Wide Dissection Trans-Sulcal Approach for Resection of Deep Intra-Axial Lesions in Eloquent Brain Areas

Round 1

Reviewer 1 Report

Dear authors, thank you for the opportunity to review your article. 

 

This is a retrospective cohort reviewing short term outcomes of the resection of intra-axial tumours using the trans-sulcal approach. The authors reported excellent resection rates and functional outcomes in this series of 17 patients over a period of 8 years. 

 

While the article is generally well written and beautifully illustrated, I have some concerns with regards to the interpretation of the results.

 

As this is article describes the surgical technique and outcomes of the transsulcal approach, the lesion size and depth, the underlying etiology of the preoperative neurological deficit (compression, infiltration or vasogenic edema related), along with its location are important in its interpretation.

 

This is a relatively small series of patients, using the median rather than average size and depth of lesion would be more representative.

 

Assuming that the averages are representative, the distance of lesion from the cortical surface was relatively short (mean depth 8.1mm). This might lean the series towards a better outcome compared to a series with deeper lesions. Perhaps a caveat on how this might impact the preservation of the projection fibres could be mentioned in limitations and in the conclusion.  

 

This series had 13 gliomas and 4 metastases located in the supratentorial eloquent regions. This ratio of gliomas (more likely infiltrative in nature) to metastasis (more likely circumscribed in nature) would lead one to think the series would either have a lower rate of GTR or a lower rate neurological preservation. Perhaps the authors can comment on whether their resection technique changes when approaching infiltrative vs circumscribed lesions.

 

Other minor details:

-       Figure 3: Image C is a coronal T1 contrasted image rather than a T2. Image E is a sagittal T1 contrasted image rather than a T2.

-       Figure 4: the tumour is on the left side rather than the right side

-       Line 221: “enhancing IaT centred in the right pre-central gyrus…” the lesion is on the left

-       Line 263: meningiomas being extra-axial should not typically require transsulcal resection

 

Best regards

 

Author Response

We have carefully considered the comments of the Reviewers and would like to respond them point-by-point as follows:

" As this is article describes the surgical technique and outcomes of the transsulcal approach, the lesion size and depth, the underlying etiology of the preoperative neurological deficit (compression, infiltration or vasogenic edema related), along with its location are important in its interpretation."

We have added a paragraph in the discussion addressing the underlining etiology of preoperative deficits and possible reasons for favorable functional recovery after surgery.

 

"This is a relatively small series of patients, using the median rather than average size and depth of lesion would be more representative."

Thank you for the suggestion. A table was added to display individual patient characteristics and outcomes for readers to have a more complete understanding of the patient population. 

Thank you for pointing this out. The lesion depth and diameter were adjusted to median values to better reflect tumor characteristics in this sample size.

“Assuming that the averages are representative, the distance of lesion from the cortical surface was relatively short (mean depth 8.1mm). This might lean the series towards a better outcome compared to a series with deeper lesions. Perhaps a caveat on how this might impact the preservation of the projection fibres could be mentioned in limitations and in the conclusion.”

Additional care was taken to expound upon the postsurgical outcomes within the discussion and conclusion, including the potential relationship of lesion depth and neuroplasticity to symptom reduction, and postoperative seizure occurrence.

 

“This series had 13 gliomas and 4 metastases located in the supratentorial eloquent regions. This ratio of gliomas (more likely infiltrative in nature) to metastasis (more likely circumscribed in nature) would lead one to think the series would either have a lower rate of GTR or a lower rate neurological preservation. Perhaps the authors can comment on whether their resection technique changes when approaching infiltrative vs circumscribed lesions.”

We have added some insights on the resection technique regarding infiltrative and circumscribed lesions.

"Other minor details:

-       Figure 3: Image C is a coronal T1 contrasted image rather than a T2. Image E is a sagittal T1 contrasted image rather than a T2.

-       Figure 4: the tumour is on the left side rather than the right side

-       Line 221: “enhancing IaT centred in the right pre-central gyrus…” the lesion is on the left

-       Line 263: meningiomas being extra-axial should not typically require transsulcal resection"

Thank you for pointing out that we have labeled Figures 3 and 4 incorrectly; we have corrected this on the figures themselves and within the text.

Reviewer 2 Report

Authors present a case series on 17 patients who underwent transsulcal (TScal) approach (15 GTR, 2 subtotal resections) on intraaxial (iaT) deep seated brain tumors in eloquent regions for patients who were not candidates for the awake craniotomy. There were no permanent deficits postoperatively.

