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Pathology: General terminology: Aneurysm = abnormal, localized dilatation of an artery
In the aorta, must distinguish aneurysm from diffuse ectasia, a lesser increase of aortic diameter due to fragmentation of elastic fibers, decrease number of smooth muscle cells, increase in acid mucopolysaccharide.
To have aortic aneurysm, either:
the diameter of a portion of the aorta has increased by 50% or more…or
a portion of the abdominal aorta has enlarged to greater than 3.5-4cm in diameter
True aneurysm: a dilatation of all three layers of the aorta (gives a bulge in the vessel wall) – two types:
True fusiform: entire circumference of a segment of the aorta is dilated (most common)
True saccular: localized outpouching involving only a portion of the circumference
Aortic aneurysms may be confined to the abdominal aorta (most common), the thoracic aorta, or both.
Pseudoaneurysm (aka false aneurysm): a contained rupture of the vessel wall that mimics the appearance of a true aneurysm – this develops when blood leaks out of lumen through a hole in the intimal and medial layers and is contained by merely the adventitia or perivascular organized thrombus.
Very unstable lesion and is prone to rupture.
Pathophysiology: Most devastating consequence of aortic aneurysm is rupture…often fatal. Aneurysm may rupture suddenly or may leak slowly, extravasating blood into the vessel walls and causing pain and local tenderness. Risk of rupture is related to the size of the aneurysm – LaPlace Law: the larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure.
5 year risk of rupture of an abdominal aortic aneurysm
<5cm in diameter is 1-2%
>5cm in diameter is 20-40%
Diagnostic tests/Imaging: Chest or Abdominal X-ray: Aortic aneurysms often first suspected when dilation is incidentally observed on an x-ray that was being taken for something else – particularly visible on x-ray if aneurysm’s walls are calcified. US, CT, MRI, or conventional arteriography: used to confirm aortic aneurysm diagnosis
Transabdominal surgical repair w/ placement of a prosthetic graft: gold standard for treatment (when diameter is >4.5-5cm or is expanding at a rate of more than 1cm/year)
Percutaneous deployment of an endovascular graft: less invasive, cost-effective, with similar morbidity and mortality to open repair.
Of these treatments, if aneurysm exceeds 6cm in diameter, surgical repair is recommended. For Marfan symdrome patients, surgical repair is often recommended at a lower threshold.