Aortic aneurysm surveillance and post-repair follow-up

NICE NG156; 2022 ACC/AHA Aortic Disease Guideline

Two different surveillance problems in one clinical thread, and one emergency that must never be answered as either. An untreated aneurysm is a diameter measurement and belongs to ultrasound; a repaired one is a leak-detection problem and needs a multiphase CT with a delayed series, because the commonest endoleak is the slowest. A painful, tender or newly symptomatic aneurysm is neither: it is a rupture until proved otherwise, and it goes to a contrast CT within the hour — or, if the patient is shocked, to theatre with the scanner not allowed to become the delay.

An aneurysm found by screening or incidentally and now under interval surveillance, or a patient who has had endovascular repair and is in a structured follow-up programme — and, on the acute arm, a patient presenting with pain, tenderness, collapse or shock in whom an aneurysm is known or suspected.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Haemodynamic state

The fact that lets a pathway waive its own requirements. A crashing patient does not wait for a score.

Where is the patient?

Some pathways change in the emergency department — an acutely threatened limb is not an elective work-up.

Recent surgery

Days since the relevant operation, where the pathway depends on it.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Ultrasound abdomen — full survey

Ultrasound abdomen

What we'd amend, and why

The decision this surveillance feeds is a single number — the maximum diameter — and ultrasound measures it reproducibly, with no radiation and no contrast, in a patient who will be measured every six to twelve months for years. Cumulative dose is the real argument: a CT-based surveillance programme delivers a substantial lifetime exposure to answer a question a probe answers in ten minutes. It is also what the national screening programme uses, so the measurements are directly comparable across the pathway.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwaysurveillance — Untreated aneurysm under surveillance

Decision support only. Local protocol takes precedence.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Symptomatic or shocked — rupture until proved otherwise

Role	Study & protocol	Why this answers the question
First line	CT Angiogram — Aorta CT Aorta — Acute Aortic Syndrome usually appropriate	The acute protocol rather than the sizing one, and for a reason that is easy to lose: the unenhanced series carries two findings that iodine erases. A hyperattenuating crescent within the mural thrombus is the sign of impending rupture, and fresh retroperitoneal or periaortic blood is high attenuation before contrast and simply blends with enhanced structures after it — so a rupture protocol that opens with the injection has thrown away the evidence. The arterial series then shows active extravasation and the anatomy the operation is chosen from: the length and angulation of the infrarenal neck, the seal zones, and the iliac and femoral calibre that decides whether an endovascular repair under local anaesthetic is possible at all. That is the whole argument for scanning a patient who can tolerate it, because emergency endovascular repair is chosen from this study and cannot be planned without it. Coverage runs to the common femoral arteries for the same reason it does in dissection. Two boundaries belong on this step and neither of them is negotiable. A patient who is shocked with a known or palpable aneurysm has a rupture until theatre says otherwise, and the operation is both the diagnosis and the treatment — permissive hypotension, blood, and a vascular team, with the scanner not permitted to become the reason the transfer is late. And a negative-looking scan in a patient who remains shocked has not excluded rupture: look again at the unenhanced series, and keep the surgical conversation running.
First line	Ultrasound abdomen Ultrasound abdomen — full survey usually appropriate	The probe at the trolley, and it earns its place here for one narrow reason: it settles whether there is an aneurysm at all, in seconds, without the patient leaving a resuscitation area. In a peri-arrest patient that is the only imaging that should happen, because it converts an undifferentiated collapse into a vascular emergency and sends the trolley to theatre rather than to a scanner corridor. Its limits are as important as its use and belong in the report and in the conversation. It is highly sensitive for the aneurysm and close to blind to the rupture itself — retroperitoneal blood is poorly seen through bowel gas — so an aorta that measures large with no visible leak is not reassurance, and a shocked patient with that finding still belongs in theatre. It measures diameter less reproducibly than CT in an acutely unwell patient who cannot hold still, and it says nothing about the neck, the seal zones or the access vessels, which is why a patient who can tolerate the scanner should have the CT as well.

This fork withholds nothing. It changes what the card recommends NOW for a patient whose aneurysm has become symptomatic, and it says out loud the thing the card previously only implied: that a surveillance ultrasound is the wrong answer to acute pain, and that in a shocked patient the operation outranks the picture.
It is entered on haemodynamic state or on an emergency department attendance, because those are the closest proxies a request carries for acuity. Both are starting assumptions rather than substitutes for reading the indication — a stable patient attending the emergency department for a routine interval ultrasound belongs on the surveillance ladder, and a ward inpatient whose aneurysm has just become tender belongs here whatever the setting field says.
Symptomatic thoracic and thoracoabdominal aneurysms belong on the acute aortic syndrome card, which carries the ECG-synchronised acquisition the ascending aorta and root need. The two cards use the same protocol and answer adjacent questions; state which segment is in question so the coverage is right.

