Aortic aneurysm
Aortic aneurysms are diseases of elderly with risk factors for atherosclerosis, like smoking, hypertension, and dyslipidaemia.
We distinguish two types of aortic aneurysms depending on the affected part of the aorta, thoracic aortic aneurysm (TAA) and abdominal aortic aneurysm (AAA). 90% of cases are abdominal. An aortic aneurysm is defined as a dilation > 50% of the normal diameter, or > 3 cm.
Aortic aneurysms are problematic because:
- They can rupture, which kills most of affected people within minutes or hours
- They can cause aortic dissection, which is also highly lethal
- Turbulent flow occurs in the aneurysm, which can cause wall thrombosis with subsequent thromboembolism, potentially causing ischaemic stroke
- They can compress other structures.
These aneurysms typically grow slowly, but the risk of rupture and compression increase with the size.
Etiology
The majority of aortic aneurysms are related to the same risk factors as for atherosclerosis, including hypertension, dyslipidaemia, and smoking. Family history of aortic aneurysm is also a significant risk factor.
However, aneurysms, especially thoracic ones, are rarely associated with inherited connective tissue disorders like Marfan syndrome and Ehlers-Danlos syndrome, as well as giant cell arteritis, Takayasu aortitis, and mycotic aneurysm.
Tertiary syphilis used to be a common cause of aneurysm, but this is much less common nowadays.
Pathology
Degeneration of elastic and collagen fibres, as well as atherosclerosis, causes the formation of the aneurysm. Degeneration occurs due to mechanical stress due to hypertension and due to activation of proteases like collagenase, elastase, matrix metalloproteinase, and plasmin.