Expansion
True aneurysms involve all layers; false aneurysms are contained ruptures
Expansion
By structure
- True: all three layers involved. Fusiform (circumferential) or saccular
- False (pseudoaneurysm): a contained rupture, with the wall formed by adventitia or surrounding tissue. Follows trauma, arterial puncture or anastomotic leak
- Dissection: blood enters the media through an intimal tear and tracks along it
By cause
- Atherosclerosis: the commonest, giving infrarenal abdominal aortic aneurysms
- Hypertension: Charcot-Bouchard microaneurysms in cerebral perforators, rupturing to cause intracerebral haemorrhage
- Connective tissue disease: Marfan and Ehlers-Danlos, causing aortic root dilatation
- Congenital: berry aneurysms at circle of Willis branch points, associated with polycystic kidney disease and coarctation
- Infection (mycotic): from endocarditis
- Syphilis: tertiary, causing thoracic aortic aneurysm from vasa vasorum endarteritis
- Vasculitis: Kawasaki, polyarteritis nodosa
Rupture risk rises steeply with diameter, following the law of Laplace: wall tension is proportional to radius, so enlargement is self-accelerating.