A landmark study shows that measuring how much an aneurysm sac shrinks in the first year after surgery can reliably forecast what that sac's diameter will do over the long haul — unlocking smarter, more personalised patient monitoring.

The Problem with Watching Arteries Heal

Abdominal aortic aneurysms — dangerous bulges in the body's main artery — kill tens of thousands of people each year when they rupture without warning. Endovascular aneurysm repair, or EVAR, is a minimally invasive surgery in which doctors thread a stent-graft through the groin to seal off the bulge from the inside, like patching a weak hose from within. It's revolutionised vascular surgery, offering patients a far quicker recovery than open surgery.

But EVAR is not a cure. The sealed sac still exists inside the body, and over months and years it can change size — ideally shrinking as blood pressure is removed from it, but sometimes stubbornly staying the same or even growing. A sac that keeps expanding after surgery can signal a dangerous leak (called an endoleak) or graft failure, either of which may require a second intervention. So, after every EVAR procedure, patients face a lifetime of periodic CT scans to check one simple thing: is the sac getting bigger or smaller?

"For years, the number clinicians relied on was a single diameter measurement — essentially, how wide is the bulge? But width alone turns out to be a surprisingly blunt instrument."

- Background context from the field of post-EVAR surveillance

The challenge is that current guidelines require follow-up CT scans roughly every year for life, which is expensive, exposes patients to radiation, and still may miss subtle warning signs until they have become obvious on a simple diameter measurement. Researchers and clinicians have long wondered: is there a better, earlier signal we could use?

What the New Research Found

A 2026 study published in the Journal of Vascular Surgery tackled exactly this question. The research team looked at patients who underwent infrarenal EVAR — repairs focused on the lower portion of the aorta, just below the kidneys — and tracked two different types of measurements over time: the familiar maximum diameter (width) of the aneurysm sac, and its total volume (how much three-dimensional space it occupied).

Their headline finding was striking: early changes in sac volume, measured in the first months to year after surgery, were reliable predictors of how the sac's diameter would behave over the long term. In other words, if a patient's sac shows meaningful volumetric shrinkage early on, that sac is very likely to continue shrinking in diameter over subsequent years — a good sign. Conversely, a sac that fails to lose volume early tends to show worrying diameter behaviour later.

Why This Matters in Plain English

Think of a partially deflated balloon inside a paper bag. If you measure only how wide it looks from the outside at a single time point, you might miss that it has started to re-inflate slightly in volume. But if you measure how much air — i.e., total volume — is inside at an early stage, you get a far earlier, more complete picture of whether it is truly deflating or not. The study found that volumetric changes early on are a strong forecast of what diameter measurements will show years later.

Why Volume Is a More Sensitive Signal

Diameter measurements have an inherent blind spot. A sac is a three-dimensional object, yet a single diameter captures it in only one direction. It is entirely possible for a sac to expand in volume — accumulating more pressurised blood — while its widest cross-section, known as the maximum sac diameter, barely changes, simply because the growth is happening in a different plane. By the time the width measurement catches up, the problem may already be well established.

Volume, measured by tracing the sac's entire three-dimensional outline on CT imaging, captures this fuller picture. A 5% increase in volume across a three-dimensional structure may represent a clinically meaningful change that a diameter measurement of the same sac would record as essentially stable. Prior research has repeatedly shown that volumetric changes precede diameter changes as a signal of post-EVAR complications — the new study extends this insight by demonstrating that those early volumetric shifts can be used to predict the longer-term diameter trajectory, not just describe the present.

What This Means for Patients and Clinicians

The clinical implications are significant. If early volumetric changes reliably forecast long-term diameter behaviour, clinicians could theoretically use a patient's first post-operative volume measurement to stratify risk — identifying early on who is on a safe trajectory toward sac shrinkage and who may need closer monitoring or earlier re-intervention.

This could mean that patients with strongly regressing sacs could safely have their surveillance intervals extended — fewer CT scans, less radiation, lower cost. Meanwhile, patients showing early volumetric warning signs could be flagged for intensified follow-up before any diameter-based guideline threshold is ever crossed.

Current Society for Vascular Surgery guidelines still define significant sac change as a 5 mm or greater shift in diameter. The new research suggests this binary threshold, while useful, leaves important predictive information on the table. 

