01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Aortic imaging has four different jobs: detect an aneurysm, measure it reproducibly, define anatomy for intervention, and diagnose an acute wall catastrophe. No single modality is ideal for every job. Ultrasound is portable, inexpensive and free of radiation, but is strongest in the abdominal aorta. CT angiography is fast and anatomically comprehensive but uses ionising radiation and iodinated contrast. MRI offers multiplanar lumen, wall and flow information without radiation, while echocardiography uniquely links proximal aortic disease to valve and pericardial consequences.
An aneurysm is a persistent pathological dilation, whereas acute aortic syndrome includes classic dissection, intramural haematoma and penetrating atherosclerotic ulcer. In dissection, blood enters or tracks within the media and may create true and false lumens; the life-threatening consequences arise from rupture, tamponade, acute aortic regurgitation, coronary compromise and static or dynamic obstruction of branch vessels. Imaging must therefore do more than confirm a flap: it determines which segment is involved and which organs are threatened.
Measurement technique matters because small apparent changes can be artefactual. Diameters should be taken perpendicular to the vessel centreline at reproducible anatomical landmarks, with the edge convention and cardiac phase recorded. Oblique axial measurements exaggerate a tortuous aorta. For abdominal ultrasound, NICE requests the inner-to-inner maximum anterior-posterior diameter. For thoracic CT or MRI, ECG synchronisation improves root and ascending-aorta precision when motion would otherwise blur the wall.
Clinical stability changes test choice. A haemodynamically stable person with suspected acute aortic syndrome usually proceeds rapidly to CT that covers the relevant aorta and branches. Transoesophageal echo can be performed at the bedside or in theatre when transport or iodinated contrast is problematic, while MRI is usually reserved for a stable patient or follow-up because access, scan duration and monitoring are more difficult. A normal chest radiograph is never an exclusion test.
Key points
- Ultrasound is the practical test for detecting and surveilling infrarenal abdominal aortic aneurysm, but it does not map the whole thoracic aorta.
- Report abdominal aortic ultrasound using the stated measurement convention; NICE specifies inner-to-inner maximum anterior-posterior diameter for AAA decisions.
- Contrast CT angiography rapidly maps the entire aorta, branch vessels, rupture signs and repair anatomy, making it central in suspected acute aortic syndrome.
- A dissection flap separates true and false lumens; the report must state proximal extent, entry features, complications and organ-vessel perfusion.
- MRI avoids ionising radiation and is valuable for serial stable assessment, but acquisition time and monitoring constraints limit emergency use in unstable patients.
- Transthoracic echo can show root dilation, aortic regurgitation or tamponade; transoesophageal echo provides better thoracic aortic detail when CT is unsuitable or transport unsafe.
- Serial growth is believable only when modality, plane, landmark, edge convention and cardiac phase are comparable.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Fusiform dilation involves the circumference over a segment, while saccular morphology is focal and asymmetric. Record maximum orthogonal diameter, length, branch relationship, thrombus and inflammatory or rupture features rather than diameter alone.
An intimal flap divides contrast flow into true and false lumens. Identify the most proximal involved segment, distal extent, branch origins, lumen thrombosis and signs of malperfusion or rupture.
Stanford type A acute dissection involves the ascending aorta regardless of the entry-tear site and requires urgent cardiothoracic or aortic surgical assessment. Type B has no ascending-aorta involvement; imaging must identify rupture, malperfusion, rapid expansion and other complications that prompt urgent specialist intervention rather than uncomplicated medical surveillance alone.
Non-contrast CT may show crescentic or circumferential high attenuation within the wall without a typical flowing false lumen. Contrast imaging then assesses ulcer-like projections, extent and complications.
Contrast extends beyond the expected intimal surface into an atherosclerotic wall, sometimes with adjacent haematoma or pseudoaneurysm. Symptoms, depth, progression and rupture features determine urgency with specialist input.
Periaortic haematoma, retroperitoneal blood, haemothorax, haemopericardium, active contrast extravasation or loss of normal tissue planes support rupture. Absence of active leak does not exclude contained rupture.
Post-EVAR imaging assesses sac size, device position, limb patency, kinking, migration and endoleak. A negative routine colour duplex examination alone does not exclude every endoleak when suspicion persists.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Aortic ultrasoundFirst step - Why
- Detect and surveil abdominal aortic aneurysm and provide an immediate bedside answer in suspected rupture.
