Expansion
True or false, fusiform or saccular, with degeneration of the media
Expansion
Definitions
- True aneurysm - involves all three layers of the wall
- False (pseudo) aneurysm - a contained rupture, the wall being haematoma and adventitia only. Follows trauma or arterial puncture
- Fusiform - symmetrical dilatation, the usual abdominal aortic pattern
- Saccular - an outpouching on one side
Mechanism: degeneration of the media, with loss of elastin and smooth muscle and increased matrix metalloproteinase activity.
Laplace’s law drives progression: tension = pressure x radius, so as the aneurysm enlarges, wall tension rises, causing further enlargement. Growth therefore accelerates, and rupture risk rises steeply with diameter.
Causes
- Atherosclerosis and degeneration, much the commonest, in the infrarenal aorta
- Connective tissue disease: Marfan’s (fibrillin), Ehlers-Danlos, giving cystic medial necrosis of the ascending aorta
- Infective (mycotic): Salmonella, staphylococci, and historically syphilis, which causes a thoracic aneurysm with tree bark intimal wrinkling
- Inflammatory, and vasculitis such as Takayasu
Complications: rupture, dissection, thrombosis and distal embolisation, and compression of adjacent structures.
Screening: UK men are offered a single abdominal ultrasound at 65.