Intraoperative Fluorophores: An Update on 5-Aminolevulinic Acid and Sodium Fluorescein in Resection of Tumors of the Central Nervous System and Metastatic Lesions—A Systematic Review and Meta-Analysis

Round 1

Reviewer 1 Report

In this paper the authors describe a systematic review and meta-analysis of two fluorophores, 5-ala and sodium fluorescein for assisted resection of brain tumors.

The topic is relevant and timely and likely of interest to the readers. Overall, the paper is interesting, well written, and has systematic and well-designed analysis. Figures are appropriate. References and discussion are appropriate.

I have only a few minor suggestions:

1.       Table 1 is rather large. If it can be reformatted to be a little more streamlined and included in the main text, that would be better. If not, perhaps it could be moved to a supplement.

2.       There is no discussion about how gross total resection is calculated and how it may be different for high grade gliomas (in which resection of all the enhancing tumor is considered total) versus low grade gliomas (which largely do not enhance). This may affect the outcomes of these individual studies and should be at least briefly discussed.

3.       Line 146 says “and” when it should probably be “or” as I suspect studies should be included if they included either of the fluorophores.

Overall, this paper is very good and a valuable addition to the literature.

Author Response

Dear Esteemed Reviewer, 

Thank you for taking the time and effort to review our manuscript. We appreciate your feedback and critical analysis of our work. We have included our responses to your thoughtful feedback below and hope to have adequately addressed all your concerns. 

1. "Table 1 is rather large. If it can be reformatted to be a little more streamlined and included in the main text, that would be better. If not, perhaps it could be moved to a supplement."

We appreciate your feedback regarding the size of table 1. We feel that an individual description of each study adds an understanding of the size and impact of each paper, but agree that the format is somewhat   bulky. Our hope is to include the papers in a landscape orientation rather than a portrait orientation, where the table appears more streamlined and less bulky. Given the formatting constraints on word, we could not do it on this draft, but will request that change be made for the final publication. Alternatively, we agree it could be included as a supplemental figure if the formatting cannot be appropriately edited for final publication.

2. "There is no discussion about how gross total resection is calculated and how it may be different for high grade gliomas (in which resection of all the enhancing tumor is considered total) versus low grade gliomas (which largely do not enhance). This may affect the outcomes of these individual studies and should be at least briefly discussed."

Thank you for the very astute point regarding the difference in calculation of GTR between tumor types. Gross total resection was calculated radiographically in these papers, but largely were defined by complete resection of the identified preoperative lesion. We agree that this might be variable from study to study, and thus have included it in the limitations section of the discussion (Line 388 to 393). Of note, the heterogenous definition of “near total resection” was why we did not include that as a separate category from subtotal resection. 

3.  "Line 146 says “and” when it should probably be “or” as I suspect studies should be included if they included either of the fluorophores."

Thank you for catching this – the wording has been changed from “and” to “or”. Line 145

Reviewer 2 Report

The authors present a systematic review about the performance of 5-ALA and sodium fluorescein regarding the extent of resection.

1.     Introduction: The authors provide an introduction structured by a short review regarding the current state of the art of both fluorophores. However, this section should be shortened and more focused.

2.     Methods: The authors describe the present article as a systematic review. There are several standardized methods to increase the scientific level of a systematic review. For instance, register the review at Cochrane or PROSPERO. Furthermore, adherence to the Cochrane Handbook and PRSIMA workflow can make the search strategy more transparent. The inclusion criteria can be formulated according to the PICOS framework. PRISMA workflow charts can enable the understanding of each step of the literature search. GRADE can be used to evaluate the overall certainty and evidence of the included studies. 

3.     Methods: Please describe the reason why the authors have chosen such a short time period (2021-2023) for the literature search.

