BARCELONA, Spain — A new randomized trial of embolization of the middle meningeal artery (EMMA) following surgery for chronic subdural hematoma showed striking results, with a major drop in hematoma recurrence.

In the EMMA-CAN trial, patients who underwent the embolization procedure were six times less likely to experience symptomatic hematoma recurrence during the 90-day follow-up period.

“These new data confirm the effectiveness of this embolization procedure for routine care of subdural hematoma. We hope that this procedure will now be adopted more widely across the world, which should transform the care of chronic subdural hematoma patients,” lead investigator Jai Shankar, MD, professor of radiology at the University of Manitoba, Winnipeg, Manitoba, Canada, told Medscape Medical News.

The results were presented on October 24 at the 17th World Stroke Congress (WSC) 2025.

A Minimally Invasive Procedure

Treatment of chronic subdural hematoma is the most common procedure conducted by neurosurgeons, Shankar noted.

The condition is caused by slow accumulation of blood leaking out of vessels onto the surface of the brain, often following mild head injury.

Chronic subdural hematoma affects an estimated 300 people per million, with incidence rising sharply with age. About half of these patients are surgical candidates; the rest either have milder disease or comorbidities that rule out surgery.

While surgery is usually effective in draining the hematoma, recurrence occurs in roughly one third of patients. “This is a major problem,” Shankar said.

EMMA is an endovascular procedure that blocks blood flow to the fragile membranes surrounding the hematoma. It is being studied both as an adjunct to surgery and as an alternative for patients who are not surgical candidates.

The investigator-initiated EMMA-CAN trial focused on the use of this technique to reduce hematoma recurrence in patients who had already had surgery.

Shankar explained that the embolization procedure is a minimally invasive endovascular technique in which a catheter is guided into the middle meningeal artery — the vessel supplying the membrane that sustains the hematoma — and a liquid embolic agent is injected to seal the bleeding membrane.

The procedure takes roughly 45 minutes to an hour and is usually performed under general anesthesia.

In the EMMA-CAN trial, 192 patients were randomly assigned to receive the EMMA procedure, using a liquid embolic agent (Onyx 18), within 72 hours of surgical drainage or to standard surgical care with no embolization.

Results showed that in those who received the EMMA procedure, there was a large reduction in symptomatic recurrence of hematoma at 90 days compared with surgery alone.

Symptomatic recurrence of hematoma occurred in 28% of the control group vs 4.3% of those who received the EMMA procedure (odds ratio [OR], 0.12; 95% CI, 0.03-0.31; P < .001).

Radiographic hematoma recurrence occurred in 49.5% of the control group compared with 14% of the EMMA group (OR, 0.17; 95% CI, 0.08-0.33; P < .001). This benefit was achieved without an increase in serious adverse events, and mortality rates were similar between the study arms.

There have been four recent trials of EMMA for the treatment of subdural hematoma, with two showing positive results and two neutral, Shankar noted.

‘Strongest Data Yet’

He said this new trial is the most methodologically rigorous to date and provides the strongest evidence in support of the EMMA procedure. In particular, he said, it was notable that the surgeons performing the initial surgery were blinded to whether these patients would also undergo embolization.

“In randomized trials, blinding is very important. If a surgeon knows that the patient is going to get EMMA, they may not be as rigorous in the initial surgical drainage. This can dilute the effect size,” said Shankar.

He noted that the EMMA-CAN trial clearly defined treatment timing and included only patients who had undergone surgery for unilateral hematoma. He also highlighted the study’s excellent retention, with only one patient lost to follow-up.

“We wanted to keep methodology very precise,” Shankar said. “As a result, our trial was much more rigorously controlled for all these variables, which is why I believe we showed a stronger result.”

He believes that these results will settle any uncertainty about the use of EMMA after surgery.

“It tips the balance toward better outcomes for these patients when they get the embolization procedure.”

To further examine the effects of the EMMA procedure, investigators from all the trials are collaborating on a meta-analysis of the combined results.

While the current results do not apply to patients who have not had surgery, Shankar said there is no reason to believe that the procedure would not work in this population because the pathologic mechanism of subdural hematoma is the same.

He added that the EMMA-CAN trial included a registry of patients who were ineligible for randomization, and preliminary findings from that group suggest that they may also benefit from the procedure.

“I think we have enough data now to show that the procedure is effective. We now need to enable it to be rolled out more extensively. This involves building up endovascular capacity, standardizing the protocol, and ensuring reimbursement so that every patient that could benefit actually gets access to this procedure,” Shankar said.

Benefit Confirmed

Commenting on the trial results for Medscape Medical News, Marc Fisher, MD, professor of neurology at Harvard Medical School, Boston, said the results confirm previous evidence of benefit with the embolization procedure for patients with chronic subdural hematoma.

He explained that the middle meningeal artery is the major blood supply to the area where the bleeding occurs, and the embolization process cuts off the blood supply to the hematoma, reducing its growth.

“This embolization procedure is being incorporated into practice now, and this trial should further encourage that,” he added.

The EMMA-CAN trial was sponsored by the University of Manitoba and funded by Medtronic. Shankar reported receiving research funding from Medtronic.