EMBOLISE 2
(2026)Objective
To compare middle meningeal artery embolisation (MMAe) versus observation alone in mildly symptomatic chronic subdural haematoma (cSDH) patients.
Study Summary
• Haematoma volume was nearly halved at 180 days with MMAe versus observation (43.8 ml vs 80 ml).
• A 5.9% stroke rate in the MMAe arm (vs 0% observation) was noted, but 5 of 6 strokes were deemed preventable with procedural optimization and maintaining antithrombotic medications.
Intervention
Middle meningeal artery embolisation (MMAe) with Onyx liquid embolic agent vs. observation alone
Inclusion Criteria
Mildly symptomatic cSDH patients with haematoma volume ≤15 ml and <5 ml midline shift; those with severe motor weakness were excluded
Study Design
Arms: MMAe vs. observation alone
Patients per Arm: 200 total (100 per arm, 1:1 randomization)
Outcome
• MMAe failed non-inferiority for mRS deterioration at 90 days but achieved non-inferiority at 180 days.
• Haematoma volume significantly reduced with MMAe at both 90 and 180 days; stroke rate 5.9% in MMAe vs 0% in observation; neurologic death rates were comparable.
Bottom Line
MMAe resulted in a twofold reduction in the composite primary endpoint compared to observation at 90 days in mildly symptomatic cSDH patients, with significant haematoma volume reduction at 180 days, though procedural stroke risk (5.9%) warrants attention to optimized technique and maintenance of antithrombotic therapies.
Major Points
- EMBOLISE 2 is the first trial specifically powered to study MMAe in mildly symptomatic cSDH patients.
- Primary composite endpoint was halved with MMAe vs observation (11.9% vs 23.2%) at 90 days with a NNT of 9.
- All three individual components of the composite endpoint showed comparable or greater reduction with MMAe.
- MMAe failed non-inferiority for mRS deterioration at 90 days but achieved it at 180 days.
- Haematoma volume at 180 days was nearly halved with MMAe (43.8 ml vs 80 ml).
- Stroke rate was 5.9% in MMAe vs 0% in observation; 5 of 6 strokes were deemed preventable.
- Key lessons: do not stop antithrombotic medications, keep the MMAe procedure simple, and avoid unnecessary catheterizations.
- Patients with higher Charlson comorbidity index scores were at greater risk for stroke and negative outcomes.
- Neurologic death rates were comparable between groups; no deaths in MMAe arm were attributed to Onyx or haematoma.
- EMBOLISE 1 previously led to FDA-updated indication for Onyx in non-acute SDH.
Study Design
- Study Type
- Prospective, multicentre, randomized controlled trial
- Randomization
- Yes
- Blinding
- Open-label (not blinded)
- Sample Size
- 200
- Follow-up
- 180 days
- Centers
- 60
- Countries
- USA
Primary Outcome
Definition: Composite of need for surgical drainage, poor clinical outcome, or clinical deterioration at 90 days
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| 23.2% | 11.9% | - |
Limitations & Criticisms
- Open-label design with no blinding.
- 5.9% stroke rate in MMAe arm vs 0% in observation raises safety concerns.
- Trial was not powered to assess individual components of the composite endpoint.
- Baseline characteristics not reported in available data.
- Exact p-values and confidence intervals for primary endpoint not provided in available presentation data.
- Mildly symptomatic population may limit generalizability to more severe cSDH patients.