An aortic aneurysm is a general term for any swelling (dilation or aneurysm) of the aorta to greater than 1.5 times normal, usually representing an underlying weakness in the wall of the aorta at that location. While the stretched vessel may occasionally cause discomfort, a greater concern is the risk of rupture, which causes severe pain; massive internal hemorrhage; and, without prompt treatment, death occurs rapidly.
Abdominal aortic aneurysms are commonly divided according to their size and symptomatology.
An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the aorta is around 2 cm).
If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large.
A ruptured AAA is a clinical diagnosis involving the presence of the triad of abdominal pain, shock and a pulsatile abdominal mass. If these conditions are present, indicating AAA rupture, no further clinical investigations are needed before surgery.
An abdominal aortic aneurysm is usually diagnosed by physical exam, ultrasound, or CT.
Plain abdominal radiographs may show the outline of an aneurysm when its walls are calcified. However, this is the case in less than half of all aneurysms.
Ultrasonography is used to screen for aneurysms and to determine the size of any present.
Additionally, free peritoneal fluid can be detected.
It is noninvasive and sensitive, but the presence of bowel gas or obesity may limit its usefulness.
CT scan has a nearly 100% sensitivity for aneurysm and is also useful in preoperative planning, detailing the anatomy and possibility for endovascular repair.
In the case of suspected rupture, it can also reliably detect retroperitoneal fluid. Alternative less often used methods for visualization of the aneurysm include MRI and angiography.
An aneurysm ruptures if the mechanical stress (tension per area) exceeds the local wall strength; consequently, peak wall stress (PWS) and peak wall rupture risk (PWRR) have been found to be more reliable parameters than diameter to assess AAA rupture risk.
Medical software allows computing these rupture risk indices from standard clinical CT data and provides a patient-specific AAA rupture risk diagnosis.
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