4.     Results: The authors clearly describe their results.

5.     Discussion: What are the clinical implications of this article? Are there any interactions of 5-ALA with anticonvulsants (PMID: 36077817

6.     Minor remark: Please revise typing errors (e.g. line 11 “5-aminiolevuliniic) and changes of the font (lines 27-30)

The meta-analysis compares 5-ala  and sodium-fluorescent with conventional microsurgery regarding extent of resection. Furthermore, the authors analyze the impact of the tumor type on fluorescence expression.

 The topic is of relevance because there is no study providing level 1 evidence regarding 5-ala compared with sodium-fluorescein in terms of extent of resection. However, there are also other intraoperative imaging tools such as intraoperative high-field MRI, which are not considered in this manuscript. Furthermore, there are already recently published meta-analyses providing strong statistical methods such as network-meta analysis which enables a more detailed insight on the comparison between those intraoperative imaging methods regarding extent of resection or survival time ( PMID:  35219089)  

I think the authors should provide a more detailed focus on the influence of histopathology on fluorescence expression. The impact on extent of resection is already known.  

The authors provide a systematic review. However, a systematic review should provide several standardized characteristics (Prospero registration, PRISMA checklist, PICO framework, GRADE approach).

The authors should explain the reason for the short time period of studies which have been analyzed.  

The conclusions are in line with the results. However, the present study does not provide novel results. The authors should debate drug interactions (e.g. antiepileptic drugs) with the fluorescent dyes.   

The references are appropriate  

The forest plots and figures are understandable.

PMID: 

Author Response

Dear Esteemed Reviewer, 
 
Thank you for taking the time and effort to review our manuscript. We appreciate your feedback and critical analysis of our work. We have included our responses to your thoughtful feedback below and hope to have adequately addressed all your concerns. 

1. "Introduction: The authors provide an introduction structured by a short review regarding the current state of the art of both fluorophores. However, this section should be shortened and more focused."

Thank you for your thoughtful analysis of the introduction. We removed some of the extraneous information as suggested (i.e. which transporters are involved in fluorescein excretion, where protoporphyrin is excreted, etc). We hope that these changes allow the introduction to continue to provide an overview of the selected fluorophores while being more concise and focused.

2. "Methods: The authors describe the present article as a systematic review. There are several standardized methods to increase the scientific level of a systematic review. For instance, register the review at Cochrane or PROSPERO. Furthermore, adherence to the Cochrane Handbook and PRSIMA workflow can make the search strategy more transparent. The inclusion criteria can be formulated according to the PICOS framework. PRISMA workflow charts can enable the understanding of each step of the literature search. GRADE can be used to evaluate the overall certainty and evidence of the included studies."

We appreciate your thoughtful recommendations regarding increasing the standardizing of the systematic review. As figure 1 indicates, we did utilize the PRISMA workflow to evaluate studies for this review. This was indicated in line 132-133. Unfortunately, as the data extraction phase of the study has already been completed, our study is not currently eligible for retrospective inclusion in the PROSPERO or Cochrane databases. Though not explicitly stated, the PICOS framework was used to develop the study question. We have now included this in our methods section (Line 142) In a similar vein as the GRADE system, we used the JBI critical appraisal tool to evaluate the bias in each included paper.

3. "Methods: Please describe the reason why the authors have chosen such a short time period (2021-2023) for the literature search."

Thank you for the thorough review of this paper, including the short time frame of the paper. We have now outlined our reasoning in the discussion section, which more clearly explains this time frame than before. We hope this is sufficient explanation for the reader to understand the value of this paper.

4. "Results: The authors clearly describe their results."

Thank you for your thoughtful analysis of our results section.

5. "Discussion: What are the clinical implications of this article? Are there any interactions of 5-ALA with anticonvulsants (PMID: 36077817)"

 Thank you for highlighting the potential for drug administration to patients to alter the efficacy of the fluorophores. We have added this to the discussion section and agree that it may be a confounding variable that most of the literature has not yet accounted for. We also more clearly outline the clinical implications of this article. (line 400 to 405, 435 to 437)

6. "Minor remark: Please revise typing errors (e.g. line 11 “5-aminiolevuliniic) and changes of the font (lines 27-30)"

Thank you for your careful reading of our manuscript. We have edited the font to be appropriate, and edited the aforementioned spelling errors.