- Interpretation and limitations
- Measure the maximum anterior-posterior diameter with the required convention, document visualisation limits, and escalate if bedside imaging is unavailable or non-diagnostic while suspicion persists.
- 02
First-line CT angiography for stable suspected acute aortic syndromeFirst line - Why
- Provide the recommended initial diagnostic imaging in most haemodynamically stable patients and map dissection, aneurysm, branch vessels, rupture signs and repair anatomy.
- Interpretation and limitations
- Review multiplanar and centreline images for proximal and distal extent, true and false lumens, organ-vessel perfusion, haematoma, leak and access anatomy.
- 03
Non-contrast CT phase - Why
- Identify acute wall blood, displaced calcification and baseline density before contrast enhancement.
- Interpretation and limitations
- Crescentic high-attenuation wall thickening supports intramural haematoma, while comparison with arterial images helps separate calcification, thrombus and active lumen.
- 04
Cardiovascular magnetic resonance and MR angiography - Why
- Characterise stable aortic anatomy, wall and flow without ionising radiation and support serial surveillance.
- Interpretation and limitations
- Use reproducible orthogonal measurements and sequence-specific assessment; movement, implanted-device conditions, access and long acquisition limit some patients.
- 05
Transthoracic and transoesophageal echocardiography - Why
- Assess proximal aorta, aortic valve, pericardium and haemodynamic complications at the bedside or in theatre.
- Interpretation and limitations
- TTE rapidly detects regurgitation, root disease or tamponade but incompletely visualises the thoracic aorta; TEE adds detail yet has recognised blind regions and procedural risks.
- 06
Chest radiography - Why
- Identify alternative chest pathology and occasionally raise suspicion through mediastinal or pleural signs.
- Interpretation and limitations
- Mediastinal widening or contour change can support concern, but normal or non-specific findings cannot rule out acute aortic syndrome.
04Clinical next stepsHow the result changes management or prompts escalation.
01Emergency aortic pathwayImage suspected acute aortic syndrome without delayFirst stepAbrupt severe pain or collapse is accompanied by high-risk aortic history, examination findings or organ malperfusion.+
- 1Assess haemodynamic stability, neurological and limb perfusion, pulses, bilateral arm pressures and features of rupture while resuscitation begins.
- 2AlternativeContact the aortic or vascular team early. In most haemodynamically stable patients with suspected acute aortic syndrome, obtain urgent CT angiography as the initial diagnostic imaging; use TEE or MRI when stability, contrast risk, access or availability makes an alternative more appropriate.
- 3Use a dedicated CT angiography protocol to map the entire aorta, entry tear, true and false lumens, branch-vessel perfusion, rupture and other complications that determine intervention.
- 4Communicate classification, proximal extent, rupture, tamponade, valve and organ-malperfusion findings directly because they determine immediate intervention.
02Suspected ruptured AAAUse bedside ultrasound as a rapid rule-in toolNew abdominal or back pain, collapse or syncope suggests symptomatic or ruptured abdominal aortic aneurysm.+
- 1Perform immediate bedside aortic ultrasound while discussing the patient with the regional vascular service.
- 2Treat a demonstrated aneurysm as clinically relevant to the presentation and continue urgent specialist assessment rather than waiting for a formal report.
- 3EscalationIf ultrasound is unavailable or non-diagnostic but suspicion remains, maintain the diagnosis and escalate immediately rather than recording a negative result.
- 4Consider thin-slice arterial CT angiography when the patient is being evaluated for repair and imaging will not create unsafe delay.
03Elective AAA pathwayMove from detection to repair planningAn asymptomatic or symptomatic abdominal aneurysm is identified clinically, incidentally or through screening.+
- 1Confirm maximum inner-to-inner anterior-posterior diameter on aortic ultrasound and document any additional measurement convention separately.
- 2Refer an asymptomatic AAA measuring 3.0 to 5.4 cm to a regional vascular service within 12 weeks of diagnosis and an AAA measuring at least 5.5 cm within 2 weeks. New aneurysm-related symptoms require immediate vascular discussion regardless of diameter; growth greater than 1 cm in 1 year also triggers prompt referral or repair consideration.
