Can We Anticipate Epidural Hematoma After Unilateral Biportal Endoscopic Surgery? Insights From Drain Output and Early Magnetic Resonance Imaging

Objective: To determine the incidence of and factors associated with magnetic resonance imaging (MRI)-detected postoperative spinal epidural hematoma after single-level unilateral biportal endoscopic (UBE) lumbar decompression with or without discectomy, and to evaluate whether early drain output and MRI metrics correlate with hematoma severity.Methods: We retrospectively reviewed 238 consecutive cases of single-level UBE decompression with or without discectomy performed between January 2022 and June 2024. Demographic characteristics, comorbidities, operative time, coagulation profile, drain output, and MRI canal measurements were analyzed. Postoperative MRI obtained within 12 hours was graded according to the degree of dural sac compression, and the critical ratio (postoperative/preoperative canal cross-sectional area) was calculated. Group comparisons were performed using appropriate parametric or nonparametric tests and the chi-square or Fisher exact test.Results: MRI-detected epidural hematoma was observed in 126 of 238 patients (52.9%), whereas only 2 patients required reoperation for symptomatic hematoma. Hematoma occurrence was associated with male sex (p=0.041) and surgical level (p=0.001). Among patients with hematoma, surgical level was associated with hematoma grade (p=0.001), with upper lumbar levels demonstrating higher compression grades. Postoperative day 1, postoperative day 2, and total drain outputs decreased with increasing hematoma grade (p=0.024, p=0.028, and p=0.020, respectively). Postoperative canal cross-sectional area and the critical ratio declined stepwise with increasing hematoma grade.Conclusion: MRI-detected postoperative epidural hematoma is common after single-level UBE lumbar decompression, but clinically significant symptomatic hematoma is uncommon. Lower early drain output and reduced MRI decompression metrics, including the critical ratio, were associated with higher compression grades, supporting selective early MRI in symptomatic or higher-risk patients.