Temporal relationship between hematoma resolution and functional recovery after middle meningeal artery embolization for chronic subdural hematoma

OBJECTIVE: The objective was to evaluate the trajectories of hematoma resolution and functional improvement after middle meningeal artery embolization (MMAE) for chronic subdural hematoma (cSDH), model the temporal pattern of cSDH resolution, and identify factors associated with favorable outcomes. METHODS: This real-world multicenter retrospective study included cSDH patients treated with MMAE at 24 centers between 2019 and 2024. Hematoma thickness was measured at baseline and at follow-up intervals (1-4 weeks, 1-3 months, 3-6 months, 6-12 months, and > 12 months after embolization). Resolution patterns were modeled using exponential decay functions. Modified Rankin Scale (mRS) scores assessed functional outcomes. Good functional outcome was defined as mRS score ≤ 2. Resolution patterns were modeled using exponential decay functions to estimate time to 50% and 80% reduction. Patients were categorized as complete resolution (≥ 99%) or by quartile of the remaining distribution (substantial [73%-98%], moderate [53%-73%], partial [27%-53%], minimal [< 27%]). The primary outcome was good functional status (mRS score ≤ 2). RESULTS: The authors analyzed a total of 1781 patients with 2295 cSDHs who underwent MMAE. The mean ± SD age was 72.8 ± 12.4 years and 68.1% of patients were male. The initial mean hematoma thickness was 15.31 ± 6.53 mm, decreasing to 5.24 ± 5.91 mm at final follow-up (mean reduction 64.3% ± 42.1%). Resolution followed an exponential decay pattern, with an estimated time to 50% reduction of 1.8 months and to 80% reduction of 8.9 months. Complete resolution occurred in 1031 of 2224 patients (46.4%) with complete follow-up. The median (IQR) mRS score improved from 1 (0-3) at baseline to 0 (0-2) at > 12 months. Good functional outcomes were more common in patients with complete versus minimal resolution (68.9% vs 35.0%, p < 0.001). Achieving ≥ 73% resolution within 90 days was associated with better outcomes (good outcome in 76.9% of those with ≥ 73% resolution vs 67.3% in those without, p < 0.001). Neurological deterioration was the strongest predictor of lack of good outcome (23.7% in patients with neurological deterioration vs 82.4% without, p < 0.001). CONCLUSIONS: After MMAE for cSDH, reduction in hematoma thickness follows a predictable exponential decay pattern. Greater extent (≥ 80%) and faster timing (within 90 days) of resolution are valuable prognostic indicators. Functional outcomes improve progressively through 6-12 months after the procedure. The relationship between resolution extent and functional outcomes provides quantitative benchmarks for evaluating treatment response.