After aortic repair

Role	Study & protocol	Why this answers the question
First line	CT Angiogram — Aorta CT Aorta — Post-EVAR Endoleak Protocol usually appropriate	Each series exists to catch a different failure mode. The unenhanced acquisition establishes what is already dense — calcification, embolisation coils, glue, retained contrast from a recent procedure — so that none of it is later called a leak. The arterial series shows the high-flow type I and III leaks that arise at the seal zones and between components. The delayed series is the one that matters most in practice, because type II leaks fill retrogradely from lumbar or inferior mesenteric branches at low flow and simply have not opacified the sac by the arterial phase; a single arterial acquisition misses the commonest endoleak there is. Matched breath-holds across all series let the sac be compared voxel for voxel rather than eyeballed.
Reasonable alternative	Ultrasound abdomen Ultrasound abdomen — full survey	Once a baseline CT has confirmed a well-sealed repair, duplex surveillance tracks the parameter that actually predicts failure — sac diameter — with no radiation and no contrast, and can demonstrate flow within the sac. It is the sensible steady-state modality for a patient facing decades of follow-up, with CT reserved for a stable-to-growing sac or a suspected leak.

Practice differs on whether the unenhanced series can be dropped once a clean baseline exists, and published delayed-phase timings range from around a minute to several minutes. Both are local decisions.

Untreated aneurysm under surveillance

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Ultrasound abdomen Ultrasound abdomen — full survey usually appropriate	The decision this surveillance feeds is a single number — the maximum diameter — and ultrasound measures it reproducibly, with no radiation and no contrast, in a patient who will be measured every six to twelve months for years. Cumulative dose is the real argument: a CT-based surveillance programme delivers a substantial lifetime exposure to answer a question a probe answers in ten minutes. It is also what the national screening programme uses, so the measurements are directly comparable across the pathway.
Second line	CT Angiogram — Aorta CT Aorta — Aneurysm Assessment and Planning	CT takes over when ultrasound cannot answer the question: a thoracic or thoracoabdominal aneurysm the probe cannot reach, obesity or bowel gas that defeats the study, an aneurysm approaching the repair threshold, or sizing before intervention. The measurement discipline changes here too — diameters are taken perpendicular to a reconstructed centreline, because an axial diameter through a tortuous aorta cuts obliquely and over-measures. Coverage must reach the common femoral arteries so the access vessels are assessed in the same study.

Pitfalls

Mixing measurement conventions across serial studies. This is the dominant source of spurious growth in aneurysm surveillance.
Accepting an arterial-only CT for post-EVAR assessment, which misses slow type II endoleaks — the commonest kind.
Reading dense material in the sac on a contrast-only study as an endoleak when it is embolisation coil, glue or calcification. The unenhanced series exists to prevent exactly this.
Reporting a sac as stable when diameter was used on one study and volume on the other; volume changes earlier and the two are not interchangeable.
Treating a symptomatic aneurysm as a surveillance request. Pain or tenderness moves the patient to the acute pathway immediately, and the answer there is a contrast CT within the hour or an operation — never the next ultrasound slot.
Cropping CT coverage above the femoral bifurcation before a planned endovascular repair, leaving the access vessels unassessed.
Letting the scan delay the operation in a shocked patient with a known or palpable aneurysm. Rupture is a theatre diagnosis; imaging that postpones the transfer costs the patient, and the only imaging a peri-arrest patient should have is the probe already at the trolley.
Using the elective sizing protocol for suspected rupture. Without the unenhanced series the hyperattenuating crescent of impending rupture and fresh retroperitoneal blood are both erased by the contrast that follows, and the study is then reported as showing an aneurysm with no leak.
Reporting "no rupture" from a bedside ultrasound. Ultrasound finds the aneurysm reliably and the retroperitoneal blood unreliably, so a large aorta with no visible leak in a shocked patient is a surgical emergency and not a negative study.
Mistaking a leaking aneurysm for renal colic in an older patient with first-episode flank pain, or for a musculoskeletal back pain in one with a known aneurysm. Both are established ways this diagnosis is missed until the second presentation.

Priors — what to pull first

Read the previous report for the measurement method, not only the number. A change from axial to centreline measurement, or from outer-to-outer to inner-to-inner wall, manufactures growth or stability that is not real.
After repair, retrieve the immediate post-procedural study: it is the reference against which sac behaviour and any pre-existing leak are judged.

What makes a good request

A good request states the last measured diameter and how it was measured, the date and technique of the comparison study, and — after repair — the type of device, the date of implantation and any previously documented endoleak.
Surveillance intervals for untreated aneurysms scale with diameter, from annual for the smallest through to short-interval review as the aneurysm approaches the repair threshold. Intervals belong to the local or national programme; this card does not set them.
A symptomatic or tender aneurysm is not a surveillance question. New back, flank or abdominal pain in a patient with a known aneurysm is a rupture or a contained leak until imaging or an operation says otherwise, and the answer is an immediate contrast CT rather than the next ultrasound slot. Say on the request that the patient is symptomatic, because that single word is what moves this card from its surveillance ladder to its acute one.
Rupture presents as renal colic often enough that it is a named trap. An older patient with first-episode flank pain, particularly one who is hypotensive or has a pulsatile mass, should have the aorta looked at deliberately before the pain is attributed to a stone.

Scoring this once it is done

The classification and risk tools this question ends in.

Solid Organ Volume (Ellipsoid)eGFR (CKD-EPI 2021 Creatinine)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Aorta — Acute Aortic Syndrome Ultrasound abdomen — full survey CT Aorta — Post-EVAR Endoleak Protocol CT Aorta — Aneurysm Assessment and Planning

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.