Suspected acute aortic syndrome

2022 ACC/AHA Aortic Disease Guideline

A time-critical study with two non-negotiable technical elements: an unenhanced series before the contrast, and coverage that runs from the thoracic inlet to the femoral arteries. The first is what makes intramural haematoma visible; the second is what defines the extent and the access.

Abrupt severe chest or interscapular pain, pulse or blood pressure asymmetry, new aortic regurgitation, malperfusion of a limb or organ, or syncope with a widened mediastinum.

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.

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

CT Aorta — Acute Aortic Syndrome

CT Angiogram — Aorta

What we'd amend, and why

Intramural haematoma is blood within the media that has not yet formed a flap, and it is visible only as a crescent of high attenuation against the lower-density wall — that difference disappears the moment iodine is in the lumen, because the enhanced blood is then denser than the haematoma. So the unenhanced series is not a dose-adding preamble but the acquisition that makes one of the three acute aortic syndromes diagnosable at all. ECG synchronisation of the thoracic portion suppresses the root pulsation that otherwise creates a double contour mimicking a flap in the ascending aorta, which is precisely the segment on which the surgical decision turns. Coverage to the femoral arteries defines the distal extent, the branch vessels at risk of malperfusion, and the access route the interventional team will use.

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

How was this decided?

pathwayadult — Adults
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-metformin — Metformin and iodinated contrast; checked by Radiographer at the scanner
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner
rulerule-pregnancy-ionising — Pregnancy status before an ionising exposure; checked by Radiographer at the scanner
rulerule-renal-iodinated — Kidney function and intravenous iodinated contrast; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(4)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Metformin and iodinated contrast
Confirm whether the patient takes metformin or a metformin-containing combination, and if so whether ACR Category II applies (eGFR below 30, known or suspected AKI, or an arterial catheter study likely to cause renal embolisation). If Category I — that is, no AKI and eGFR at or above 30 — no action of any kind is needed.
Radiographer at the scannerAt the scanner
Flags back if: The patient takes metformin AND meets ACR Category II — eGFR below 30 mL/min/1.73 m2, known or suspected acute kidney injury, or an arterial catheter procedure with likely renal arterial embolisation. Metformin plus a normal or mildly reduced eGFR is explicitly NOT a flag-back: there is no need to stop metformin before or after intravenous iodinated contrast in Category I patients, and no need to re-check creatinine afterwards.
Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.
Pregnancy status before an ionising exposure
Make the pregnancy enquiry immediately before the exposure and record the answer. In the UK this is a statutory operator duty discharged at the time of exposure under the employer’s written procedures required by IR(ME)R 2017 — it is not something the vetting radiologist can perform or pre-empt, and a request is complete without it.
Radiographer at the scannerAt the scanner
Flags back if: The patient states that she is, or may be, pregnant AND the uterus is in or near the primary beam. The exposure is then paused for re-justification by the IR(ME)R practitioner before it proceeds.
Pregnancy is not a reason to defer or dilute this study. Acute aortic syndrome is over-represented in pregnancy — the third trimester and the early puerperium are the peak, and connective tissue disease, bicuspid valve aortopathy and hypertension are the usual substrates — and the untreated maternal mortality is what actually threatens the fetus. Conceptus dose from a chest-to-femoral CT angiogram is well below any deterministic threshold and, with the uterus mostly outside the primary beam, is dominated by internal scatter; it is not a quantity that should be traded against a type A dissection. The justification conversation and the dose-reduction measures happen alongside the scan, not in front of it. Where the patient is stable and the question is genuinely confined to the ascending aorta, transthoracic and then transoesophageal echocardiography answer it with no radiation at all, and cardiac MRI without gadolinium is an option in a stable patient after the first trimester — but neither should be allowed to delay a CT in an unstable one.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

Pathways

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

Haemodynamically unstable — bedside echocardiography before the transfer

Role	Study & protocol	Why this answers the question
First line	Transthoracic echocardiography Transthoracic echocardiography — standard adult study usually appropriate	Shock in acute aortic syndrome has a short list of causes and every one of them is answerable at the bedside in minutes: pericardial blood with tamponade physiology, acute severe aortic regurgitation, a proximal flap seen in the root, or free rupture. Those findings send a patient to theatre rather than to a scanner, and the transfer is itself the risk — a peri-arrest patient moved onto a CT table is a patient who arrests on a CT table, out of reach of the surgical team. Where transthoracic windows are poor and the expertise is present, transoesophageal echocardiography answers the ascending aorta more completely and can be done in the anaesthetic room or in theatre. Two things this step does NOT license. It does not license waiting: a hypotensive patient who can be moved safely should be moved, because the operation is planned from the extent, the branch vessels and the access route, and only the CT shows those. And a negative bedside echocardiogram excludes nothing below the arch, so it must never be used to close the question.
Second line	CT Angiogram — Aorta CT Aorta — Acute Aortic Syndrome usually appropriate	The definitive study, and it follows the resuscitation by minutes rather than by hours — as soon as there is a monitored transfer and an airway, or immediately if the bedside study is equivocal and the patient is holding a pressure. It is the same acquisition as on the default pathway and it is not degraded for the sick patient: the unenhanced series still carries the intramural haematoma, and coverage still runs to the femoral arteries because the malperfusion and the access route are exactly what a shocked patient needs decided. The renal and premedication overrides on this card apply with more force here, not less — contrast is given and the kidney managed afterwards, and a steroid regimen that takes hours has no place in front of this scan.