Volume change early in the post-operative period is not just a companion metric — it is an upstream predictor of the very metric everyone is already watching.

"The ability to forecast long-term sac behaviour from early volumetric measurements would allow us to move from reactive surveillance to truly proactive, personalised follow-up care."

- Concept from post-EVAR surveillance research

The Practical Barrier — And How AI Is Removing It

Despite volumetric measurement's advantages, it has historically been underused in routine clinical practice. The reason is simple: manually tracing the boundaries of an aneurysm sac across dozens of CT image slices is painstaking, time-consuming work that can add 20 minutes or more to a radiologist's workflow per patient. In a busy hospital, that adds up fast.

This is precisely where artificial intelligence changes the equation. Modern AI-powered segmentation algorithms can automatically identify and trace the aneurysm sac across a full CT scan in under three minutes — with accuracy comparable to manually corrected expert segmentation. The bottleneck that once made volumetrics impractical dissolves.

• Speed — from 22 min to under 3
• AI segmentation reduces per-patient measurement time by over 85%, making volumetrics viable at scale.

• Accuracy on par with experts
• Studies show AI volumetry closely matches manually corrected senior surgeon segmentation across thousands of slices.

• Consistent, reproducible results
• AI removes inter-observer variability that plagues manual measurement, especially across different imaging centres.

• Better risk stratification
• Consistent volumetric data over time enables AI-driven classification of sac evolution, improving surveillance decisions.

cvi42 | Vascular CT

This is exactly the kind of clinical advance that cvi42 | Vascular CT is designed to enable. In March 2026, Circle Cardiovascular Imaging expanded its flagship cvi42 platform by integrating AI-driven vascular analysis technology developed by Astute Imaging — bringing automated, quantitative vascular CT analysis into the same unified platform already trusted for cardiac imaging by over 2,100 hospitals across 90+ countries.

The platform supports the full continuum of EVAR care: pre-operative anatomical planning, intra-operative device sizing via AI-enabled virtual device simulation, and — critically — post-operative longitudinal surveillance including automated aneurysm sac segmentation and volumetric tracking. For every follow-up CT scan, cvi42 can automatically generate volumetric measurements, flag changes relative to prior studies, and provide the kind of 3D sac evolution data that the new JVS study identifies as a key predictor of long-term outcomes.

The platform supports the full continuum of EVAR care: pre-operative anatomical planning, intra-operative device sizing via AI-enabled virtual device simulation, and — critically — post-operative longitudinal surveillance including automated aneurysm sac segmentation and volumetric tracking. For every follow-up CT scan, cvi42 can automatically generate volumetric measurements, flag changes relative to prior studies, and provide the kind of 3D sac evolution data that the new JVS study identifies as a key predictor of long-term outcomes.

The result is a workflow where the early predictive volumetric signal described in this research can be captured routinely, rapidly, and reproducibly — without adding burden to an already stretched radiology team.

• Automated Segmentation – aorta, thrombus, lumen, dissection – fully AI driven
• Volumetric Tracking – Longitudinal sac volume change over serial studies
• Virtual device planning – AI-enabled stent-graft sizing and anatomical fit simulation
• Unified cardiac and vascular workflow – one platform for all CV imaging needs

The Bigger Picture: From Surveillance to Prediction

The shift from measuring what has happened to predicting what will happen is one of the defining ambitions of modern imaging. Diameter tells you where a sac is today. Volume — especially early volume change — tells you where it is headed.

As the evidence base grows, volumetric thresholds may begin to inform surveillance guidelines the way diameter thresholds do today. Hospitals that already have automated volumetric tools in place will be well positioned to act on these evolving recommendations — and to participate in the research studies that will shape them.

More immediately, the findings from this study offer a compelling argument for any vascular or radiology programme still relying solely on diameter: you may be watching the right thing but starting too late. The signal that predicts where a sac is going is available from the very first post-operative scan, in three dimensions, if you have the tools to read it.

The research discussed in this post reinforces a growing body of evidence that volumetric sac analysis after EVAR delivers clinical intelligence that diameter measurement alone cannot provide — and that AI-enabled platforms like cvi42 | Vascular CT are making that intelligence practical at the point of care. 

Primary source: "Early Sac Volume Changes Predict Long-term Diameter Sac Dynamics After Infrarenal EVAR." Journal of Vascular Surgery, 2026. View original paper →