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

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.