Postoperative pneumocephalus in unilateral chronic subdural hematoma and its correlation with recurrence: a retrospective single-center study

Objectives Pneumocephalus emerged as a risk factor for recurrence of chronic subdural hematoma (CSDH). However, data on volumetric assessment of subdural air (SA), its risk factors, and correlation with recurrence remain limited.Materials and Methods We retrospectively included patients with unilateral CSDH who underwent surgery. Three analyses were performed: (1) comparison of absolute versus relative SA to preoperative hematoma volume (HV) for predicting recurrence; (2) evaluation of the relationship between SA and recurrence using regression and stratification into four SA-volume subgroups; (3) identification of risk factors for pneumocephalus.Recurrence was defined as symptomatic re-accumulation of CSDH requiring re-surgery within the first three months of surgery.Results 142 patients were included. Absolute SA demonstrated a stronger correlation with recurrence, with a cut-off value of 6.95 ml. Each additional 1 ml of SA was associated with a 4.3% increase in the odds of recurrence, and rates ranged from 12.4% in patients (<7 ml) to 45% (>21 ml) (p < 0.001). Patients with ≥7 ml of SA were older (p = 0.04), more frequently had hemispheric hematomas (p = 0.02), and exhibited greater mass effect, reflected by width, HV, and midline shift (all p < 0.001). Multivariate analysis and ROC-analysis revealed preoperative HV ≥ 105.5 ml as a relevant parameter of increased SA (p < 0.001).Conclusion Preoperative HV demonstrated strongest relation to elevated postoperative SA. Absolute postoperative SA correlates better with recurrence. Patients with ≤6.95 ml of SA have a lower recurrence risk, whereas higher volumes are associated with progressively increased recurrence.