The trials, in proportion.

2026 SNIS recommendations

The Society of NeuroInterventional Surgery (SNIS) published recommendations endorsed by ANZSNR and ESMINT. The strongest recommendation supports MMAE as an adjunct to surgical drainage to reduce recurrence requiring further intervention, while weighing procedural risk: Class I, Level A.

For standalone MMAE in special circumstances—including some patients at high surgical risk, with bleeding disorders, or older patients—the recommendation is Class IIa, Level B-NR. This supports individualized consideration, not automatic treatment based on age alone.

The guideline also emphasizes checking for dangerous arterial connections before embolization.

EMBOLISE: fewer repeat operations

Who was studied: 400 patients with symptomatic subacute or chronic subdural hematoma for whom surgical evacuation was indicated.

Comparison: MMAE plus surgery versus surgery alone.

Main result: recurrence or progression leading to repeat surgery within 90 days occurred in 4.1% versus 11.3% (relative risk 0.36; P=0.008). The absolute difference was 7.2 percentage points.

Safety: serious adverse events attributed to embolization occurred in 2.0% of the MMAE group by 30 days, including two disabling strokes. Ninety-day mortality was 5.1% versus 3.0%; these raw rates do not establish that embolization caused the difference.

Interpretation: the trial supports lower reoperation risk with adjunctive MMAE; it does not establish that every patient benefits or that the procedure is risk-free.

STEM: lower composite treatment failure

Who was studied: 310 patients with symptomatic chronic subdural hematoma. A surgical or nonsurgical standard-treatment plan was chosen before randomization.

Main result: in the primary efficacy analysis, an outcome event occurred in 16% (19/120) with MMAE and 36% (47/129) with standard treatment alone (P=0.001).

This was a composite endpoint: residual or recurrent collection greater than 10 mm at 180 days, reoperation or surgical rescue, or specified major events including disabling stroke, myocardial infarction, or neurologic death. It is not simply a repeat-surgery rate.

Safety: disabling stroke or death within 30 days occurred in about 3% of each group. All-cause mortality through 180 days was 8% versus 5%; longer-term safety needs continued study.

MAGIC-MT: an important difference

Who was studied: 722 patients in China with symptomatic nonacute subdural hematoma and mass effect; approximately 78% underwent burr-hole drainage. Patients requiring craniotomy were excluded.

Main result: symptomatic recurrence or progression by 90 days occurred in 6.7% versus 9.9%. This difference did not reach statistical significance (P=0.10).

Serious adverse events were less frequent in the MMAE group (6.7% versus 11.6%; P=0.02). The primary efficacy result remains important when discussing the overall evidence.

Is MMAE now standard care?

MMAE is a guideline-supported treatment option for chronic subdural hematoma, with the strongest recommendation for use alongside surgical drainage. That is more precise than saying it is the standard treatment for every subdural hematoma.

The practical next step is a discussion with a specialist who can apply the evidence to your symptoms and scans.