Ethics and Registration

This study was approved by the Ethics Committee of the Second Affiliated Hospital of Chongqing Medical University and has been registered in Chinese Clinical Trial Registry (Registration No.: ChiCTR2300068129). All patients participating in the study signed informed consent forms.

Inclusion and Exclusion Criteria

Inclusion Criteria: ≥ 18 years; Preoperative CT confirmed diagnosis of CSDH; Signed the informed consent form; Unilateral occurrence; Initial episode; With clinical symptoms; Treated with hard channel burr hole drainage surgery for subdural hematoma; Complete imaging data available during the perioperative period and within three months after the initial surgery.

Exclusion Criteria: < 18 years; Refusal to participate in the study; not undergoing surgical treatment; Incomplete clinical data; Recurrence of CSDH; Received corticosteroids, NSAIDs, or immunomodulators within 30 days pre-surgery; Currently treatment with anticoagulant or antiplatelet medications; Malignant tumors or immune-related diseases. (Exclusion of patients on corticosteroids/NSAIDs aimed to eliminate confounding effects on macrophage polarization. Anticoagulant users were excluded due to bleeding risk.) (Fig. 1).

Fig. 1

Flowchart for patient inclusion. NSAIDs: Non-Steroidal Anti-Inflammatory Drugs

Indications for CSDH hard channel burr hole drainage surgery:

Progressive neurological dysfunction: such as hemiplegia, aphasia, gait instability, decreased level of consciousness (drowsiness, coma), etc. Signs of increased intracranial pressure: persistent or worsening headache, nausea and vomiting, papilledema, etc. Cognitive or psychiatric symptoms: memory decline, disorientation, personality changes, or abnormal behavior.

Hematoma thickness > 1 cm: CT or MRI shows significant hematoma thickness (usually ≥ 1 cm) with a mass effect. Midline shift > 5 mm: Brain tissue compression leads to midline structure displacement, indicating a risk of increased intracranial pressure. Progressive enlargement of the hematoma: Follow-up imaging shows an increase in hematoma volume; intervention should be considered even if symptoms are mild.

General Information

Data were collected on patient demographics, including age, sex, personal history (smoking: an average of ≥ 1 cigarette per day for the past year; drinking: an average of ≥ 1 drink per day), and comorbidities (hypertension, diabetes, coronary heart disease and so on), as well as any history of head trauma. Additionally, relevant laboratory tests were conducted on peripheral venous blood samples, including complete blood count, coagulation profile, and liver and kidney function tests.

Imaging Data

Nakaguchi CT classification: All hematomas were classified into four types based on their imaging appearance and density changes. The homogeneous type is characterized by a uniform density, which can be categorized into hypo-, iso-, or hyperdense subtypes. The laminar type is identified by a high-density laminar structure that runs along the inner membrane, believed to consist of fresh blood originating from the hematoma membrane. The separated type is defined as a hematoma containing two components of differing densities: a lower density component situated above a higher density component, with a clear boundary separating them. If the boundary is indistinct, with low and high-density areas mingling at the border, this is referred to as the gradation subtype. The trabecular type is characterized by inhomogeneous contents featuring high-density septa, formed by fibrosis, that run between the inner and outer membranes against a low-density to isodense background [13].

The following data were also collected: hematoma volume (ml, calculated using the ABC/2 formula), maximum hematoma thickness (mm), degree of midline shift (mm), Mean hematoma density (HU), postoperative midline shift (mm), midline re-expansion (mm, calculated as postoperative midline shift—preoperative midline shift), and volume re-expansion rate (postoperative volume/preoperative volume * 100%). Brain atrophy was assessed preoperatively using the cortical atrophy scale (CAS), adjusting for midline shift compression [14], categorized as severe atrophy or non-severe atrophy. All imaging indicators were independently evaluated by two researchers, and any discrepancies in their assessments were resolved through discussion.

Sample Collection

All patients with CSDH underwent subdural hematoma hard channel burr hole drainage surgery, using a YL-1 type hematoma suction needle (20 mm, Wanteff, Beijing, China) to puncture the thickest part of the hematoma. And 5 ml of CSDH fluid samples were collected during the procedure. Among them, 2 ml of the CSDH fluid sample was centrifuged at 4000 rpm for 15 min at 4 °C using a centrifuge (Thermo Fisher Scientific model 8881). The supernatant was then aliquoted into different tubes and stored at −80 °C for further analysis. The remaining 3 ml of CSDH fluid was used for flow cytometry analysis. During the surgery, 300 ml of 9% sodium chloride solution at 37 °C was used to irrigate the hematoma cavity. Postoperatively, subdural drainage was performed for 48 h, and the drainage volume was recorded.

Flow Cytometry (FCM)

Red blood cells were lysed using a lysis buffer (BioLegend, CA, USA), and the cells were centrifuged at 1000 rpm for 5 min, then washed with cold PBS. Primary antibodies were CD11b-FITC, CD45-PE, CD86-cyanine 5.5 and CD206-APC(1:1000, BioLegend, CA, USA)。M1 macrophages were identified using fluorescent antibodies CD11b-FITC, CD45-PE, and CD86-cyanine 5.5, while M2 macrophages were identified using CD11b-FITC, CD45-PE, and CD206-APC. After removing excess antibodies, a flow cytometer (Beckman Coulter's CytoFLEX) and FlowJo 10 (Tree Star, California, USA) software were used to detect the percentages of M1 and M2 macrophages. Besides, the M1 to M2 ratio was calculated. FCM analyses included three technical replicates per sample.

Enzyme-Linked Immunosorbent Assay(ELISA)

Macrophage-related factors in CSDH fluid were assessed by ELISA, including inflammatory factors IL-1β, IL-6, IL-12, TNF-α, IL-4, IL-10, IL-13, and TGF-β. The detection reagents were from LEGEND MAX™ ELISA kits (BioLegend, CA, USA), and all procedures were strictly followed according to the instrument manual and reagent instructions. Each sample was tested three times, and the differences among the three measurements did not exceed 10%. The final result for each sample was taken as the average of these measurements.

Follow-Up and Definition of Recurrence

All patients were followed up in the outpatient clinic once a month for three consecutive months. The endpoint observation event was postoperative hematoma recurrence. Recurrence was defined as an expansion of the hematoma on the surgical side within three months accompanied with hematoma-related neurological symptoms and signs [15].

Statistical Analysis

Data analysis was performed using SPSS 25.0. First, the Kolmogorov–Smirnov test was used to estimate the normality of all measurement data. Normally distributed measurement data were expressed as mean (standard deviation) [Mean (SD)], and comparisons between two groups were made using the t-test. Non-normally distributed measurement data were expressed as Median (Q25, Q75), and comparisons were made using the Mann–Whitney U non-parametric test. Count data were expressed as the number of cases (percentage) [n (%)], and comparisons were made using the χ2 test. Statistically significant variables from univariate analysis were included in multivariate logistic regression analysis to determine the risk factors for postoperative recurrence of CSDH. Based on the multivariate results, a nomogram prediction model was established using the rms package in R 3.4.0 software. Receiver operating characteristic (ROC) curves were plotted to evaluate the predictive value of macrophage polarization and the prediction model for postoperative recurrence. Finally, internal validation was performed using the Bootstrap method, and the consistency index (C-index) for discrimination evaluation was calculated, along with calibration plots. P value of < 0.05 was considered statistically significant. CT classifications and lab assays were performed by researchers blinded to clinical outcomes.