KEYWORDS chronic subdural hematoma; acute intracranial hemorrhage; recurrence; burr hole drainage; intraoperative irrigation 3 Abstract Background To investigate predictors of postoperative acute intracranial hemorrhage (AIH) and recurrence of chronic subdural hematoma (CSDH) after burr hole drainage. Methods A multicenter retrospective study of patients who underwent burr hole drainage for CSDH A total of 448 CSDH patients were enrolled in the study. CSDH recurrence occurred in 60 patients,

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... h a recurrence rate of 13.4%. The mean time interval between initial burr hole drainage and recurrence was 40.8±28.3 days. Postoperative AIH developed in 23 patients, with an incidence of 5.1%. The mean time interval between initial burr hole drainage and postoperative AIH was 4.7±2.9 days. Bilateral hematoma, hyperdense hematoma and anticoagulant drug use were independent predictors of recurrence in the multiple logistic regression analyses. Preoperative headache was an independent risk factor of postoperative AIH in the multiple logistic regression analyses, however, intraoperative irrigation reduced the incidence of postoperative AIH. Conclusions This study found that bilateral hematoma, hyperdense hematoma and anticoagulant drug use were independently associated with CSDH recurrence. Clinical presentation of headache was the strongest predictor of postoperative AIH, and intraoperative irrigation decreased the incidence of postoperative AIH. hemorrhage; however, its pathogenic mechanism remains unclear. The incidence of CSDH is ~3.4-5/100 000 per year in the general population and 60-80/100 000 per year in those aged ≥65.[1-5] The treatment is often surgical evacuation, using techniques such as twistdrill craniotomy and burr hole drainage (BHD) or craniotomy. BHD is the most widely used technique, and has a satisfactory outcome, but has a CSDH recurrence rate of 4-38%.[6-12] Several studies have revealed that predictors of CSDH recurrence following surgical evacuation include age, sex, antiplatelet or anticoagulation therapy, Glasgow Coma Scale (GCS), diabetes mellitus, hypertension, bilateral hematoma, preoperative hematoma size, midline shift, hematoma density, intraoperative irrigation, type of surgery and postoperative air collection, however, these results are inconsistent.[7, 13-19] The more controversial risk factors include surgery type and intraoperative irrigation.[9, 10, 20-22] Previous reports have shown a CSDH mortality rate of 1.8-32%.[6, 23] Surgical complications, such as irritability, wound infection and acute intracranial hemorrhage (AIH), occur at a rate of 0-38%.[24-26] AIH, in particular, can cause severe neurological dysfunction, leading to a poor prognosis. However, the mechanism is still unclear and there is limited information on risk factors associated with AIH following surgery for CSDH. Some previous studies have evaluated recurrence risk following CSDH surgery using only a single or few predictors, however, the majority of these were singlecenter retrospective studies and lacked interaction between other variables and confounding factors. It is, therefore, important to identify the clinical and perioperative risk factors associated with AIH and CSDH recurrence following BHD surgery. In this multicenter retrospective study we evaluated the clinical factors associated with postoperative AIH and CSDH recurrence, to determine an optimal perioperative management strategy for BHD with or without irrigation in CSDH patients. Methods 5 We retrospectively analyzed the medical records of all patients diagnosed with CSDH at