- 3For asymptomatic screen-detected AAA, arrange annual ultrasound at 3.0 to 4.4 cm and ultrasound every 3 months at 4.5 to 5.4 cm through the NHS AAA Screening Programme. Do not wait for the next surveillance slot if symptoms develop, diameter reaches 5.5 cm or growth exceeds 1 cm in 1 year.
- 4Obtain thin-slice arterial-phase CT angiography when elective repair is being evaluated to define morphology, neck, branches and access.
04Post-EVAR pathwayInvestigate sac growth and endoleakSurveillance shows aneurysm-sac enlargement, device concern or a possible endoleak after endovascular repair.+
- 1Review prior sac measurements, device position, imaging modality and the quality of the current duplex examination.
- 2Use contrast CT angiography when an endoleak is suspected; use contrast-enhanced ultrasound if CT contrast is contraindicated.
- 3Classify the leak source where possible and assess device seal, component integrity, branches and sac expansion.
- 4Discuss type 1 or type 3 leaks, expanding type 2 leaks and unexplained expansion promptly with the vascular team.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- For asymptomatic screen-detected AAA, use annual ultrasound at 3.0 to 4.4 cm and 3-monthly ultrasound at 4.5 to 5.4 cm. Refer without waiting for routine surveillance when the aneurysm reaches at least 5.5 cm or grows by more than 1 cm in 1 year, and seek immediate vascular advice for new aneurysm-related symptoms.
- Use the same modality, orthogonal plane, anatomical landmark, edge convention and cardiac phase when judging aortic growth whenever clinically feasible.
- Enrol every person after EVAR in a surveillance imaging programme whose frequency reflects individual risk of graft-related complications.
- For suspected post-EVAR endoleak, use contrast CT angiography or contrast-enhanced ultrasound when CT contrast is contraindicated; do not rely on negative colour duplex alone.
- After acute dissection or repair, surveillance should cover residual diseased aorta and branch vessels, with modality chosen to balance information, renal function, radiation and implanted devices.
- Escalate an apparent rapid size increase only after checking technical comparability, then treat confirmed growth or new symptoms as a clinical decision point rather than a measurement exercise.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Classification predicts the threatened structures
Proximal involvement matters because the ascending aorta lies beside the valve, coronary origins and pericardium. A distal dissection can still be complicated by rupture or visceral, renal, spinal and limb malperfusion.
True and false lumen clues are combined
Continuity with an undissected lumen, branch origin, relative enhancement, lumen expansion and flap geometry can help distinguish lumens. No single visual sign should replace full multiplanar review.
Motion can mimic proximal dissection
The root and ascending aorta move during the cardiac cycle. Non-gated CT may create pulsation artefact, so ECG-synchronised acquisition or confirmatory imaging can prevent a false flap diagnosis.
Diameter is one risk dimension
Symptoms, growth, morphology, family history, inherited aortopathy, body size and valve phenotype can alter decisions. The report should supply reproducible anatomy rather than present diameter as the complete risk assessment.
Renal impairment changes planning
When iodinated contrast is risky, the team balances immediate diagnostic danger against renal risk and may use TEE, MRI or tailored CT. In a life-threatening syndrome, diagnostic delay also causes harm.
Aneurysm and occlusive disease coexist
Pre-intervention CT should describe iliac and access-vessel calibre, tortuosity, thrombus, calcification and branch disease because device delivery and organ perfusion depend on the entire route.
07Common pitfallsFrequent interpretation and management errors.
- 01
Using a normal chest radiograph to exclude acute aortic syndrome despite a high-risk history or examination.
- 02
Allowing a non-diagnostic bedside abdominal scan to end assessment when rupture remains clinically plausible.
- 03
Measuring a tortuous aorta on an oblique axial slice and labelling the exaggerated value as true interval growth.
- 04
Reporting only aneurysm diameter while omitting morphology, branch vessels, thrombus, rupture signs and repair-relevant anatomy.
- 05
Confirming a dissection flap without assessing the ascending aorta, aortic valve, pericardium, coronaries and organ malperfusion.
- 06
Excluding endoleak from negative colour duplex alone in a patient with sac expansion after EVAR.
- 07
Choosing MRI for an unstable emergency without accounting for scanner access, acquisition time and limits on monitoring or treatment.