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Aortic Intramural Hematoma (IMH) is a subtype of acute aortic syndrome characterized by:

• Hemorrhage into the media of the aortic wall without an intimal tear or communication with the aortic lumen.
• It is often described as a “non-communicating dissection”. </aside>

Etiopathogenesis

• IMH typically results from rupture of the vasa vasorum within the aortic media.
• It may be spontaneous, hypertension-related, post-traumatic, or secondary to a penetrating atherosclerotic ulcer (PAU).
• It may remain localized or propagate to cause frank dissection or rupture.

Radiology

Intramural haematoma

CT Imaging

• Non-contrast CT (NECT):
  • Shows a hyperdense crescent (50–70 HU) within the aortic wall.
  • The hematoma is subintimal, without a flap.
• Contrast-enhanced CT (CECT):
  • Crescentic hyperattenuating rim within the aortic wall, without contrast extravasation or flow communication.
  • No luminal reduction (cf. dissection where true lumen may be compressed).
  • A displaced intimal calcification is suggestive of IMH.

https://www.revportcardiol.org/en-aortic-intramural-hematoma-an-unpredictable-articulo-S217420491400155X

Initial CTA, showing circumferential thickening of the aortic wall (arrows) consistent with intramural hematoma, beginning immediately after the emergence of the left subclavian artery and involving the entire descending aorta and the proximal segment of the abdominal aorta (A); patent ductus arteriosus (arrowhead) and a partially calcified atherosclerotic plaque (arrow) (B); two ulcers in the proximal descending aorta wall (arrows) (C).

Control CTA on the eighth day, showing a slight increase in hematoma thickness to 15 mm and a crescent-shaped formation (C), still extending from the left subclavian artery to the emergence of the renal arteries (A); one of the aortic wall ulcers observed on the initial exam now presenting a deeper and more irregular appearance (arrow) (B).

IMH follows the Stanford classification used for aortic dissection:

• Type A: Involves ascending aorta — surgical emergency.
• Type B: Confined to descending aorta — often treated medically.

Differentials