Mechanical thrombectomy is a minimally invasive procedure that physically removes a blood clot from an artery in the brain during a stroke. It’s the most effective treatment available for strokes caused by large clots blocking major brain arteries, and it can be performed up to 24 hours after symptoms begin in select patients. The procedure involves threading a thin catheter through a blood vessel, navigating it up to the brain, and either pulling or suctioning the clot out.
Why It’s Needed
Most strokes happen when a blood clot blocks blood flow to part of the brain. For smaller clots, a clot-dissolving medication given through an IV can do the job. But when a large clot blocks one of the brain’s major arteries (called a large vessel occlusion, or LVO), that medication alone often isn’t enough. The clot is simply too big to dissolve quickly, and every minute without blood flow means more brain tissue dies.
Mechanical thrombectomy was proven superior to standard medical care for these large vessel occlusion strokes in a wave of landmark clinical trials published between 2015 and 2016. Those trials focused on patients treated within 6 hours of symptom onset. Two later trials, DAWN and DEFUSE-3, pushed that window dramatically further, showing that patients could still benefit from the procedure 6 to 24 hours after stroke onset, as long as brain imaging showed there was still salvageable tissue. These “late window” patients tend to be slow progressors, meaning their brain tissue dies more gradually thanks to strong backup blood flow from surrounding vessels.
How the Procedure Works
The procedure starts with a small puncture in the femoral artery, a large blood vessel near the groin. Through this entry point, doctors insert a thin, flexible tube called a catheter and guide it through the body’s arterial system, up through the aorta, into the neck arteries, and ultimately into the brain’s blood vessels. Real-time X-ray imaging guides the catheter’s path the entire way.
Once the catheter reaches the clot, doctors use one of two main techniques to remove it, and sometimes a combination of both.
Stent Retrievers
A small wire mesh device is pushed through the catheter and deployed directly into the clot. The mesh expands, embedding itself in the clot material, and immediately restores some blood flow through the blocked artery. After a few minutes of allowing the clot to integrate into the mesh, the doctor slowly pulls the entire device back, dragging the clot out with it.
Aspiration Catheters
A larger catheter is advanced right up to the face of the clot. A vacuum pump then applies continuous suction, pulling the clot into the catheter like a vacuum cleaner. Doctors confirm the clot is engaged when flow through the suction system stops, indicating the clot is sealed against the catheter tip. The catheter is then carefully withdrawn with the clot attached.
Some techniques combine both approaches, trapping the clot between a stent retriever and an aspiration catheter to reduce the chance of any fragments breaking loose.
Sedation During the Procedure
Patients undergo thrombectomy under either conscious sedation (awake but relaxed) or general anesthesia (fully asleep). This choice matters more than it might seem. Data from a large propensity-matched analysis found that patients under general anesthesia had significantly higher in-hospital mortality (25% vs. 12%) and roughly double the rate of pneumonia (17% vs. 9.3%) compared to those under conscious sedation. Bleeding rates in the brain were similar between the two groups. The general anesthesia group also had longer hospital stays and higher costs. That said, some patients need general anesthesia because they can’t stay still or their condition is too severe for sedation alone.
Success Rates and How They’re Measured
Doctors measure success using a grading system called the TICI score, which rates how completely blood flow has been restored after the clot is removed. A score of TICI 2b or 3 means substantial or complete restoration of flow, and this is the benchmark for a successful procedure. In clinical practice, roughly 85% to 90% of patients achieve this level of reperfusion.
Successful blood flow restoration translates to real differences in recovery. Across multiple studies, about 55% to 65% of thrombectomy patients achieve functional independence at 90 days, meaning they can carry out daily activities without significant help. This is measured on a disability scale where scores of 0 to 2 (out of 6) represent a good outcome. Meta-analyses involving over 2,300 patients have found that adding clot-dissolving medication before thrombectomy doesn’t meaningfully improve these outcomes compared to thrombectomy alone, though the medication is still commonly given if the patient arrives early enough.
Risks and Complications
The most serious complication is bleeding inside the skull after the procedure. In one study of 135 patients, any bleeding on a follow-up brain scan occurred in about 38.5% of cases, but most of this was minor and caused no symptoms. Symptomatic bleeding, the kind that causes noticeable neurological worsening, occurred in 12.6% of patients. This type of bleeding can be life-threatening.
Three factors consistently predict higher bleeding risk: arriving late (more than about 4.5 hours from stroke onset to the start of the procedure), having a large area of early brain damage visible on the initial CT scan, and requiring more than three passes with the stent retriever device to remove the clot. Each additional pass with the device roughly doubles the odds of symptomatic bleeding. Other potential complications include damage to blood vessel walls during catheter navigation and clot fragments breaking off and blocking a previously unaffected artery, though combined stent-and-suction techniques are designed to minimize this.
Recovery and Hospital Stay
After the procedure, patients are closely monitored, typically in an intensive care unit or specialized stroke unit. A follow-up CT scan is performed about 24 hours later to check for bleeding. The median hospital stay for thrombectomy patients is about 6.5 days, roughly 2.5 to 3 days shorter than patients with similar strokes who receive only medical treatment. Data from the DEFUSE-3 trial showed this represented a 29% reduction in hospital time, and results from other trials have been consistent.
Recovery beyond the hospital varies enormously depending on how much brain tissue was damaged before blood flow was restored, where in the brain the stroke occurred, and the patient’s overall health. Some people walk out of the hospital with mild deficits. Others face weeks or months of rehabilitation for speech, movement, or cognitive function. The single biggest factor in long-term outcome is time: the faster blood flow is restored, the more brain tissue survives, and the better the recovery. This is why stroke systems are designed to route patients with suspected large vessel occlusions directly to hospitals equipped to perform thrombectomy, skipping facilities that can only offer medication.