A crescentic, high-attenuation thickening of the aortic wall on the non-contrast series that does not enhance and has no flap (IMH), or contrast outpouching through calcified intima (PAU) — classified by Stanford type like dissection.
Orient first
- Acute aortic syndrome = classic dissection, intramural haematoma (IMH) and penetrating atherosclerotic ulcer (PAU).
- IMH is blood within the media without an intimal tear visible on CT; it is best seen BEFORE contrast, where it is brighter than blood.
- Type A (ascending) IMH is usually surgical; type B is usually medical with imaging surveillance.
Acquire the study
- Non-contrast series of the chest first (mandatory for IMH), then ECG-gated CT angiography chest to pelvis with thin axial, multiplanar and curved reformats.
The manoeuvre
- Non-contrast series: crescentic wall thickening > 5 mm with attenuation higher than luminal blood (typically 60–70 HU).
- Angiographic phase: no intimal flap, no false-lumen flow; displaced intimal calcification inward.
- Extent: ascending aorta involvement (Stanford A) vs distal to the left subclavian (B); maximal wall thickness in mm and aortic diameter in mm.
- Ulcer-like projections or PAU: contrast outpouching beyond the intimal calcification — depth and neck width in mm.
- Complications: pericardial or pleural haemorrhage, periaortic stranding, mediastinal haematoma, branch involvement.
What confirms it
- Crescentic hyperattenuating wall thickening on non-contrast CT without an intimal flap or false-lumen enhancement.
What licenses you to exclude it
- A normal non-contrast aortic wall (no hyperattenuating crescent) excludes IMH; a CTA acquired without the non-contrast series cannot.
The classic misread
- Skipping the non-contrast series — IMH can be missed or mistaken for mural thrombus.
- Calling mural thrombus IMH: thrombus lies inside the intimal calcification, IMH displaces it inward.
- Missing the pericardial effusion that marks a type A IMH as an emergency.