Combined Exoscopic and Endoscopic Two-Step Keyhole Approach for Intracranial Meningiomas

Round 1

Reviewer 1 Report

The authors revised their manuscript according to the criticisms previously detected on the first round of revision process. 

However, many typing errors are still evident, including the one in the first author affiliation. 

I've found this manuscript and its concepts interesting for the neurosurgical readership, let alone well documented.

 

Author Response

Thank you very much for taking the time to review our paper and for your feedback.

We have corrected the typing error you indicated as follows.

 

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 Department of Neurosurgery, Aichi Medical University, Nagakute, Aichi Japan

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 The tools with slightly curved tip are useful in endoscopic surgery (Figure 4a).

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 The data were obtained from 30 patients in Micro group whose mean age was 59.5 years old, including 8 male and 22 female patients.

Reviewer 2 Report

Dear authors, I recommend that you review the conclusions which are based on a limited number of cases from a single institution. You should report: the criteria used for the surgical indication (accidental finding or following specific symptoms) the length of stay in hospital and the learning curve of the proposed technique.

Best regards

Author Response

Thank you very much for taking the time to review our paper and for your feedback.

 

• Limited institutions and cases are additionally described in Limitation section as follows.

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This study targeted a variety of meningiomas and was not a prospective study, featuring a limited number of cases from 2 institutions and a limited follow-up period.

 

• The following text regarding surgical indications has been inserted in the Materials and Methods section.

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With regard to surgical indications, both groups were patients who presented with neurological symptoms due to the tumor or who showed an increase on follow-up imaging studies.

 

• Since the hospital stay includes the rehabilitation period, we have inserted the following phrase in Materials and Methods section.

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Patients’ age, gender, blood loss (mL), operation time (min), hospitalization period including rehabilitation period (days),……

 

 

• We have inserted the following text in Limitation section regarding learning curves.

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Although some experience is required to become familiar with endoscopic manipulation in order to perfect this technique, with scopist's support, the learning curve can be shortened.

Reviewer 3 Report

A nice technique of exoscope/endoscope based minimal invasive surgery is presented. A comparison with the microscopic based surgery is attempted.

Some methodological errors are present. It is stated, that "convexity meningiomas of 3 cm in diameter or less were not included in the EEKA group, they were also excluded from the Micro group", however Table 1 shows, that 2 meningiomas is both groups are present.

"Lumber spondylosis" (must be lumbar) is included in postoperative complication's group. I suppose, that lumbar spondylosis is not related to any type of cranial surgery and should not be used in this manner. Furthermore, how can the neurological symptoms be evaluated, if lumbar canal stenosis symptoms were not differentiated from brain-related symptoms? This rise a question about the clinical data validity. Taking into account the age of the patients, lumbar spondylosis is present in majority of cases.

Ki67 index is included in surgical technique comparison. It seems interesting (or requires explanation) - can the biology of the tumor make difference in surgical technique decision making?

The size of craniotomy is emphasised. The fact that in minimally invasive techniques craniotomy is smaller is obvious without any calculations. This is equipment, surgeon, and technique dependent. Although to prove this fact the patient selection is questionable. In EEKA group, majority of the patients had a posterior fossa tumor (17 vs. 9 in Micro group). I suppose, that retrosigmoid craniotomy was used. However, retrosigmoid craniotomy is smaller as compared to convexity craniotomies no matter which operative technique is used.

The illustrative case on Figure 6 and interpretation in the discussion is incorrect. It is said, that "In this case, where the combined petrosal approach would have been selected in conventional microsurgery". However if the brain stem decompression and not the total removal of the tumor is the aim of the surgery, quick and small retrosigmoid craniotomy would probably involved in conventional microsurgery only.

Author Response

Thank you very much for taking the time to review our paper and for your feedback.

 

• About the complication

In this paper, we considered a prolonged hospital stay due to the need for treatment for a new disease after surgery as a complication and evaluated it as such. As you pointed out, the actual neurological examination determined that the patient's lower limb weakness was a combination of upper and lower neuron damage, which was difficult to discern. In fact, although there was partial recovery of the lower extremity weakness after surgery, the recovery was not sufficient and the patient continued to have gait disturbance. It was also possible that the patient's postural problems during surgery may have contributed to the progression of his spinal canal stenosis symptoms. In any case, we recognized it as a perioperative complication because it required treatment and prolonged hospitalization, resulting in lumbar spine surgery and improvement of symptoms. However, we removed it from the list of complications because it was not the result of intracranial surgery, as you indicated.

