Acute Aortic Syndrome (AAS) is a spectrum of life-threatening conditions that share a common clinical presentation: abrupt, severe chest or back pain and hypertension. It includes three primary interrelated entities — all categorized using the Stanford classification:
| Stanford | Anatomy | Default management |
|---|---|---|
| Type A | Involves the ascending aorta | Typically surgical |
| Type B | Excludes the ascending aorta | Typically medical or endovascular |
1 Aortic dissection
Pathophysiology. Blood enters the media of the aortic wall through an intimal defect, splitting the wall longitudinally.
CT findings. Imaging reveals two distinct lumina separated by an intimal flap.
| True lumen | False lumen | |
|---|---|---|
| Cross-sectional area | Smaller | Larger |
| Continuity | Maintains continuity with the undissected aorta | Discontinuous |
| Characteristic signs | — | “Beak sign” · “cobweb sign” · delayed contrast enhancement · higher propensity for thrombosis |
2 Intramural hematoma (IMH)
Pathophysiology. Spontaneous hemorrhage from the vasa vasorum directly into the media — typically without an identifiable intimal tear or flap.
CT findings:
- Non-contrast CT (NECT): characteristic crescentic or eccentric hyperdensity along the aortic wall.
- CTA: crescentic wall thickening that narrows the aortic lumen.
Complications. IMH carries a higher rate of aortic rupture (up to 35%) compared to classic dissection — because the hematoma forms closer to the outer adventitial layer, leading to increased wall permeability and periaortic hemorrhage.
High-risk features that predict poor prognosis and increased mortality:
- Dilated aorta — ascending > 48 mm
- IMH thickness > 10 mm
- Ulcer-Like Projections (ULPs) — outpouchings of contrast with a wide intimal opening (> 3 mm) that do not extend beyond the aortic wall
3 Penetrating aortic ulcer (PAU)
Pathophysiology. An atheromatous ulcer that completely breaches the aortic intima and penetrates into the media. A prerequisite for a PAU is the presence of calcified atherosclerosis — the calcification acts like “glue” that prevents a full longitudinal dissection but allows focal ulceration.
CT findings:
- A contrast outpouching that extends beyond the expected confines of the aortic wall.
- Most common in the descending thoracic aorta.
- Frequently associated with an adjacent focal intramural hematoma.