTS

Altogether, 79 patients were included, and strong fluorescence was present in 62 cases (79%), vague fluorescence was in 4 cases (5%), and no fluorescence was in 13 cases (16%). The diagnostic rate was comparable in biopsies with strong fluorescence without intraoperative histopathology and cases with vague/no fluorescence with intraoperative histopathology (98% vs 100%; P = 1.000). A significantly shorter length of surgery (41 vs 77 min; P < .001) and reduced average number of biopsy samples (3.6 vs 4.9; P = .011) was found in patients with strong compared to vague/no fluorescence. However, no statically significant difference in periprocedural complications between cases with strong and vague/no fluorescence was found (7% vs 18%; P = .166).

CONCLUSION

Our data demonstrate the clinical benefits of a novel strategy for stereotactic brain tumor biopsies with assistance of 5-ALA. Thus, this biopsy strategy will increase the efficiency of this standard neurosurgical procedure in the future.

TCGA mRNA Expression Analysis of the Heme Biosynthesis Pathway in Diffusely Infiltrating Gliomas: A Comparison of Typically 5-ALA Fluorescent and Non-Fluorescent Gliomas

5-Aminolevulinic acid (5-ALA) is a fluorescent dye that after metabolization to Protoporphyrin IX (PpIX) by the heme biosynthesis pathway typically leads to visible fluorescence in WHO grade IV but not grade II gliomas. The exact mechanism for high PpIX levels in WHO grade IV gliomas and low PpIX levels in WHO grade II gliomas is not fully clarified. To detect relevant changes in mRNA expression, we performed an in-silico analysis of WHO grade II and IV glioma sequencing datasets provided by The Cancer Genome Atlas (TCGA) to investigate mRNA expression levels of relevant heme biosynthesis genes: Solute Carrier Family 15 Member 1 and 2 (SLC15A1 and SLC15A2), Aminolevulinate-Dehydratase (ALAD), Hydroxymethylbilane-Synthase (HMBS), Uroporphyrinogen-III-Synthase (UROS), Uroporphyrinogen-Decarboxylase (UROD), Coproporphyrinogen-Oxidase (CPOX), Protoporphyrinogen-Oxidase (PPOX), ATP-binding Cassette Subfamily B Member 6 (ABCB6)/G Member 2 (ABCG2) and Ferrochelatase (FECH). Altogether, 258 WHO grade II and 166 WHO grade IV samples were investigated. The mRNA expression levels showed significant differences in 8 of 11 examined genes between WHO grade II and IV gliomas. Significant differences in mRNA expression included increases of HMBS, UROD, FECH and PPOX as well as decreases of SLC15A2, ALAD, UROS and ABCB6 in WHO IV gliomas. Since the majority of changes was found in directions that might actually impair PpIX accumulation in WHO grade IV gliomas, additional studies are needed to analyze the corresponding factors of the heme biosynthesis also on protein level.

Improved Diagnostic Imaging of Brain Tumors by Multimodal Microscopy and Deep Learning

Fluorescence-guided surgery is a state-of-the-art approach for intraoperative imaging during neurosurgical removal of tumor tissue. While the visualization of high-grade gliomas is reliable, lower grade glioma often lack visible fluorescence signals. Here, we present a hybrid prototype combining visible light optical coherence microscopy (OCM) and high-resolution fluorescence imaging for assessment of brain tumor samples acquired by 5-aminolevulinic acid (5-ALA) fluorescence-guided surgery. OCM provides high-resolution information of the inherent tissue scattering and absorption properties of tissue. We here explore quantitative attenuation coefficients derived from volumetric OCM intensity data and quantitative high-resolution 5-ALA fluorescence as potential biomarkers for tissue malignancy including otherwise difficult-to-assess low-grade glioma. We validate our findings against the gold standard histology and use attenuation and fluorescence intensity measures to differentiate between tumor core, infiltrative zone and adjacent brain tissue. Using large field-of-view scans acquired by a near-infrared swept-source optical coherence tomography setup, we provide initial assessments of tumor heterogeneity. Finally, we use cross-sectional OCM images to train a convolutional neural network that discriminates tumor from non-tumor tissue with an accuracy of 97%. Collectively, the present hybrid approach offers potential to translate into an in vivo imaging setup for substantially improved intraoperative guidance of brain tumor surgeries.

High Diagnostic Accuracy of Visible 5-ALA Fluorescence in Meningioma Surgery According to Histopathological Analysis of Tumor Bulk and Peritumoral Tissue

Background and Objectives

Complete neurosurgical resection of intracranial meningiomas is essential to avoid residual tumor tissue and thus minimize the risk of tumor recurrence. However, local recurrence of meningiomas is not uncommon mainly due to insufficient intraoperative detection of residual tumor tissue within the tumor bulk or peritumoral tissue such as bone and satellite lesions. Although 5‐aminolevulinic acid (5‐ALA) induced fluorescence was found to visualize the majority of meningiomas, no comprehensive histopathological assessment of fluorescing samples from the tumor bulk and peritumoral tissue is available. The aim of our study was thus to histopathologically analyze a large series of tissue samples derived from meningioma surgery to assess the positive predictive value (PPV) of visible 5‐ALA fluorescence.

Study Design/Materials and Methods

In this study, we retrospectively investigated a series of tissue samples with visible 5‐ALA fluorescence collected during surgery of intracranial meningiomas from the tumor bulk and peritumoral tissue including the bone flap, dura/dural tail, arachnoidea, adjacent cortex, and satellite lesions. The tumor diagnosis was established according to the World Health Organization (WHO) criteria and all collected fluorescing samples were screened for presence of tumor tissue to calculate the PPV.

Results

Altogether, 191 tissue samples with visible 5‐ALA fluorescence derived during surgery of 85 meningiomas (63 WHO grade I, 17 WHO grade II, and 5 WHO grade III) were included. In detail, 158 samples from the tumor bulk and 33 specimens from the peritumoral tissue were investigated. According to histopathological analysis, the PPV of 5‐ALA fluorescence was significantly higher in samples from the tumor bulk (100%) as compared with peritumoral tissue (73%; P < 0.001). With regard to peritumoral tissue, tumor tissue was present in most fluorescing samples from the satellite lesions (100%), the bone flap (92%), arachnoidea (83%), and dura/dural tail (75%). In contrast, tumor tissue was absent in the majority of samples from fluorescing cortex (six of seven samples; 86%). However, distinct reactive tissue alterations were found in all six tumor‐free fluorescing cortex samples and additional vascular proliferation in two cases.

Conclusion

In this largest series to date, visible 5‐ALA fluorescence is characterized by a high PPV detecting tumor bulk and peritumoral tissue in intracranial meningiomas. Thus, 5‐ALA fluorescence supports the neurosurgeon in identifying residual tumor tissue at relevant surgical sites to optimize meningioma surgery and minimize the risk of local recurrence. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC