Postoperative Density of Residual Hematoma Is a Predictor of Chronic Subdural Hematoma Recurrence—A Single-Center Retrospective Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This observational retrospective study investigates postoperative residual content density as measured by CT scan for predicting chronic subdural hematoma treatment outcome. This is an interesting hypothesis, with sound patophysiological background.

I do have some comments regarding the methodology and results presentation:

1. CT scanner type and calibration procedures. Where all scans done on the same equipment, and what was calibration procedure? HU are not really standardized accross different equpiment. This would be helpful to explain
2. Figure 1. is largely unneccessary, and can be omitted from the manuscript.
3. Figure 2. should be editet for presentation and content.
4. "Number of drainages" in Table 2. It is unclear what consitutes the number of drainages? Bilateral procedure? Multiple drains in the same cavity?

Author Response

1. CT scanner type and calibration procedures. Where all scans done on the same equipment, and what was calibration procedure? HU are not really standardized accross different equpiment. This would be helpful to explain

We thank the reviewer for his/her advice and revised the section “Calculation of Density” to clarify the used CT scanner: Postoperative CT scans were performed with the same scanner (Philips IQon Spectral CT) and analyzed using iPlan Smartbrush software (Brainlab, Feldkirchen, Bavaria, Ger-many).”

 

2. Figure 1. is largely unneccessary, and can be omitted from the manuscript.

We omitted this Figure from the manuscript.

 

3. Figure 2. should be editet for presentation and content.

The ROC-Curve was revised and significant content was added to the figure.

 

4. "Number of drainages" in Table 2. It is unclear what consitutes the number of drainages? Bilateral procedure? Multiple drains in the same cavity?

As said in section “Clinical Management”: “Placement of subdural drainage was left to the discretion of the attending neurosurgeon.” This meant that the attending neurosurgeon placed up to 2 drains per cavity. We agree with the reviewer that the lettering may be misleading and misunderstood. We therefore revised Table 2 as well as Table 1 and added the term “Number of Drainages per cavity”

Reviewer 2 Report

Comments and Suggestions for Authors

Please consider to update abstract to include

• AUC (0.578), limiting interpretation of predictive performance.
• Sensitivity and specificity.
• Retrospective design.

Introduction

• Limited novelty already previously investigated please add how it the current study is different

Methods

• Any blinding during density measurement to avoid risk of measurement bias.
• Measurement protocol details (region selection, entire hematoma vs selected areas, averaging method).
• Inter- and intra-rater reliability of density measurements.
• What was the management of bilateral hematomas.
• Postoperative CT timing exact details as the current timeline is too broad.
• Add sample size or power calculation.
• Please add important covariates (hematoma thickness, midline shift, preoperative density) and their impact.
• Did the study follow STROBE reporting standards.

Results

• Inconsistency between abstract and results regarding OR and CI:

o          Abstract: OR 1.9 (95% CI 1.2–3.0)

o          Results: OR 1.88 (95% CI 0.97–3.65)

• Statistical significance needs review due to CI inconsistency.
• AUC 0.578 indicates limited discriminative ability.

Overall, please review the findings and their interpretations including clinical applicability.

Comments on the Quality of English Language

Minor editing

Author Response

Please consider to update abstract to include

• AUC (0.578), limiting interpretation of predictive performance.
• Sensitivity and specificity.
• Retrospective design.

We revised the abstract and included a limitation statement at the end: “Nevertheless, the low AUC limits interpretation of predictive performance.” Also, we included the sensitivity and specificity of ROC analysis. The retrospective desing was stated in the methods section of the abstract.

 

Introduction

• Limited novelty already previously investigated please add how it the current study is different

To underline the novelty of our study, we improved the last paragraph of the introduction: “The aim of the present study was to evaluate the association between postoperative residual hematoma density and recurrence in patients surgically treated for cSDH, and to determine whether this simple postoperative imaging marker has independent prognostic value. Moreover, if residual hematoma density confirms as an prognostic marker, we want to establish an easy-to-use cutoff for routine use.”

 

Methods

• Any blinding during density measurement to avoid risk of measurement bias.
• Measurement protocol details (region selection, entire hematoma vs selected areas, averaging method).
• Inter- and intra-rater reliability of density measurements.
• What was the management of bilateral hematomas.
• Postoperative CT timing exact details as the current timeline is too broad.
• Add sample size or power calculation.
• Please add important covariates (hematoma thickness, midline shift, preoperative density) and their impact.
• Did the study follow STROBE reporting standards.

We thank the reviewer for his/her advice. Blinding was not possible as all CT data were visible during measurement. Measurement protocol can be found in the “Clinical Management” section: “The measurement region was restricted to the residual hematoma between the brain sur-face and the skull, and drainage devices and obvious artifacts were excluded.” These measurements were performed by one of the authors to improve inter-rater reliability. Intra-rater reliability was improved by preceding training of the measurements. Bilateral hematomas were individually considered. To clarify this, we revised the “Calculation of Density” section: “Mean density values were calculated for each cavity (bilateral hematomas were counted as two individual cases).” Timing of postoperative CT scans was aimed for the third day after surgery following our institutional guideline. Only in case of complications, postoperative CT scans were preferred. The important covariates were analyzed in multivariate analysis and showed no significant association with recurrence rate. To clarify the adherence to the STROBE standards, we included a statement in the “Study Design” section: “Reporting followed the STROBE standard.”

 

Results

• Inconsistency between abstract and results regarding OR and CI:

o          Abstract: OR 1.9 (95% CI 1.2–3.0)

o          Results: OR 1.88 (95% CI 0.97–3.65)

• Statistical significance needs review due to CI inconsistency.
• AUC 0.578 indicates limited discriminative ability.

Overall, please review the findings and their interpretations including clinical applicability.

The different OR and CI arise from the uni- and multivariate analyses. Multivariate analysis is stated at the end of the “results” section: “In multivariable logistic regression, higher residual density remained an independ-ent predictor of cSDH recurrence (p = 0.008, OR 1.9; 95% CI 1.2–3.0; Nagelkerke’s R² = 25%).”

Because of the low AUC, we added the following limitation to the discussion: “Finally, due to the low AUC of 0.578 the discriminative ability of the ROC analysis is limited and should be interpreted with caution. Therefore, the cutoff identified in this cohort requires external validation before it can be incorporated into clinical decision-making.”

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Authors have made suggested changes, may be accepted for publication.

Comments on the Quality of English Language

Minor editing