Background
Acute ischemic stroke caused by occlusion of medium or distal cerebral vessels is increasingly recognized as an important stroke subtype. These vessels are smaller and farther downstream than the large arteries typically targeted in standard thrombectomy trials, but they can still supply critical brain regions. When one of these arteries is blocked, parts of the brain are placed at risk of irreversible injury unless blood flow is restored quickly.
Endovascular treatment (EVT), often called mechanical thrombectomy, aims to remove the clot directly from the blocked vessel. Best medical treatment (BMT) generally includes intravenous thrombolysis when appropriate, antiplatelet therapy, anticoagulation if indicated, blood pressure and glucose management, and comprehensive stroke unit care. For medium or distal vessel occlusions, the clinical benefit of EVT has been less certain than for large vessel occlusion stroke, so imaging-based analyses are especially useful for understanding who may benefit most.
This post hoc analysis of the DISTAL randomized clinical trial examined whether adding EVT to BMT helps preserve brain tissue that was initially at risk, and whether that tissue preservation is linked to better recovery at 90 days.
Study design and methods
The analysis used data from the DISTAL trial, a multicenter randomized clinical trial conducted in 55 hospitals across 11 countries between December 2021 and July 2024. Patients were randomized to EVT plus BMT or BMT alone, and the original trial used blinded end point assessment. For this secondary imaging analysis, only patients who had baseline perfusion imaging and follow-up imaging at about 24 hours were included.
Perfusion imaging helps estimate the “tissue at risk,” meaning brain tissue that has reduced blood flow but may still be saved if reperfusion happens in time. In this study, the key perfusion measure was the volume of tissue with time to maximum of the residue function greater than 6 seconds, commonly abbreviated as Tmax > 6 seconds, also referred to as Tmax6 volume. Final infarct volume was measured on follow-up imaging, reflecting the amount of brain tissue that ultimately became permanently damaged.
The main outcome was the change in relative volume preservation, calculated as the difference between tissue at risk and final infarct volume divided by the tissue at risk. This was called change in Vrel. A Vrel of 0.8 or greater was defined as a good imaging outcome, meaning at least 80% of the initially threatened tissue was spared from infarction at 24 hours.
The investigators also assessed whether a good imaging outcome was associated with better clinical recovery, as measured by functional outcome at 90 days.
Who was included
A total of 447 patients were included in the secondary analysis. The median age was 77 years, and 56.4% were men. Of these patients, 226 received EVT plus BMT and 221 received BMT alone.
The median time to follow-up imaging was 22.9 hours, which is close to the planned 24-hour assessment window. The median initial tissue-at-risk volume, based on Tmax6, was 34.0 mL. The median final infarct volume was 7.0 mL, showing that many patients had relatively limited permanent injury despite the initial perfusion deficit.
Key imaging findings
The amount of brain tissue saved differed between treatment groups. The median absolute reduction in threatened tissue volume was 23.6 mL in the EVT plus BMT group and 14.8 mL in the BMT-alone group. In other words, patients who underwent thrombectomy tended to preserve more at-risk tissue.
When expressed as relative tissue preservation, the median change in Vrel was 0.8 in the EVT plus BMT group compared with 0.6 in the BMT group. This suggests that EVT improved the odds of salvaging a larger proportion of brain tissue that was initially in jeopardy.
Statistical analysis showed that the odds of achieving a good imaging outcome, defined as Vrel of 0.8 or greater, were higher with EVT plus BMT than with BMT alone. The adjusted odds ratio was 1.6, with a 95% confidence interval of 1.1 to 2.3. This means the association remained significant after accounting for relevant baseline factors.
The analysis also found that successful reperfusion was strongly associated with a good imaging outcome. Compared with no successful reperfusion, the adjusted odds ratio for reaching Vrel 0.8 or greater was 2.5, with a 95% confidence interval of 1.3 to 4.8. This reinforces the biological logic of thrombectomy: reopening the vessel improves the chances of preserving threatened tissue.
Clinical meaning at 90 days
The study went beyond imaging alone and examined whether tissue preservation translated into better patient-centered outcomes. Patients who achieved a good imaging outcome, meaning that most of the initially endangered brain tissue was not infarcted, had better clinical outcomes at 90 days.
This finding is important because imaging success is only valuable if it helps patients regain function, independence, or quality of life. The results suggest that the amount of brain tissue saved early after stroke is not just a radiological measure; it is meaningfully linked to long-term recovery.
Interpretation
This analysis supports the idea that EVT can improve brain tissue preservation in selected patients with medium or distal vessel occlusion stroke. Although the benefits of thrombectomy have historically been most established for large vessel occlusion, these findings indicate that smaller, more distal clots may also be worth targeting when patients are appropriately selected.
The use of perfusion imaging is especially helpful in this setting. Because symptoms and vessel size may vary widely in medium or distal occlusions, the presence of salvageable tissue can help identify patients most likely to benefit from invasive treatment. In practical terms, a patient with a relatively small clot but a substantial penumbra, or area of brain at risk, may still benefit from EVT if the tissue has not yet progressed to irreversible infarction.
The study also highlights the importance of reperfusion quality. Merely attempting thrombectomy is not enough; successful reopening of the vessel appears to be a key determinant of whether threatened tissue can truly be saved.
Strengths and limitations
One strength of this work is its randomized trial origin, which reduces the risk of selection bias compared with purely observational studies. The inclusion of blinded end point assessment and imaging-based measurements also adds rigor.
There are, however, some limitations to keep in mind. This was a post hoc analysis, meaning it was planned after the main trial question and therefore is hypothesis-generating rather than definitive on its own. The imaging analysis included only patients who had both baseline perfusion imaging and follow-up imaging at 24 hours, which may reduce generalizability. Also, follow-up infarct volume is an early surrogate outcome; while it is strongly informative, it does not replace direct evaluation of disability and quality of life.
Another limitation is that medium and distal vessel occlusions are heterogeneous. The benefit of EVT may differ depending on the exact vessel involved, clot location, collateral circulation, baseline severity, and time to treatment. These factors are important for clinicians when deciding between thrombectomy and medical therapy.
Clinical implications
For stroke teams, these results suggest that imaging can help guide treatment decisions in medium or distal vessel occlusion stroke. The data support a strategy of considering EVT when there is a meaningful volume of threatened brain tissue and when the procedure can be performed safely and effectively.
For patients and families, the take-home message is that stroke care is becoming more personalized. Not every clot is the same, and not every patient benefits equally from thrombectomy. Advanced imaging may help clinicians identify when an intervention is likely to preserve brain tissue and improve the chance of recovery.
Conclusion
In this post hoc analysis of the DISTAL trial, EVT plus best medical treatment was associated with a higher likelihood of achieving a good imaging outcome than best medical treatment alone. A good imaging outcome, defined as preservation of at least 80% of the initially threatened brain tissue, was linked to better clinical recovery at 90 days.
These findings strengthen the case for using imaging-based selection and reperfusion success as key markers of benefit in medium or distal vessel occlusion stroke. While further studies will help refine patient selection, the results suggest that mechanical thrombectomy may play an important role in saving brain tissue and improving outcomes in this challenging stroke population.
