Find the intimal flap, then answer the three questions that decide the operation: where it starts, how far it goes, and what is malperfused.
Orient first
- A dissection is blood in the aortic wall separating intima from media, creating a true and a false lumen divided by an intimal flap.
- The classification that drives management is whether the ASCENDING aorta is involved (Stanford A, usually surgical) or not (Stanford B, usually medical).
- The report is not complete when the flap is found. Branch-vessel involvement and end-organ malperfusion are what the surgeon acts on.
Acquire the study
- ECG-gated CT angiography where available — cardiac pulsation artefact at the aortic root mimics a flap and is the classic false positive.
- A NON-CONTRAST series first: intramural haematoma appears as a high-attenuation crescent in the wall and is invisible once contrast is given.
- Arterial phase, covering from the thoracic inlet through the femoral arteries — you need the whole extent, not just the chest.
- Reconstruct sagittal obliques and coronals; the arch is poorly assessed on axials alone.
The manoeuvre
- On the non-contrast series look for a hyperdense crescent (intramural haematoma) and for displaced intimal calcification.
- On the arterial phase identify the intimal FLAP and follow it continuously from its most proximal to its most distal extent.
- Determine whether the ASCENDING aorta is involved — this is the single most consequential sentence in the report.
- Identify the primary entry tear and any re-entry tears.
- Distinguish TRUE from FALSE lumen: the true lumen is usually smaller, continuous with the undissected aorta, and carries the calcification; the false lumen is often larger, may show the beak sign, and may contain thrombus.
- Assess every branch: coronaries, arch vessels, coeliac, SMA, renals, iliacs — for each, say whether it arises from the true or false lumen and whether it is compromised.
- Assess end organs for malperfusion: renal or bowel ischaemia, cord, limb.
- Look for complications: pericardial effusion or tamponade, aortic regurgitation, mediastinal haematoma, haemothorax, rupture.
What confirms it
- An intimal flap separating two lumina.
- Intramural haematoma and penetrating atherosclerotic ulcer are part of the same acute aortic syndrome and are reported as such, not dismissed because there is no flap.
What licenses you to exclude it
- A well-opacified, motion-free CTA covering the whole aorta with no flap, no intramural haematoma and no ulcer excludes acute aortic syndrome.
- ⚠️ Without a non-contrast series, intramural haematoma can be missed entirely. If none was acquired, say the study is not complete for acute aortic syndrome.
The classic misread
- Calling cardiac pulsation artefact at the root a type A dissection — check whether the study was gated and whether the "flap" crosses anatomical boundaries.
- Mistaking a streak artefact or a left brachiocephalic vein for a flap.
- Reporting the flap without reporting branch-vessel origins.
- Confusing true and false lumen and thereby misdirecting an endovascular plan.