CT Case 034

There is an acute aortic intramural haematoma (IMH) involving the descending aorta. It is seen as hyperdense crescentic eccentric thickening of the aortic wall which does not enhance on aortogram.

The haematoma starts from the level of the aortic isthmus (anatomically located between the origin of the subclavian artery and the ligamentum arteriosum) and continues until just above the coeliac trunk.

There is a small left pleural effusion.

There is no dissection flap or intimal tear seen.

On additional views the was no sign of involvement of the ascending aorta, aortic root or coronary arteries.

An aortic intramural haematoma is part of the spectrum of acute aortic syndrome

The Acute aortic syndromes comprise;

• Aortic dissection
• Intramural haematoma (IMH)
• Penetrating atherosclerotic ulcer

Pathogenesis of IMH

An intramural haematoma is confined within the medial layer of the aorta (the tunica media) in the absence of a detectable intimal tear, which is the key difference between IMH and aortic dissection.

The definite mechanism of intramural haematoma formation is unclear. Two mechanisms have been described; rupture caused by penetrating atherosclerotic ulcer and spontaneous rupture of the vasa vasorum vessels within the tunica media.

An intramural haematoma can be a precursor to aortic dissection or rupture.

Classification

As with aortic dissections, intramural haematomas are categorised according to the Stanford classification.

• Type A; pathology involves the ascending aorta (with or without descending aorta involvement)
• Type B; limited to the descending aorta

Radiographic features of intramural haematoma

There are certain radiographic features that tell us this is an intramural haematoma rather than an aortic dissection

• The absence of an intimal flap (see case 006 for example of dissection flap seen)
• There is a crescent shape (representing the haematoma) along the aortic wall. On non-contrast scan this is hyperdense relative to the aortic lumen
• On the post-contrast scan the intramural haematoma is hypodense compared to the aortic lumen as it does not enhance with contrast
• There is absence of compression of the aortic lumen

Note, this patient had both non-contrast and arterial phase CT scans, the non-contrast scan helps quickly identify the intramural haematoma.

Management decisions

The management principles of intramural haematoma are the same as for aortic dissection.

As a general rule the treatment of Type A syndromes is surgical and Type B syndromes are usually managed medically (that is analgesia and aggressive BP and HR control).