EMBOLISE-2 finds early artery-blocking treatment cuts deterioration and surgery needs by half
Los Angeles, United States, 10 February 2026 – A minimally invasive procedure known as middle meningeal artery embolization may significantly reduce disease progression in patients with mildly symptomatic subdural hematoma, according to new results from the second phase of the EMBOLISE clinical trial.
The findings show that treating patients early with embolization lowered the risk of needing surgery or experiencing clinical deterioration by about 50 percent compared with careful observation alone. The results were presented at the International Stroke Conference 2026 and mark an important step forward for patients who are not considered candidates for surgery.
Subdural hematoma occurs when blood slowly collects between the brain and its outer covering, often causing headaches, balance problems, and gradual neurological decline. Many patients with mild symptoms are typically managed conservatively, with doctors waiting to see if the condition worsens.
The EMBOLISE-2 trial suggests that this wait-and-see approach may leave patients vulnerable over time.
The study evaluated embolization of the middle meningeal artery using Onyx, a liquid embolic agent developed by Medtronic. The treatment works by blocking the artery that feeds fragile membranes responsible for ongoing bleeding, helping stop further blood leakage into the subdural space.
Conducted across 60 medical centers in the United States, the trial enrolled 200 patients with relatively small subdural hematomas and mild symptoms such as headache and gait instability. Participants were randomly assigned to either observation alone or upfront embolization with Onyx.
Results showed that the primary composite outcome, defined as the need for surgical drainage, poor clinical outcome, or neurological deterioration within 90 days, occurred in 11.9 percent of patients treated with embolization, compared with 23 percent in the observation group. This translates to a number needed to treat of nine, meaning one adverse outcome was prevented for every nine patients treated.
Jared Knopman, MD, neurosurgeon and interventional neuroradiologist at Weill Cornell Medical College and a lead investigator in the study, said the findings have major implications for a condition that is becoming increasingly common, especially among older adults.
He noted that although patients started with smaller hematomas, those managed conservatively often continued to carry a significant blood burden over time, eventually leading to worsening symptoms.
Imaging results supported this view. Hematoma volume was substantially lower in the embolization group at both 90 and 180 days, while patients under observation showed persistently larger collections of blood.
The study also closely examined safety. Stroke occurred more frequently in the embolization group, but investigators reported that none of the events were directly caused by the embolic material itself. Many were linked to interruption of antiplatelet or anticoagulant medications or to avoidable catheter-related complications.
Neurological deaths were also higher in the embolization arm, though these were strongly associated with severe underlying medical conditions rather than the treatment itself.
Knopman emphasized that maintaining medications used for secondary stroke prevention and simplifying procedural techniques could further reduce risk.
Commenting on the findings, Bijoy Menon, MD, vice-chair of the International Stroke Conference and professor of neurology at the University of Calgary, said the results are encouraging for patients with mild symptoms who are not surgical candidates. However, he cautioned that larger studies with more complete follow-up are needed to better define which patients benefit most.
Still, EMBOLISE-2 represents the first trial specifically designed to study this patient population and adds growing evidence that early embolization may change how mild subdural hematomas are managed.
