August 18, 2009

Aortic Intramural Hematoma (IMH)

Figure 1: Contrast-enhanced CT image shows thickening of the aortic wall at the anteromedial aspect of the descending aorta (arrow). There is linear calcification, indicating atherosclerosis.

Figure 2: Axial CT without IV contrast at the same level shows the area of aortic wall thickening as a slightly hyperdense wall of the aorta (arrow). The linear calcification (arrowhead) is indeed located close to the aortic lumen (likely in the intima), therefore the wall thickening is 'subintimal' or 'intramural'. The nonenhanced CT helps in the way that if one looks only at contrast-enhanced images, one might think that the findings represent atherosclerotic change of the aorta (with calcification and intraluminal thrombus) and defers the diagnosis of IMH.

Facts: Intramural Hematoma (IMH)
  • Less common variant of aortic dissection
  • Hemorrhage occurs within aortic wall without initial intimal disruption believed to be due to medial degeneration predisposing the vasa vasorum toward hemorrhage
  • Increasingly recognized with the use of CT imaging (in the past, it is believed to be underdiagnosed on angiography because there is no intimal flap)
  • Limited data suggests a similar clinical course and mortality rate to acute aortic dissection
  • Common presentations = chest pain and interscapular back pain (similar to aortic dissection)
  • Unlike aortic dissection, IMH occurs in men equal to women, with absence of traditional risk factors for dissection (e.g. bicuspid aortic valve, Marfan syndrome, collagen vascular disease)
Imaging Features
  • Focal or diffuse, smooth thickening of the aortic wall
  • No intimal flap or any communication between aortic lumen and IMH
  • Intimal calcium (if present) is superficial (closer to lumen) to the hematoma
It May Be Confused With:
  • Aortic dissection with thrombosed false lumen
  • Penetrating atherosclerotic ulcer - usually irregular thickening of the aortic wall
  • Aortic aneurysm with intraluminal thrombus - if intimal calcium is present, it will be deeper to the hematoma. The thrombus usually is irregular and rough - not smooth.
Our case - Intramural hematoma of the descending thoracic aorta.

Sawhney NS, DeMaria AN, Blanchard DG. Aortic intramural hematoma. Chest 2001;120:1340-1346.

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