The phrase "time is brain" is meant to convey the urgency of stroke treatment, emphasizing how a swift response can significantly improve odds of recovery.
A typical stroke patient, for instance, loses an estimated 1.9 million neurons for every minute a stroke goes untreated, along with 14 billion synapses and 12 kilometers (7.5 miles) of myelinated fibers.
Yet strokes are not always caught in the early stages. For a wide range of reasons, people sometimes arrive for medical care several hours or even days into a stroke, potentially limiting treatment options.
According to a new study, however, the treatment window for certain strokes may be longer than previously thought – albeit with some noteworthy caveats.
A stroke occurs when blood stops reaching part of the brain – either due to impeded blood flow (known as an ischemic stroke) or bleeding (hemorrhagic stroke) – and results in cell death.
Many ischemic strokes are caused by clots blocking blood flow to the brain, and are thus treated by attempting to remove the blockage and restore blood flow.
This may be done via thrombolysis, which entails breaking up a blood clot with medication, or via thrombectomy, a procedure to mechanically remove a clot from a blood vessel.
Thrombolysis is traditionally recommended within the first few hours after stroke onset, although research suggests it may be effective for longer in some patients with salvageable brain tissue.
A thrombectomy is often performed endovascularly, with a catheter inserted into a patient's blood vessel to help doctors access and extract the blockage, and is a standard treatment for removing occlusions in large vessels.
Endovascular thrombectomy is an established treatment for acute ischemic stroke, the authors of the new study note, and while it was long thought to help only in the first few hours after a stroke begins, research has since extended that treatment window up to 24 hours.
More recently, research has suggested endovascular thrombectomy may yield benefits even beyond the 24-hour window, although this remains uncertain.
To investigate that possibility, the authors of the new study conducted an open-label, randomized trial with blinded outcome assessment at 35 comprehensive stroke centers in China.
Between November 2022 and December 2025, the researchers screened 1,088 patients for eligibility. This included a requirement that they arrived at a participating stroke center 24 to 72 hours after symptom onset or after the time they were last known to be well, and that brain scans showed tissue that could still be saved.
This yielded 341 subjects, whom the researchers randomly split into two groups, and after five withdrew, 336 remained. The intervention group received endovascular therapy plus standard medical care, while the control group received standard medical care alone.
After 90 days, the results generally favored endovascular therapy over standard medical care, although the treatment effect varied by occlusion site and origin.
Odds for a better functional outcome seem to be higher in patients with occlusion of the internal carotid artery than in those with occlusion of the middle cerebral artery, the study found, and higher in those with non-large-artery atherosclerosis than in those with large-artery atherosclerosis.
"Among patients who presented 24 to 72 hours after an acute ischemic stroke from large-vessel occlusion of the anterior circulation and had imaging-identified salvageable tissue, endovascular therapy resulted in better functional outcomes than standard care," the researchers write.
But there's an important disclaimer, they note: Endovascular therapy came with a higher risk of intracranial hemorrhage (brain bleed) and death for these patients.
Within 90 days, 6 percent of the intervention group had died, compared with 1.8 percent of the control group – though with only 13 deaths in total, random chance can't be ruled out as the cause of that difference.
An intracranial hemorrhage occurred in 28.3 percent of the intervention group, the study found, compared with 5.5 percent of the control group.
Symptomatic intracranial hemorrhage occurred in 4.8 percent of the intervention group and not at all among control subjects.
Serious adverse events were also more common in the intervention group (22 percent) than in the control group (13.1 percent).
"Careful judgment is therefore warranted with respect to the balance of the potential benefits and harms of intervening when patients are in the late time window," the authors write.
The research has been published in The New England Journal of Medicine.
This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.