Read this fork as ordering, never as withholding. The card's standing advice — that this is the indication where a request should be expedited rather than queried — is unchanged; the only claim here is that a crashing patient gets a probe on the chest while the scanner is being cleared, not instead of it.
A shocked patient with a known aneurysm is the other version of this presentation, and it resolves the same way: rupture is a theatre diagnosis, and imaging that delays the operation is imaging that costs the patient.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Angiogram — Aorta CT Aorta — Acute Aortic Syndrome usually appropriate	Intramural haematoma is blood within the media that has not yet formed a flap, and it is visible only as a crescent of high attenuation against the lower-density wall — that difference disappears the moment iodine is in the lumen, because the enhanced blood is then denser than the haematoma. So the unenhanced series is not a dose-adding preamble but the acquisition that makes one of the three acute aortic syndromes diagnosable at all. ECG synchronisation of the thoracic portion suppresses the root pulsation that otherwise creates a double contour mimicking a flap in the ascending aorta, which is precisely the segment on which the surgical decision turns. Coverage to the femoral arteries defines the distal extent, the branch vessels at risk of malperfusion, and the access route the interventional team will use.
Reasonable alternative	CT Coronary Angiogram (CCTA) CT Chest — Triple Rule-Out	The triple rule-out acquisition covers the coronary arteries, the thoracic aorta and the pulmonary arteries in one ECG-synchronised pass, and is reasonable in the narrow group where all three diagnoses carry similar probability. The trade-off is explicit: a single injection cannot optimally opacify three vascular beds, so each is imaged less well than in its dedicated protocol, at higher contrast load and higher dose.

Pitfalls

Losing the unenhanced series to save time or dose. It is the only sequence in which intramural haematoma is visible, and its omission is the classic protocol failure in this indication.
Diagnosing a flap in the ascending aorta on a non-gated study. Root motion produces a double contour that is indistinguishable from a real flap, and the consequence is an unnecessary sternotomy.
Cropping the coverage at the diaphragm, which leaves the distal extent, the visceral vessels and the access route undefined and forces a repeat.
Accepting a routine venous-phase CT chest for this question — by 60 seconds the true and false lumens have equilibrated and the flap can be invisible.
Treating a normal chest radiograph as reassuring. A normal mediastinal contour does not exclude dissection.
Streak artefact from dense contrast in the left brachiocephalic vein simulating disease at the arch; a right arm injection and saline chaser mitigate it.
Reporting the aorta and stopping there. Malperfusion is what kills in type B disease and what changes the operation in type A, and it has to be sought deliberately in every bed the dissection reaches: the coronary ostia, the arch vessels, the spinal supply, the coeliac, superior mesenteric and renal arteries, and the iliofemoral segment. Two mechanisms behave differently and the report should name which one it is — dynamic obstruction, where a mobile flap intermittently covers an otherwise normal branch ostium and is usually relieved by proximal repair or fenestration, and static obstruction, where the dissection extends into the branch itself and generally needs that branch stented. An underperfused kidney, a hypodense bowel wall or an unopacified iliac artery on the same study is the finding, not an incidental observation.
Reading a technically imperfect study as a negative one. A mistimed bolus in a low-output patient, root motion on an ungated acquisition, an omitted unenhanced series or arms-down streak can each hide the finding, so "no dissection seen" from such a study does not exclude an acute aortic syndrome. Where the clinical picture is strong the answer is to repeat with correct timing and gating, or to go to transoesophageal echocardiography — not to reassure.
Forgetting the electrocardiogram and the troponin. A proximal dissection can occlude a coronary ostium and present as an inferior infarct, and thrombolysis, dual antiplatelet therapy or heparin given on that basis is catastrophic — which is one more reason this study is expedited rather than queued behind a cardiology decision.
Missing the intramural haematoma that has already been made invisible. If the unenhanced series was not acquired, the study cannot be reported as excluding intramural haematoma at all, and saying so plainly is more useful than a negative conclusion.

Priors — what to pull first

Retrieve any previous aortic imaging before reporting — a chronic dissection flap that has been present for years produces the same appearance as an acute one, and the distinction is entirely historical.
Note previous aortic or cardiac surgery: graft material, felt pledgets and surgical anatomy all mimic pathology on an unfamiliar aorta.

What makes a good request

A good request states the onset and character of the pain, the blood pressure in both arms, any connective tissue disorder or previous aortic surgery, and the renal function if it is already known — but none of these should delay the scan.
This is the indication where a request should be expedited rather than queried. Untreated type A dissection carries a mortality that rises by the hour.
Where the differential genuinely includes coronary disease and pulmonary embolism equally, a single ECG-synchronised acquisition covering all three beds is an option — but a genuinely equal three-way probability is uncommon, and the compromise costs image quality in every bed.

Scoring this once it is done

The classification and risk tools this question ends in.

AAST Thoracic Vascular Injury Scale eGFR (CKD-EPI 2021 Creatinine)

How these studies are acquired

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

Transthoracic echocardiography — standard adult study CT Aorta — Acute Aortic Syndrome CT Chest — Triple Rule-Out

Confirm locally

CT Aorta — Acute Aortic Syndrome: timings are typical — confirm against local protocol.
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.