Reviewer 3 Report

This study discusses recent advancements in tumor visualization techniques for the central nervous system (CNS) and their impact on the extent of resection (EOR) of primary and secondary tumors. Specifically, it focuses on the use of intraoperative fluorophores such as 5-aminiolevuliinic acid (5-ala) and sodium fluorescein for tumor visualization. The authors conducted a systematic review and meta-analysis of studies published between 2021 and 2023 to update the current literature on the topic. The findings suggest that both 5-ala and sodium fluorescein demonstrate intraoperative fluorescence in various types of CNS tumors. In terms of EOR, the meta-analysis indicates a higher but not statistically significant rate of gross total resection (GTR) in the 5-ala group compared to controls, while the fluorescein group showed statistically significant higher odds of GTR. The authors conclude that both 5-ala and sodium fluorescein show promise in improving EOR and warrant further investigation for their potential use in CNS tumor surgery.

While the study presents valuable findings, there are a few potential flaws in this review that should be considered:

1. The review should start with a description of resection of process for the readers who are not directly from the field. If possible an real-time image that shows the tumor (with both or just one dye) would be a great addition.

2. Some information regarding why these tumor cells are more prone to take up these particular dye would be useful for the readers.

3. Inclusion and exclusion criteria: The study does not provide detailed information on the criteria used to exclude studies from the review. They mention studies being not included on the basis of being wrong for outcome, population, study design, meta-analysis, systematic review, biopsy only, before accepted. Some words such “biopsy only and before accepted” are incoherent. This lack of transparency raises questions about the potential inclusion bias and whether all relevant studies were considered. The adequacy and comprehensiveness of the search strategy remain unclear.

4. Quality assessment: The study does not mention any quality assessment or risk of bias evaluation of the included studies. Assessing the quality of individual studies is crucial in meta-analyses to ensure reliable and valid conclusions.

5. Lack of discussion on limitations: The study does not explicitly discuss the limitations of the review, such as potential publication bias, heterogeneity across studies, or the presence of confounding factors. Acknowledging and addressing these limitations would enhance the interpretation of the results.

This study discusses recent advancements in tumor visualization techniques for the central nervous system (CNS) and their impact on the extent of resection (EOR) of primary and secondary tumors. Specifically, it focuses on the use of intraoperative fluorophores such as 5-aminiolevuliinic acid (5-ala) and sodium fluorescein for tumor visualization. The authors conducted a systematic review and meta-analysis of studies published between 2021 and 2023 to update the current literature on the topic. The findings suggest that both 5-ala and sodium fluorescein demonstrate intraoperative fluorescence in various types of CNS tumors. In terms of EOR, the meta-analysis indicates a higher but not statistically significant rate of gross total resection (GTR) in the 5-ala group compared to controls, while the fluorescein group showed statistically significant higher odds of GTR. The authors conclude that both 5-ala and sodium fluorescein show promise in improving EOR and warrant further investigation for their potential use in CNS tumor surgery.

While the study presents valuable findings, there are a few potential flaws in this review that should be considered:

1. The review should start with a description of resection of process for the readers who are not directly from the field. If possible an real-time image that shows the tumor (with both or just one dye) would be a great addition.

2. Some information regarding why these tumor cells are more prone to take up these particular dye would be useful for the readers.

3. Inclusion and exclusion criteria: The study does not provide detailed information on the criteria used to exclude studies from the review. They mention studies being not included on the basis of being wrong for outcome, population, study design, meta-analysis, systematic review, biopsy only, before accepted. Some words such “biopsy only and before accepted” are incoherent. This lack of transparency raises questions about the potential inclusion bias and whether all relevant studies were considered. The adequacy and comprehensiveness of the search strategy remain unclear.

