Postoperative Pneumocephalus as a Predictor of Recurrence in Chronic Subdural Hematoma: A Propensity Score - Matched Retrospective Observational Study

Summary

This study was undertaken to systematically evaluate the relationship between postoperative pneumocephalus and recurrence in patients undergoing burr-hole drainage for chronic subdural hematoma (CSDH).

Abstract

Chronic subdural hematoma (CSDH) is a common neurosurgical condition with a high recurrence rate after burr‑hole drainage. Postoperative pneumocephalus is frequently observed, but its relationship with recurrence remains unclear. This retrospective observational study evaluated whether postoperative pneumocephalus volume predicts CSDH recurrence. Patients who underwent first‑time burr‑hole drainage for CSDH between January 2021 and June 2025 were included and classified according to head CT findings within 24 h after surgery. Propensity score matching (PSM; 1:1, caliper 0.02) balanced baseline characteristics (age, sex, hematoma side, antiplatelet/anticoagulant use), yielding 150 matched patients (75 per group). The primary outcome was ipsilateral hematoma recurrence requiring reoperation within 6 months. Pneumocephalus volume was measured using the Tada formula, with inter‑observer reliability assessed by the intraclass correlation coefficient (ICC = 0.964, 95% CI: 0.941–0.978). The recurrence rate was significantly higher in the pneumocephalus group than in the non‑pneumocephalus group (22.7% vs. 5.3%; OR = 5.20, 95% CI: 1.66–16.32; p = 0.002). Multivariate logistic regression showed that the presence of pneumocephalus was independently associated with recurrence (OR = 3.26, 95% CI: 1.45–7.30, p = 0.004), and each 1 mL increase in volume was associated with a 9% higher risk (OR = 1.09, 95% CI: 1.02–1.15, p = 0.008). ROC analysis yielded an AUC of 0.754 (95% CI: 0.645–0.864), with an optimal cut‑off of 12.5 mL (sensitivity 76.2%, specificity 70.5%). Bootstrap internal validation confirmed stability (mean cut‑off 12.6 mL, optimism‑corrected AUC 0.745). In conclusion, postoperative pneumocephalus volume is associated with CSDH recurrence after burr‑hole drainage and may help identify patients needing closer follow‑up; however, prospective multicenter validation is required before any specific volume threshold can be adopted in clinical practice.

Introduction

Chronic subdural hematoma (CSDH) is a common neurosurgical condition whose incidence has been increasing with the aging population^1,2. Its pathophysiology is thought to involve tearing of bridging veins after mild head trauma, leading to blood accumulation in the subdural space, local inflammation, and eventual formation of a hematoma capsule^3,4. Because of repeated microbleeding and fibrinolysis hyperactivity, most patients cannot absorb the hematoma spontaneously and require surgical intervention^5,....

Protocol

Ethical statement
The study protocol was reviewed and approved by the Sanming First Hospital Affiliated to Fujian Medical University Ethics Committee (No. 2026-38), and the investigation was conducted in accordance with the ethical standards set forth in the Declaration of Helsinki. As this is a retrospective observational study without any intervention, the collected data were generated during routine clinical diagnosis and treatment, without adding any additional burden or risk to patients’ examinations. Therefore, an application for exemption from informed consent was submitted, and all patients’ personal information has been kept strictly conf....

Results

Baseline information
The inter‑observer reliability for postoperative pneumocephalus volume measurement was excellent, with an intraclass correlation coefficient (ICC) of 0.964 (95% CI: 0.941–0.978). Table 1 presents a comparison of baseline characteristics between the two groups after PSM (n = 75 per group). There were no statistically significant differences between the pneumocephalus group and the non‑pneumocephalus group in terms of age (68.45 ± 10.23 years vs 67.89 ± 11.07 years.......

Discussion

Postoperative pneumocephalus after CSDH burr-hole drainage has long been controversial. This propensity-score-matched study of 150 patients showed that the presence of pneumocephalus was associated with a 3.26 - fold higher recurrence risk (OR = 3.26, 95% CI: 1.45–7.30) and a dose-response relationship (each 1 mL increase in volume corresponded to a 9% higher risk, OR = 1.09, 95% CI: 1.02–1.15). The optimal cut-off for pneumocephalus volume was 12.5 mL (AUC = 0.754; sensitivity = 76.2%; specificity = 70.5%). .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
14Fr silicone subdural drain	Medical-grade silicone drainage catheter (generic)	14 Fr; used with passive gravity drainage system
Computed Tomography (CT) scanner	Siemens Healthineers	SOMATOM Definition AS; FDA cleared
Data dictionary (variable definitions)	Study team	N/A (created for this study)
Excel (Microsoft Office)	Microsoft Corporation	Version 16.0+; https://www.microsoft.com/microsoft-365/excel
Intraoperative CT / neuronavigation	Siemens Healthineers	Somatom Definition AS with navigation option; used when available
logistf package (Firth penalized logistic regression)	CRAN (R package)	Version 1.26.1; https://CRAN.R-project.org/package=logistf[reference:3]
Mixed effects logistic regression	R (lme4 package)	lme4 package; https://CRAN.R-project.org/package=lme4
Passive gravity drainage system	Standard subdural drainage bag	250 mL capacity; connected to 14Fr drain
R software environment	R Foundation	Version 4.4.x; https://www.r-project.org[reference:5]
SPSS Statistics	IBM Corporation	Version 26.0; https://www.ibm.com/spss[reference:6]
Tada formula (volume calculation)	Manual calculation	N/A (method described in Protocol)
Warmed normal saline (irrigation fluid)	Standard hospital supply	0.9% NaCl, warmed to 37–38 °C