Major drawbacks of the study are low number of patients, non-existance of the control group, different pathologies included, as well as the retrospective character of the analysis. If this manuscript was intended to show which possibility does a surgeon posses when dealing with a deep seated eloquent region tumor without using neuromonitoring in the setting of awake craniotomy, then we would expect to have a control group of 17 patients with identical or similar pathology and similar baseline data, who underwent awake craniotomy and then to compare their outcomes. I suggest to reconsider inclusion of the control group.

Use of awake craniotomy is not a standard of care in many neurosurgical departments. There are groups which solely rely on the imaging, intraoperative MRI, intraoperative ultrasound, 5-ALA, tractography and recently augmented reality. Therefore, if authors present a case series of patients which are not operated according to the standard of care in their department, then this should be clearly stated and the control group should be incorporated.

Two demonstrated illustrative cases are impressive with good quality of imaging. However, an operative video showing the surgical technique would be far more better for understanding of the principles of transsulcal dissection. If ultrasound, 5-ALA and neuronavigation were utilized, I suggest to show this utilization through a further illustrative case. Please include a table with all patients, age, diagnosis, outcome. Is there any explanation for the high complication rate (6/17)? For new postoperative seizures following surgery - do you use routinely a perioperative seizure prophlyaxis? Was this a single-surgeon study? Was any intraoperative imaging used?

For the Discussion, I suggest to include a passage on the use of tractography and intaoperative imaging for resection of lesions in the eloquent region. I suggest to add and comment:

Kuhnt D, Bauer MH, Becker A, Merhof D, Zolal A, Richter M, Grummich P, Ganslandt O, Buchfelder M, Nimsky C. Intraoperative visualization of fiber tracking based reconstruction of language pathways in glioma surgery. Neurosurgery. 2012 Apr;70(4):911-9; discussion 919-20. doi: 10.1227/NEU.0b013e318237a807. PMID: 21946508.

 

 

 

Author Response

We have carefully considered the comments of the Reviewers and would like to respond to them point-by-point.

 

"Major drawbacks of the study are low number of patients, non-existance of the control group, different pathologies included, as well as the retrospective character of the analysis. If this manuscript was intended to show which possibility does a surgeon posses when dealing with a deep seated eloquent region tumor without using neuromonitoring in the setting of awake craniotomy, then we would expect to have a control group of 17 patients with identical or similar pathology and similar baseline data, who underwent awake craniotomy and then to compare their outcomes. I suggest to reconsider inclusion of the control group."

Reviewer 2 has suggested adding a control group. While we agree this would be an interesting experiment,  this manuscript only seeks to describe our personal experience of our case series. This type of study, contrary to cohort studies, does not typically include a control group. 

 

"Use of awake craniotomy is not a standard of care in many neurosurgical departments. There are groups which solely rely on the imaging, intraoperative MRI, intraoperative ultrasound, 5-ALA, tractography and recently augmented reality. Therefore, if authors present a case series of patients which are not operated according to the standard of care in their department, then this should be clearly stated and the control group should be incorporated."

We have carefully considered your comment. Indeed we would like to clarify that as the paper is a case series focused on patients that are unable to tolerate awake craniotomy, we do not have a control group. Comparisons of awake craniotomy to the trans-sulcal approach were only to illustrate the efficacy of the procedure when careful navigation of cortex and white matter is deemed necessary, yet awake craniotomy is contraindicated.

"Two demonstrated illustrative cases are impressive with good quality of imaging. However, an operative video showing the surgical technique would be far more better for understanding of the principles of transsulcal dissection. If ultrasound, 5-ALA and neuronavigation were utilized, I suggest to show this utilization through a further illustrative case. Please include a table with all patients, age, diagnosis, outcome. Is there any explanation for the high complication rate (6/17)? For new postoperative seizures following surgery - do you use routinely a perioperative seizure prophlyaxis? Was this a single-surgeon study? Was any intraoperative imaging used?"

Although we agree that additional imagery may be beneficial, we do not have intraoperative video of the procedure nor other images of other navigational techniques that we wish to include. 

We appreciate the thoughtful comment to include more information on the patients. A table was added to display individual patient characteristics and outcomes. 

The prophylactic administration of levetiracetam is part of our surgical protocol, and has been specified within the methods. 

This is a single-center retrospective analysis, in which we report two surgeons’ experiences. A sentence has been modified to reflect this in the introduction. 

 

"For the Discussion, I suggest to include a passage on the use of tractography and intaoperative imaging for resection of lesions in the eloquent region. I suggest to add and comment"

We would like to thank the reviewer once again for his careful review of our study. We added the citation and elaborated on it in the discussion section.

 

 

Round 2

Reviewer 2 Report

Authors have responded sufficiently to reviewers remarks.