Aneurysms are defined as a permanent dilation of the artery to twice the normal diameter - this is > 3cm for the abdominal aorta
Aetiology
The incidence increases with age - AAAs are present in 5% of the population over 60 years of age
Arise five times more frequently in men
Higher risk if patient has first degree relative with AAA
Aneurysms may occur secondary to atherosclerosis (most common), infection (syphilis, Escherichia coli, Salmonella) and trauma, or may be genetic (Marfan’s or Ehlers–Danlos syndrome)
Pathophysiology
Usually results from the degeneration of the media of the arterial wall - most commonly due to atherosclerosis
During the formation of atheromatous plaques, macrophages release enzymes which break down the collagen and elastin of the media → media expands
AAAs most commonly occur below the renal arteries (infrarenal) - 80%
In a ruptured AAA, the wall of the aorta completely fails and blood escapes freely into a body cavity e.g. abdominal cavity
Emergency - 75% fatal, most usually die before getting to hospital
Majority are retroperitoneal (rupture contained); intraperitoneal ruptures are rapidly fatal
Clinical features
Asymptomatic
75% asymptomatic (incidental finding)
Symptomatic
Can have epigastric/central pain with no rupture or dissection
Pain is risk factor for rupture
A ruptured AAA will present as sudden onset abdominal pain radiating to back with an expansile abdominal mass
Other signs
Patients may present with ‘trash feet’, dusky discolouration of the digits secondary to emboli from the aortic thrombus