4. Lack of discussion on limitations: The study does not explicitly discuss the limitations of the review, such as potential publication bias, heterogeneity across studies, or the presence of confounding factors. Acknowledging and addressing these limitations would enhance the interpretation of the results.

Author Response

Dear Esteemed Reviewer, 
 
Thank you for taking the time and effort to review our manuscript. We appreciate your feedback and critical analysis of our work. We have included our responses to your thoughtful feedback below and hope to have adequately addressed all your concerns. 

1. "The review should start with a description of resection of process for the readers who are not directly from the field. If possible a real-time image that shows the tumor (with both or just one dye) would be a great addition."

Thank you for your careful and thoughtful review of our manuscript. We feel that while the resection process would be beneficial to describe (and would be something we could include in a supplementary table), the resection methods used were standard with the exception of the use of the fluorophores. We agree that a real-time image that shows the tumor would be a great addition; however, we do not currently have access to said images at our institution. We would gladly explore this further if deemed necessary.

2. "Some information regarding why these tumor cells are more prone to take up these particular dye would be useful for the readers."

Thank you for this suggestion. We feel that noting that these particular dyes either accumulate as a result of tumor metabolism at the BBB breakdown (5-ALA), or at the disrupted BBB (fluorescein) in the introduction explains why tumors intracranially are more prone to uptake of these dyes.

3. "Inclusion and exclusion criteria: The study does not provide detailed information on the criteria used to exclude studies from the review. They mention studies being not included on the basis of being wrong for outcome, population, study design, meta-analysis, systematic review, biopsy only, before accepted. Some words such “biopsy only and before accepted” are incoherent. This lack of transparency raises questions about the potential inclusion bias and whether all relevant studies were considered. The adequacy and comprehensiveness of the search strategy remain unclear."

We appreciate the in depth review of the inclusion and exclusion criteria. We have updated figure 1 to include more detailed examples of exclusion criteria. Of note, the text in figure 1 was truncated as a result of uploading for submission, and did not include the full detail of the table. Regardless, the table has been updated to more accurately reflect exclusion criteria and examples.

4. "Quality assessment: The study does not mention any quality assessment or risk of bias evaluation of the included studies. Assessing the quality of individual studies is crucial in meta-analyses to ensure reliable and valid conclusions."

Thank you for assessing this paper in great detail. In the methods section we do note the use of the JBI critical appraisal tool to evaluate the risk of bias in these studies (Line 154 to 155)

5. "Lack of discussion on limitations: The study does not explicitly discuss the limitations of the review, such as potential publication bias, heterogeneity across studies, or the presence of confounding factors. Acknowledging and addressing these limitations would enhance the interpretation of the results."

Thank you for you thoughtful analysis of our discussion section, specifically the limitations. We have updated the discussion section to include these factors, from line 368 to 425.

Round 2

Reviewer 2 Report

Thank you for carefully reviewing the manuscript. The authors responded to most of the points.

However, I still cannot understand the reason for the short analyzed time-period.

Furthermore, there is also data regarding the influence of levetiracetam application in 5-ALA guided surgery of glioblastoma. The authors should also include this in the discussion.

Author Response

Dear Esteemed Reviewer, 

Thank you for taking the time and effort to review our manuscript. We appreciate your feedback and critical analysis of our work. We have included our responses to your thoughtful feedback below and hope to have adequately addressed all your concerns. 

1. However, I still cannot understand the reason for the short analyzed time-period.

We appreciate your thoughtful review of our manuscript and identifying this as an area where we can clarify our methods more clearly for the reader. We have included in lines 140 and 141 a more detailed rationale for the short time period of study.

2. Furthermore, there is also data regarding the influence of levetiracetam application in 5-ALA guided surgery of glioblastoma. The authors should also include this in the discussion.

Thank you for your very astute observations regarding the influence of antiepileptic medications on the efficacy on 5-ALA during surgery. We agree that including a more robust discussion of the effect of antiepileptic medications allows for a more comprehensive evaluation of 5-ALA’s efficacy during surgery, and have included this in lines 403 to 416.