Efficacy and safety of standalone middle meningeal artery embolization for chronic subdural hematoma: a single-center retrospective cohort study

BACKGROUND: Chronic subdural hematoma (CSDH) is a prevalent neurosurgical disorder with high clinical morbidity, particularly in the elderly, and conventional treatments are plagued by high recurrence rates and perioperative complications. This study aimed to rigorously evaluate the short- and mid-term efficacy and safety of standalone middle meningeal artery (MMA) embolization as a first-line minimally invasive treatment for CSDH patients who are intolerant to conventional surgical interventions. METHODS: A retrospective cohort study was conducted on consecutively screened patients with CSDH who underwent standalone MMA embolization at a tertiary academic hospital between January 2020 and December 2025. Strict and quantified inclusion and exclusion criteria were applied to ensure cohort homogeneity. The embolization technique was standardized with Onyx 18 as the exclusive embolic agent. Primary outcomes included hematoma resolution rate, complete hematoma absorption rate, and hematoma recurrence rate at 3, 6, and 12 months of follow-up (all patients completed 12-month scheduled follow-up). Secondary outcomes comprised neurological functional recovery (modified Rankin Scale, mRS), midline shift improvement, and procedure-related complications (graded by the Clavien-Dindo classification). Hematoma volume was calculated using the ellipsoid formula, and linear regression analysis was performed to explore the correlation between initial hematoma volume and time to complete absorption (as an exploratory analysis). RESULTS: A total of 85 patients with 99 CSDHs (14 bilateral cases) were enrolled, accounting for 18.6% of the total CSDH patients admitted to our hospital during the same period, with a mean age of 63.6 ± 9.2 years (32 patients ≥ 70 years, 37.6%). All MMA embolization procedures achieved 100% technical success with no intraprocedural conversion to open surgery. At the 12-month follow-up, the mean hematoma volume was significantly reduced from a baseline of 59.4 ± 21.8 mL to 4.1 ± 8.7 mL (P < 0.001, 95% CI: 51.2-59.9), and the mean midline shift was completely resolved from 2.0 ± 2.9 mm to 0 mm (P < 0.001, 95% CI: 1.4-2.6). The complete hematoma absorption rates were 42.4% (95% CI: 32.9-52.4), 75.8% (95% CI: 66.8-83.2), and 80.8% (95% CI: 72.2-87.4) at 3, 6, and 12 months, respectively, with a mean hematoma resolution rate of 1.84 ± 0.69 days per milliliter (95% CI: 1.69-1.99); a strong positive linear correlation was observed between initial hematoma volume and time to complete absorption in CSDHs with complete resolution (R²=0.90, P < 0.001), which reflects limited variability in this homogeneous subgroup rather than generalizable predictive power. Neurological function was significantly improved (P < 0.001, Wilcoxon signed-rank test), with 70.6% (95% CI: 59.7-79.5) of patients achieving mRS 0 and 29.4% (95% CI: 20.5-40.3) achieving mRS 1 at 12 months (no patients with mRS ≥ 2). No severe procedure-related complications (Clavien-Dindo ≥ II) were observed; only 26 patients reported mild postoperative headache, which resolved with conservative management within 3 days. Hematoma density (hypodense/mixed/hyperdense) was not associated with hematoma absorption outcomes (P > 0.05). CONCLUSIONS: Standalone MMA embolization with Onyx 18 is a safe and effective minimally invasive treatment for CSDH patients who are intolerant to conventional surgical interventions, yielding a 0% mid-term recurrence rate, significant hematoma resolution, and excellent neurological functional recovery in the selected cohort. This technique represents a promising alternative to conventional surgical interventions for the above-mentioned patient population. The linear correlation between initial hematoma volume and time to complete absorption provides a single-center exploratory quantitative tool for personalized patient follow-up, and its clinical value needs to be verified in multi-center cohorts. TRIAL REGISTRATION: The study was approved by the Institutional Review Board (IRB) of Sir Run Run Shaw Hospital.