 

• About Ki67 index

We included the Ki67index as one of the evaluations of the information obtained postoperatively, not the surgical technique. This information was not available preoperatively, and was shown as a result after the surgery with the technique we took, showing that there was no difference between two groups.

 

• As you pointed out, we intentionally performed minimally invasive surgery, so it is obvious that differences would occur, but our intention was to compare the data objectively and explicitly by comparing them with actual postoperative 3DCT evaluations. As you pointed out, it is possible that the craniotomy size statistics could have been affected due to the posterior fossa case bias, and we will mention this in the Limitation section.

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It is undeniable that the relatively large number of posterior fossa lesions in EEKA group may have influenced the results of the surgical invasiveness comparison.

 

• About Fig.6

The following changes have been made in the figure legend to describe the case for maximum removal of the tumor, including the tumor around the midbrain

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In this case, where the combined petrosal approach or staged surgery would have been selected in conventional microsurgery to achieve maximum resection, the tumor was partially removed by a lateral suboccipital approach using an exoscope (e), and the tumor in the ambient cistern that compressed the midbrain was removed by endoscopic observation (f).

Round 2

Reviewer 3 Report

Thank you for the answers and corrections. The paper is more attractive after the corrections had been made.

Regarding the spinal problem of the patient, I think this patient must be removed from the group (bad selection bias). This was a different medical condition, that had a serious influence on a hospitalization time and was not related to the technique the intracranial tumor had been removed. Just hiding the exact cause of prolonged hospitalization time is not a scientifically sound.

About the size of craniotomy and posterior fossa approach. The problem is indicated in limitations section now. However I suggest to change the control (craniotomy) group. The groups You are comparing must be more or less equal.

Author Response

Thank you very much again for your careful suggestions.

Regarding the spinal problem of the patient, he underwent lumbar spine surgery one week after craniotomy and was transferred to a rehabilitation facility after discharge. The hospital stay was 25 days, which includes the rehabilitation period. We believe that the lumbar surgery had little impact on the rehabilitation period. As with other patients who required postoperative rehabilitation, this patient was evaluated for length of hospital stay, including the rehabilitation period. In addition, even using data from this patient, the length of hospital stay for EEKA is still significantly shorter.

 

According to the suggestion, we statistically adjusted for the operation site as well as tumor size, operative position in the comparison of cratiotomy size. The multivariable-adjusted analyses were carried out in the comparisons of the amount of blood loss, operation time, and length of hospital stay.

Round 3

Reviewer 3 Report

Corrections were made.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

1. The material is too heterogenous in several respects. First, the patient material is heterogenous as regarding location of tumor, tumor size and presenting symtoms. Second, the operative techniques are heterogenous and presented in an unclear way.

2. A comparison with conventional open surgery as regarding the results is completely lacking.

3. The operative techniques are not suffiently and in detailed described wich makes reproduction of the results impossible.

4. The follow up time is short, no longer term results are evident from the study.

5. The benefit of the presented endoscopic and exoscopic techniques are far from obvious. For example, the hospital stays are 13 days, which has to be considered a long time.

 

 

 

Reviewer 2 Report

The authors present they surgical technical strategy with limited size craniotomies and endoscopic use for meningiomas, evolved in exoscope in the latter 28 cases, switching to endoscope at the final stages of the surgery. The paper, after revision might interesting for neurosurgeons who want to be familiar with this strategy. However, I am not sure that this is the most appropriate journal for this purpose. The authors analyzed the results of this strategy, but of course being the description of a single strategy, the results cannot be compared with standard techniques. This is more suitable and strongly suggested as a "how I do it" paper in a neurosurgical journal, adding more technical details. This should be an editorial decision.

Considerations:

1. It is clear from the paper that the surgery was started with an exoscope, and after volume resection switched to endoscope. It should also be clear in the title and in the abstract.
2. Patient selection should be discussed.
3. The foot pedal exoscope, which is quite simple was not used, and the scopist was preferred. Discuss why.
4. The authors in Material and Methods, page 2, line 87 state: “malleable bipolar coagulation". Could you please describe better and maybe tell the producer? We use curved or angled bipolar, but I was not aware of malleable bipolars.
5. In Discussion, line 266, 267, the authors state that a small craniotomy automatically limits brain retraction. This is not true, it depends on brain relaxation. Brain retraction, without brain relaxation, increases with a small craniotomy.
6. Limitations: patient selection to be included.
7. Conclusions: "omits bone removal", I would change in convexity bone removal, skull base bone removal is not grossly limited.