What is a chronic subdural hematoma?
A chronic subdural hematoma is a collection of old blood that builds up slowly between the brain and its outer covering. It is most common in older adults, often after a minor fall or bump to the head that may not seem serious at the time. As the collection grows, it can cause headaches, confusion, weakness or trouble walking.
Many patients are treated with surgery to drain the blood, or are watched closely if symptoms are mild. The challenge is that these hematomas often come back, sometimes requiring another operation.
What is middle meningeal artery embolization?
The middle meningeal artery supplies blood to the fragile membranes around a chronic subdural hematoma, which can keep it growing. In middle meningeal artery (MMA) embolization, a thin catheter is guided through a blood vessel, usually from the wrist or groin, up to this artery. A liquid embolic material is then used to close it off, cutting the blood supply so the hematoma is less likely to grow back.
What the STEM trial found
The trial enrolled 310 patients with symptomatic chronic subdural hematoma at centers in the United States and Europe. Patients received standard care, either surgery or close observation, with or without MMA embolization. Over 180 days, researchers tracked treatment failure: a hematoma that persisted or returned, the need for another surgery, or a serious complication such as a disabling stroke.
Adding embolization lowered the risk of treatment failure, without increasing the rate of disabling stroke or death in the first 30 days. The benefit was largest in patients who were managed without surgery. Embolization did not change overall death or disability at six months, and researchers continue to study which patients benefit most.
What this means for patients
For many people with chronic subdural hematoma, especially those who want to avoid surgery or have had a hematoma come back, MMA embolization offers a minimally invasive option backed by high-quality evidence. Following this research, the embolic agent used in the trial received FDA approval for this use.
As a neurosurgeon dual trained in endovascular neuroradiology, Dr. Arias can offer both surgical drainage and embolization, and help you decide which approach, or combination, is right for you.
Talk with Dr. Arias
If you or a loved one has been diagnosed with a chronic subdural hematoma, request an appointment or call (303) 515-2320 in Denver or (970) 810-5996 in Fort Collins.
Fiorella D, Monteith SJ, Hanel R, et al., for the STEM Investigators. Embolization of the Middle Meningeal Artery for Chronic Subdural Hematoma. N Engl J Med 2025;392:855–864. doi:10.1056/NEJMoa2409845
